198
CLINICAL IMAGING 1992;16:198-200
THYROID CYST MISTAKEN FOR CAROTID PSEUDOANEURYSM BY MR ANGIOGRAPHY CASE REPORT CHARLES M. ANDERSON, MD, PHD, GRETCHEN A.W. GOODING, MD, AND RALPH E. LEE, A hormal volunteer for magnetic resonance angiography of the carotid arteries had an abnormal examination that suggested a common carotid pseudoaneurysm. High resolution sonography identified a normal carotid artery immediately adjacent to a thyroid lesion, part of which was cystic and which mimicked carotid aneurysmal disease. KEY WORDS:
Thyroid;
MR angiography;
Carotid;
Pseudoaneurysm
INTRODUCTION Magnetic Resonance Angiography (MRA) has recently been demonstrated as a screening method for atherosclerotic disease of the carotid arteries (1). While early experience is encouraging, the limitations of this modality are not fully explored. We have developed an imaging coil (2) that permits visualization of the aortic arch and proximal common carotid arteries (CGA) by MRA. During the course of testing this coil, we have encountered an ambiguity in interpretation not previously described.
CASE REPORT A 3%year-old male volunteer underwent MRA of the aortic arch and proximal carotid arteries using an experimental transmit-receive head coil that was
From the Radiology Service, the San Francisco VA Medical Center, San Francisco, California. Address reprint requests to: Gretchen A.W. Gooding, MD, Chief, Radiology Service (114), San Francisco VA Medical Center, 4150 Clement Street, San Francisco, CA 94121. Received December, 1991; accepted February 1992. 0 1992 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, 0899-7071/92/$5.00
New York, NY 10010
RT
modified to be positioned over the lower neck. This coil was similar in principle to a previously described coil (2). A three-dimensional time-of-flight angiogram (1) was acquired in the coronal plane to include the top of the transverse aortic arch and proximal CCA (TR = 40 ms, TE = 7 ms, Theta = 20”) on a 1.5 T imager (Siemens AG, Erlangen, Germany). The images revealed an apparent 12 mm pseudoaneurysm of the proximal left CCA (Figure 1). On rotated views, the apparent lesion moved with the vessel and extended anteromedially from it. While on some views the lesion did not precisely touch the carotid, this was thought to result from turbulence in the aneurysm neck. The patient had no prior history of trauma or infection in the area, and there was no palpable neck mass. In order to verify the abnormality and characterize it more fully, a sonogram of the lower neck was undertaken with a 10 MHz linear array transducer (Diasonics, Sunnyvale, CA) with a water bath interface in transverse and longitudinal plane. The images revealed a normal proximal left CCA immediately adjacent to a well circumscribed complex lesion of the thyroid gland that was both solid and cystic (Figure 2). The thyroid mass measured 13 by 14 mm. The remainder of the thyroid gland was normal. No cervical adenopathy was present. Subsequent Tl weighted MRI images of the thyroid demonstrated that the contents of this lesion were bright, consistent with hemorrhage or proteinaceous material (Figure 3). Implications of these findings were discussed and the patient elected to be followed. DISCUSSION MRA using the time-of-flight principle generates predominantly Tl weighted images. Bright signal may reflect inflow of relaxed intravascular blood or a tis-
IULY-SEPTEMBER
THYROID CYST MISTAKEN BY MR ANGIOGRAPHY
1992
199
FIGURE
3. Transverse spin-echo Tl weighted image of neck (TR = 500, TE = 15) shows cystic bright lesion of left thyroid (arrow] adjacent to left CCA (C).
FIGURE 1. MRA of proximal
jection. thought
Bright focus adjacent to be pseudoaneurysm.
left CCA (C) in saggital proto left CCA (arrow) was V = Left vertebral artery.
sue with short Tl. In this case, a thyroid mass, which was immediately adjacent to the CCA and was bright on a Tl weighted image, was mistaken for blood fliw in a pseudoaneurysm. Previously,
FIGURE
FIGURE
2. Ten MHz transverse sonogram demonstrates discrete complex mass of left lower thyroid gland (arrows), which is immediately anteromedial to CCA (C).
we have seen other
instances
in which
4. MRA of neck with saturation bands (open arrows) placed above and below thyroid cyst. Arteries are not seen while cyst remains bright (closed arrow), confirming that lesion is not vascular.
