The differential diagnosis of cystic neck masses by the determination of thyroglobulin concentrations in the aspirates.

Thyroglobulin (Tg) concentrations in the aspirates of various types of cystic neck masses were measured by RIA to assess the usefulness of this determination in differential diagnosis. The subjects consisted of 16 patients, whose final diagnoses were all established on the basis of operative results; three patients had follicular thyroid adenomas (F-Ad), 11 had papillary thyroid carcinomas (P-Ca), one had a thyroglossal duct cyst (TDC) and one had a lateral cervical cyst (LCC). Tg concentrations in the cyst fluids of F-Ad and P-Ca were very high (0.042-2.83 mg/ml) compared with serum Tg concentrations. There was no difference in Tg concentrations in the fluids of P-Ca between primary lesions (n = 5) and metastatic lesions (n = 6). On the other hand, Tg concentrations of TDC and LCC were very low (less than 100 ng/ml). Difficulty was experienced in diagnosing three patients, even though they had been examined by all nonsurgical diagnostic techniques. However, an occult thyroid carcinoma with lymph node metastasis was diagnosed by demonstrating a high Tg concentration in the aspirate of the cystic lymph node. T3 concentrations in cyst fluids of F-Ad were higher than those of P-Ca. T3 concentrations in the fluids of P-Ca, TDC and LCC did not differ, and were similar to serum T3 levels. Cytology of cyst fluids was positive in four of 10 patients examined with P-Ca. In conclusion, we can clearly confirm the thyroid origin of a cystic neck mass by demonstrating a high Tg concentration in the aspirate. This is especially useful for diagnosis in patients with thyroid carcinoma, including occult thyroid carcinomas with cystic lymph node metastasis.