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A Case Report: The Incidental Finding of Neuroendocrine Tumor of Appendix Presenting as an Acute Appendicitis

Background: Neuroendocrine tumours (NETs) are well-differentiated epithelial neoplasms with morphological and immunohistochemical features of neuroendocrine differentiation. Case Description: We report a 22-year-old woman with lower right abdominal pain. Patient underwent appendectomy and the specimen was sent for histopathological examination. On macroscopic examination, we received tissue originating from mass in the appendix, showed mass was brownish gray and irregular. The size was approximately 4 cm. On cut section, tumor mass appeared at apical of the appendix, 0.5 cm from the end of resection margin. On microscopic examination, tissue from the mass in appendix consist of mucosal layer to serosa layer. Mucosal layer with columnar epithelial lining partially atrophy, columnar epithelium with normal nuclear morphology. In the subepithelial, the proliferation of tumor cells appears to form nests, trabeculae, acini, and ribbon-like structures. Tumor cells are relatively uniform with round nuclei, salt & pepper chromatin, abundant and granular cytoplasm. Mitoses (<20 mitoses/10 HPF). We also found rosette like. The stroma consists of thick fibrotic connective tissue, infiltrated by tumor cells forming a single file appearance. On immunohistochemical examination in case showed synaptophysin (+), chromogranin A (+), ki67 proliferation index value is 3% and CK20 (-). Discussion and Conclusion: NETs most typically showing organoid architecture, uniform nuclei, and coarsely granular cromatin. NETs can be low-grade (G1), intermediate-grade (G2), or high-grade (G3). For the diagnosis of NETs, expression of synaptophysin or chromogranin A must be present. Based on histopathology and immunohistochemical results, this case was diagnosed as Appendiceal neuroendocrine tumours, NOS, intermediate-grade (G2), ICD-O 8249/3, topography morphology (C18.1).