Occurrence and significance of vascular invasion in multinodular adenomatous goiter.

Solitary follicular neoplasms of the thyroid gland are usually classified as adenomas or carcinomas according to two main criteria: vascular invasion and capsular penetration. No information is available on the occurrence of vascular invasion in multinodular goiter lesions, except for the case of a follicular carcinoma within a goiter. One thousand consecutive cases of multinodular adenomatous goiter were reviewed. After screening all H&E-stained slides, 5 patients with histological features typical of adenomatous goiter but displaying foci of vascular invasion at the periphery of the nodes were selected. A single vessel (2 patients) and 2-4 vessels (3 patients) at the periphery of different nodules were involved, with clusters of follicular cells lined by endothelium and partly filling the lumen. Clinical information was obtained from all patients: No recurrences or progressive disease were reported 14 to 16 years after operation. These findings indicate that presence of minimal vascular invasion, although a valuable criterion of differentiation in solitary follicular lesions of the thyroid, has little diagnostic importance in the setting of multinodular adenomatous goiter. It does not appear to justify a diagnosis of malignancy and does not indicate a need for further therapy.