Benign tumors of the peripheral nerve sheaths

: Benign tumors from sheaths of peripheral nerves (25 neurolemmomas and 6 neurofibromas) were studied. The ultrastructural data presented attest to the principal differences between these tumors and the possibility of their differential diagnosis. The typical signs of tumor cells of neurilemmoma include numerous complicatedly interwoven processes not infrequently forming " pseudomesaxonal " structures, and the presence of permanent basal membrane. These signs indicate the histogenetic relationship of neurilemmoma with cells of the Schann sheath of the peripheral nerve ( lemmocytes ). Neurofibroma tumor cells were characterized by the presence of bipolar thin, long non-interwoven cytoplasmic processes with inconstant basal membrane, desmosome-like contacts between the processes, and pinocytic vesicles in the cytoplasm. The revealed ultrastructural signs indicate the histogenetic relationship of neurofibroma with cells of the perineurium of peripheral nerves.