We report the rare case of a 34-year-old woman with primary cystic teratoma of the rectum, pinpointed in a colonoscopy. A tumor with a hair ball that fled easily was found in the anterior rectum about 8cm from the anal verge in colonoscopy. Magnetic resonance imaging showed a tumor protruding from the anterior wall of the rectum to ventral side. The tumor showed high intensity in Tl-weighted imaging, and low intensity in T2-weighted imaging, which was markedly enhanced in diffusion imaging. Laboratory findings showed anemia, and poor nutrition. At laparoscopy, the tumor was found at Douglas fossa with highly adhesion with uterus, necessitating open total uterectomy and low anterior resection. The tumor was resected en-block with the uterus and rectum. Histopathological findings showed cystic teratoma ruptured into the rectum from the rectal wall.
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