Pediatric Superficial Malignant Perineurioma/Perineuriomatous Malignant Peripheral Nerve Sheath Tumor of the Groin With NF1 Loss: A Case Report and Focused Review of the Literature.

Malignant perineurioma, also referred to as perineuriomatous malignant peripheral nerve sheath tumor (MPNST), is an exceptionally rare neoplasm with limited clinicopathologic characterization, particularly in children. We report a 12-year-old boy with a 3.0-cm superficial right groin lesion. Histopathologic examination showed a spindle cell neoplasm with fascicular-to-swirling architecture in myxoid to collagenous stroma, moderate cytologic atypia and nuclear variability, mitotic activity, focal necrosis, and admixed inflammation. Epithelial membrane antigen, GLUT1, and claudin-1 positivity supported perineurial differentiation, while a broad negative immunohistochemical panel helped exclude potential mimics. Tumor-only sequencing demonstrated 17q loss with focal homozygous NF1 deletion, a BRCA2 frameshift, and low tumor mutational burden (3.4 mutations/Mb); RNA sequencing identified no pathogenic gene fusion. These molecular findings were interpreted as adjunctive rather than independently diagnostic. The tumor extended to the inked specimen edge, and subsequent management and follow-up information was unavailable. To our knowledge, this is the first reported superficial cutaneous malignant perineurioma/perineuriomatous MPNST in a pediatric patient.