The differentiation of atypical adenomas and encapsulated follicular carcinomas in the thyroid gland.

Abstract

From 1968 to 1977 a total of 1,394 follicular neoplasms were seen in surgical material containing 4,612 thyroid glands. 1,159 tumors were obviously benign adenomas. All remaining follicular tumors with equivocal histological appearances were extensively re-examined, together with all apparently invasive follicular carcinomas. Thereby, 125 atypical adenomas, 55 encapsulated and 55 widely invasive follicular carcinomas were diagnosed. In 102 tumors a definite diagnosis was reached after excision and histological examination of ten tissue blocks from preserved wet material. In each case the number of blood vessel invasions and penetrations of tumor capsule was recorded. Among these tumors, 17/36 (47%) encapsulated carcinomas proved to be only slightly invasive. All their tissue blocks were cut into sequential sections and in 6/17 cases additional vascular invasions found. It was shown by this study that the proof of vascular invasion is more often successful than the proof of capsular penetration and therefore a better indication of malignancy in encapsulated follicular tumors. Examination of 10 tissue blocks represents the minimum effort to estimate the invasive capability of a follicular tumor, whereas sequential sections through less than 10 blocks are of little help in most cases. A follow-up study of all patients included here seems to justify the distinction we have made between atypical adenomas and encapsulated follicular carcinomas.