Why do frozen sections have limited value in encapsulated or minimally invasive follicular carcinoma of the thyroid?

The diagnosis of encapsulated or minimally invasive follicular carcinoma of the thyroid requires the proof of vascular or capsular invasion. The aim of the present study was to evaluate the relationship between intraoperative diagnosis (benign, suggestive of carcinoma, or malignant) and the final histopathologic criteria for encapsulated or minimally invasive follicular carcinoma (tumor size, capsular invasion, vascular invasion, and differentiation). This was a retrospective study of 63 cases of encapsulated or minimally invasive carcinomas, with the final histopathologic diagnosis taken as the "gold standard." The sensitivity of frozen sections for the diagnosis of malignant neoplasm was 17%. The median number of vascular invasions was 1, identified with a mean number of 9 paraffin-blocks of the tumor. In most cases, intraoperative frozen sections are unable to establish the proof of malignant neoplasm. Intraoperative study of tumor differentiation is useful to select follicular tumors that require a rapid definitive diagnosis and a completion thyroidectomy within 48 to 72 hours (73% of the cases in our study).