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73
Sonography of the Cervix During the Third Trimester of Pregnancy: Value of the Transperineal
Barbara
S. Jarnes Therese Barbara Mark Sheryl
Hertzberg1 D. Bowie M. Weber A. Carroll A. Kliewer G. Jordan
Transabdominal
trimesters third
sonography
of pregnancy,
trimester
reliably
but cervical
progresses.
To
Approach
depicts
the
visualization
evaluate
the
cervix
during
becomes
possibility
the
first
increasingly
of using
and
second
difficult
a perineal
as the
approach
to
bypass the fetus and image the cervix during the third trimester, we used transperineal sonography to image the cervix of 158 third-trimester patients in whom transabdominal visualization was inadequate. The internal os and upper cervix were successfully visualized on transperineal sonograms in all 158 patients, but the region of the external Os was
obscured
portion
of the cervix
by rectal
gas
in 22 (14%)
was obscured
cases.
In some
patients
in whom
the
external
by bowel
gas, the problem could be overcome scanning with the patient in the lateral decubitus position or by rotating the patient. Transperineal sonography is an effective technique for imaging the cervix during third
trimester
of pregnancy,
transabdominal
sonography
AJR
157:73-76,
July
allowing
cervical
visualization
in most
patients
by the
in whom
of this area is unsuccessful.
1991
Visualization of the maternal cervix is an important component of the obstetric sonographic examination, aiding in the detection and management of placenta previa, preterm labor, and cervical incompetence [1 -9]. Transabdominal sonognaphy reliably depicts the cervix in most patients during the first and second tnimesters, but cervical visualization becomes increasingly difficult as the third trimester progresses, predominantly because of attenuation of sound by the presenting part of the fetus [1 0, 1 1 ]. A variety of techniques, including external fetal manipulation, overdistension of the maternal urinary bladder, and Trendelenburg positioning, have been used to elevate the presenting part of the fetus from the pelvis and facilitate visualization of the cervix [1 1 0-1 2]. However, such maneuvers can be uncomfortable for the patient, distort the appearance of the cervix, and are frequently unsuccessful late in the third trimester [2, 1 0]. Given the problems inherent in evaluating the third-trimester cervix by tnansabdominal sonography, we undertook this study to evaluate the feasibility of using a transpenineal approach for imaging the cervix. ,
Subjects
and Methods
Between meal Received October 12, 1990; vision January 8, 1991.
accepted
after
re-
attempts with
November
sonography
to image
a 3.5-MHz,
1989 and April 1990, we prospectively evaluated the use of transperthe cervix of 158 third-trimester patients in whom transabdominal
to visualize
the cervix
were unsuccessful.
electronically
focused,
CA), with the patient’s
bladder
Transabdominal
phased-array
empty.
sector
Graded
sonography transducer
pressure
was performed
(Acuson
was applied
1 28,
Moun-
to the maternal
authors: Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC 27710. Address reprintrequests to B S. Hertzberg.
tam View,
0361-803X/91/1571-0073 0 American Roentgen
After completion of the transabdominal portion of the examination, a protective covering (Hefty Baggie, Mobile Chemical Co., Pittsford, NY) was applied to the transducer head,
1
All
Ray Society
pelvis the
with cervix
the before
transducer
in an attempt
transabdominal
to elevate
visualization
the
of the
presenting cervix
was
part
of the fetus
considered
away
from
unsuccessful.
HERTZBERG
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74
ET AL.
AJR:157,
July 1991
located posterior to the urethra and anterior to the vagina. Under sonographic guidance, mild pressure was applied to the perineum with the transducer, and the location and angle of the transducer were altered slightly in order to optimize visualization of the cervix. In most
cases
pleted
the
in less
obtained
and
improved
compared
zation
was
cervix,
not
reviewed
seen
copy
with the transabdominal improved
when
was
cervical
the
were was
visuali-
portion
identified
sonography
com-
Cervical
a significant
of whether
was
cervix
visualization
study.
was
kept
study
of the
if cervical
by transperineal
with
of the
images
determine
transabdominally,
imaged
encountered
Hard
to
a record
was
component
5 mm.
considered
Additionally, cervix
transperineal
than
of
the
transperineally. entire
and
length
of any
of the
problems
visualization.
