When the Appendix Takes a Detour: A Rare Case of the Appendix Intussuscepting Into the Caecum Mimicking an Appendiceal Mucocele.

Acute appendicitis is a common condition, whereby accurate diagnosis relies on multiple modalities in conjunction with a thorough history and clinical examination. Imaging, particularly computed tomography (CT), is highly sensitive in reliably determining the position of the appendix. It is not unusual for appendicitis to present in atypical ways or be masked as other intra-abdominal conditions, complicating the diagnosis. This report discusses a rare case of intussusception of the appendix into the caecum, with a histopathological specimen later proving the intraoperative specimen as endometrial tissue, highlighting an uncommon presentation. We report the case of a 51-year-old woman who experienced worsening abdominal pain, nausea, and early satiety over several months. Initial evaluation revealed microcytic anaemia and a smoking history of 25 pack-years. Imaging strongly suggested an appendiceal mucocele. A colonoscopy revealed a large caecal polyp originating from within the appendiceal orifice. A multidisciplinary team discussion recommended performing a diagnostic laparoscopy to further guide management. While conducting the laparoscopic surgery, a lump on the taenia coli obscured the view of the appendix, necessitating a partial caecectomy. Postoperative examination of the specimen confirmed intussusception of the appendix into the caecum, later verified by a pathologist to be appendiceal endometriosis. This case highlights the significant diagnostic challenges linked to adult intussusception. Although CT scans and colonoscopy are vital in preoperative assessments, correctly identifying the underlying condition can be difficult. The laparoscopic approach has shown both safety and effectiveness in diagnosis and treatment. Prompt surgical intervention is crucial for resolving intussusception and treating appendicitis to prevent serious complications.