Acute appendicitis with a neuroendocrine tumor G1 (carcinoid): pitfalls of conservative treatment

A man in his early thirties presented to our clinic with right lower abdominal pain. Computed tomography (CT) and ultrasonography (US) revealed a swollen appendix and an appendicolith. Abscess formation was not observed but ongoing appendiceal rupture was not ruled out. Three months after successful conservative therapy, the lumen of the apical portion was kept dilated and laparoscopic interval appendectomy was performed. No tumorous findings were observed macroscopically. However, histology revealed many tiny nests infiltrating the submucosa, muscular layer, and subserosa at the root of the appendix. An appendiceal neuroendocrine tumor G1 (NET G1; carcinoid) was diagnosed immunohistologically. Neither CT nor US visualized the tumor because of its non-tumor-forming but infiltrative growth. In conclusion, after successful conservative treatment, interval appendectomy should be considered to uncover a possible appendiceal NET G1 (carcinoid), particularly when dilatation of the distal lumen is kept under observation.