| Summary: | Background: Neuroendocrine tumors (NETs) are rare tumors that arise from neuroendocrine cells and are the most common tumors of the appendix. NETs of the appendix usually cause no symptoms and often go unnoticed until they cause acute appendicitis or are discovered during an accidental appendectomy. As the trend towards the conservative treatment of acute appendicitis increases in the pediatric population, the question arises as to whether the majority of NETs go undetected and are only discovered at an advanced stage. The purpose of the proposed study is to review the incidence and outcomes of treatment for NETs of the appendix in children and include the data presented in the data pool for further review. Methods: From 1 January 2009 to 1 November 2023, a total of 6285 appendectomies were performed in two large pediatric centers in Croatia. After a retrospective review of the case records and histopathologic findings, a total of 31 children (0.49%) were diagnosed with NET of the appendix and included in the further analysis. The primary outcome of this study was the incidence and treatment outcome of pediatric patients diagnosed with NET of the appendix. Secondary outcomes included the patients’ demographic, clinical, and laboratory data and the histopathologic characteristics of tumor species. Results: The overall incidence of NETs of the appendix was stable over the study years, with minor fluctuations. The median age of patients was 14 (interquartile range—IQR: 12, 16) years, with a female predominance (64.5%). The majority of patients (96.8%) presented with acute abdominal pain and underwent appendectomy because acute appendicitis was suspected. Acute appendicitis was confirmed by histopathology in 18 (58%) cases. NETs of the appendix were not detected preoperatively in any of the patients. Among patients with confirmed acute appendicitis, most (<i>n</i> = 14; 77.8%) were found to have non-perforated acute appendicitis. In most children, the tumor was located at the tip of the appendix (<i>n</i> = 18; 58.1%), and the majority of tumors had a diameter of less than 1 cm (<i>n</i> = 21, 67.7%). The mitotic count (<i>n</i> = 25, 80.6%) and Ki-67 proliferation index (<i>n</i> = 23, 74.2%) were low in most patients, so most tumors were classified as NET G1 (<i>n</i> = 25, 80.6%), while NET G2 and NET G3 were found in four (12.9%) and two (6.5%) patients, respectively. All children were treated with appendectomy only. The median follow-up time was 54 (IQR: 24, 95) months. Conclusions: The incidence of appendiceal NET among pediatric patients is very low. NET occurs most frequently in adolescents, with a female predominance. Most tumors are less than 1 cm in diameter, located at the tip, and associated with non-perforated appendicitis. Appendectomy is the treatment of choice, and major surgery was not necessary in our cohort.
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