A Case of Extragonadal Teratoma in the Pouch of Douglas and Literature Review.

Mature cystic teratoma is a germ cell tumor of the ovaries and is often observed in clinical practice. However, extragonadal teratomas are rare tumors and have been reported outside the ovaries, (e.g., in the greater omentum). The mechanism underlying the development of extragonadal teratomas remains unknown. We encountered a case of extragonadal teratoma in the pouch of Douglas that appeared to be a parasitic dermoid cyst. From our experience and the literature review, we discuss the potential mechanism leading to the development of extragonadal teratomas. A 41-year-old nonpregnant woman was referred to our department due to myoma and anemia. A 4-cm asymptomatic mass in the pouch of Douglas was observed, and the patient was diagnosed with ovarian mature cystic teratoma. She underwent laparoscopic surgery, and intraoperative findings revealed that the fallopian tube was injured and torn, and a residual small ovary was observed in the left side of the ovary. A tumor measuring approximately 4 cm observed in the pouch of Douglas was extracted without rupturing. The tumor was diagnosed as a parasitic dermoid cyst by macroscopic and histopathological findings. Auto-amputation could be the underlying mechanism that leads to an isolated parasitic dermoid cyst in the pouch of Douglas.