First, an area of abnormal contrast filling must be identified; this area must correlate with the patient's clinical presentation. For example, a patient who presents with symptoms of neurological dysfunction in a right L5 distribution should demonstrate a SOL involving the right L5 nerve root. A SOL involving an unaffected nerve root is not clinically significant. In other words, a space-occupying lesion warrants epidurolysis only when it is identified at the site predicted by the patient's symptomatology.
This does not mean that a steroid injection cannot or should not be performed at the predicted site in the absence of a contrast filling defect—only that in the absence of evidence of epidural adhesions (lack of a SOL), epidurolysis is not indicated. Ironically, it is in patients with no evidence of a SOL that a site-specific, epidurally administered steroid is likely to have its best clinical effect. This is often a circumstance when the pathology is simple radiculitis without adhesions of the nerve root within the neuroforamen. Long-term improvement is more likely if there is not adherence of the nerve root to surrounding tissue, which can reproduce a neuroinflammatory response after the steroid effect has worn off.
One must be well acquainted with the appearance of a typical epidurogram (Figure 10.1) to identify one that is abnormal or pathological (Figure 10.2).
Pathological filling defects can be produced by the following structural abnormalities:
Epidural scarring or fibrosis Vascular congestion Disc material Tumor
Epidural fibrosis can be produced by a variety of mechanisms. The most common of these mechanisms is postsurgical scarring, producing the ill-defined and primarily descriptive diagnosis of "failed back surgery syndrome."22 One must recognize that postoperative fibrosis is not necessarily limited to the level or side of surgical intervention. Many "failed" back surgeries are due to an inaccurate diagnostic assumption of discogenic pain in a patient whose nociceptive stimulus may have been post-disc disruption epidural fibrosis. An abnormal-appearing disc is not necessarily painful, just as a normal-appearing disc is not necessarily nonpainful. McCarron used a dog model to demonstrate the intense inflammatory reaction that occurs in the epidural space in response to exposure to intradiscal nuclear material following disc disruption with or without discogenic pain.2
Vascular compromise secondary to venous compression and proximal distention can produce tissue edema and fibrosis, as well as an epidural filling defect with neuroforaminal compressive injury.
Degenerative disease of the discs, vertebrae, or facets can produce an inflammatory epidural response. Likewise, disc disruption with bulging, herniation, or frank extrusion can produce a space-occupying lesion identifiable by epidurography with thecal sac impingement, nerve root compression, and/or painful distention of the posterior longitudinal ligament.5
Tumor of either primary or metastatic origin can be responsible for the appearance of a filling defect in the epidural space. The highly vascular nature of such tissue predisposes the patient to a higher risk of epidural hematoma with catheterization and mechanical disruption. A high level of suspicion must be maintained for such pathology when space-occupying lesions are identified.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.