Urol Radiol 13:29-40 (1991)
Urologic Radiology © Springer.VeflagNewYorkInc. 1991
Gynecologic Magnetic Resonance Imaging Cynthia Janus Department of Radiology, University of Virginia, Health Sciences Center, Charlottesville, Virginia, USA
Abstract. Magnetic resonance imaging (MRI) is an excellent modality with which to delineate normal anatomic structures and a variety of pathologic conditions in the female pelvis. It excels at demonstrating the extent of local tumor involvement in cases ofendometrial and cervical cancer. It can help to elucidate the origin and nature of a variety of benign pelvic masses in cases where ultrasound findings are equivocal, and it is an accurate tool in demonstrating congenital abnormalities of the female reproductive tract. As technology continues to evolve, MRI will likely assume an even greater role in evaluating the female pelvis. Key words: Cervical cancer -- Myometrial invasion -- Endometrial cancer -- Adenomyosis -- Endometriosis -- Congenital abnormalities.
Magnetic resonance imaging (MRI) has made detailed visualization of female pelvic anatomy possible [1-5]. While ultrasound has proved to be an excellent modality for evaluating the female pelvis, it is limited in its ability to delineate the deeper portions of the pelvis and to provide specific tissue characterization. Although it can provide valuable information regarding the extent and nature of a variety of pelvic masses, it is not sufficient for staging pelvic malignancies. Computed tomography (CT) is superior to ultrasound in visualizing the deep pel-
Address offprint requests to: Cynthia Janus, M.D., Department of Radiology, University of Virginia, Health Sciences Center, Box 170, Charlottesville, VA 22908, USA
vis and pelvic sidewalls but also has some limitations in soft tissue contrast resolution. Ionizing radiation and the need for intravenous contrast are other disadvantages. MRI can demonstrate the deeper portions of the pelvis and the pelvic sidewalls and can also depict the internal architecture of the uterus. Changes in appearance of the uterine zonal anatomy in response to the ho'rmonal environment during different phases of the menstrual cycle [6-8] and with age [3] can be appreciated on M R images. The multiplanar imaging capability of MRI and lack of ionizing radiation [9, 10] are other attractive features of this modality. Principles While ultrasound utilizes high-frequency sound waves and CT involves ionizing radiation, M R I is based upon the interaction between radio waves and hydrogen nuclei in the body in the presence of a strong magnetic field [1 l, 12]. When a patient is undergoing an M R exam, a small percentage (< l/ 1,000,000) of the protons in the body tend to align in the same direction of the magnetic field within the bore of the magnet. The protons absorb energy and their alignment is changed when subjected to radio waves of a certain frequency and they re-align with the magnetic field as they release radio-wave energy that subsequently comprises the M R signal. The radio-wave energy is absorbed and released at different characteristic rates by the tissues. The signal intensity of a tissue depends upon several factors. TR and TE are two of these variables and can be manipulated by the radiologist. T R is the time between the administered radio-frequency pulses or the time in which the protons are allowed to align
30 with the direction o f the m a i n magnetic field. T E is the length o f t i m e for the a b s o r b e d r a d i o - w a v e energy to be released. T h e tissue properties T 1 and T2 are also i m p o r t a n t factors in d e t e r m i n i n g signal intensity. T1 is a t i m e constant that reflects h o w quickly a specific tissue will be ready to a b s o r b the r a d i o - w a v e energy to which it is exposed. T h e t i m e
Fig. I. T2-weighted (TR 2200 msec, TE 80 msec) sagittal view demonstrates normal zonal anatomy in a retroverted uterus. E, endometrial region; M, myometrium; junctional zone is the low signal band between the small curved arrows; small straight arrows demarcate cervix.
C. Janus: Gynecologic MRI constant T2 indicates h o w rapidly a specific tissue will lose the r a d i o - w a v e energy that it has absorbed. Last, the n u m b e r o f p r o t o n s in a particular tissue a n d the m o t i o n or flow o f these p r o t o n s also influence signal intensity.
Imaging Protocol T h e r e is no p r e p a r a t i o n for a M R I e x a m o f the pelvis. While full distension o f the urinary b l a d d e r is u n c o m f o r t a b l e a n d unnecessary, partial distension facilitates delineation o f the b l a d d e r wall a n d allows for d e t e r m i n a t i o n o f invasion in cases o f gynecologic malignancy. Basic imaging sequences for evaluation o f the pelvis include T2-weighted images in the sagittal plane (Fig. 1) a n d T 1- a n d T2-weighted images in the axial (transverse) plane (Figs. 2 a n d 3). T 1- and T2-weighted imaging sequences in the coronal plane are also often utilized (Fig. 4). Zonal a n a t o m y o f the uterus is best d e m o n s t r a t e d on sagittal T2-weighted images. T h e sagittal projection also aids in directly d e m o n s t r a t i n g the cephalocaudal extent o f a m a s s
Fig. 2. Axial T 1-weighted (TR 500 msec, TE 17 msec) images at the level of the vagina (between arrows) (A), cervix (between curved arrows) (B), and uterus (C). These structures appear relatively featureless and zonal anatomy is not distinct. A small cyst in the left ovary (arrow) in (C) contains blood and is of high signal intensity. U, uterus.
Fig. 3. T2-weighted axial images at the level of the lower vagina (A), vaginal fornices (B), cervix (between arrows) (C), and uterus (D). Zonal anatomy is clearly visualized and follicles are seen in both ovaries in this 38-year-old woman. U, urethra; 1I, vagina; B, urinary bladder; O, ovary with follicles.
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Fig. 4. CoronalTl-weighted(A) and T2-weighted(B) images show the uterus and adnexae. Ovarian follicles(arrows) are of low signal intensityon Tl-weighted images and of high signal intensityon T2-weightedscans. and is helpful in assessing invasion of the urinary bladder and rectum. The transverse plane is best for evaluation oflymphadenopathy and parametrial extension of tumor. Tl-weighted images are most helpful in delineating the uterus and parametria from the surrounding fat. The ovaries are evaluated with T 1- and T2-weighted sequences using transaxial and coronal planes.
Fig. 5. A SagittalT2-weightedimageshows the uterine zonal anatomyon day 5 of the menstrualcycle.B Increasein thickness of the endometrial zone is seen on day 12 of the cycle. E, endometrium.
Normal Anatomy
The zonal anatomy of the uterus can be delineated on T2-weighted sequences, best seen in the sagittal projection (Fig. 1). The endometrium is depicted as a central area of high signal intensity and is distinguished from the peripheral area of moderate signal intensity representing myometrium. Between these areas there is a low signal intensity band which has been termed the junctional zone and which is currently believed to correspond to the inner one third of the myometrium [2, 3]. The uterus displays a relatively homogeneous moderate signal intensity on T l-weighted images and appears relatively featureless (Figs. 2C and 4A). The endometrial region and junctional zone appear prominent in women of reproductive age. Both zones increase in width during the menstrual cycle with the most rapid increase in the peri-ovulatory period (days 8-16) (Fig. 5). A general decrease in signal intensity from the endometrium is seen just prior to menstruation and discrete areas of low signal representing blood clots can be seen within the endometrial region during the menstrual phase. Endometrial atrophy has been demonstrated in women taking oral contraceptives [6]. The endometrium appears thin, measuring 2 m m or less, and the cyclic changes are absent in premenarchal girls and in postmenopausal women not taking exogenous hormones [3] (Fig. 6). The junctional zone also appears thin and may not be visible as a distinct band. The myometrium reveals an intermediate signal intensity, less than that seen in women of reproductive
The uterus is small and the endometrialzone is thin in this elderlywoman. B, urinarybladder.
