Florid capsular and pericapsular papillary endothelial proliferation associated with poorly differentiated thyroid...

Papillary endothelial hyperplasia (PEH) occurring within or around the capsule of thyroid neoplasms is rare. Such Masson-like lesions, which have been attributed to fine needle aspiration-induced injury and thrombosis, can mimic tumor angioinvasion or vascular neoplasms. This study reports the case of a poorly differentiated carcinoma of the thyroid that was accompanied by more than 10 foci of pericapsular and peritumoral papillary endothelial hyperplasia, one of which contained a tumor embolus. The vessels within the papillary fronds had CD31- and CD34-staining blood vessels but were lined by D2-40 staining endothelial cells, which were continuous with the lining of the spaces within which PEH had developed. This suggests that, in contrast to Masson's lesions that develop within blood vessels as a result of thrombosis, pericapsular PEH associated with thyroid neoplasms develops within lymphatics, possibly related to lymphangiogenic factors secreted by the thyroid neoplasms.