Ovarian Extravascular Papillary Endothelial Hyperplasia (Masson Tumor) Mimicking a Primary Gynecologic Malignancy.

Papillary endothelial hyperplasia or Masson tumor most commonly occurs within the extremities and head and neck. It is usually of intravascular type, associated with thrombus formation and organization within a preexisting vessel or vascular malformation, but rarely can be extravascular. We describe the first 2 cases of this extravascular type to occur within the ovary, one of which mimicked malignancy radiologically. This condition is thought to represent a reactive phenomenon with reparative response secondary to thrombosis although with an unclear underlying pathogenesis. The prognosis is generally good, with complete surgical resection usually representing adequate treatment.