Accidental subdural catheterization: radiological evidence of a possible mechanism for spinal cord damage.

We describe the inadvertent subdural insertion of a lumbar extradural catheter in a primiparous woman in labour. A small quantity of local anaesthetic resulted in extensive motor and sensory block. Computed tomography performed after contrast injection demonstrated unequivocally that the catheter was in the subdural space. The catheter and injected fluid produced considerable displacement of the arachnoid within the thecal sac. We postulate that this could result in arterial compression or direct damage to the spinal nerve roots. Such a mechanism might explain some of the cases of permanent neurological damage associated with extradural analgesia.