Thyroid Nodules

Thyroid nodules are common, and depending on the size and age group, may be found in up to 15 % of the adult population. Most nodules are small (0.5 cm in diameter) and rarely are they malignant (95 % benign). The best way to work up a nodule is with your fingers. Clinical criteria are helpful in establishing the risk of malignancy. Nodule that are large (> 3 cm), fixed, stony hard, associated with MEN syndrome or head and neck irradiation are more likely to be malignant. Small nodules and multinodular goiter are less likely to be malignant. When several clinical criteria suggest malignancy, the risk that the nodule is malignant increases to 30-40 %.
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The next step is to inquire about symptoms and signs of thyrotoxicosis, especially if the nodule is 3 cm or greater. Check a TSH level to rule out thyrotoxicosis. If the patient is thyrotoxic, obtain a radioactive iodine scan to look for a hot nodule. A toxic nodule, for all practical purposes, is never malignant and can be ablated with radioactive iodine therapy. The majority of patients, however, will not be thyrotoxic and they need fine needle aspiration biopsy (FNA) of the nodule.

FNA can make a definitive diagnosis of any malignancy but it is most useful for papillary carcinoma (most common type, 80 %) where the appearance is unmistakable. Follicular carcinoma (15% of carcinomas)is difficult to distinguish from a benign follicular adenoma on FNA because this diagnosis is only made with certainly when there is evidence of vascular or capsular invasion or distant metastases. Some clues for malignancy are small follicles with a low amount of colloid or follicular cell crowding. Since most nodules are underactive or necrotize benign follicular adenomas this is a big problem. Fortunately experienced pathologists can readily establish the diagnosis of a benign nodule. This leaves maybe 10-30 % of biopsies that are either indeterminate or suspicious for malignancy.

All suspicious follicular neoplasms should be excised without any additional tests. There are two ways to deal with the indeterminate biopsy: thyroid hormone suppression therapy and surgery later if needed, or immediate surgery. Most indeterminate nodules are benign (at least half) and therefore a number of unnecessary operations will be performed if immediate surgery is advocated. Alternatively, many patients are unwillingly to wait to see if their nodule grows on suppression therapy to receive surgery. The management here depends on the patient.

RAI scans are usually unhelpful unless you suspect thyrotoxicosis for the reasons listed above. Most nodules are underactive or burnt out follicular adenomas and appear cold on the scan. Malignant nodules are also underactive and appear cold on the scan. Ultrasound is even less helpful. First, if you want to find nodules order an ultrasound. They are very sensitive and can detect very small nodules (several mm). Unfortunately when you find them, it’s hard to know what to do with them. FNA of small nodules is not recommended because the sample you obtain may not be from the nodule. Thus a second ultrasound-guided biopsy is needed to sample the nodule. This is a very expensive test and most (>98 %) nodules are benign. Ultrasound should only be reserved for patients where the thyroid exam is unclear by a specialist.

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