Histopathologic types and clinical behaviour of occult papillary carcinoma of the thyroid.

On studying 182 papillary neoplasms of the thyroid, 32 nonencapsulated lesions were found to be occult papillary carcinomas (maximum diameter 1.5 cm); out of these 32 patients 18 cases of cervical lymph node metastases were observed. Histologically, 4 circumscribed microcarcinomas, 3 partially encapsulated carcinomas, and 25 occult sclerosing carcinomas were distinguished. The mean diameter of the 4 circumscribed tumours as compared to that of the remaining 28 lesions proved to be statistically significantly smaller, but no significant differences could be observed regarding the rate of lymph node metastasis. One occult sclerosing carcinoma showed a morphologic pattern different from the remaining cases--namely that it had an exclusively solid appearance in the primary lesion and also in its lymph nodes metastases. The follicle cell origin of this lesion was established immunohistochemically by patchy thyroglobulin synthesis. The excellent prognosis of the occult category of papillary thyroid carcinoma was confirmed by a follow-up (mean 7.7 years, range 1.1 to 16.3 years), in which only 2 instances of eradicable recurrent lymph node metastases within the group of occult sclerosing carcinomas were recorded.