Fig. 6.
age. However, in postmenopausal women who are being treated with exogenous estrogens, the uterus has a similar appearance to that of women of reproductive age. The cervix is represented by a central area of high signal intensity that comprises the region of the endocervical glands surrounded by an area of low signal intensity which represents the fibrous cervical stroma (Figs. 1 and 3C). The pericervical tissues are normally of moderate signal intensity and of variable increased signal intensity on T2 images. The vagina is most clearly demonstrated on T2weighted images in the transverse plane (Figs. 2A, 3A, and 3B). The lateral fornices mark the upper one third of the vagina while the middle third is
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Fig. 7. A Small developing follicles are seen in a close-up T2weighted view of the ovary (between arrows) on day 5 of a normal cycle. B A dominant follicle ( f ) is seen on day 12.
seen at the level o f the bladder base and the lower third is found at the level of the urethra. The central high signal portion representing mucus is thin in premenarchal girls and the vaginal wall is of low signal intensity. In women of reproductive age during the early proliferative phase of the cycle, a central area of high signal intensity representing mucus and epithelium surrounded by a low signal intensity component representing the vaginal wall is seen on T2 images. The high signal intensity portion increases in thickness during the early secretory phase and this is usually accompanied by some loss of contrast differentiating the central mucus from the medium high signal intensity of the vaginal wall. In pregnant patients the vaginal wall characteristically demonstrates high signal intensity, particularly during the second and third trimesters. As to be expected, in postmenopausal women who are not taking estrogens, the central high signal mucus portion is thin and the vaginal wall is of low signal intensity. The ovaries can be recognized on MR images in most women of reproductive age but may be difficult to delineate in premenarchal girls and elderly women. On Tl-weighted images they are of low to medium signal intensity (Fig. 4A), whereas on T2-weighted sequences, signal intensity is high and individual follicles can be delineated (Fig. 4B). Changes in follicular size and appearance can be appreciated on T2-weighted imaging sequences [8] (Fig. 7).
Gynecologic Tumors Perhaps the most important application of MRI of the female pelvis is in helping to delineate, characterize, and stage gynecologic malignancies. Ac-
Fig. 8. The endometrial zone of the uterus (e) is abnormally enlarged in this elderly woman. This appearance may be seen in endometrial cancer but is nonspecific. The junctional zone is intact with no evidence of invasion of the myometrium by tumor.
curacy in staging is important in determining prognosis and in choosing the optimal treatment protocol. FIGO staging is often inaccurate because of limitations in evaluating the parametria, pelvic sidewalls, and lymph node chains.
Endometrial Cancer Endometrial carcinoma has a variable and nonspecific appearance on magnetic resonance imaging [ 13, 14]. It may manifest as expansion of the central area of high signal intensity on T2-weighted images (Fig. 8) and/or an area of decreased attenuation within the high signal endometrial region. Adenomatous
C. Janus: GynecologicMRI hyperplasia and blood clots in the endometrial cavity m a y simulate endometrial cancer [ 13]. The uterus m a y appear n o r m a l with early lesions. Prognosis is related to the location o f the tumor, the depth o f m y o m e t r i a l invasion, l y m p h node inv o l v e m e n t , and the stage o f the disease, as well as patient age, cell type, and histologic grade o f the tumor. Visualization o f an intact junctional zone indicates that the t u m o r is confined to the endom e t r i u m (Fig. 8). With superficial m y o m e t r i a l invasion, there is segmental interruption o f the junctional zone (Fig. 9A). It should be noted that the junctional zone m a y not be visible in some postmenopausal w o m e n and, in these cases, irregularity o f the interface between e n d o m e t r i u m and m y o m e t r i u m m a y indicate superficial m y o m e t r i a l invasion
Fig. 9. A There is a focal interruption of the junctional zone (between arrows) on the ~gittal T2-weighted view of the uterus in this patient with known endometrial cancer indicating superficial invasion of the myometrium. B Irregularity of the interface between the high signal intensity endometrium and the moderate signal intensity myometrium in another patient with superficial myometrial invasion by endometrial cancer is shown on an axial T2-weighted view (uterus shown between arrows).
33 (Fig. 9B). In cases o f deep m y o m e t r i a l invasion (Fig. 10), the area o f a b n o r m a l signal representing the t u m o r extends across m o r e than one half o f the thickness o f the m y o m e t r i u m . Stage I endometrial cancer is generally treated with surgery. Since a significant percentage o f w o m e n with stage I disease will have l y m p h node involvement, M R imaging can help the surgeon decide whether sampling o f pelvic a n d / o r aortic lymph nodes is appropriate [13]. Specific sites o f lymph node i n v o l v e m e n t are diagnosed by the d e m o n s t r a t i o n o f enlargement o f the nodes a n d / o r l y m p h nodes with a b n o r m a l high signal intensity on T2-weighted images. M R I is proving to be highly accurate in staging histologically d o c u m e n t e d endometrial cancer. In a study o f 51 patients clinically suspected o f having endometrial carcinoma and in w h o m 45 this diagnosis was confirmed histologically, Hricak et aL [13] d e t e r m i n e d the overall accuracy o f M R imaging in staging endometrial carcinoma to be 92% with an overall accuracy o f 82% in showing the depth o f myometrial invasion. In this study M R I d e m o n strated limitations in delineating adnexal and peritoneal metastases and l y m p h node involvement. In another prospective study, Chert et aL [14] evaluated 50 patients by M R I with stage I endometrial cancer who had primary surgical treatment. T h e M R exam resulted in an advance in staging in 18% o f the patients and accurately predicted deep m y o m e trial invasion in 94% o f the patients. T h e authors concluded the M R I should be considered in the routine workup o f patients with stage I disease.
Carcinoma of the Cervix Cervical carcinoma is revealed on T2-weighted images as a high signal intensity mass which is easily
Fig. 10. Sagittal(A) and axial (B) T2-weighted views reveal widening of the endometrial zone with areas of heterogeneous low signal intensity. Extension of the abnormal signal intensity is seen to involve greater than one half the thickness of the myometrium in a patient with deep myometrial invasion by endometrial carcinoma. T, irregularly shaped heterogeneous low signal intensity endometrial carcinoma with deep invasion of the myometrium.
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Fig. 11. There is an area of abnormally high signal intensity in the region of the cervix and widening of the endocervical canal (between arrows) in this patient with known carcinoma of the cervix. B, distended urinary bladder.
delineated from the normal low signal intensity cervical stroma [ 15-19] (Fig. l 1). Cervical cancer confined to the cervix and/or uterine corpus is classified as stage IB. The outer low signal intensity cervical stroma is sharply delineated from the pericervical tissue. Preservation of the low signal intensity stripe of the peripheral cervical stroma on T2-weighted images is a reliable sign that full-thickness involvement of the cervical stroma and parametrial invasion by tumor is not present (Fig. 12). Stage IIA cervical cancers extend into the upper two thirds of the vagina, depicted by loss of the normally low signal intensity vaginal wall. Signs of pericervicalparametrial involvement (IIB) include irregularity of the lateral cervical margin and a mass or area of abnormal signal intensity in the parametrial region (Fig. 13). Signal intensity of the abnormality is lower than fat on T 1-weighted images and of high signal intensity on T2-weighted sequences and may be difficult to differentiate from active inflammatory tissue. Since evaluation of the parametrium is considered to be one of the most important parameters in staging cervical cancer, it has been recommended that MRI be utilized in place of CT as a routine imaging procedure for preoperative staging [20]. Cervical carcinoma is classified as stage IIIA if the high signal intensity mass extends to the lower one third of the vagina and as stage IIIB if there is extension to the pelvic sidewall. Involvement of the bladder (Fig. 14) or bowel wall (stage IVA) is revealed as loss of the normal low signal intensity wall of these structures on T2-weighted images and loss of the normal fat planes between them and the cer-
C. Janus: Gynecologic MRI
Fig. 12. The low signal intensity zone of the peripheral cervical stroma (between arrows) is seen to be intact on this T2-weighted axial image in a patient with known cervical carcinoma without parametrial extension.
