Necrotic mature ovarian teratoma associated with anti-N-methyl-D-aspartate receptor encephalitis.

A 20-year-old female with a diagnosis of autoimmune encephalitis against N-methyl-D-aspartate receptor was found to have a 13 mm teratoma in the left ovary. The tumor had undergone massive coagulative necrosis within a normal ovary, a previously unreported feature. Necrosis of a mature cystic teratoma is very rare in the absence of ovarian torsion.