High resolution ultrasound (54k bytes) confirmed an abnormal, hypoechoic, right lower pole (arrow, 54k bytes) as well as rounded isoechoic (to the normal thyroid) 1-3 cm masses anterior and lateral to the right common carotid artery (arrowheads).
A gallium scan (not shown) showed no evidence for gallium avid disease. 400 uCi I-123 thyroid scan (50k bytes) subsequently demonstrated findings identical to the Tc-99m scan. Whole body imaging showed no evidence of disease elsewhere.
Contrast enhanced CT scan of the neck showed a dominant nodule in the right lobe of the thyroid with rounded, 1-3 cm, enhancing structures (59k bytes) in the right neck containing low attenuation central portions (arrow, 59k bytes).
FNA (Fine Needle Aspiration) was performed and yielded benign appearing small microthyroid acini consistent with microfollicular adenoma from a right neck lymph node. FNA of the right thyroid nodule was unsatisfactory. Total thyroidectomy and right neck dissection was performed and the pathology was follicular adenocarcinoma of the right lobe of the thyroid with metastatic disease to multiple right cervical lymph nodes. I-131 scan 6 months following surgery demonstrated several foci of increased activity in the thyroid bed and right neck. A 29 mCi I-131 treatment dose was given and follow- up I-131 scan 22 months after surgery showed no definite residual activity. Patient was without complaint.
The possibility of thyroid malignancy is inherent whenever a palpable nodule is detected. The difficulty arises in that thyroid malignancy is uncommon but nodules are extremely common. In 1993 there were 12,700 new cases of thyroid malignancy with 1000 deaths. 3-4%% of the adult population will have a palpable thyroid nodule yielding a total of 2000-3000 benign nodules found for each malignancy detected. An additional issue of interest is that the vast majority of thyroid malignancies, 80%% being papillary and follicular CA, have a non-aggressive natural history. The ideal, high sensitivity and high specificity, screening exam does not exist.
Scintigraphy is often the first imaging modality employed with a well defined role of identifying the autonomously functioning nodule (an invariably benign entity). However, the high sensitivity (close to 100%%) and very low specificity (15-20%%) of scintigraphy eliminates only a small percentage of benign lesions. There continues to be some debate with regard to the use of Tc-99m versus I-123. It has been demonstrated that Tc-99m, while subjectively less appealing, is diagnostically similar. Discordant nodules are uncommon (less than 10 total reported cases of malignancy). High resolution ultrasound will frequently be the next test employed but suffers from nearly identical sensitivity and specificity values. In fact, because of the increased resolution of US (2mm), ten times more nodules will be detected without significantly reducing the chance of the dominant nodule being malignant. This serves to complicate the issue when the palpable nodule is not adequately correlated with the ultrasound findings. CT, MRI and Ga-67 do not have a primary role in evaluation of the solitary or dominant thyroid nodule.
FNA has been advocated by an increasing number of clinicians as the primary mode of evaluation of the solitary palpable nodule in a euthyroid patient. When performed in experienced centers the sensitivity is near 100%% with a specificity of >90%%. It has been calculated that overall cost savings when utilizing FNA as the initial test are about 25%%. While theoretically the best screening test there are several practical limitations to the widespread application of FNA. The most basic of these limitations includes the necessity for experienced clinicians and cytopathologists and the invasive nature of the technique (particularly with respect to patient anxiety).
Ultrasound, scintigraphy, and FNA clearly all have application in specific situations. They all also have weaknesses with regard to screening for thyroid malignancy. Clinical factors must be used to determine the pace and aggressiveness of the evaluation. Just as important will be the need to balance the demands of the referring clinician, endocrinologist, surgeon and patient. In the current capitation climate there will be less tolerance for the shotgun approach to problem solving. The radiologist and nuclear medicine physician will be called upon to help guide patients and clinicians through an increasingly complex maze of diagnostic modalities.
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