vical tumor. Enlargement of lymph nodes with variable increase in signal intensity on T2-weighted images (Fig. 15), while nonspecific, is seen with metastatic involvement. Several recent studies have shown M R imaging to be very accurate in staging cervical cancer. In a study of 10 patients with stage IB cervical carcinoma, Angel et al. [17] found that MRI more accurately predicted size of the tumor and extent of stromal involvement than did the clinical exam when compared with findings at pathology. Some investigators have proposed that MRI be used in conjunction with clinical staging to determine appropriate therapy in women with stage IB tumors. Togashi et al. [18] demonstrated an accuracy of 95% for MRI in demonstrating invasive disease (stage IB or higher). MRI was 89% accurate in evaluation of the parametria. Overall accuracy for staging carcinoma of the cervix was 76%. Hricak et al. [19] found MRI to be accurate in demonstrating tumor location in 91% of cases and 70% accurate in determining tumor size within 0.5 cm. Accuracy rates were also high for evaluation of vaginal extension (93%) and parametrial involvement (88%). The lack of pelvic, sidewall, bladder, and rectal involvement was accurately predicted in all cases, while the positive predictive values were 75, 67, and 100%, respectively. MRI demonstrated an overall accuracy of 81% in staging cervical carcinoma in this study. In another correlative study, Kim et al. [20] reported on 30 patients with cervical carcinoma who underwent CT scan, M R imaging, and surgical exploration. This group found MRI to excel in staging cer-
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Fig. 13. Tl-weighted axial images at the level of the cervix (A) and vagina (B) demonstrate a bulky cervical cancer with involvement of the vagina and extension into the parametrium (arrows). The patient had undergone a supracervical hysterectomy 10 years previously. (C) T2weighted axial view at the level of the cervical carcinoma. Areas of low signal on Tl-weighted and areas of high and low signal on T2-weighted views are secondary to necrosis. B, urinary bladder.
vical carcinoma with an accuracy rate o f 83% c o m p a r e d to 63% for C T scan and 70% for clinical examination. M R I cannot be used to screen for cervical cancer since N a b o t h i a n cysts (Fig. 16), hemorrhage, and changes second to cervical biopsy m a y appear similar. Its benefits in more accurate staging, however, have i m p o r t a n t applications. Surgery, radiation therapy, or both are used to treat stage I and limited stage II disease [21-23]. Since there are m a n y variations in t u m o r size and location included in the stage I category, knowledge o f t u m o r size and location can aid the gynecologist in making the decision between surgery alone or combining with radiation therapy. Gestational Trophoblastic Neoplasia Gestational trophoblastic neoplasia ( G T N ) comprises a spectrum o f pathology that includes the benign hydatidiform mole, the invasive mole (cho-
rioadenoma), and the highly malignant choriocarc i n o m a [24, 25]. Elevated levels o f h u m a n chorionic gonadotropin help diagnose trophoblastic disease and serial levels are an indicator o f t u m o r activity. Sonography has been used to demonstrate size o f the t u m o r and the uterus and CT scan has been helpful in finding metastases. Uterine G T N is usually manifest as a hypervascular mass on T2weighted M R images and the distortion or destruction o f zonal a n a t o m y is revealed (Fig. 17). Signal intensity o f the t u m o r on T 1-weighted images is often like that o f n o r m a l m y o m e t r i u m but there m a y be areas o f high signal intensity corresponding to the presence o f blood. T h e r e m a y also be tortuous vessels in the region o f the t u m o r and adjacent normal m y o m e t r i u m , as well as in the adnexae. Associated theca lutein cysts are easily visualized. M R imaging can he especially useful when the t u m o r deeply invades the m y o m e t r i u m but does not extend to the endometrial surface in which case uterine curettage specimens are not helpful. M R I has also
36 been utilized to exclude the uterine source for elev a t e d H C G levels in patients with extrauterine germ cell t u m o r s . It m a y also be used, along with H C G levels, to evaluate response to therapy. C T has generally been considered the imaging procedure o f choice in evaluating the patient with G T N for evidence o f metastases. M R I has been advocated, however, to evaluate the uterus as the site o f the p r i m a r y t u m o r , to follow response to therapy, and in cases where there is a contraindication to iodinated i n t r a v e n o u s contrast [24, 25].
c. Janus: Gynecologic MRI
Leiomyosarcoma L e i o m y o s a r c o m a m a y a p p e a r as uterine enlargem e n t with distortion or destruction o f the zonal a n a t o m y a n d areas o f a b n o r m a l signal intensity [26, 27] (Fig. 18). It m a y simulate e n d o m e t r i a l carcin o m a with m y o m e t r i a l i n v o l v e m e n t or c o m p l i c a t e d l e i o m y o m a s . M R imaging can, however, accurately define the extent o f the t u m o r in the uterus a n d its extension to adjacent tissues.
Carcinoma of the Vagina T h e usefulness o f M R imaging in evaluation o f tum o r i n v o l v e m e n t o f the vagina has also been investigated. Chang et al. [28] studied w o m e n in w h o m primary, metastatic, or recurrent vaginal cancer was suspected clinically. Diagnosis o f t u m o r was based on c o n t o u r d e f o r m i t y a n d / o r a b n o r m a l high signal intensity on T2-weighted images (Fig. 19). In d e m onstration o f metastatic i n v o l v e m e n t , the accuracy o f M R I was 92% with a sensitivity o f 95% a n d a specificity o f 90%. M R I very accurately excluded t u m o r extension but s o m e cases o f i n f l a m m a t i o n
Fig. 14. Sagittal T2-proton-density-weighted view in an advanced case of cervical carcinoma. There is obstruction of the endometrial cavity (E) and invasion of the urinary bladder, manifested by loss of the normal low signal intensity line representing posterior bladder wall (small arrows) and intervening high signal intensity cleavage fat plane at the level of the tumor. C, large cervical tumor; large curved arrow points to Foley catheter balloon.
Fig. 16. Focal areas of high signal intensity at the level of the cervix (between arrows) are seen on sagittal (A) and axial (B) T2weighted images and represent Nabothian cysts.
Fig. 15. Metastatic adenopathy (arrow) from cervical carcinoma at the level of the fight iliac chain is demonstrated on proton density (A) and T2-weighted (B) axial images.
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Fig. 19.
An axial Tl-weighted image in a patient with vaginal cancer shows abnormal thickness and contour on the left (between arrows).
Fig. 17.
A high signalintensitymass (M) is seen in this patient
with choriocarcinoma.Zonal anatomyis indistinct.
Recurrent pelvic tumor generally reveals a high signal intensity on long TR/long TE (T2 weighted) imaging sequences, while the signal intensity of focal fibrosis is variable. Changes of early fibrosis, occurring 1 to 6 months after therapy, may overlap in signal intensity with tumor recurrence largely due to accompanying changes of edema and/or inflammation. Late fibrosis, seen 12 months or more after surgery or therapy, demonstrates low signal intensity on long TR/long TE sequences and can be differentiated from tumor [30]. Benign Gynecologic Abnormalities
Fig. 18. An axial T2-weightedimage at the level of the uterus demonstrates a large mass (M) representinga leiomyosarcoma. The tumor is of heterogeneousbut mainlyhigh signal intensity and there is destructionof the normal zonal architecture.
and congestion could not be distinguished from tumor causing some false-positive diagnoses. MRI was capable of distinguishing tumor and fibrotic tissue in cases of suspected recurrent vaginal cancer. Recurrent vaginal carcinoma could be diagnosed by MR with an accuracy rate of 82% [28]. Recurrent Gynecologic Tumors
The ability of MRI to differentiate residual or recurrent tumor from fibrosis following surgery or radiation therapy [29, 30] varies with the primary site of tumor and the length of time since treatment. While excellent results have been reported for diagnosing recurrent tumors of the cervix and vagina, accuracy rates may not be as high for tumors of the bladder and rectum.
The leiomyoma is the most common uterine tumor occurring in approximately 20-30% of women of reproductive age. Accurate delineation of the number, size, and location of leiomyomas is important in certain clinical situations including infertility [31 ], recurrent abortion, or surgical planning for myomectomy [32, 33]. Leiomyomas are well circumscribed and sharply demarcated from adjacent myometrium. Uncomplicated fibroids will demonstrate low signal intensity on both T1- and T2-weighted imaging sequences (Fig. 20). Variable and higher signal intensities may be seen in association with hyaline or myxomatous degeneration or with hemorrhage (Fig. 21). Foci of calcification may be identified. In comparison with ultrasound, one study found that MRI was more accurate in evaluating uterine volume and its contents [32]. The more lateral and posterior areas of the true and false pelvis were better visualized by MRI even if uterine size was massive and uterine contours were grossly distorted [32]. It is felt that MRI provides a noninvasive means to distinguish between uterine leiomyomas and other solid pelvic masses in cases where ultrasound findings are ambiguous [33].
