STRUCTURAL OR FUNCTIONAL? APPROACHING VASCULAR FACTORS IN LUMBOSACRAL COMPRESSION RADICULOPATHY IN DOGS

Neuroforaminal stenosis results in compression and deformation of nerve roots with possible consequences to their microcirculation. Malperfusion and impaired venous drainage have been associated with nerve root dysfunction in rodents. However, the evidence and clinical impact of ischaemia and changes to the vascular supply of compressed nerve roots remain to be documented. To approach circulatory impairment, we evaluated the vascular density and expression of the vascular endothelial growth factor (VEGF) in DRG of dogs with chronic nerve root compression using brightfield microscopy, immunohistochemistry and digital image analysis. Altogether, 14 L7-DRG were evaluated from eight dogs suffering from painful lumbosacral neuroforaminal stenosis. The results were compared to age-/breed-matched non-compressed DRG. Histological examination identified thickening of arterial walls (7/14) and endothelial prominence (4/14) within the endoneurium as well as dilatation of capsular veins (2/14). On stereological analysis, there was not difference of vascular density in between DRG of affected dogs and control nerve roots (p ≥ 0.33). All entrapped DRG, however, showed a significant increase of endothelial VEGF expression throughout the endoneurium (p=0.0002) and perineurium (p=0.0003). Furthermore, a focal increase of neuronal VEGF expression was seen in entrapped DRG (p=0.006) with an emphasis on subcapsular areas. Nerve root compression goes with morphological changes of entrapped blood vessels while the vascular density remains unchanged even though endothelial expression of the angiogenic factor VEGF is widely increased. Local increase of neuronal VEGF expression, on the other hand, indicates hypoxia and therefore supports the hypothesised circulatory impairment in entrapped nerve roots.