Appendiceal Endometriosis: A Rare Case of Endometriosis Mimicking Acute Appendicitis.

Appendiceal endometriosis (AE) is a rare type of extragonadal endometriosis with symptoms of right lower abdominal pain, nausea, and vomiting that mimic acute appendicitis. The gold standard for a definitive diagnosis is a histopathological examination of the excised appendix. We report a case of AE in a 39-year-old female patient, G10P3, with a past surgical history of cholecystectomy, seven dilation and curettage procedures, and one prior cesarean section presenting with a right lower quadrant pain with intermittent non-bloody diarrhea, nausea, and vomiting that is not exacerbated by movement. The patient was mildly tachycardic with otherwise stable vitals and no leukocytosis. The beta-hCG test was negative with a CT-confirmed Mirena® intrauterine contraceptive device (IUD) (Bayer AG, Leverkusen, Germany) placement. The patient denied heavy bleeding or vaginal discharge. The CT scan of the abdomen and pelvis with oral contrast demonstrated findings suggestive of appendicitis, leading to a subsequent laparoscopic appendectomy. The resected specimen showed histopathology features of endometriosis, confirming AE. AE poses diagnostic challenges due to its nonspecific imaging findings along with variable symptomatic presentations. The recommended management of AE is an appendectomy with a gynecological follow-up postoperatively. AE is a rare condition that can masquerade as acute appendicitis in female patients. We highlight the importance of including AE in the differential diagnosis of female patients presenting with lower abdominal pain.