Endometriosis of the Vermiform Appendix Presenting as a Tumor

Endometriosis of the vermiform appendix is a rare condition. Most patients with this disease are asymptomatic or present as acute or chronic appendicitis. The author herein reports a case of appendiceal endometriosis presenting as a tumor at the appendiceal oriffice. A 41-year-old woman complained of chronic abdominal pain. A colon endoscopy showed a tumor in the appendiceal orifice. Two biopsies of the tumor showed no remarkable changes. Imaging modalities including CT and MRI also revealed an appendiceal tumor. Resection of appendix, cecum, ascending colon, terminal ileum, and 16 lymph nodes were performed under the clinical diagnosis of gastrointestinal stromal tumor. Grossly, a tumor measuring 3 x 3 x 3 cm was recognized in the appendiceral orifice. Histologically, the tumor was endometriosis consisting of islands of endometrial glands and stroma. Immunohistochemically, the lesion was positive for estrogen receptor and progesterone receptor, but it was negative for p53 protein and Ki-67 labeling was very low (0.5%). Similar endometriosis-like glands or Mullerian duct remnants were recognized in six out of 16 regional lymph nodes. The present case suggests that appendiceal endometriosis may present as a tumor.