Histologic and electrophysiologic changes following subepineurial hematoma induction in rat sciatic nerve

The sciatic nerves of 34 rats were used to study the effects of intraneural, extrafascicular hematoma, exclusive of any other trauma. Electrodiagnostic, histologic, and electron microscopic techniques were used. The amount of nerve fiber damage was assessed using computerized planimetry. The effects of hematoma evacuation were also investigated. Changes consistent with partial denervation, such as prolongation of insertion activity and distal latency, and the presence of positive waves and fibrillations, were present in the blood-injected but not in the control groups. Degenerative nerve fiber changes localized to the area of hematoma were present in the blood-injected group and were significantly higher than those in the control group. Although there was a difference in the amount of nerve damage between the blood-injected and the hematoma-evacuated group (less damage), this difference was not statistically significant. These findings suggest that intraneural extrafascicular hematoma produces electrophysiologic and histologic evidence of axonal degeneration affecting nerve fibers in the vicinity of the hematoma. Early evacuation of the intraneural hematoma appears to slightly reduce the deleterious effects of the lesion.