Capsular intravascular endothelial hyperplasia: a peculiar form of vasoproliferative lesion associated with thyroid carcinoma

AIMS: Florid vasoproliferative processes are uncommon in the thyroid gland. We report three cases of an unusual vasoproliferation involving the capsular blood vessels of thyroid carcinoma. METHODS AND RESULTS: The histological diagnoses of the three cases were made on conventional histological sections. Two cases were minimally invasive follicular carcinomas and one case was an encapsulated variant of papillary carcinoma. Some blood vessels in the tumour fibrous capsule were filled with spindly cellular proliferations forming irregular vascular clefts and papillae. Immunohistochemical studies for CD31, CD34 and muscle-specific actin confirmed that the spindly cells were mostly endothelial cells variably supported by pericytes. CONCLUSION: This peculiar intravascular endothelial hyperplasia by itself should not be mistaken for vascular invasion by tumour, but evidence of malignancy must be diligently sought by extensive sampling because the lesion has thus far been consistently associated with malignant thyroid neoplasms.