Intranodular reactive endothelial hyperplasia in adenomatous goitre.

Endothelial hyperplasia has rarely been recognized in the thyroid. Ischaemic events or hemorrhage, sometimes as a result of fine needle aspiration procedures, have been regarded as possible causes. To clarify the morphological pattern and the clinical significance of this lesion, we studied a series of adenomatous goitres and selected 11 cases showing prominent endothelial hyperplasia in an individual nodule. Grossly, the parenchyma of the affected nodule was substituted by greyish, friable tissue surrounded by a fibrous capsule and by a thin rim of residual thyroid parenchyma. Microscopically, fibrinous and haemorrhagic material was crossed by intercommunicating vascular channels or papillary structures. These were lined by plump endothelial cells. In only one case had pre-operative fine needle aspiration biopsy been performed: smears yielded a haemorrhagic background, fibrin and numerous elongated cells; colloid and follicular cells were virtually absent. In both surgical and cytological specimens a differential diagnosis with a vascular neoplasm, a rare occurrence in the thyroid, was taken into consideration. We conclude that intranodular reactive endothelial hyperplasia is a relatively common occurrence (1.6%) in adenomatous goitre and is of diagnostic interest in both surgical and cytological specimens, since it can mimic vascular tumours and may lead to unnecessary treatment if misdiagnosed.