AJR 2000; 175:898
© American Roentgen Ray Society
Sonography Case of the Day |
Case 1
Thyroid Hemiagenesis with Adenoma
Kuldeep Vaswani,
Kenneth M. Vitellas and
William F. Bennett
Sonography (Fig. 1A) reveals
absence of the left thyroid lobe and enlargement of the right thyroid lobe,
which contains a mixed echogenic nodule. The incidence of a thyroid nodule is
4-8% by palpation and approximately 50% at autopsy or sonography. Thyroid
nodules are multiple in approximately 40% of patients and solitary in
approximately 10% of patients. Adenomatous nodules predominate. Imaging
studies cannot reliably distinguish between carcinoma and benign adenoma.
Fine-needle aspiration is usually performed for diagnosis, with 60-90%
diagnostic accuracy. Large needle core biopsies usually result in more
complications and no significant increase in diagnostic accuracy.
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Fig. 1A. —70-year-old woman with multiple nodular densities in cervical region
that are palpable on physical examination. Sonogram of neck shows no left
thyroid lobe, consistent with congenital absence. Right lobe is enlarged, with
mixed echogenic mass (arrows). Fine-needle aspiration was consistent
with adenoma.
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Thyroid-related anomalies usually result from abnormal descent of the
thyroglossal duct. Low or arrested descent can result in ectopic thyroid
tissue [1]. Obliteration can
result in cysts, sinus tracts, and absence. Thyroid agenesis is uncommon.
Hemiagenesis is also uncommon; however, when it does occur, it often involves
the left lobe. This may result in dysfunction or hypertrophy of the remaining
lobe [2]. At times, a pyramidal
lobe can also be seen [3].
Thyroid nodules are incidental findings in 4-8% of adults. Most of these
are benign adenomas, follicular nodules, or colloid cysts. They can hemorrhage
and become infected. Malignancy is always a consideration. Patients with a
history of radiation who are younger than 20 or older than 60 years are at
increased risk for malignancy. Metastatic disease to the thyroid is less
common, usually originating from the breast, lung, renal primary cancer, or
melanoma. Imaging studies cannot reliably distinguish between benign and
malignant processes [4,
5].
Lymphoma is not the correct diagnosis because no other lymph nodes or
masses were appreciated on examination. A single reactive lymph node could
still be in the differential diagnosis. However, the sonogram
(Fig. 1A) shows a
well-circumscribed mass containing mixed echogenic nodule, corresponding to
the right lobe of the thyroid.
Carotid artery aneurysm is incorrect because the mass seen here is not
originating from the carotid artery. Furthermore, no bruits were found on
physical examination. CT performed several months before this examination
(Fig. 1B) showed this mass to
be originating from the right lobe of the thyroid.
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Fig. 1B. —70-year-old woman with multiple nodular densities in cervical region
that are palpable on physical examination. CT scan obtained 9 months before
sonogram shows absent left thryoid lobe and enlarged right thryoid lobe with
small low-attenuation lesion (arrows). Patient denied any past
surgical intervention.
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References
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Murray-Carpenter BL, Merten DF. Radiographic manifestations of
congenital anomalies affecting airways. Radiol Clin North
Am 1991;29:219
-240[Medline]
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Vazquez E, Enriquez I, Castellote A, Lucaya J, Creixell S. US, CT
and MR imaging of neck lesions in children.
RadioGraphics
1995;15:105
-122[Abstract]
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Chiles C, Davis KW, Williams DW. Navigating the thoracic inlet.
RadioGraphics
1999;19:1161
-1176[Abstract/Free Full Text]
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Harvey HK. Diagnosis and management of the thyroid nodule.
Otolaryngol Clin North Am
1990;23:303
-307[Medline]
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Loevner LA. Imaging of the thyroid gland. Semin
Ultrasound CT MR
1996;17:539
-562[Medline]
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