Pathology of local anesthetic-induced nerve injury

Nerve fiber injury and endoneurial edema were induced by the injection of the local anesthetic 2-chloroprocaine, tetracaine, procaine, etidocaine or mepivacaine into the soft tissue and fascia surrounding the sciatic nerve of Sprague-Dawley rats. Light microscopy demonstrated that the perineurial barrier was not mechanically damaged by the surgical procedure but, at 48 h post-injection, perineurial permeability was increased. Previous observations of leakage of horseradish peroxidase and the present report of neutrophils and eosinophils in the endoneurium indicate a disruption of blood-nerve barrier systems. Endoneurial edema was observed in the subperineurial, interstitial and perivascular regions. Axonal degeneration and demyelination occurred; the latter associated with accumulation of large lipid droplets in Schwann cells. Degranulation of mast cells, proliferation of fibroblasts and macrophage activity were noteworthy in affected areas. The findings are remarkable in that this is the first model of endoneurial edema by a neurotoxin which penetrates the perineurium, disrupting barrier system and inducing nerve fiber injury.