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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.
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