Intraneural perineurioma--not restricted to major nerves.

The intraneural perineurioma is an uncommon proliferation of perineural cells that forms onion bulb-like structures surrounding the nerve axons within a portion of a single affected nerve. The etiology is idiopathic, and it is controversial whether the process is reactive or neoplastic. All previously reported cases have involved major nerves and have been associated with motor deficits and, less frequently, sensory signs or symptoms. The current case represents the first example shown to arise in a small unnamed nerve before the development of clinically detectable nerve dysfunction. The process appears to be progressive; and when detected in a small nerve, excision is recommended to prevent proximal extension and possible development of motor or sensory deficits.