Papillary endothelial hyperplasia developing in j33 cell adenoma of thyroid Papillary endothelial hyperplasia is a benign and reactive lesion which is also known as “Masson”s pseudoangioma, intravascular angiomatosis, intravascular endothelial proliferation”. Although this lesion is most commonly located on the head and neck, it can be seen in various parts of the body. Etiologically three different forms of this lesion have been described; pure form develops in dilated vessels, mixed form accompanies with other vascular lesions and indetermined form with an unknown etiology. In this paper a case of 40 year old woman presenting with a papillary endothelial hyperplasia developing in Hürtle cell adenoma of thyroid has been presented.