Pathological studies of aberrant peripheral nerve bundles of spinal cords.

Aberrant peripheral nerve fiber bundles, i.e., masses of peripheral nerve fibers without perineural sheath cells, are found in the perivascular spaces of some spinal cords. The 514 spinal cords examined for these structures were separated into two groups; 507 spinal cords without definite necrotic lesions (group 1) and 7 spinal cords (group 2) with old necrotic lesions in which there were numerous aberrant peripheral never bundles (APNB). In group 1, APNB were found in 41.0% of spinal cords. The incidence was the same for both sexes and increased in proportion to age. APNB were found predominantly in the middle and lower thoracic segments. On the transverse sections, APNB were located mainly in the central gray matter and in the anterior median fissure. Ultrastructural and histochemical studies showed that the myelin in APNB was peripheral in origin. Serial sections showed continuity between APNB and nerve roots. In group 2 cases, APNB were diffusely distributed throughout the old necrotic lesions and not restricted to perivascular areas.