Neuroendocrine tumor of the appendix masquerading as acute appendicitis with a mucocele on CT scan: a rare finding
Authors: Al-Darwish Abdullah S. , Alsubaie Waad Rashaid , AlShammari Waleed , AlaSheikh Muath , AlRashed Muath 
Published: March 2024

Abstract
Introduction
Neuroendocrine tumors (NETs) of the appendix are rare and are often discovered incidentally during surgery for acute appendicitis or other unrelated conditions (Modlin et al. in Gastroenterology 128:1717–1751, 2005, Alsaad et al. in Oncol Rep 16:1105–1109, 2006, Frilling et al. in Lancet Oncol 15:e8–e21, 2014). These tumors can range from asymptomatic incidental findings to clinically significant tumors with metastases (Alsaad et al. in Oncol Rep 16:1105–1109, 2006, Gomes et al. in World J Emerg Surg 10:60, 2015, Paiva et al. in Eur J Cancer 38:702–705, 2002, Burke et al. in Am J Surg Pathol. 9:661–674, 1985). This case report presents a rare case of a NET of the appendix presenting as acute appendicitis.

Case description
A 23-year-old male presented with right lower quadrant abdominal pain, nausea, and vomiting for 2 days. A CT scan revealed a mucocoele of the appendix. The patient underwent laparoscopic appendectomy, and the appendix was sent for histopathological examination. The final pathological report confirmed a NET of the appendix with a Ki-67 index of 1% and no lymphovascular invasion. Due to tumor invasion to the cecum and its large size (3–4 cm), the patient underwent right hemicolectomy. The final histopathology report of the resected specimen confirmed the diagnosis of NET of the appendix.

Discussion
The clinical diagnosis of NETs of the appendix can be challenging due to their rarity and non-specific presentation. Symptoms of NETs of the appendix can mimic those of acute appendicitis, making it difficult to differentiate between the two conditions. Imaging studies, such as CT scans, can provide valuable information about the size and location of the tumor (Gomes et al. in World J Emerg Surg 10:60, 2015, Maggard et al. in Ann Surg 240:117–122, 2004, Burke et al. in Am J Surg Pathol. 9:661–674, 1985, Frilling et al. in Lancet Oncol 15:e8–e21, 2014). However, the definitive diagnosis is made through histopathological examination of the resected specimen. The treatment of NETs of the appendix depends on factors such as the size, location, and grade of the tumor. Small tumors confined to the appendix with no lymph-vascular invasion can be treated with appendectomy alone, while larger tumors or those that have spread beyond the appendix may require more extensive surgery, such as right hemicolectomy (Gomes et al. in World J Emerg Surg 10:60, 2015, Mestier et al. in Dig Liver Dis 52:899–911, 2020, Maggard et al. in Ann Surg 240:117–122, 2004, Burke et al. in Am J Surg Pathol. 9:661–674, 1985, Frilling et al. in Lancet Oncol 15:e8–e21, 2014, Pavel et al. in Neuroendocrinology 103:172–185, 2016). In some cases, additional treatments such as chemotherapy or radiation therapy may be recommended.

Conclusion
This case report emphasizes the importance of considering NETs of the appendix in the differential diagnosis of acute appendicitis. Imaging studies can provide valuable information, but the definitive diagnosis is made through histopathological examination. The treatment approach for NETs of the appendix depends on various factors and requires a multidisciplinary approach for optimal management.