After completing the initial series of 1 58 patients, we continued to incorporate transperineal views of the cervix in our routine obstetric sonographic
quate. images
study were
p
secured with a rubber band, and covered with sterile sonographic gel or KY Jelly (Johnson & Johnson, New Brunswick, NJ). Scans were performed by sonographers, sonologists, sonographic fellows, and senior radiology residents who received instruction on performing the before
and
observed
attempting
transperineal
transperineal
studies
sonography.
performed A female
by others
chaperone
was
present in the room during all transperineal scanning done by men. The technique and indications for transperineal scanning were explained
to the
supine,
with
patient, the
lateral angulation
thighs
and
examination
abducted
was
sufficiently
begun to allow
with
the
placement
patient and
The transducer was positioned on the perineum in a sagittal orientation between the labia majora, usually applied directly over the labia minora, but occasionally placed between
the
labia
of the transducer.
minora
(Fig.
1 ). The
supine
portion
whether
these
with
positions were
after the
because suboptimal
of the cervix additional
positions
images
the initial
patients
series,
in both
transperineal owing
the
scans to
were
made-
transperineal right
and
obtained
shadowing
by rectal gas. We kept a record improved
transperineal
left
with of the
of
visualiza-
tion of the cervix.
Fig. 1.-Schematic diagram of perineum shows location of transducer (T) during transperineal sonography. Transducer is applied directly over labia minora (LMi) in a sagittal plane just posterior to urethra (U). Transducer location and angle are adjusted under sonographic control to optimize visualization of cervix. A = anterior, LMa = labia majora, V = vaginal orifice, R = rectal orifice, P = posterior.
technique
patient
external
transabdominal
scanned
attempted
lateral decubitus the
whenever
In 1 1 patients
center
of the transducer
was
Results Compared with transabdominal sonography, the transpenineal approach resulted in improved visualization of the cervix in all 1 58 patients scanned. On transpenineal sonograms, the cervix contained a central echogenic stripe, which was frequently surrounded by a hypoechoic region in the expected position of the endocervical canal, similar to the pattern seen by transabdominal scanning (Fig. 2) [10]. The entire length of the cervix was seen in 1 36 (86%) of the 1 58 patients scanned transpenineally. In the remaining 22 patients, the internal os and upper portion of the cervix were successfully visualized, but the external os and caudal portion of the cervix were not seen because of shadowing from gas in the adjacent rectum (Fig. 3). Results in the 1 1 patients who underwent transpenineal scanning in the right and left lateral decubitus positions because the external portion of the cervix was not visualized on transpenineal sonograms obtained with them supine were
Fig.
2.-Transperineal sonogram of thirdcervix (black arrows) reveals endocervical canal (solid white arrows) in a horizontal plane, approximately perpendicular to ultrasound beam. Region of canal is depicted as a central echogenic stripe surrounded by a hypoechoic region, similar to pattern seen during transabdominal sonography. Vagina is oriented in a nearly vertical plane. BL = maternal urinary bladder, AF = amniotic fluid, R = rectal gas, H = fetal head, open arrows = vagina.
trimester
Fig. 3.-Internal os (open arrow) and upper portion of cervix (solid arrows) are visualized by transperineal sonography, but shadowing from rectal gas (R) obscures area of external os. B = maternal urinary bladder, H = fetal head.
