Inadvertent Subdural Injection

A subdural space exists in the cerebral meninges and may extend down to the spinal segment of the meninges, leading to unexpected sensory, sympathetic and motor blocks when local anesthetics are deposited there in the absence of any evidence of subarachnoid injection. Such a space has been demonstrated myelographically in 1–13% of patients. The space lies between the dura and arachnoid membranes and injection of drugs there may produce effects similar to those of subarachnoid injection but after an interval of 20 minutes or more, in contrast to 1–2 minutes after actual subarachnoid injection.