200
ANDERSON ET AL.
short Tl tissues have been mistaken for vascular lesions. A colloid cyst of the third ventricle was at first thought to be an intracranial aneurysm on MRA. A bright lesion in the antecubital brachial vein on MRA in a patient with a revised Cimino shunt was discovered to be fresh thrombus. Thyroid lesions are extremely common, Asymptomatic thyroid nodules are frequently noted by sonography during carotid examinations and are present by sonography in at least 40% of those being examined for parathyroid adenoma (3, 4). A single thyroid nodule in a male has a 5 to 25% risk of malignancy. The most common lesion of the thyroid is adenomatous hyperplasia, while most cystic lesions of the thyroid are thought to be related to degenerating thyroid adenomas. Sonographically cystic thyroid lesions tend to be benign, and, upon aspiration, usually have either bloody fluid, chocolate fluid, or xanthochromic fluid, reflecting the stage of breakdown of blood products. On MRA, the thyroid is not appreciated per se. Chronic hemorrhage in thyroid lesions produces high signal on Tl weighted spin echo images (5). Heme products could have accounted for the high signal on MRA images in this case. Pitfalls in interpretation are encountered in any
CLINICAL IMAGING VOL. 16, NO. 3
new imaging modality. As the pitfalls of MRA are recognized and described, appropriate steps can be made to confirm suspected findings in order to reach an accurate diagnosis. In this case, Tl weighted spin echo images of the thyroid could have been obtained at the time of the initial study and would have revealed the true nature of this lesion. Alternatively, saturation bands could be placed across the neck above and below the suspected lesion and the MRA sequence repeated. In such a case, a pseudoaneurysm would become dark and disappear from the image, while a hemorrhagic thyroid cyst would remain bright (Figure 4). REFERENCES 1.
Masaryk TJ, Ross JS, Medic MT, et al. Carotid bifurcation: imaging. Radiology 1988;166:461.
MR
2. Anderson CM, Saloner D, Lee RE, Fortner A. Dedicated coil for carotid MR angiography. Radiology 1990;176:868-872. 3. Carrol BA. Asymptomatic thyroid nodules: graphic detection. AJR 1981;133:399-501.
incidental
sono-
4. Stark D, Clark OH, Gooding GAW, Moss AA. High resolution ultrasound and computerized tomography of thyroid lesions in patients with hyperparathyroidism. Surgery 1983;863868. 5. Noma S, Kanaoka M, Minami S. Thyroid masses: MR imaging and pathologic correlation. Radiology 1988;168:759-764.
CLINICAL IMAGING 1992;16:198-200
THYROID CYST MISTAKEN FOR CAROTID PSEUDOANEURYSM BY MR ANGIOGRAPHY CASE REPORT CHARLES M. ANDERSON, MD, PHD, GRETCHEN A.W. GOODING, MD, AND RALPH E. LEE, A hormal volunteer for magnetic resonance angiography of the carotid arteries had an abnormal examination that suggested a common carotid pseudoaneurysm. High resolution sonography identified a normal carotid artery immediately adjacent to a thyroid lesion, part of which was cystic and which mimicked carotid aneurysmal disease. KEY WORDS:
Thyroid;
MR angiography;
Carotid;
Pseudoaneurysm
INTRODUCTION Magnetic Resonance Angiography (MRA) has recently been demonstrated as a screening method for atherosclerotic disease of the carotid arteries (1). While early experience is encouraging, the limitations of this modality are not fully explored. We have developed an imaging coil (2) that permits visualization of the aortic arch and proximal common carotid arteries (CGA) by MRA. During the course of testing this coil, we have encountered an ambiguity in interpretation not previously described.