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AJR:157,
TRANSPERINEAL
July 1991
SONOGRAPHY
OF CERVIX
75
Fig. 4.-A, Transperineal sonogram with patient supine fails to show external portion of cervix because of shadowing by rectal gas (R). B, Transperineal sonogram of same patient in left lateral decubitus position successfully reveals entire cervix. Rotating patient into a decubitus position caused bowel gas to shift into a more favorable location, facilitating cervical visualization. B = maternal urinary bladder, H = fetal head, open arrow = internal Os, curved arrow = external os, solid arrows = cervix.
cervical visualization optimized by left lateral decubitus position in five patients, visualization optimized by right lateral decubitus position in two patients, and no improvement with decubitus views in three patients (Fig. 4A and 4B). In one additional case, the external portion of the cervix could not be seen during the initial attempt with the patient supine, and there was no improvement with right and left lateral decubitus views, but the entire cervix was successfully imaged after the patient was rotated back from the right lateral decubitus position to supine. One other problem encountered during initial scans of three of the patients imaged early in the study involved mistaking the urethra for the cervix and the urinary bladder for amniotic fluid. In all three cases, this difficulty was overcome by increasing the field of view, and with the increasing transpenineal imaging experience gained as the study progressed, this interpretative error did not recur. All patients tolerated the transpenineal scanning procedure
cervical incompetence, because early changes occur at the level of the internal os, which is inaccessible by routine vaginal
well,
demonstration
without
significant
physical
discomfort,
and
the
proce-
dune was uniformly accepted by our population of patients. We are not aware of any complications attributed to use of the transpenineal technique. To date, formal follow-up documenting the absence of complications up to the time of delivery is available on 1 1 6 patients who delivered at our institution.
Discussion The importance of attempting to visualize the cervix during obstetric sonography is well established [1 -1 2]. Sonographic depiction of the cervix is of particular value in the diagnosis and management of placenta previa, preterm labor, and cervical incompetence, as well as in examining patients with ruptured membranes in whom repeated digital examinations may be undesirable because of the risk of infection. In the case of placenta previa, direct visualization of the cervix is necessary to establish the relationship between the lower edge of the placenta and the internal cervical os [1 2, 101 2]. Similarly, sonographic changes may be the first indicators of impending cervical failure in patients with preterm labor or ,
examination
[4-6,
8].
Our study reveals that use of transpenineal sonography dramatically increases the chances of cervical visualization during the third trimester. After instruction was given regarding the anatomic orientations displayed during transpenineal sonography, the technique was readily learned by radiologists and technicians with various levels of sonographic expertise and added a minimum oftime to the sonographic examination. The internal os and upper cervix were successfully shown by transpenineal sonography in all 1 58 patients in whom transabdominal visualization was inadequate. Although the region of the external os was not imaged in 22 (14%) patients because of shadowing from adjacent rectal gas, we expect that in many patients visualization of the internal os and upper cervix will be sufficient to evaluate for placenta previa or cervical shortening. However, for those patients in whom of
the
entire
length
of the
cervix
is desirable
because cervical shortening is suspected after initial views, scanning with the patient in the decubitus position or supine after being rotated can be used in an attempt to shift gas away from the external portion of the cervix. Because of the different transducer positions used during transabdominal and transpenineal sonography, the cervix is displayed in different orientations with the two techniques. With tnansabdominal sonography, the long axis of the cervix is oriented in an approximately vertical plane, whereas with transpenineal sonography, the vagina is depicted in a vertical plane with the cervix horizontal, its long axis approximately perpendicular to the ultrasound beam (Figs. 5A and 5B) [10]. Endovaginal sonography offers an alternative approach for visualizing the cervix and lower uterine segment when transabdominal views are inadequate [1 3-1 5]. The use of endovaginal sonography has been shown to improve the chances of cervical visualization, but this technique is not always successful in imaging the cervix and has the disadvantages of requiring a specialized transducer and vaginal penetration, neither of which are necessary to perform the transpenineal technique.
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76
HERTZBERG
A
ET AL.
July 1991
B
Fig. 5.-A, Sagittal illustration of gravid uterus in a supine patient with transducer positioned during transperineal sonography. B, Before display, scanning plane depicted in A is rotated 900 counterclockwise. As a result, displayed at top of image in traditional fashion. Long axis of cervix is displayed in an approximately plane. U = urethra, R = rectum, B = bladder, V = vagina, c = cervix.
