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Case Reports

Abstract

Hybrid nerve sheath tumors are rare neoplasms consisting of multiple peripheral nerve sheath tumors (PNSTs). They present as well-circumscribed, painless masses on the dermis or subcutaneous adipose tissue. Neurofibroma-perineurioma is the rarest entity and is usually associated with NF-1 mutations. Fewer than ten cases have been cited of this tumor to our knowledge.  A 17-year-old male presents with a left arm lesion of 1 year duration.  He denies any change in size or pain. Physical examination shows a mobile, skin-colored, round firm papule measuring 6 x 6 x 3 mm. Punch biopsy is performed without complications. Microscopic examination shows a diffuse intradermal spindle cell proliferation of small, bland-appearing spindle cells with oval nuclei and eosinophilic cytoplasm arranged in a loosely fascicular/whorled pattern, extending into the deep dermis. SOX10 and S100 highlight a subset of spindle cells, while CD34 highlights another subset of spindle cells with fingerprint pattern, characteristic of neurofibroma component. EMA highlights some cells in whorled pattern, characteristic of perineurioma component. BRAF, Factor XIIIa, p16, panTRK and ALK stains are negative. Ki-67 proliferation rate is <1%. Targeted DNA/RNA sequencing is negative for DNA mutations and gene fusions in common cancer-related genes. These findings are consistent with a hybrid neurofibroma-perineurioma. Standard treatment for neurofibroma-perineuriomas is surgical resection, as these tumors are typically benign and have a low recurrence rate. We present a rare case of extradigital neurofibroma-perineurioma in a young male. Our case is especially unique because the patient did not have any DNA mutations (such as NF-1) that this tumor is usually associated with.