Micronodular PEComa of the appendix: a case report.

Appendiceal micronodular perivascular epithelioid cell tumor (PEComa) is an extremely rare mesenchymal neoplasm. Historically termed "appendiceal granular cell nodules" or "granular degeneration of smooth muscle," this entity has recently been reclassified as an indolent variant within the PEComa family, with only isolated cases reported. We report a case of a 23-year-old man with a 4-year history of recurrent right lower quadrant pain, who underwent laparoscopic appendectomy. Histologic examination revealed multiple micronodular nests of epithelioid cells scattered within the muscularis propria, featuring abundant eosinophilic granular cytoplasm and small, round nuclei without significant pleomorphism or mitotic activity. Immunohistochemical analysis showed diffuse positivity for SMA, Desmin, and HMB-45, weak-to-moderate nuclear staining for TFE3, and a Ki-67 proliferation index of less than 1%, supporting the diagnosis of micronodular PEComa of the appendix. This case underscores a rare and frequently underrecognized mesenchymal lesion of the appendix. Further accumulation of cases is necessary to elucidate its pathogenesis, molecular profile, and long-term clinical course.