A Pediatric Case of Neuroendocrine Tumor of the Appendix Diagnosed after Appendicitis Surgery

A 7-year-old female presented with a chief complaint of right lower quadrant pain. Contrast-enhanced CT revealed swelling of the appendix, with continuous fluid accumulation at the distal appendix. Based on an abscess formation, the patient was suspected to have acute appendicitis. Appendectomy was performed, but the laparotomic findings did not include an abscess. The appendix had swollen in a cystoid manner and was excised, and the condition was found to be gangrenous appendicitis. Circumferential wall thickening was observed in a region 1 cm distal to the appendectomy site, and the distal portion had expanded in a cystoid manner due to an obstruction. Histopathological examination detected an infiltrating tumor reaching the subserous layer of the site of wall thickening of the appendix, with small and relatively evenly sized cells forming a rosette-like structure and a funicular sequence. Immunostaining was strongly positive for chromogranin A, synaptophysin, and CD56, and slightly positive for Ki-67, while D2-40 and CD31 showed infiltration in lymphatic vessels and veins. Thus, the patient was diagnosed with neuroendocrine tumor G2. Given the vascular infiltration, ileocecal resection and D3 lymph node dissection were performed. The patient showed good progress, with no recurrence for 2 years postoperatively.