Spinal Infection: Epidural Abscesses
Epidural abscesses are infections that form in the space around the dura, the tissue envelope that surrounds the spinal cord and nerve root. These pockets of purulent fluid may surround the spinal cord and/or the nerve roots and generate enough pressure to affect neurological function. The symptoms can be subtle with (paresthesis - a sensation like pins and needles) or mild weakness. Back examination should be performed for evaluation of asymmetry, paravertebral swelling and tender vertebrae and careful neurological examination should be performed. The same diagnostic tests are employed with erythrocyte sedimentation rate being the most consistent abnormal laboratory value. The white blood cell count and blood cultures are useful as baseline parameters. Plain radiographs are not helpful. Magnetic resonance imaging (MRI) is the study of choice for further evaluation. This single study will define spinal cord compression and the status of the spinal cord, determine the presence and extent of the abscess, provide a diagnosis of co-existing osteomyelitis, and exclude a drainable paraspinal fluid collection. The indications for surgical decompression of the spinal cord would be an increasing neurological deficit, persistent severe pain, or increasing temperature and white blood cell count.
Finally, the frequency of post-operative wound infections have increased with increased usage of spinal instrumentation. The advantages of rigidly fixing a spine with instrumentation in order to increase fusion rate and decrease post-operative external immobilization have become apparent. Infection is a major disadvantage of implanting foreign bodies in the spine. The use of prophylactic antibiotics helps but a small percentage cannot be avoided. It has recently been shown that in particular, smokers are a very high risk group for infection. The diagnosis of post-operative infections is usually based on drainage from the wound or extraordinary pain. Other signs are elevated temperature, hematoma formation, erythema and edema at the wound site, elevated erythrocyte sedimentation rate, and increased white blood cell count. Once an infection is suspected, prompt exploration of the wound is indicated in the operating room with the patient under general anesthesia. Facilities must be available for aggressive debridement of the entire wound. Imaging studies are of limited value. Treatment of infected wounds includes debridement, systemic antibiotics, and either closed suction, suction irrigation or open treatment. Multiple debridements may be required. If the infection persists despite multiple debridements, removal of hardware and all bone graft is indicated. The most common bacteria is Staphylococcus aureus. Duration of the intravenous antibiotics is variable depending upon the infection. The cost of a post-operative infection can be considerable and the results less than optimal.