Clinical and Pathological Features of a Schwannoma Harboring a <i>SH3PXD2A::HTRA1</i> Gene Fusion in a Pre-pubescent Patient

An 11-year-old girl presented with a soft tissue lesion on the dorsal aspect of the left middle finger. Ultrasound imaging demonstrated a 2.8 cm × 0.8 cm × 0.8 cm lesion overlying the dorsal aspect of the base of the digit near the metacarpophalangeal joint. The patient's past medical history is remarkable for neuroblastoma, diagnosed at 9 months of age, with no MYCN amplification or 1p loss. We report a pediatric schwannoma harbouring a <i>SH3PXD2A::HTRA1</i> gene fusion with a distinctive serpentine histology. The lesion consisted of well-circumscribed nodules surrounded by thin EMA-positive perineural capsules. Each nodule was composed of lesional cells arranged in short fascicles with occasional clefting and a distinct "serpentine" palisading pattern. The lesion demonstrated Antoni A regions with Verocay body formation. No significant Antoni B areas were seen. The lesional Schwannian cells were bland with elongated and tapered nuclei, showing strong and diffuse positivity for S100. This pre-pubescent girl (Tanner Stage 2) is currently the youngest reported case of fusion-positive schwannoma. In addition, she has a significant prior history of a malignant neoplasm, and the lesion arose in an appendicular location.