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Fig. 21. A large fibroid tumor is seen to distort the uterine cavity and is of mainly low but heterogeneoussignal intensity.f, fibroid. Fig. 20. An area of homogeneous low signal intensity that is sharply demarcated from surrounding myometrium is seen on a sagittal T2-weighted image and is characteristic of an uncomplicated fibroid Or). In adenomyosis, endometrial glands and stroma are present deep within the e n d o m e t r i u m . The endometrial glands in adenomyosis are o f the basalis type and are not affected by h o r m o n a l stimulation as in the case o f endometriosis. With diffuse inv o l v e m e n t by adenomyosis, the uterus is enlarged. Thickening o f the low signal intensity band representing junctional zone has been described on T2weighted sequences [34]. This appears to correspond to an a b n o r m a l zone o f hypertrophied m y o m e t r i u m seen a r o u n d the uterine cavity at pathologic exam. An area o f focal adenomyosis is sometimes referred to as an a d e n o m y o m a . Although this condition m a y simulate a l e i o m y o m a at gross inspection, the ade n o m y o m a differs in that it interdigitates with normal s m o o t h muscle. This is presented on T2-weighted M R images as a focal area o f low signal intensity that is poorly delineated from the surrounding myometrium.
Congenital Abnormalities M R imaging has m a d e it possible to diagnose m a n y congenital abnormalities o f the pelvic organs in a noninvasive m a n n e r [35-38]. Absence o f the vagina or uterus is readily identified [35-37]. H e m a t o m e tria and h e m a t o c o l p o s [35, 38] are visualized as distension o f the uterus a n d / o r vagina and the med i u m to high signal intensity o f the fluid contents on T1 images identifies the presence o f blood. Bicornuate uterus can be recognized by identifying m y o m e t r i a l tissue separating the endometrial car-
Fig. 22. A cystadenocarcinoma of the ovary (T) is seen as a large complex ovarian mass on T2-weighted images in the axial projection. The mass contains solid material and septations and is located above the level of the uterine fundus. MRI is not necessarilymore reliable than ultrasound in differentiatingbenign from malignant ovarian masses. ities and by the typical configuration o f the uterine fundus, while uterine septations appear as low signal intensity bends within the high signal intensity endometrial zone.
Adnexal Pathology Currently, the role o f M R I in evaluating ovarian pathology is limited. By its ability to demonstrate uterine zonal a n a t o m y independent o f patient b o d y habitus and its multiplanar imaging capability, M R I can, however, help determine the uterine or ovarian origin o f a mass in cases where ultrasound e x a m is equivocal [39-42] (Fig. 22). M R I can also help to
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exogenous hormonal influences and with aging. With the further improvement of technology, the advent of faster imaging sequences, and the possible future use of spectroscopy, the role of MRI in evaluating the female pelvis may assume even greater importance. References
Fig. 23. A mass (between arrows) in the right pelvis represents a hematoma following hysterectomy. A T 1-weighted coronal image reveals a low signal intensity peripheral rim, an inner area of high signal intensity, and a low to moderate central portion. B The hematoma is of uniform high signal intensity on axial T2weighted image.
characterize an adnexal mass by its ability to distinguish the presence of fat in a dermoid or blood in an endometrioma [40--42] (Fig. 23). Studies have shown MRI to be capable of demonstrating the changes ofendometriosis [41, 42] but it has not been found to reliably demonstrate extraovarian adhesions and intraperitoneal endometrial implants. Indeed, MRI should not be utilized in place of laproscopy to definitively diagnose endometriosis or to accurately define its extent. It has been used, however, to monitor treatment once the diagnosis is established [41, 42]. Conclusion
MRI, with its multiplanar imaging capabilities, excellent contrast resolution, and superior ability to delineate uterine zonal anatomy, is making important contributions in diagnosing pathology in the female pelvis. Ultrasound will undoubtedly remain the first line of imaging and the initial procedure in evaluating clinically suspected pelvic pathology. CT has proved useful in evaluating complex pelvic masses and in demonstrating metastases in patients with gynecologic malignancies. MRI has added important information in staging malignant tumors of the uterus and indications suggest that it may supplant CT in the future. It can help to determine the origin and nature of certain benign masses when findings on ultrasound are ambiguous and has proved valuable in evaluating congenital abnormalities of the female reproductive tract. M R also shows potential in adding to our understanding of the changes that occur in the normal uterus with normal and
1. Bliss JR, Elias JH, Kopecky KK, et al.: Assessment of primary gynecologic malignancies: Comparison of 0.15T resistive MRI with CT. AJR 143:1249-1257, 1984 2. Heiken JP, Lee JKT: MR imaging of the pelvis. Radiology 166:11-16, 1988 3. Hricak H: MRI of the female pelvis: A review. A JR 146: l115-1122, 1986 4. Worthington JL, Balfe DM, Lee JKT, et al.: Uterine neoplasms: MR imaging. Radiology 159:725-730, 1986 5. Mintz MC, Thickman DI, Gussman D, et aL : MR evaluation of uterine anomalies. AJR 148:287-290, 1987 6. McCarthy S, Tauber C, Gore J: Female pelvic anatomy: MR assessment of variations during the menstrual cycle with use of oral contraceptives. Radiology 160:119-123, 1986 7. Haynor DR, Mack LA, Soules MR, et aL: Changing appearance of the normal uterus during the menstrual cycle: MR studies. Radiology 161:459--462, 1986 8. Janus CL, Wiczyk HP, Laufer N: Magnetic resonance imaging of the menstrual cycle. Magn Reson Imaging 6:669674, 1988 9. Schwartz JL, Crooks LE: NMR imaging produces no observable mutations or cytotoxicity in mammalian cells. Radiology 139:583-585, 1983 10. Wolff S, Crooks LE, Brown P, et al.: Tests for DNA and chromosomal damage induced by nuclear magnetic resonance imaging. Radiology 136:707-710, 1980 11. Pykett IL, Newhouse JH, Buonanno FS, et al.: Principles of nuclear magnetic resonance imaging. Radiology 143:157168, 1982 12. FuUerton GD: Magnetic resonance imaging signal concepts. Radiographics 7:579-596, 1987 13. Hricak H, Stern JL, Fisher MR, et al.: Endometrial carcinoma staging by MR imaging. Radiology 162:297-305, 1987 14. Chen SS, Rumancik WM, Spiegel G: Magnetic resonance imaging in stage I endometrial carcinoma. Obstet Gynecol 75:274-277, 1990 15. Togashi K, Nishimura K, Itoh K, et al.: Uterine cervical cancer: Assessment with high-field MR imaging. Radiology 160:431--435.17, 1986 16. Waggenspack GA, Amparo EG, Hannigan EV: MR imaging of uterine cervical carcinoma. J Comput Assist Tomogr 12: 409-414, 1988 17. Angel C, Beecham JB, Rubens DJ, Thornbury JR, Stoler MH: Magnetic resonance imaging and pathologic correlation in stage IB cervix cancers. Gynecol Oncol 2:357-365, 1987 18. Togashi K, Nishimura K, Sagoh T, et al.: Carcinoma of the cervix: Staging with MR imaging. Radiology 171:245-251, 1989 19. Hricak H, Lacey CG, Sandles LG, et aL: Invasivc cervical carcinoma: Comparison of MR imaging and surgical findings. Radiology 166:623--631, 1988 20. KJm SH, Choi BI, Lee HP, et aL: Uterine cervical carcinoma: Comparison of CT and MR findings. Radiology 175:45-51, 1990
