DP20 Soft-tissue perineurioma presenting as a painless nasal papule

Abstract A 49-year-old man presented to the dermatology outpatient department with a 6-month history of an asymptomatic lesion at the left nasal ala, which had recently decreased in size. His past medical history was unremarkable. Clinical examination revealed a 7 × 7-mm firm flesh-coloured papule with a central keratin crust. Dermoscopy was notable for peripheral vessels and a central scab with no definitive features of basal cell carcinoma. A diagnostic 4-mm punch biopsy was subsequently performed. Histopathology revealed a bland, dermal-based spindle cell lesion with a myxoid background without significant cytological atypia or mitotic activity. The epidermis was normal. Immunohistochemistry showed diffuse but weak positivity for epithelial membrane antigen (EMA), variable positivity for CD34, and patchy weak positivity for CD10 and factor XIIIa. Negative stains were noted for S100, melan-A and desmin. These findings were consistent with a diagnosis of soft-tissue perineurioma. Perineuriomas are rare, benign peripheral nerve sheath tumours composed of perineurial cells. They are classified into intraneural and extraneural (soft-tissue) variants. While the exact underlying aetiology remains unclear, cytogenic studies have shown a link with chromosome 22 abnormalities. Intraneural perineuriomas are less common than soft-tissue variants and are characterized by neoplastic perineurial cells that proliferate throughout the endoneurium. In contrast, soft-tissue peri­neuriomas are not grossly associated with a nerve. They usually present in adults and are rare in children. They typically present as a solitary, slow-growing, firm painless mass or nodule and tend to occur on the extremities and trunk. Histologically, most cases of soft-tissue perineuriomas appear as nonencapsulated, well-circumscribed spindle cell tumours. They are commonly situated in the subcutis followed by the deep soft tissue. They are usually composed of perineurial cells, which have a wavy or tapering nucleus, an eosinophilic nucleolus and indistinct cell borders. The stroma is usually collagenous, but occasionally it is myxoid predominant or mixed. Diagnosis can be challenging due to histopathological mimics including myxoid neurofibroma, myxoid dermatofibroma and myxoid dermatofibrosarcoma protuberans. Immunohistochemistry is often helpful in differentiating between these similar entities. Perineuriomas typically express antigens that are identical to normal perineurium, namely EMA, glucose transporter type 1 and claudin. CD34, type IV collagen, laminin and C10 are also occasionally positive. S100, SOX10, neurofilament and desmin are typically negative. While perineuriomas behave in a benign fashion, complete surgical excision is recommended.