Colocalized cellular schwannoma and plexiform neurofibroma in the absence of neurofibromatosis. Case report.

The authors report on a patient without neurofibromatosis Type 1 or 2 (NF1 or NF2) and without evidence of schwannomatosis, who was found to have an unusual combination of nerve sheath tumors-a large cellular schwannoma and multifascicular involvement of a plexiform neurofibroma arising from the same site within the radial nerve and posterior cord of the infraclavicular brachial plexus. This case broadens the spectrum of combined pathological features of nerve sheath tumors. Genetic studies revealed a combined loss of neurofibromin and merlin in both regions and chromosome arm 22q deletion within the neurofibroma component only. The latter finding supports the suggestion that these were two different clonal neoplasms, and is consistent with a collision tumor pattern.