Incidental finding of synchronous neuroendocrine tumor of appendix and rectal adenocarcinoma. A case report and literature review

Objectives: Colorectal cancers represent the predominant malignancies affecting the gastrointestinal tract. In contrast, appendiceal tumors occur less frequently. Among them, appendiceal neuroendocrine tumors (ANETs) account for approximately 50 % of cases and are often detected incidentally during unrelated procedures. Case presentation: We present an extremely rare case of an incidental neuroendocrine tumor of the appendix discovered during surgery for rectal adenocarcinoma and provide a review of the relevant literature. A 70-year-old patient with radiologically and endoscopically diagnosed rectal cancer underwent a low anterior resection with total mesorectal excision and a temporary diverting ileostomy following preoperative chemotherapy and radiation therapy. Intraoperatively, a small appendiceal mass was discovered and excised. Histopathological examination confirmed a well- differentiated NET of the appendix measuring 0.4 cm in diameter. Conclusions: This case report emphasizes the importance of thorough intraoperative examination during colorectal surgeries and highlights the need for increased awareness of appendiceal NETs among surgeons.