Variations on the transpenineal sonographic technique descnibed here (use of stand-off pads, linear transducers, etc.) have been used to assess female stress urinary incontinence, vaginal atresia, and umbilical cord presentation and to image the gravid cervix, but to date the potential of using transpenmeal sonography in the pregnant patient has not received widespread recognition [1 6-22]. The current study demonstrates that transperineal sonography is a safe, simple to
perform,
AJR:157,
effective
method
of imaging
the cervix
in the third
trimester of pregnancy, and we now routinely incorporate transpenineal views of the cervix in our obstetric sonographic studies when transabdominal visualization is inadequate. Furthen investigations are under way to assess the accuracy of transpenineal sonography in specific clinical situations, such
as the evaluation
for placenta
previa
and cervical
incompe-
tence. REFERENCES 1 . Townsend AR, Laing FC, Nyberg factors responsible for “placental Radiology 1986;160: 105-1 08
2. Artis AA, Bowie JO, Rosenberg
DA, Jeffrey migration”:
VW. Technical assessment.
ER, Rauch RF. The fallacy of placental AJR 1985;144:79-81
migration: effect of sonographic techniques. 3. Main OM, Hadley CB. The role of ultrasound labor. Clin Obstet Gyneco! 1988;31 :53-60
4. Michaels WH, Montgomery
RB, Wing sonographic
in the management
of preterm
C, Karo J, Temple J, Arger J, Olson J. Ultra-
sound differentiation of the competent from the incompetent cervix: prevention of preterm delivery. Am J Obstet Gynecol 1986;1 54:537-546 5. Ayers JWT, DeGrood AM, Compton AA, Barclay M, Ansbacher A. Sonographic evaluation of cervical length in pregnancy: diagnosis and management of preterm cervical effacement in patients at risk for premature delivery. Obstet Gyneco! 1988;71 :939-944 6. Podobnik M, Bulic M, Smiljanic N, Bistncki J. Ultrasonography in the detection of cervical incompetency. J Clin Ultrasound 1988;1 3: 383-391
on perineum
reveals
typical
scanning
plane
obtained
portion of image closest to transducer (open arrow) is horizontal orientation with vagina oriented in a vertical
7. Ludmir J. Sonographic detection of cervical incompetence. C!in Obstet Gyneco! 1988;31 :101 -1 09 8. Bartolucci L, Hill WC, Katz M, Gill PJ, Kitzmiller JL. Ultrasonography in preterm labor. Am J Obstet Gynecol 1984;149:52-56 9. Brook I, Feingold M, Schwartz A, Zakut H. Ultrasonography in the diagnosis of cervical incompetence in pregnancy: a new diagnostic approach. Br J Obstet Gynaecol 1981;88:640-643 1 0. Bowie JD, Andreotti RF, Rosenberg ER. Sonographic appearance of the uterine cervix in pregnancy: the vertical cervix. AJR 1983;140:737-740 1 1 . Jeffrey RB, Laing FC. Sonography of the low-lying placenta: value of Trendelenburg and traction scans. AJR 1981;137:547-549 12. Lee TG, Knochel JQ, Melendez MG, Henderson SC. Fetal elevation: a new technique for placental localization in the diagnosis of previa. J Clin Ultrasound 1981 9:467-471 13. Brown JE, Thieme GA, Shah DM, Fleischer AC, Boehm FH. Transabdominal and transvaginal endosonography: evaluation of the cervix and lower uterine segment in pregnancy. Am J Obstet Gynecol 1986;1 55:721 -726 14. Farine D, Fox HE, Jakobson S, Trimor-Tntsch IE. Is it really a placenta previa? Europ J Obstet Gynecol Reprod Bio! 1989;31 :103-108 1 5. Farine D, Fox HE, Trimor-Tritsch. Vaginal ultrasound for ruling out placenta previa (case report). Br J Obstet Gynaecol 1989;96: 117-119 1 6. Kohorn El, Scioscia AL, Jeanty P, Hobbins JC. Ultrasound cystourethrography by permneal scanning for the assessment of female stress urinary incontinence. Obstet Gyneco! 