40 21. Walsh JW, Vick CW: Staging of female genital tract cancer. In: Walsh JW (ed): Computed Tomography of the Pelvis. New York: Churchill Livingstone, 1985, pp 163-184 22. Rubens D, Thornbury JR, Angel C, et aL: Stage IB cervical carcinoma: Comparison of clinical, MR and pathologic staging. AJR 150:135-138, 1988 23. Whitley NO, Brenner DE, Francis A, et al.: Computed tomographic evaluation of carcinoma of the cervix. Radiology 142:439-446, 1982 24. Hricak H, Demas BE, Braga CA, et al.: Gestational trophoblastic neoplasm of the uterus: MR assessment. Radiology 161:11-16, 1986 25. Mirich DR, Hall JT, Kraft WL, et al.: Metastatic adnexal trophoblastic neoplasm: Contribution of MR imaging. J Comput Assist Tomogr 12:1061-1067, 1988 26. Janus CL, White M, Dottino P, et al.: Uterine leiomyosarcoma--Magnetic resonance imaging. Gynecol Onco132:7981, 1989 27. Shapeero LG, Hricak H: Mixed Mullerian sarcomas of the uterus: MR imaging findings. AJR 153:317-319, 1989 28. Chang YCF, Hricak H, Thurnher S, et al.: Vagina: Evaluation with MR imaging. Park II neoplasms. Radiology 169: 175-179, 1988 29. Sugimura K, Carrington BM, Quivey JM, Hricak H: Postirradiation changes in the pelvis: Assessment with MR imaging. Radiology 175:805-813, 1990 30. Ebner F, Kressel HY, Mintz MC, et aL: Tumor recurrence versus fibrosis in the female pelvis: Differentiation with MR imaging at 1.5T. Radiology 166:333-340, 1988 31. Dudiak CM, Turner DA, Patel SK, et al.: Uterine leiomyomas in the infertile patient: Preoperative localization with
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MR imaging versus US and hysterosalpingngraphy. Radiology 167:627-630, 1988 Zawin M, McCarthey S, Scoutt LM, et al.: High-field MRI and US evaluation of the pelvis in women with leiomyomas. Magn Reson Imaging 8:371-376, 1990 Weinreb JC, Barkoff ND, Megibow A, et al.: The value of MR imaging in distinguishingleiomyomas from other solid pelvic masses when sonography is indeterminate. AJR 154: 295-299, 1990 Togashi K, Nishimura K, Itoh K, et al.: Adenomyosis: Diagnosis with MR imaging. Radiology 166:111-114, 1988 Dietrich RB, Kangerloo H: Pelvic abnormalities in children: Assessment with MRI imaging. Radiology 163:367-372, 1987 Hricak H, Chang YCF, Thurnher S: Vagina: Evaluation with MR imaging. Part I: Normal anatomy and congenital anomalies. Radiology 169:169-174, 1988 Togashi K, Nishimura K, Itoh H, et al.: Vaginal agenesis: Classification by MR imaging. Radiology 162:675-677, 1987 Vainright JR, Fulp CJ, Schiebler ML: MR imaging of vaginal agenesis with hematocolpos. J Comput Assist Tomogr 12: 891-893, 1988 Togashi K, Nishimura K, Itoh K, et al.: Ovarian cystic teraromas: MR imaging. Radiology 162:669-673, 1987 Nyberg DA, Porter BA, Olds MO, et al.: MR imaging of hemorrhagic adnexal masses. J Comput Assist Tomogr 11: 664-669, 1987 Zawin M, McCarthy S, Scoutt L, et al.: Endometriosis: Appearance and detection at MR imaging. Radiology 171:693696, 1989 Arriv6 L, Hricak H, Martin MC: Pelvic endometriosis: MR imaging. Radiology 171:687-692, 1989
Urologic Radiology © Springer.VeflagNewYorkInc. 1991
Gynecologic Magnetic Resonance Imaging Cynthia Janus Department of Radiology, University of Virginia, Health Sciences Center, Charlottesville, Virginia, USA
Abstract. Magnetic resonance imaging (MRI) is an excellent modality with which to delineate normal anatomic structures and a variety of pathologic conditions in the female pelvis. It excels at demonstrating the extent of local tumor involvement in cases ofendometrial and cervical cancer. It can help to elucidate the origin and nature of a variety of benign pelvic masses in cases where ultrasound findings are equivocal, and it is an accurate tool in demonstrating congenital abnormalities of the female reproductive tract. As technology continues to evolve, MRI will likely assume an even greater role in evaluating the female pelvis. Key words: Cervical cancer -- Myometrial invasion -- Endometrial cancer -- Adenomyosis -- Endometriosis -- Congenital abnormalities.
Magnetic resonance imaging (MRI) has made detailed visualization of female pelvic anatomy possible [1-5]. While ultrasound has proved to be an excellent modality for evaluating the female pelvis, it is limited in its ability to delineate the deeper portions of the pelvis and to provide specific tissue characterization. Although it can provide valuable information regarding the extent and nature of a variety of pelvic masses, it is not sufficient for staging pelvic malignancies. Computed tomography (CT) is superior to ultrasound in visualizing the deep pel-
Address offprint requests to: Cynthia Janus, M.D., Department of Radiology, University of Virginia, Health Sciences Center, Box 170, Charlottesville, VA 22908, USA
vis and pelvic sidewalls but also has some limitations in soft tissue contrast resolution. Ionizing radiation and the need for intravenous contrast are other disadvantages. MRI can demonstrate the deeper portions of the pelvis and the pelvic sidewalls and can also depict the internal architecture of the uterus. Changes in appearance of the uterine zonal anatomy in response to the ho'rmonal environment during different phases of the menstrual cycle [6-8] and with age [3] can be appreciated on M R images. The multiplanar imaging capability of MRI and lack of ionizing radiation [9, 10] are other attractive features of this modality. Principles While ultrasound utilizes high-frequency sound waves and CT involves ionizing radiation, M R I is based upon the interaction between radio waves and hydrogen nuclei in the body in the presence of a strong magnetic field [1 l, 12]. When a patient is undergoing an M R exam, a small percentage (< l/ 1,000,000) of the protons in the body tend to align in the same direction of the magnetic field within the bore of the magnet. The protons absorb energy and their alignment is changed when subjected to radio waves of a certain frequency and they re-align with the magnetic field as they release radio-wave energy that subsequently comprises the M R signal. The radio-wave energy is absorbed and released at different characteristic rates by the tissues. The signal intensity of a tissue depends upon several factors. TR and TE are two of these variables and can be manipulated by the radiologist. T R is the time between the administered radio-frequency pulses or the time in which the protons are allowed to align
30 with the direction o f the m a i n magnetic field. T E is the length o f t i m e for the a b s o r b e d r a d i o - w a v e energy to be released. T h e tissue properties T 1 and T2 are also i m p o r t a n t factors in d e t e r m i n i n g signal intensity. T1 is a t i m e constant that reflects h o w quickly a specific tissue will be ready to a b s o r b the r a d i o - w a v e energy to which it is exposed. T h e t i m e
Fig. I. T2-weighted (TR 2200 msec, TE 80 msec) sagittal view demonstrates normal zonal anatomy in a retroverted uterus. E, endometrial region; M, myometrium; junctional zone is the low signal band between the small curved arrows; small straight arrows demarcate cervix.
C. Janus: Gynecologic MRI constant T2 indicates h o w rapidly a specific tissue will lose the r a d i o - w a v e energy that it has absorbed. Last, the n u m b e r o f p r o t o n s in a particular tissue a n d the m o t i o n or flow o f these p r o t o n s also influence signal intensity.
Imaging Protocol T h e r e is no p r e p a r a t i o n for a M R I e x a m o f the pelvis. While full distension o f the urinary b l a d d e r is u n c o m f o r t a b l e a n d unnecessary, partial distension facilitates delineation o f the b l a d d e r wall a n d allows for d e t e r m i n a t i o n o f invasion in cases o f gynecologic malignancy. Basic imaging sequences for evaluation o f the pelvis include T2-weighted images in the sagittal plane (Fig. 1) a n d T 1- a n d T2-weighted images in the axial (transverse) plane (Figs. 2 a n d 3). T 1- and T2-weighted imaging sequences in the coronal plane are also often utilized (Fig. 4). Zonal a n a t o m y o f the uterus is best d e m o n s t r a t e d on sagittal T2-weighted images. T h e sagittal projection also aids in directly d e m o n s t r a t i n g the cephalocaudal extent o f a m a s s
Fig. 2. Axial T 1-weighted (TR 500 msec, TE 17 msec) images at the level of the vagina (between arrows) (A), cervix (between curved arrows) (B), and uterus (C). These structures appear relatively featureless and zonal anatomy is not distinct. A small cyst in the left ovary (arrow) in (C) contains blood and is of high signal intensity. U, uterus.
