Pigmented Neurofibroma in the Appendix Diagnosed with Colonoscopy

Pigmented (melanotic) neurofibromas in the appendix are extremely rare. To our knowledge, this is the first case of appendiceal pigmented neurofibroma in a patient without neurofibromatosis 1, which was colonoscopically diagnosed. Histologically, the tumor cells were spindle shaped with indistinct cell borders. The tumor cells had cytoplasms with many gray-brown pigments. Immunohistochemical examinations showed that the tumor cells were strongly positive for S-100 protein, and were focally positive for Melan-A. They were also diffusely positive for Leu7 (CD57), or neuron-specific enolase (NSE). No positive expression of tumor cells was observed for -smooth muscle actin, desmin, CD34, c-kit, HMB45. No mitotic figures were observed. The Ki-67 labeling index was less than 1%. The tumor was thus diagnosed as primary pigmented neurofibroma in the appendix. In the present case, tumor cells showed no mitotic activity and a Ki-67 index of less than 1%, suggesting a benign tumor.