Patients should be made aware that a very small proportion of patients experience increased radicular pain for three to five days after the procedure. This may be related to a chemical sensitivity to the inactive components of the steroid preparation. Patients should be reassured that the pain will resolve; if they require future injections, a different steroid preparation can be used.
As with any procedure utilizing iodinated contrast, the patient should be informed that a contrast reaction could occur. To minimize this possibility, only nonionic contrast should be used. Patients with a history of allergy should first receive a course of oral steroid prophylaxis. Bleeding risk is minimal; nevertheless, to avoid epidural hematoma, these procedures should not be performed on anticoagulated patients, and patients on chronic aspirin therapy should stop the medication a week prior to the spinal injection.
Contrast injection with active fluoroscopic observation verifies proper location of the needle tip and minimizes the risk of subsequent intravascular injection of medication (11,12,14,15,17). Venous collaterals are commonplace in the neural foramina and epidural space of the thoracic and lumbar spine; inadvertent injection of a small amount of medication into these vessels is not generally problematic, although the medication will not deposit in the intended location. However, arterial collaterals of the spinal artery occasionally pass through the thoracic neural foramina, and injection of anesthetic or steroid suspension into these vessels could potentially result in cord infarction and paralysis. This is primarily a consideration in the region of the artery of Adamcowitz at approximally the T7 to T8 level. Injection more inferiorly within the neural foramen could potentially avoid these branches, which course directly beneath the pedicle.
Injection of steroid has its own risks, even though the biodistribution is quite different than a preparation administered orally or intravenously. Risks include avascular necrosis, propagation of infectious processes, elevation of blood glucose in diabetics, suppression of the adrenal-pituitary axis, tendon tears, and deposition of fat in various locations around the body (theoretically including the epidural space, resulting in epidural lipomatosis).
Inadvertent intrathecal or subarachnoid injection is a known complication of epidural injection, but is mainly a consequence of nonselective interlaminar injection (13); intrathecal injection is exceedingly rare when using a proper selective transforaminal approach or a caudal approach through the sacral hiatus. Some potential sequelae of an intrathecal injection include spinal anesthesia (if anesthetic is used), dural leakage, headache, hypotension, meningitis, and arachnoiditis (20,21). Hypotension may also occur from caudal injection if a large amount of fluid is injected in order to "push" the medication superiorly (21). In order to minimize these complications, many prefer the selective transforaminal approach for needle placement. Again, whatever approach is used, verification of needle position with contrast injection is essential to minimize complications. Rarely, intraneural injection can occur, which can injure the nerve. If the needle is placed within the nerve itself, contrast injection will reveal a thin, linear pattern of opacification corresponding to the course of the nerve root, and the patient will experience severe radicular pain. At this point, the injection should be stopped immediately and the needle repositioned.
Vasovagal reaction is occasionally seen, and best treated with supportive measures and termination of the procedure. Facial flushing can also be seen. Finally, as with any procedure, infection is a potential risk that can be minimized by using careful sterile technique.
As outlined previously, lidocaine is typically injected along with steroid for epidural injection procedures; long-acting anesthetics such as Bupivacaine or Marcaine have been used instead of lidocaine by some authors (21,22). With these medications, the extreme numbness (and occasional weakness) after the procedure will last six to eight hours (as opposed to one to two hours with lidocaine). For some patients, especially the elderly, this effect can be temporarily debilitating. This prolonged anesthesia provides no additional diagnostic information compared to injection of a short-acting anesthetic, and anesthetic is not a therapeutic medication; therefore, we do not encourage the use of a long-acting anesthetic for spinal injections. In fact, for elderly patients with spinal stenosis, an argument can be made for avoiding use of epidural anesthetic entirely; in this population, the diagnostic benefit of anesthetic injection is marginal.
Despite this rather long discourse on the potential complications of epidural injection, it should be recognized that these injections are, in actuality, very safe if performed with image guidance and contrast injection. Two large series report few complications, the vast majority of which are mild; this has been our experience as well.
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