Incidental Grade 2 Appendiceal Neuroendocrine Tumor Presenting as Acute Appendicitis in a Young Adult Male Patient.

Neuroendocrine tumors (NETs) are epithelial neoplasms with neuroendocrine differentiation that can arise throughout the gastrointestinal tract, including the appendix. Appendiceal NETs are rare neoplasms that frequently present as or mimic acute appendicitis. We report the case of a 28-year-old male patient who presented with right lower quadrant abdominal pain and was found to have early acute appendicitis on imaging. He underwent laparoscopic appendectomy, and final histopathology revealed a 0.5 cm well-differentiated Grade 2 NET at the tip of the appendix. The tumor was confined to the submucosa, with negative margins and no lymphovascular invasion. Immunohistochemistry was positive for chromogranin and synaptophysin, and the Ki-67 proliferation index was approximately 5%. Given the tumor's small size, complete resection, and absence of high-risk features, no further surgery was performed. The patient was referred to oncology for multidisciplinary follow-up. This case highlights the importance of histologic grading and proliferation index in the postoperative evaluation of appendiceal NETs and supports the need for routine histopathologic analysis in all appendectomy specimens.