USMLE – Solitary Thyroid Nodule
Palpable thyroid nodules occur in approximately 5% of females and are even more commonly found at postmortem examination. Whereas multinodular goiter is benign, solitary nodules may be malignant. In those who seek medical attention it is important, therefore, to determine whether the nodule is benign, e.g. cyst or colloid nodule or malignant. With the exception of hemorrhage into a cyst when thyroid enlargement is of rapid onset and painful or the presence of cervical lymphadenopathy which is highly suggestive of carcinoma, it is rarely possible to make this distinction on clinical grounds alone. However, a solitary nodule presenting in childhood or adolescence, particularly if there is a past history of head and neck irradiation or presenting in the elderly, should raise the suspicion of malignancy. Very occasionally, a secondary deposit from a renal, breast or lung carcinoma presents as a painful, rapidly growing solitary thyroid nodule.
The most useful is fine-needle aspiration of the nodule. This is performed in the outpatient clinic without local anaesthetic, using a standard 21 gauge venepuncture needle and a 20 ml syringe. Aspiration may be therapeutic in the small proportion of patients in whom the swelling is a pure cyst, although recurrence on more than one occasion is an indication for surgery. Usually 2-3 aspirates are taken from the nodule. Cytological examination will differentiate benign (80%) from suspicious or definitely malignant nodules (20%), of which half are confirmed as cancer at surgery. The advantage of fine-needle aspiration over long established tests such as isotope and ultrasound scanning is that a much higher proportion of patients avoid surgery. The limitation of the method is that it cannot differentiate between follicular adenoma and carcinoma.
It is important to measure serum T3, T4 and TSH in all patients with a solitary thyroid nodule. The finding of undetectable TSH is very suggestive of an autonomously functioning thyroid adenoma which can only be confirmed by thyroid isotope scanning is for practical purposes always benign and is treated with 131-I or surgery.