Membranous fat necrosis in mature cystic teratomas of the ovary.

We identified and documented the occurrence of membranous fat necrosis (MFN) in 217 mature cystic teratomas (MCTs) of the ovary. Cysts lined by an eosinophilic and scalloped membrane with pseudopapillary infoldings, the characteristic histologic features of MFN, were identified in 9 tumors. The membranes had the histochemical staining properties of ceroid, as evidenced by periodic acid-Schiff, sudan black, and long Ziehl Neelsen (ZN) positivity, diastase resistance, and autofluorescence. The causes and pathogenesis of MFN are enigmatic, but trauma, torsion, and ischemia are probable factors. MFN is a distinct entity in ovarian MCTs and heightened awareness will increase its histopathologic recognition.