epidural Epidural strictly means ‘on the dura’. In anatomical usage it means outside or around the dura mater, which is the outermost of the membranes (meninges) that ensheath the brain and spinal cord. In the vertebral canal there is a narrow space between the dura mater and the lining (periosteum) of the bones; local anaesthetic injected into this space abolishes sensation from those parts of the body served by nerves that enter the spinal cord below the level of injection. In the skull, the dura has two layers, and the outermost is itself the lining of the bone and firmly adherent to it. Head injury that involves fracture in the region of the temple where there are particularly vulnerable blood vessels, can lead to an epidural (‘extradural’) collection of blood, stripping the dura from the bone, and requiring drainage by trephining to alleviate compression of the brain.

Stuart Judge

ep·i·du·ral / ˌepiˈd(y)oŏrəl/ • adj. Anat. & Med. on or around the dura mater, in particular, (of an anesthetic) introduced into the space around the dura mater of the spinal cord.• n. an epidural anesthetic, used esp. in childbirth to produce loss of sensation below the waist.

epidural (extradural) (epi-dewr-ăl) adj. on or over the dura mater. e. anaesthesia suppression of sensation in the lower part of the body by injecting a local anaesthetic into the epidural space, which anaesthetizes spinal nerve roots. It is used especially to provide pain relief during childbirth or to reduce the need for deep general anaesthesia. e. space the space between the dura mater of the spinal cord and the vertebral canal.