Intraneural perineurioma

Intraneural perineurioma is a rare, benign peripheral nerve sheath tumor that arises from perineurial cells, which are specialized cells that normally form the protective perineurium surrounding nerve fascicles. This tumor grows within the nerve itself (intraneural location), causing a segmental, fusiform (spindle-shaped) enlargement of the affected peripheral nerve. It is classified under the broader category of perineuriomas and is distinct from the soft tissue (extraneural) variant. Intraneural perineurioma most commonly affects peripheral nerves of the extremities, particularly the sciatic nerve, brachial plexus, and nerves of the upper and lower limbs. Patients typically present with slowly progressive, painless weakness and muscle atrophy in the distribution of the affected nerve. Sensory loss may also occur but is often less prominent than motor deficits. The condition predominantly affects children, adolescents, and young adults. On imaging, MRI characteristically shows fusiform nerve enlargement with a distinctive fascicular pattern. Histologically, the tumor is composed of proliferating perineurial cells that form pseudo-onion bulb structures around nerve fibers, and the cells characteristically express epithelial membrane antigen (EMA) and claudin-1 while being negative for S-100 protein. There is no established medical therapy for intraneural perineurioma. Management is primarily conservative, with observation and monitoring, as the tumor is benign and does not undergo malignant transformation. Surgical resection may be considered in selected cases, but complete excision is often difficult without sacrificing nerve function. Nerve grafting or reconstruction may be attempted in cases with significant functional impairment. Physical therapy and rehabilitation play supportive roles in maintaining function. The prognosis is generally favorable, though neurological deficits may persist or slowly progress over time.

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