Fig. 3. T2-weighted axial images at the level of the lower vagina (A), vaginal fornices (B), cervix (between arrows) (C), and uterus (D). Zonal anatomy is clearly visualized and follicles are seen in both ovaries in this 38-year-old woman. U, urethra; 1I, vagina; B, urinary bladder; O, ovary with follicles.
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•
~
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•
Fig. 4. CoronalTl-weighted(A) and T2-weighted(B) images show the uterus and adnexae. Ovarian follicles(arrows) are of low signal intensityon Tl-weighted images and of high signal intensityon T2-weightedscans. and is helpful in assessing invasion of the urinary bladder and rectum. The transverse plane is best for evaluation oflymphadenopathy and parametrial extension of tumor. Tl-weighted images are most helpful in delineating the uterus and parametria from the surrounding fat. The ovaries are evaluated with T 1- and T2-weighted sequences using transaxial and coronal planes.
Fig. 5. A SagittalT2-weightedimageshows the uterine zonal anatomyon day 5 of the menstrualcycle.B Increasein thickness of the endometrial zone is seen on day 12 of the cycle. E, endometrium.
Normal Anatomy
The zonal anatomy of the uterus can be delineated on T2-weighted sequences, best seen in the sagittal projection (Fig. 1). The endometrium is depicted as a central area of high signal intensity and is distinguished from the peripheral area of moderate signal intensity representing myometrium. Between these areas there is a low signal intensity band which has been termed the junctional zone and which is currently believed to correspond to the inner one third of the myometrium [2, 3]. The uterus displays a relatively homogeneous moderate signal intensity on T l-weighted images and appears relatively featureless (Figs. 2C and 4A). The endometrial region and junctional zone appear prominent in women of reproductive age. Both zones increase in width during the menstrual cycle with the most rapid increase in the peri-ovulatory period (days 8-16) (Fig. 5). A general decrease in signal intensity from the endometrium is seen just prior to menstruation and discrete areas of low signal representing blood clots can be seen within the endometrial region during the menstrual phase. Endometrial atrophy has been demonstrated in women taking oral contraceptives [6]. The endometrium appears thin, measuring 2 m m or less, and the cyclic changes are absent in premenarchal girls and in postmenopausal women not taking exogenous hormones [3] (Fig. 6). The junctional zone also appears thin and may not be visible as a distinct band. The myometrium reveals an intermediate signal intensity, less than that seen in women of reproductive
The uterus is small and the endometrialzone is thin in this elderlywoman. B, urinarybladder.
Fig. 6.
age. However, in postmenopausal women who are being treated with exogenous estrogens, the uterus has a similar appearance to that of women of reproductive age. The cervix is represented by a central area of high signal intensity that comprises the region of the endocervical glands surrounded by an area of low signal intensity which represents the fibrous cervical stroma (Figs. 1 and 3C). The pericervical tissues are normally of moderate signal intensity and of variable increased signal intensity on T2 images. The vagina is most clearly demonstrated on T2weighted images in the transverse plane (Figs. 2A, 3A, and 3B). The lateral fornices mark the upper one third of the vagina while the middle third is
32
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Fig. 7. A Small developing follicles are seen in a close-up T2weighted view of the ovary (between arrows) on day 5 of a normal cycle. B A dominant follicle ( f ) is seen on day 12.
seen at the level o f the bladder base and the lower third is found at the level of the urethra. The central high signal portion representing mucus is thin in premenarchal girls and the vaginal wall is of low signal intensity. In women of reproductive age during the early proliferative phase of the cycle, a central area of high signal intensity representing mucus and epithelium surrounded by a low signal intensity component representing the vaginal wall is seen on T2 images. The high signal intensity portion increases in thickness during the early secretory phase and this is usually accompanied by some loss of contrast differentiating the central mucus from the medium high signal intensity of the vaginal wall. In pregnant patients the vaginal wall characteristically demonstrates high signal intensity, particularly during the second and third trimesters. As to be expected, in postmenopausal women who are not taking estrogens, the central high signal mucus portion is thin and the vaginal wall is of low signal intensity. The ovaries can be recognized on MR images in most women of reproductive age but may be difficult to delineate in premenarchal girls and elderly women. On Tl-weighted images they are of low to medium signal intensity (Fig. 4A), whereas on T2-weighted sequences, signal intensity is high and individual follicles can be delineated (Fig. 4B). Changes in follicular size and appearance can be appreciated on T2-weighted imaging sequences [8] (Fig. 7).
Gynecologic Tumors Perhaps the most important application of MRI of the female pelvis is in helping to delineate, characterize, and stage gynecologic malignancies. Ac-
Fig. 8. The endometrial zone of the uterus (e) is abnormally enlarged in this elderly woman. This appearance may be seen in endometrial cancer but is nonspecific. The junctional zone is intact with no evidence of invasion of the myometrium by tumor.
curacy in staging is important in determining prognosis and in choosing the optimal treatment protocol. FIGO staging is often inaccurate because of limitations in evaluating the parametria, pelvic sidewalls, and lymph node chains.
Endometrial Cancer Endometrial carcinoma has a variable and nonspecific appearance on magnetic resonance imaging [ 13, 14]. It may manifest as expansion of the central area of high signal intensity on T2-weighted images (Fig. 8) and/or an area of decreased attenuation within the high signal endometrial region. Adenomatous
C. Janus: GynecologicMRI hyperplasia and blood clots in the endometrial cavity m a y simulate endometrial cancer [ 13]. The uterus m a y appear n o r m a l with early lesions. Prognosis is related to the location o f the tumor, the depth o f m y o m e t r i a l invasion, l y m p h node inv o l v e m e n t , and the stage o f the disease, as well as patient age, cell type, and histologic grade o f the tumor. Visualization o f an intact junctional zone indicates that the t u m o r is confined to the endom e t r i u m (Fig. 8). With superficial m y o m e t r i a l invasion, there is segmental interruption o f the junctional zone (Fig. 9A). It should be noted that the junctional zone m a y not be visible in some postmenopausal w o m e n and, in these cases, irregularity o f the interface between e n d o m e t r i u m and m y o m e t r i u m m a y indicate superficial m y o m e t r i a l invasion
Fig. 9. A There is a focal interruption of the junctional zone (between arrows) on the ~gittal T2-weighted view of the uterus in this patient with known endometrial cancer indicating superficial invasion of the myometrium. B Irregularity of the interface between the high signal intensity endometrium and the moderate signal intensity myometrium in another patient with superficial myometrial invasion by endometrial cancer is shown on an axial T2-weighted view (uterus shown between arrows).
33 (Fig. 9B). In cases o f deep m y o m e t r i a l invasion (Fig. 10), the area o f a b n o r m a l signal representing the t u m o r extends across m o r e than one half o f the thickness o f the m y o m e t r i u m . Stage I endometrial cancer is generally treated with surgery. Since a significant percentage o f w o m e n with stage I disease will have l y m p h node involvement, M R imaging can help the surgeon decide whether sampling o f pelvic a n d / o r aortic lymph nodes is appropriate [13]. Specific sites o f lymph node i n v o l v e m e n t are diagnosed by the d e m o n s t r a t i o n o f enlargement o f the nodes a n d / o r l y m p h nodes with a b n o r m a l high signal intensity on T2-weighted images. M R I is proving to be highly accurate in staging histologically d o c u m e n t e d endometrial cancer. In a study o f 51 patients clinically suspected o f having endometrial carcinoma and in w h o m 45 this diagnosis was confirmed histologically, Hricak et aL [13] d e t e r m i n e d the overall accuracy o f M R imaging in staging endometrial carcinoma to be 92% with an overall accuracy o f 82% in showing the depth o f myometrial invasion. In this study M R I d e m o n strated limitations in delineating adnexal and peritoneal metastases and l y m p h node involvement. In another prospective study, Chert et aL [14] evaluated 50 patients by M R I with stage I endometrial cancer who had primary surgical treatment. T h e M R exam resulted in an advance in staging in 18% o f the patients and accurately predicted deep m y o m e trial invasion in 94% o f the patients. T h e authors concluded the M R I should be considered in the routine workup o f patients with stage I disease.
