Intraneural granular cell tumor: Histologic spectrum and histogenetic implication.

Granular cell tumor (GCT), despite its putative neural origin, commonly occurs in extraneural sites; only six single case reports of intraneural GCT have been described. We report an unique case as the only one with motor dysfunction, the longest duration of symptoms, and largest tumor size with resultant muscle atrophy and fatty infiltration. Upon review of these cases, the striking feature of intraneural GCT lies in its histologic variety, ranging from benign GCT, through plexiform, hybrid GCT and perineurioma to malignant GCT, encompassing the full spectrum of extraneural GCT. As the immunophenotypes of schwannoma and GCT are not exactly identical, together with evidence from ultrastructural studies, the more reasonable and likely possibility is that GCT originates from undifferentiated mesenchymal cells acquiring partial schwannian differentiation. Such postulation by virtue of the widespread occurrence of mesenchymal cells in the soft tissue, better explains the topographic distribution of GCT in extraneural and intraneural location.