1986;68:269-272 17. Kolbl H, Bernaschek G, Wolf G. A comparative study of permneal ultrasound scanning and urethrocystography in patients with genuine stress incontinence. Arch Gyneco! Obstet 1988;244:39-45 1 8. Scanlan KA, Pozniak MA, Fagerholm M, Shapiro S. Value of transpermneal sonography in the assessment of vaginal atresia. AJR 1990;154:545-548 1 9. Graham 0, Nelson MW. Combined permneal-abdommnal sonography in the evaluation of vaginal atresia. J Clin Ultrasound 1986;14:735-738 20. Sakamoto H, Takagi K, Masaoka N, et al. Clinical application of the perineal scan: prepartum screening for cord presentation. Am J Obstet Gynecol 1986;1 55: 1041 -1 043 21 . Mahony BS, Nyberg DA, Luthy DA, Hirsch JH, Hickok DE, Petty CN. Translabial ultrasound of the third trimester uterine cervix: correlation with digital examination. J Ultrasound Med 1990;9:717-723 22. Jeanty P, dAlton M, Romero R, Hobbins JC. Penneal scanning. Am J Perinatol 1986;3: 289-295
73
Sonography of the Cervix During the Third Trimester of Pregnancy: Value of the Transperineal
Barbara
S. Jarnes Therese Barbara Mark Sheryl
Hertzberg1 D. Bowie M. Weber A. Carroll A. Kliewer G. Jordan
Transabdominal
trimesters third
sonography
of pregnancy,
trimester
reliably
but cervical
progresses.
To
Approach
depicts
the
visualization
evaluate
the
cervix
during
becomes
possibility
the
first
increasingly
of using
and
second
difficult
a perineal
as the
approach
to
bypass the fetus and image the cervix during the third trimester, we used transperineal sonography to image the cervix of 158 third-trimester patients in whom transabdominal visualization was inadequate. The internal os and upper cervix were successfully visualized on transperineal sonograms in all 158 patients, but the region of the external Os was
obscured
portion
of the cervix
by rectal
gas
in 22 (14%)
was obscured
cases.
In some
patients
in whom
the
external
by bowel
gas, the problem could be overcome scanning with the patient in the lateral decubitus position or by rotating the patient. Transperineal sonography is an effective technique for imaging the cervix during third
trimester
of pregnancy,
transabdominal
sonography
AJR
157:73-76,
July
allowing
cervical
visualization
in most
patients
by the
in whom
of this area is unsuccessful.
1991
Visualization of the maternal cervix is an important component of the obstetric sonographic examination, aiding in the detection and management of placenta previa, preterm labor, and cervical incompetence [1 -9]. Transabdominal sonognaphy reliably depicts the cervix in most patients during the first and second tnimesters, but cervical visualization becomes increasingly difficult as the third trimester progresses, predominantly because of attenuation of sound by the presenting part of the fetus [1 0, 1 1 ]. A variety of techniques, including external fetal manipulation, overdistension of the maternal urinary bladder, and Trendelenburg positioning, have been used to elevate the presenting part of the fetus from the pelvis and facilitate visualization of the cervix [1 1 0-1 2]. However, such maneuvers can be uncomfortable for the patient, distort the appearance of the cervix, and are frequently unsuccessful late in the third trimester [2, 1 0]. Given the problems inherent in evaluating the third-trimester cervix by tnansabdominal sonography, we undertook this study to evaluate the feasibility of using a transpenineal approach for imaging the cervix. ,
Subjects
and Methods
Between meal Received October 12, 1990; vision January 8, 1991.
