OBJECTIVETo study the clinicopathological features of thyrotropin-secreting pituitary adenoma (TSH adenoma).

METHODSClinical and pathological features of 7 TSH adenoma cases were studied by review of patients' medical records, light and electronic microscopy, and immunohistochemistry.

RESULTSAll seven patients presented with clinical hyperthyroidism and high levels of plasma free T3, free T4, total T3 and total T4. The levels of TSH failed to be suppressed by thyroxin administration. MRI showed macro or giant pituitary adenomas in all seven patients with tumor diameters ranging from 2.0 to 5.0 cm. Under light microscope, there were 5 cases of chromophobe cell adenoma, 1 case of acidophil cell adenoma, and 1 case of mixed acidophil and chromophobe cell adenoma. Immunohistochemical stains showed a strong positivity of TSH in all the tumors, PRL positive cells in 1 tumor, GH positive cells in 2 tumors and scattered GH and PRL double positive cells in 3 tumors. Ki-67 proliferation index ranged from 0 approximately 0.4%. P53 immunostain was negative in all tumors. After initial surgery, 2 cases had recurrences. However, the Ki-67 proliferation index was not elevated in these two tumors.

CONCLUSIONSThe histological features of TSH pituitary adenomas are heterogeneous with chromophobe as the most common subtype. Secretion of TSH was detected by immunohistochemistry in all cases. P53 mutation is not a feature of TSH adenoma and the proliferation marker, such as Ki-67, may not predict clinical behavior of the tumor. Recurrence is likely due to incomplete resection.