Surgical pathology of spinal schwannoma: Has the nerve of its origin been preserved or already degenerated during tumor growth?

Objective: This study was aimed to understand ultrastructural pathology of nerves of tumor origin of spinal schwannomas, which has not been reported so far, in order to understand the mechanism of the postoperative functional restoration after the nerve transection. Methods: From 13 patients who underwent sacrifice of an affected nerve root at total removal of spinal schwannomas (C2 conus), the proximal (spinal cord side, n = 12) and distal (dorsal root ganglion side, n = 10) stumps of the nerves of the tumor origin were collected and examined by light and electron microscope, followed by morphometric analysis (n = 9). Results: Almost all of affected nerves at both proximal and distal to the lesion were composed of well-preserved myelin sheath and axons with mild disturbance of endo- and perineurial structures at light microscopic level except one case, which showed severe fibrosis. Electronmicroscopically, regenerated axons with thin myelin were found in part in the proximal and distal nerves with few macrophages in three cases. The area of nerves (mm ²), density of myelinated axons (axons/mm²) and total number of myelinated axons in the proximal stump (0.552 ± 0.430, 10,400 ± 5,240 and 5,480 ± 4,790) was approximately 70%, 80% and 60%, respectively, of those in the distal stump (0.765 ± 0.333, 12,400 ± 5,180 and 9,970 ± 8,630). Conclusions: This data combined with no permanent deficits after nerve transection suggest that the nerves of tumor origin are in the processes of slowly progressed deterioration with repeated degeneration and regeneration/remyelination, and the postoperative rapid recovery from the transient neurological deficit may be explained by functional compensation by the adjacent non-affected nerves with slow tumor growth.