Carcinoma of the Cervix Cervical carcinoma is revealed on T2-weighted images as a high signal intensity mass which is easily
Fig. 10. Sagittal(A) and axial (B) T2-weighted views reveal widening of the endometrial zone with areas of heterogeneous low signal intensity. Extension of the abnormal signal intensity is seen to involve greater than one half the thickness of the myometrium in a patient with deep myometrial invasion by endometrial carcinoma. T, irregularly shaped heterogeneous low signal intensity endometrial carcinoma with deep invasion of the myometrium.
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Fig. 11. There is an area of abnormally high signal intensity in the region of the cervix and widening of the endocervical canal (between arrows) in this patient with known carcinoma of the cervix. B, distended urinary bladder.
delineated from the normal low signal intensity cervical stroma [ 15-19] (Fig. l 1). Cervical cancer confined to the cervix and/or uterine corpus is classified as stage IB. The outer low signal intensity cervical stroma is sharply delineated from the pericervical tissue. Preservation of the low signal intensity stripe of the peripheral cervical stroma on T2-weighted images is a reliable sign that full-thickness involvement of the cervical stroma and parametrial invasion by tumor is not present (Fig. 12). Stage IIA cervical cancers extend into the upper two thirds of the vagina, depicted by loss of the normally low signal intensity vaginal wall. Signs of pericervicalparametrial involvement (IIB) include irregularity of the lateral cervical margin and a mass or area of abnormal signal intensity in the parametrial region (Fig. 13). Signal intensity of the abnormality is lower than fat on T 1-weighted images and of high signal intensity on T2-weighted sequences and may be difficult to differentiate from active inflammatory tissue. Since evaluation of the parametrium is considered to be one of the most important parameters in staging cervical cancer, it has been recommended that MRI be utilized in place of CT as a routine imaging procedure for preoperative staging [20]. Cervical carcinoma is classified as stage IIIA if the high signal intensity mass extends to the lower one third of the vagina and as stage IIIB if there is extension to the pelvic sidewall. Involvement of the bladder (Fig. 14) or bowel wall (stage IVA) is revealed as loss of the normal low signal intensity wall of these structures on T2-weighted images and loss of the normal fat planes between them and the cer-
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Fig. 12. The low signal intensity zone of the peripheral cervical stroma (between arrows) is seen to be intact on this T2-weighted axial image in a patient with known cervical carcinoma without parametrial extension.
vical tumor. Enlargement of lymph nodes with variable increase in signal intensity on T2-weighted images (Fig. 15), while nonspecific, is seen with metastatic involvement. Several recent studies have shown M R imaging to be very accurate in staging cervical cancer. In a study of 10 patients with stage IB cervical carcinoma, Angel et al. [17] found that MRI more accurately predicted size of the tumor and extent of stromal involvement than did the clinical exam when compared with findings at pathology. Some investigators have proposed that MRI be used in conjunction with clinical staging to determine appropriate therapy in women with stage IB tumors. Togashi et al. [18] demonstrated an accuracy of 95% for MRI in demonstrating invasive disease (stage IB or higher). MRI was 89% accurate in evaluation of the parametria. Overall accuracy for staging carcinoma of the cervix was 76%. Hricak et al. [19] found MRI to be accurate in demonstrating tumor location in 91% of cases and 70% accurate in determining tumor size within 0.5 cm. Accuracy rates were also high for evaluation of vaginal extension (93%) and parametrial involvement (88%). The lack of pelvic, sidewall, bladder, and rectal involvement was accurately predicted in all cases, while the positive predictive values were 75, 67, and 100%, respectively. MRI demonstrated an overall accuracy of 81% in staging cervical carcinoma in this study. In another correlative study, Kim et al. [20] reported on 30 patients with cervical carcinoma who underwent CT scan, M R imaging, and surgical exploration. This group found MRI to excel in staging cer-
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Fig. 13. Tl-weighted axial images at the level of the cervix (A) and vagina (B) demonstrate a bulky cervical cancer with involvement of the vagina and extension into the parametrium (arrows). The patient had undergone a supracervical hysterectomy 10 years previously. (C) T2weighted axial view at the level of the cervical carcinoma. Areas of low signal on Tl-weighted and areas of high and low signal on T2-weighted views are secondary to necrosis. B, urinary bladder.
vical carcinoma with an accuracy rate o f 83% c o m p a r e d to 63% for C T scan and 70% for clinical examination. M R I cannot be used to screen for cervical cancer since N a b o t h i a n cysts (Fig. 16), hemorrhage, and changes second to cervical biopsy m a y appear similar. Its benefits in more accurate staging, however, have i m p o r t a n t applications. Surgery, radiation therapy, or both are used to treat stage I and limited stage II disease [21-23]. Since there are m a n y variations in t u m o r size and location included in the stage I category, knowledge o f t u m o r size and location can aid the gynecologist in making the decision between surgery alone or combining with radiation therapy. Gestational Trophoblastic Neoplasia Gestational trophoblastic neoplasia ( G T N ) comprises a spectrum o f pathology that includes the benign hydatidiform mole, the invasive mole (cho-
rioadenoma), and the highly malignant choriocarc i n o m a [24, 25]. Elevated levels o f h u m a n chorionic gonadotropin help diagnose trophoblastic disease and serial levels are an indicator o f t u m o r activity. Sonography has been used to demonstrate size o f the t u m o r and the uterus and CT scan has been helpful in finding metastases. Uterine G T N is usually manifest as a hypervascular mass on T2weighted M R images and the distortion or destruction o f zonal a n a t o m y is revealed (Fig. 17). Signal intensity o f the t u m o r on T 1-weighted images is often like that o f n o r m a l m y o m e t r i u m but there m a y be areas o f high signal intensity corresponding to the presence o f blood. T h e r e m a y also be tortuous vessels in the region o f the t u m o r and adjacent normal m y o m e t r i u m , as well as in the adnexae. Associated theca lutein cysts are easily visualized. M R imaging can he especially useful when the t u m o r deeply invades the m y o m e t r i u m but does not extend to the endometrial surface in which case uterine curettage specimens are not helpful. M R I has also
36 been utilized to exclude the uterine source for elev a t e d H C G levels in patients with extrauterine germ cell t u m o r s . It m a y also be used, along with H C G levels, to evaluate response to therapy. C T has generally been considered the imaging procedure o f choice in evaluating the patient with G T N for evidence o f metastases. M R I has been advocated, however, to evaluate the uterus as the site o f the p r i m a r y t u m o r , to follow response to therapy, and in cases where there is a contraindication to iodinated i n t r a v e n o u s contrast [24, 25].
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Leiomyosarcoma L e i o m y o s a r c o m a m a y a p p e a r as uterine enlargem e n t with distortion or destruction o f the zonal a n a t o m y a n d areas o f a b n o r m a l signal intensity [26, 27] (Fig. 18). It m a y simulate e n d o m e t r i a l carcin o m a with m y o m e t r i a l i n v o l v e m e n t or c o m p l i c a t e d l e i o m y o m a s . M R imaging can, however, accurately define the extent o f the t u m o r in the uterus a n d its extension to adjacent tissues.