accepted
after
re-
attempts with
November
sonography
to image
a 3.5-MHz,
1989 and April 1990, we prospectively evaluated the use of transperthe cervix of 158 third-trimester patients in whom transabdominal
to visualize
the cervix
were unsuccessful.
electronically
focused,
CA), with the patient’s
bladder
Transabdominal
phased-array
empty.
sector
Graded
sonography transducer
pressure
was performed
(Acuson
was applied
1 28,
Moun-
to the maternal
authors: Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC 27710. Address reprintrequests to B S. Hertzberg.
tam View,
0361-803X/91/1571-0073 0 American Roentgen
After completion of the transabdominal portion of the examination, a protective covering (Hefty Baggie, Mobile Chemical Co., Pittsford, NY) was applied to the transducer head,
1
All
Ray Society
pelvis the
with cervix
the before
transducer
in an attempt
transabdominal
to elevate
visualization
the
of the
presenting cervix
was
part
of the fetus
considered
away
from
unsuccessful.
HERTZBERG
Downloaded from www.ajronline.org by Biblio Astrazeneca Des Science De La Sante Du Chul on 07/06/14 from IP address 132.203.227.63. Copyright ARRS. For personal use only; all rights reserved
74
ET AL.
AJR:157,
July 1991
located posterior to the urethra and anterior to the vagina. Under sonographic guidance, mild pressure was applied to the perineum with the transducer, and the location and angle of the transducer were altered slightly in order to optimize visualization of the cervix. In most
cases
pleted
the
in less
obtained
and
improved
compared
zation
was
cervix,
not
reviewed
seen
copy
with the transabdominal improved
when
was
cervical
the
were was
visuali-
portion
identified
sonography
com-
Cervical
a significant
of whether
was
cervix
visualization
study.
was
kept
study
of the
if cervical
by transperineal
with
of the
images
determine
transabdominally,
imaged
encountered
Hard
to
a record
was
component
5 mm.
considered
Additionally, cervix
transperineal
than
of
the
transperineally. entire
and
length
of any
of the
problems
visualization.
After completing the initial series of 1 58 patients, we continued to incorporate transperineal views of the cervix in our routine obstetric sonographic
quate. images
study were
p
secured with a rubber band, and covered with sterile sonographic gel or KY Jelly (Johnson & Johnson, New Brunswick, NJ). Scans were performed by sonographers, sonologists, sonographic fellows, and senior radiology residents who received instruction on performing the before
and
observed
attempting
transperineal
transperineal
studies
sonography.
performed A female
by others
chaperone
was
present in the room during all transperineal scanning done by men. The technique and indications for transperineal scanning were explained
to the
supine,
with
patient, the
lateral angulation
thighs
and
examination
abducted
was
sufficiently
begun to allow
with
the
placement
patient and
The transducer was positioned on the perineum in a sagittal orientation between the labia majora, usually applied directly over the labia minora, but occasionally placed between
the
labia
of the transducer.
minora
(Fig.
1 ). The
supine
portion
whether
these
with
positions were
after the
because suboptimal
of the cervix additional
positions
images
the initial
patients
series,
in both
transperineal owing
the
scans to
were
made-
transperineal right
and
obtained
shadowing
by rectal gas. We kept a record improved
transperineal
left
with of the
of
visualiza-
tion of the cervix.
Fig. 1.-Schematic diagram of perineum shows location of transducer (T) during transperineal sonography. Transducer is applied directly over labia minora (LMi) in a sagittal plane just posterior to urethra (U). Transducer location and angle are adjusted under sonographic control to optimize visualization of cervix. A = anterior, LMa = labia majora, V = vaginal orifice, R = rectal orifice, P = posterior.
