Microscopic epidural lesions in goats given repeated epidural injections of morphine: use of a modified autopsy procedure

Epidural catheterization was performed in six goats. Five days later either saline or 20 mg (5 mg/ml) preservative free morphine was injected epidurally once daily for 8 days. The goats were sacrificed 4, 24 or 48 hours after the last injection. The lumbar part of columna was removed in toto for microscopic examination of the spinal cord and the entire epidural space after decalcification and transverse sectioning. After saline, minimal changes including a fibrous membrane surrounding the catheter, scattered fat cell necrosis, scattered small focal cell infiltrations and occasionally focal haemorrhages were seen. After morphine the changes were considerably more severe including diffuse cellular inflammatory reaction in the epidural space, fat cell necrosis, occasionally focal exudative inflammation and chronic inflammatory reaction in the vicinity of the fibrous membrane demarcating position of the catheter. It is concluded that the present modified autopsy procedure permits microscopic examination of the epidural space. It has been shown that repeated administration of morphine caused tissue damage in the epidural space of goats. The human predictability of the results obtained is unknown. However, the results are encouraging for investigations with similar procedure in humans.