CASE REPORT A 3%year-old male volunteer underwent MRA of the aortic arch and proximal carotid arteries using an experimental transmit-receive head coil that was
From the Radiology Service, the San Francisco VA Medical Center, San Francisco, California. Address reprint requests to: Gretchen A.W. Gooding, MD, Chief, Radiology Service (114), San Francisco VA Medical Center, 4150 Clement Street, San Francisco, CA 94121. Received December, 1991; accepted February 1992. 0 1992 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, 0899-7071/92/$5.00
New York, NY 10010
RT
modified to be positioned over the lower neck. This coil was similar in principle to a previously described coil (2). A three-dimensional time-of-flight angiogram (1) was acquired in the coronal plane to include the top of the transverse aortic arch and proximal CCA (TR = 40 ms, TE = 7 ms, Theta = 20”) on a 1.5 T imager (Siemens AG, Erlangen, Germany). The images revealed an apparent 12 mm pseudoaneurysm of the proximal left CCA (Figure 1). On rotated views, the apparent lesion moved with the vessel and extended anteromedially from it. While on some views the lesion did not precisely touch the carotid, this was thought to result from turbulence in the aneurysm neck. The patient had no prior history of trauma or infection in the area, and there was no palpable neck mass. In order to verify the abnormality and characterize it more fully, a sonogram of the lower neck was undertaken with a 10 MHz linear array transducer (Diasonics, Sunnyvale, CA) with a water bath interface in transverse and longitudinal plane. The images revealed a normal proximal left CCA immediately adjacent to a well circumscribed complex lesion of the thyroid gland that was both solid and cystic (Figure 2). The thyroid mass measured 13 by 14 mm. The remainder of the thyroid gland was normal. No cervical adenopathy was present. Subsequent Tl weighted MRI images of the thyroid demonstrated that the contents of this lesion were bright, consistent with hemorrhage or proteinaceous material (Figure 3). Implications of these findings were discussed and the patient elected to be followed. DISCUSSION MRA using the time-of-flight principle generates predominantly Tl weighted images. Bright signal may reflect inflow of relaxed intravascular blood or a tis-
IULY-SEPTEMBER
THYROID CYST MISTAKEN BY MR ANGIOGRAPHY
1992
199
FIGURE
3. Transverse spin-echo Tl weighted image of neck (TR = 500, TE = 15) shows cystic bright lesion of left thyroid (arrow] adjacent to left CCA (C).
FIGURE 1. MRA of proximal
jection. thought
Bright focus adjacent to be pseudoaneurysm.
left CCA (C) in saggital proto left CCA (arrow) was V = Left vertebral artery.
sue with short Tl. In this case, a thyroid mass, which was immediately adjacent to the CCA and was bright on a Tl weighted image, was mistaken for blood fliw in a pseudoaneurysm. Previously,
FIGURE
FIGURE
2. Ten MHz transverse sonogram demonstrates discrete complex mass of left lower thyroid gland (arrows), which is immediately anteromedial to CCA (C).
we have seen other
instances
in which
4. MRA of neck with saturation bands (open arrows) placed above and below thyroid cyst. Arteries are not seen while cyst remains bright (closed arrow), confirming that lesion is not vascular.
200
ANDERSON ET AL.
short Tl tissues have been mistaken for vascular lesions. A colloid cyst of the third ventricle was at first thought to be an intracranial aneurysm on MRA. A bright lesion in the antecubital brachial vein on MRA in a patient with a revised Cimino shunt was discovered to be fresh thrombus. Thyroid lesions are extremely common, Asymptomatic thyroid nodules are frequently noted by sonography during carotid examinations and are present by sonography in at least 40% of those being examined for parathyroid adenoma (3, 4). A single thyroid nodule in a male has a 5 to 25% risk of malignancy. The most common lesion of the thyroid is adenomatous hyperplasia, while most cystic lesions of the thyroid are thought to be related to degenerating thyroid adenomas. Sonographically cystic thyroid lesions tend to be benign, and, upon aspiration, usually have either bloody fluid, chocolate fluid, or xanthochromic fluid, reflecting the stage of breakdown of blood products. On MRA, the thyroid is not appreciated per se. Chronic hemorrhage in thyroid lesions produces high signal on Tl weighted spin echo images (5). Heme products could have accounted for the high signal on MRA images in this case. Pitfalls in interpretation are encountered in any
CLINICAL IMAGING VOL. 16, NO. 3
new imaging modality. As the pitfalls of MRA are recognized and described, appropriate steps can be made to confirm suspected findings in order to reach an accurate diagnosis. In this case, Tl weighted spin echo images of the thyroid could have been obtained at the time of the initial study and would have revealed the true nature of this lesion. Alternatively, saturation bands could be placed across the neck above and below the suspected lesion and the MRA sequence repeated. In such a case, a pseudoaneurysm would become dark and disappear from the image, while a hemorrhagic thyroid cyst would remain bright (Figure 4). REFERENCES 1.
Masaryk TJ, Ross JS, Medic MT, et al. Carotid bifurcation: imaging. Radiology 1988;166:461.
MR
2. Anderson CM, Saloner D, Lee RE, Fortner A. Dedicated coil for carotid MR angiography. Radiology 1990;176:868-872. 3. Carrol BA. Asymptomatic thyroid nodules: graphic detection. AJR 1981;133:399-501.
incidental
sono-
4. Stark D, Clark OH, Gooding GAW, Moss AA. High resolution ultrasound and computerized tomography of thyroid lesions in patients with hyperparathyroidism. Surgery 1983;863868. 5. Noma S, Kanaoka M, Minami S. Thyroid masses: MR imaging and pathologic correlation. Radiology 1988;168:759-764.