technique
patient
external
transabdominal
scanned
attempted
lateral decubitus the
whenever
In 1 1 patients
center
of the transducer
was
Results Compared with transabdominal sonography, the transpenineal approach resulted in improved visualization of the cervix in all 1 58 patients scanned. On transpenineal sonograms, the cervix contained a central echogenic stripe, which was frequently surrounded by a hypoechoic region in the expected position of the endocervical canal, similar to the pattern seen by transabdominal scanning (Fig. 2) [10]. The entire length of the cervix was seen in 1 36 (86%) of the 1 58 patients scanned transpenineally. In the remaining 22 patients, the internal os and upper portion of the cervix were successfully visualized, but the external os and caudal portion of the cervix were not seen because of shadowing from gas in the adjacent rectum (Fig. 3). Results in the 1 1 patients who underwent transpenineal scanning in the right and left lateral decubitus positions because the external portion of the cervix was not visualized on transpenineal sonograms obtained with them supine were
Fig.
2.-Transperineal sonogram of thirdcervix (black arrows) reveals endocervical canal (solid white arrows) in a horizontal plane, approximately perpendicular to ultrasound beam. Region of canal is depicted as a central echogenic stripe surrounded by a hypoechoic region, similar to pattern seen during transabdominal sonography. Vagina is oriented in a nearly vertical plane. BL = maternal urinary bladder, AF = amniotic fluid, R = rectal gas, H = fetal head, open arrows = vagina.
trimester
Fig. 3.-Internal os (open arrow) and upper portion of cervix (solid arrows) are visualized by transperineal sonography, but shadowing from rectal gas (R) obscures area of external os. B = maternal urinary bladder, H = fetal head.
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AJR:157,
TRANSPERINEAL
July 1991
SONOGRAPHY
OF CERVIX
75
Fig. 4.-A, Transperineal sonogram with patient supine fails to show external portion of cervix because of shadowing by rectal gas (R). B, Transperineal sonogram of same patient in left lateral decubitus position successfully reveals entire cervix. Rotating patient into a decubitus position caused bowel gas to shift into a more favorable location, facilitating cervical visualization. B = maternal urinary bladder, H = fetal head, open arrow = internal Os, curved arrow = external os, solid arrows = cervix.
cervical visualization optimized by left lateral decubitus position in five patients, visualization optimized by right lateral decubitus position in two patients, and no improvement with decubitus views in three patients (Fig. 4A and 4B). In one additional case, the external portion of the cervix could not be seen during the initial attempt with the patient supine, and there was no improvement with right and left lateral decubitus views, but the entire cervix was successfully imaged after the patient was rotated back from the right lateral decubitus position to supine. One other problem encountered during initial scans of three of the patients imaged early in the study involved mistaking the urethra for the cervix and the urinary bladder for amniotic fluid. In all three cases, this difficulty was overcome by increasing the field of view, and with the increasing transpenineal imaging experience gained as the study progressed, this interpretative error did not recur. All patients tolerated the transpenineal scanning procedure
cervical incompetence, because early changes occur at the level of the internal os, which is inaccessible by routine vaginal
well,
demonstration
without
significant
physical
discomfort,
and
the
proce-
dune was uniformly accepted by our population of patients. We are not aware of any complications attributed to use of the transpenineal technique. To date, formal follow-up documenting the absence of complications up to the time of delivery is available on 1 1 6 patients who delivered at our institution.
Discussion The importance of attempting to visualize the cervix during obstetric sonography is well established [1 -1 2]. Sonographic depiction of the cervix is of particular value in the diagnosis and management of placenta previa, preterm labor, and cervical incompetence, as well as in examining patients with ruptured membranes in whom repeated digital examinations may be undesirable because of the risk of infection. In the case of placenta previa, direct visualization of the cervix is necessary to establish the relationship between the lower edge of the placenta and the internal cervical os [1 2, 101 2]. Similarly, sonographic changes may be the first indicators of impending cervical failure in patients with preterm labor or ,
examination
[4-6,
8].
