Adhesive arachnoiditis can occur after intrathecal administration of corticosteroids. The cause of arachnoiditis is unknown, but particulate corticosteroids in suspension and additives used as preservatives have been implicated. Arachnoiditis can occur if a portion of an epidural corticosteroid injection is delivered to the intrathecal space. Negative aspiration, however, does not guarantee that inadvertent partial injection into the intrathecal space will be prevented.

Administration of a contrast agent under fluoroscopy before injection of a corticosteroid can localize the needle in the epidural space. Use of a microbore attachment (“pigtail”) limits movement of the needle during syringe changes, thereby limiting the chance of needle migration into the intrathecal space. Attention must be paid to the contents of the epidural kit and injectant to ensure that they do not contain neurotoxic agents or preservatives. Antimicrobial skin preparations should be allowed to dry before needle placement because these agents may be neurotoxic.

Paralysis after epidural corticosteroid injection can have immediate or late onset. In cases of immediate-onset paralysis, a vascular source is usually suspected, such as vascular trauma or embolism from intravascular injection. The vessels of particular concern are radicular arteries feeding the spinal cord and, at the cervical level, the ascending cervical, deep cervical, and vertebral arteries. The anterior two-thirds of the cord is supplied by the anterior spinal artery. At the cervical level, the radicular and segmental medullary arteries are fed by the ascending cervical and deep cervical arteries. A recent cadaveric study demonstrated that 22% of the posterior portion of the cervical vertebral foramina, once considered the “safe” location for needle placement, contained radicular cervical or segmental medullary arteries.

In the thoracic and lumbar spine, the anterior spinal artery is fed by radicular arteries from the lumbar and intercostal arteries. Of particular concern is the artery of Adamkiewicz, typically located between T5 and L2 on the left. Its origin has considerable anatomic variability. Radicular arteries enter the spinal column through the foramen, putting them at risk during transforaminal injections. Previous spine surgery appears to be a risk factor for anterior spinal cord infarctions associated with epidural injections.

To limit the possibility of intravascular injection, needle placement should be confirmed by administering contrast agent under fluoroscopic imaging. Digital subtraction angiography provides increased sensitivity in detecting intravascular injections. A test dose of local anesthetic can confirm intravascular needle placement by resulting in temporary paralysis, or, in cases of cervical injections, seizures. Use of a microbore attachment limits needle movement while syringes are changed between injections. A pencil-point spinal needle may decrease the risk of vascular cannulation. Corticosteroid solutions rather than particulate formulations may decrease the possibility of embolism during inadvertent intravascular injection. Cases of cervical anterior cord syndrome and cerebellar injury have occurred after cervical transforaminal epidural injections, despite needle placement using fluoroscopy and real-time computed tomography (CT). We recommend that such injections be performed only with extreme caution and after careful consideration of the risks and benefits.