Anatomic Pathology: Gastrointestinal Pathology

• Appendiceal neuroendocrine tumors occur with an incidence of 2 million to 3 million per year, with a 2:1 female-male ratio.

• Most appendiceal neuroendocrine tumors are diagnosed incidentally during appendectomy (1% of appendectomies); they are not related to a specific clinical presentation. The diagnosis is associated with, but not related to, acute appendicitis. Most tumors are located at the tip of the appendix (60% to 75%) and do not induce obstruction.

• Immunohistochemical analysis with chromogranin A and synaptophysin antibodies helps to confirm the diagnosis.

• Prognosis is related to the size of the tumor, and a maximal diameter larger than 2 cm is the most important parameter for prognosis. Another parameter related to prognosis is the presence and extent of mesoappendiceal invasion (>3 mm).

• The surgical margins of the appendectomy specimen (R0/R1) must be reported clearly. If the resection margin is positive for a tumor, a right hemicolectomy is generally required.

• Goblet cell carcinoids are considered to represent a separate clinicopathologic entity, distinct from classic appendiceal neuroendocrine tumors and adenocarcinomas, with an uncertain histogenesis. They are more aggressive than classic neuroendocrine tumors and require a different diagnostic and therapeutic approach.