Our study reveals that use of transpenineal sonography dramatically increases the chances of cervical visualization during the third trimester. After instruction was given regarding the anatomic orientations displayed during transpenineal sonography, the technique was readily learned by radiologists and technicians with various levels of sonographic expertise and added a minimum oftime to the sonographic examination. The internal os and upper cervix were successfully shown by transpenineal sonography in all 1 58 patients in whom transabdominal visualization was inadequate. Although the region of the external os was not imaged in 22 (14%) patients because of shadowing from adjacent rectal gas, we expect that in many patients visualization of the internal os and upper cervix will be sufficient to evaluate for placenta previa or cervical shortening. However, for those patients in whom of
the
entire
length
of the
cervix
is desirable
because cervical shortening is suspected after initial views, scanning with the patient in the decubitus position or supine after being rotated can be used in an attempt to shift gas away from the external portion of the cervix. Because of the different transducer positions used during transabdominal and transpenineal sonography, the cervix is displayed in different orientations with the two techniques. With tnansabdominal sonography, the long axis of the cervix is oriented in an approximately vertical plane, whereas with transpenineal sonography, the vagina is depicted in a vertical plane with the cervix horizontal, its long axis approximately perpendicular to the ultrasound beam (Figs. 5A and 5B) [10]. Endovaginal sonography offers an alternative approach for visualizing the cervix and lower uterine segment when transabdominal views are inadequate [1 3-1 5]. The use of endovaginal sonography has been shown to improve the chances of cervical visualization, but this technique is not always successful in imaging the cervix and has the disadvantages of requiring a specialized transducer and vaginal penetration, neither of which are necessary to perform the transpenineal technique.
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76
HERTZBERG
A
ET AL.
July 1991
B
Fig. 5.-A, Sagittal illustration of gravid uterus in a supine patient with transducer positioned during transperineal sonography. B, Before display, scanning plane depicted in A is rotated 900 counterclockwise. As a result, displayed at top of image in traditional fashion. Long axis of cervix is displayed in an approximately plane. U = urethra, R = rectum, B = bladder, V = vagina, c = cervix.
Variations on the transpenineal sonographic technique descnibed here (use of stand-off pads, linear transducers, etc.) have been used to assess female stress urinary incontinence, vaginal atresia, and umbilical cord presentation and to image the gravid cervix, but to date the potential of using transpenmeal sonography in the pregnant patient has not received widespread recognition [1 6-22]. The current study demonstrates that transperineal sonography is a safe, simple to
perform,
AJR:157,
effective
method
of imaging
the cervix
in the third
trimester of pregnancy, and we now routinely incorporate transpenineal views of the cervix in our obstetric sonographic studies when transabdominal visualization is inadequate. Furthen investigations are under way to assess the accuracy of transpenineal sonography in specific clinical situations, such
as the evaluation
for placenta
previa
and cervical
incompe-
tence. REFERENCES 1 . Townsend AR, Laing FC, Nyberg factors responsible for “placental Radiology 1986;160: 105-1 08
2. Artis AA, Bowie JO, Rosenberg
DA, Jeffrey migration”:
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ER, Rauch RF. The fallacy of placental AJR 1985;144:79-81
migration: effect of sonographic techniques. 3. Main OM, Hadley CB. The role of ultrasound labor. Clin Obstet Gyneco! 1988;31 :53-60
4. Michaels WH, Montgomery
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sound differentiation of the competent from the incompetent cervix: prevention of preterm delivery. Am J Obstet Gynecol 1986;1 54:537-546 5. Ayers JWT, DeGrood AM, Compton AA, Barclay M, Ansbacher A. Sonographic evaluation of cervical length in pregnancy: diagnosis and management of preterm cervical effacement in patients at risk for premature delivery. Obstet Gyneco! 1988;71 :939-944 6. Podobnik M, Bulic M, Smiljanic N, Bistncki J. Ultrasonography in the detection of cervical incompetency. J Clin Ultrasound 1988;1 3: 383-391
on perineum
reveals
typical
scanning
plane
obtained
portion of image closest to transducer (open arrow) is horizontal orientation with vagina oriented in a vertical
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