H. Rubén Harach

The thyroids from 101 consecutive autopsies from Finland were subserially sectioned at 2- to 3-mm intervals. From 36 thyroids, 52 foci of occult papillary carcinoma (OPC) were found, giving a prevalence rate of 35.6%, the highest reported rate in the world. The rate was higher, although not significantly, in males (43.3%) than in females (27.1%), but it did not correlate to the age of the patients. Twenty-six glands contained one tumor focus and ten glands contained two to five tumor foci. Only a minority of the smallest tumors can be detected with the method used. The probable number of OPCs over 0.15 mm in diameter was calculated to be about 300 in this material. The tumor diameter varied from 0.15 mm to 14.0 mm, with 67% of tumors under 1.0 mm. The smallest tumors were usually circumscribed and were composed almost solely of follicles. Larger tumors had more papillary structures and were often invasive. Fibrosis and, in the largest OPCs, lymphocytic reaction were seen around the invasive islands. All tumors were positively stained for thyroglobulin and all but one of the tumors stained positively for epidermal keratin. OPC appears to arise from follicular cells of normal follicles. Apparently the great majority of the tumors remain small and circumscribed and even from those few tumors that grow larger and become invasive OPCs only a minimal proportion will ever become a clinical carcinoma. According to the study, OPC can be regarded as a normal finding which should not be treated when incidentally found. In order to avoid unnecessary operations it is suggested that incidentally found small OPCs (less than 5 mm in diameter) were called occult papillary tumor instead of carcinoma.

The histopathologic diagnosis of follicular variant of papillary thyroid carcinoma (FVPCA) can be difficult. Recent reports have suggested that this neoplasm may be frequently overdiagnosed by pathologists. We examined the observer variation in the diagnosis of FVPCA in 87 tumors by 10 experienced thyroid pathologists. The criteria that the reviewers considered most helpful for making a diagnosis of FVPCA were also assessed. A concordant diagnosis of FVPCA was made by all 10 reviewers with a cumulative frequency of 39%. In this series, 24.1% of the patients had metastatic disease (n = 21). In the cases with metastatic disease, a diagnosis of FVPCA was made by all 10 reviewers with a cumulative frequency of 66.7%, and 7 of the reviewers made a diagnosis of FVPCA with a cumulative frequency of 100%. The most important criteria used to diagnose FVPCA included the presence of cytoplasmic invaginations into the nucleus (pseudo-inclusions), abundant nuclear grooves, and ground glass nuclei. These results suggest that although the diagnosis of FVPCA is variable even among experienced thyroid pathologists, most reviewers agreed on this diagnosis for patients with metastatic disease. The use of well-defined histopathologic features should improve the consistency in diagnosing FVPCA. Since most cases with metastatic disease had obvious invasion, caution should be used in making a diagnosis of FVPCA in the absence of the major histopathologic features or clear-cut invasive growth.