Retrovesical Hybrid Benign Peripheral Nerve Sheath Tumor with a Heterozygous Germline NF2 Deletion in a 12-Year-Old Boy: A Case Report.

Background: Hybrid benign peripheral nerve sheath tumors (BPNSTs) combine schwannomatous, neurofibromatous, and/or perineuriomatous components and are frequently associated with NF2-related schwannomatosis. Pediatric cases at retrovesical sites have not previously been reported. Case report: A 12-year-old boy presented with one-year voiding difficulty. Pelvic magnetic resonance imaging showed an indeterminate 27 × 33 mm retrovesical lesion in the seminal vesicle region. Laparoscopic excision yielded a solid mass composed of distinct schwannomatous and neurofibromatous components. The schwannomatous areas were strongly S-100 positive and CD34 negative, whereas the neurofibromatous areas showed patchy S-100 and diffuse CD34 positivity; factor XIIIa was more extensive in the neurofibromatous component. Ki-67 was 3%, without necrosis or mitoses. Multiplex ligation-dependent probe amplification identified a heterozygous germline NF2 deletion (upstream-exon 9). At 6 months, the patient was symptom-free without recurrence. Conclusion: Hybrid BPNST should be considered in pediatric indeterminate retrovesical masses; integrated histopathologic, immunohistochemical, and molecular analysis-including germline NF2-guides diagnosis and long-term surveillance.