Carcinoma of the Vagina T h e usefulness o f M R imaging in evaluation o f tum o r i n v o l v e m e n t o f the vagina has also been investigated. Chang et al. [28] studied w o m e n in w h o m primary, metastatic, or recurrent vaginal cancer was suspected clinically. Diagnosis o f t u m o r was based on c o n t o u r d e f o r m i t y a n d / o r a b n o r m a l high signal intensity on T2-weighted images (Fig. 19). In d e m onstration o f metastatic i n v o l v e m e n t , the accuracy o f M R I was 92% with a sensitivity o f 95% a n d a specificity o f 90%. M R I very accurately excluded t u m o r extension but s o m e cases o f i n f l a m m a t i o n
Fig. 14. Sagittal T2-proton-density-weighted view in an advanced case of cervical carcinoma. There is obstruction of the endometrial cavity (E) and invasion of the urinary bladder, manifested by loss of the normal low signal intensity line representing posterior bladder wall (small arrows) and intervening high signal intensity cleavage fat plane at the level of the tumor. C, large cervical tumor; large curved arrow points to Foley catheter balloon.
Fig. 16. Focal areas of high signal intensity at the level of the cervix (between arrows) are seen on sagittal (A) and axial (B) T2weighted images and represent Nabothian cysts.
Fig. 15. Metastatic adenopathy (arrow) from cervical carcinoma at the level of the fight iliac chain is demonstrated on proton density (A) and T2-weighted (B) axial images.
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Fig. 19.
An axial Tl-weighted image in a patient with vaginal cancer shows abnormal thickness and contour on the left (between arrows).
Fig. 17.
A high signalintensitymass (M) is seen in this patient
with choriocarcinoma.Zonal anatomyis indistinct.
Recurrent pelvic tumor generally reveals a high signal intensity on long TR/long TE (T2 weighted) imaging sequences, while the signal intensity of focal fibrosis is variable. Changes of early fibrosis, occurring 1 to 6 months after therapy, may overlap in signal intensity with tumor recurrence largely due to accompanying changes of edema and/or inflammation. Late fibrosis, seen 12 months or more after surgery or therapy, demonstrates low signal intensity on long TR/long TE sequences and can be differentiated from tumor [30]. Benign Gynecologic Abnormalities
Fig. 18. An axial T2-weightedimage at the level of the uterus demonstrates a large mass (M) representinga leiomyosarcoma. The tumor is of heterogeneousbut mainlyhigh signal intensity and there is destructionof the normal zonal architecture.
and congestion could not be distinguished from tumor causing some false-positive diagnoses. MRI was capable of distinguishing tumor and fibrotic tissue in cases of suspected recurrent vaginal cancer. Recurrent vaginal carcinoma could be diagnosed by MR with an accuracy rate of 82% [28]. Recurrent Gynecologic Tumors
The ability of MRI to differentiate residual or recurrent tumor from fibrosis following surgery or radiation therapy [29, 30] varies with the primary site of tumor and the length of time since treatment. While excellent results have been reported for diagnosing recurrent tumors of the cervix and vagina, accuracy rates may not be as high for tumors of the bladder and rectum.
The leiomyoma is the most common uterine tumor occurring in approximately 20-30% of women of reproductive age. Accurate delineation of the number, size, and location of leiomyomas is important in certain clinical situations including infertility [31 ], recurrent abortion, or surgical planning for myomectomy [32, 33]. Leiomyomas are well circumscribed and sharply demarcated from adjacent myometrium. Uncomplicated fibroids will demonstrate low signal intensity on both T1- and T2-weighted imaging sequences (Fig. 20). Variable and higher signal intensities may be seen in association with hyaline or myxomatous degeneration or with hemorrhage (Fig. 21). Foci of calcification may be identified. In comparison with ultrasound, one study found that MRI was more accurate in evaluating uterine volume and its contents [32]. The more lateral and posterior areas of the true and false pelvis were better visualized by MRI even if uterine size was massive and uterine contours were grossly distorted [32]. It is felt that MRI provides a noninvasive means to distinguish between uterine leiomyomas and other solid pelvic masses in cases where ultrasound findings are ambiguous [33].
38
C. Janus: Gynecologic MRI
Fig. 21. A large fibroid tumor is seen to distort the uterine cavity and is of mainly low but heterogeneoussignal intensity.f, fibroid. Fig. 20. An area of homogeneous low signal intensity that is sharply demarcated from surrounding myometrium is seen on a sagittal T2-weighted image and is characteristic of an uncomplicated fibroid Or). In adenomyosis, endometrial glands and stroma are present deep within the e n d o m e t r i u m . The endometrial glands in adenomyosis are o f the basalis type and are not affected by h o r m o n a l stimulation as in the case o f endometriosis. With diffuse inv o l v e m e n t by adenomyosis, the uterus is enlarged. Thickening o f the low signal intensity band representing junctional zone has been described on T2weighted sequences [34]. This appears to correspond to an a b n o r m a l zone o f hypertrophied m y o m e t r i u m seen a r o u n d the uterine cavity at pathologic exam. An area o f focal adenomyosis is sometimes referred to as an a d e n o m y o m a . Although this condition m a y simulate a l e i o m y o m a at gross inspection, the ade n o m y o m a differs in that it interdigitates with normal s m o o t h muscle. This is presented on T2-weighted M R images as a focal area o f low signal intensity that is poorly delineated from the surrounding myometrium.
Congenital Abnormalities M R imaging has m a d e it possible to diagnose m a n y congenital abnormalities o f the pelvic organs in a noninvasive m a n n e r [35-38]. Absence o f the vagina or uterus is readily identified [35-37]. H e m a t o m e tria and h e m a t o c o l p o s [35, 38] are visualized as distension o f the uterus a n d / o r vagina and the med i u m to high signal intensity o f the fluid contents on T1 images identifies the presence o f blood. Bicornuate uterus can be recognized by identifying m y o m e t r i a l tissue separating the endometrial car-
Fig. 22. A cystadenocarcinoma of the ovary (T) is seen as a large complex ovarian mass on T2-weighted images in the axial projection. The mass contains solid material and septations and is located above the level of the uterine fundus. MRI is not necessarilymore reliable than ultrasound in differentiatingbenign from malignant ovarian masses. ities and by the typical configuration o f the uterine fundus, while uterine septations appear as low signal intensity bends within the high signal intensity endometrial zone.
Adnexal Pathology Currently, the role o f M R I in evaluating ovarian pathology is limited. By its ability to demonstrate uterine zonal a n a t o m y independent o f patient b o d y habitus and its multiplanar imaging capability, M R I can, however, help determine the uterine or ovarian origin o f a mass in cases where ultrasound e x a m is equivocal [39-42] (Fig. 22). M R I can also help to
C. Janus: Gynecologic MR/
39
exogenous hormonal influences and with aging. With the further improvement of technology, the advent of faster imaging sequences, and the possible future use of spectroscopy, the role of MRI in evaluating the female pelvis may assume even greater importance. References
Fig. 23. A mass (between arrows) in the right pelvis represents a hematoma following hysterectomy. A T 1-weighted coronal image reveals a low signal intensity peripheral rim, an inner area of high signal intensity, and a low to moderate central portion. B The hematoma is of uniform high signal intensity on axial T2weighted image.
characterize an adnexal mass by its ability to distinguish the presence of fat in a dermoid or blood in an endometrioma [40--42] (Fig. 23). Studies have shown MRI to be capable of demonstrating the changes ofendometriosis [41, 42] but it has not been found to reliably demonstrate extraovarian adhesions and intraperitoneal endometrial implants. Indeed, MRI should not be utilized in place of laproscopy to definitively diagnose endometriosis or to accurately define its extent. It has been used, however, to monitor treatment once the diagnosis is established [41, 42]. Conclusion
MRI, with its multiplanar imaging capabilities, excellent contrast resolution, and superior ability to delineate uterine zonal anatomy, is making important contributions in diagnosing pathology in the female pelvis. Ultrasound will undoubtedly remain the first line of imaging and the initial procedure in evaluating clinically suspected pelvic pathology. CT has proved useful in evaluating complex pelvic masses and in demonstrating metastases in patients with gynecologic malignancies. MRI has added important information in staging malignant tumors of the uterus and indications suggest that it may supplant CT in the future. It can help to determine the origin and nature of certain benign masses when findings on ultrasound are ambiguous and has proved valuable in evaluating congenital abnormalities of the female reproductive tract. M R also shows potential in adding to our understanding of the changes that occur in the normal uterus with normal and
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