Epidurography is generally performed to document the accurate delivery of therapeutic substances into the epidural space prior to the injection of epidural steroids and local anesthetic. The study also imparts important information regarding the anatomy of the epidural compartment. In addition, postinjection films provide visual feedback regarding the actual distribution of the therapeutic agents. An important role of the imaging study is to exclude intrathecal injection, which is a contraindication for the subsequent injection of therapeutic substances. The contrast agent utilized for epidurography is safe for myelography; thus an inadvertent dural puncture is harmless. However, the introduction of therapeutic substances into the thecal sac may lead to complications, especially with repeated injections. This is an important consideration, because without fluoroscopic guidance, incorrect needle placement occurs in up to half of cases, depending on the operator's experience.30,31 If accurate needle placement is not achieved, the therapeutic substances may be delivered into the paraspinous soft tissues, where they are ineffective, albeit harmless. On the other hand, if such drugs are injected into the thecal sac or a blood vessel, untoward sequelae may result. Unfortunately, negative aspiration for blood does not exclude an intravenous injection. In fact, intravascular injection may occur in up to 9% of cases, even with negative aspiration of blood.30 Epidurography is thus useful for documenting the anatomy of the epidural space, ensuring accurate delivery and distribution of therapeutic substances, and preventing injection into the thecal sac or a vessel.
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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.