99 Spinal Epidural Abscess

Cristian Gragnaniello and Remi Nader

Fig. 99.1 Sagittal T2-weighted magnetic resonance image through the lumbar spine.

Clinical Presentation

A 39-year-old man presents to your ofce 2 weeks after he has undergone a hemilaminectomy at L3–L4 for degenerative spinal stenosis.

He has a previous history of L4–5 and L5–S1 posterolateral fusion with pedicle screw fxation.

He presents now with a 2-day history of severe back pain radiating to the buttocks bilaterally.

There is mild erythema around the recent surgical wound.

There are no defcits or pain in his lower extremities.

Magnetic resonance imaging (MRI) of the lumbar spine is obtained (Fig. 99.1).

Questions

Interpret the MRI and give a differential diagnosis.
What are the characteristics of epidural abscess on MRI?
What are the risk factors for this condition?
What are the most common microorganisms involved in epidural abscesses in the immunocompetent patient?
What is the incidence of this condition in the postsurgical patient?
How do you manage this condition?

You decide to operate. You decompress the thecal sac and perform a sharp debridement of the wound. During surgery, you send cultures and are told that there are numerous Gram-positive cocci. Once down to the thecal sac, you notice that, for the most part, there is thick granulation tissue over the sac. As you tease this tissue off the dura, you get a dural tear.
How do you handle a dural tear in this specific setting?
Why do you not remove the instrumentation of the previous fusion?

After you decompress the thecal sac, you notice a piece of floating bone, you remove it, and you notice that it comprises the inferior facet joint of L3 that is detached and free floating (you did not detach it during your current decompression).
Why is the piece of facet detached?
What condition do you now worry about, given the detached facet, and how do you manage it?

Answers

Interpret the MRI and give a differential diagnosis.

There is a posterior epidural collection from L2–L4, hyperintense on T2-weighted images. This could be a cerebrospinal fluid (CSF) collection, abscess, or infected hematoma.1–4

The disk space looks normal, and so do the vertebral bodies. This finding is important to assess the radiographic presence of concomitant osteomyelitis.

There is loss of lumbar lordosis.

Given the clinical presentation, the most likely diagnosis is epidural abscess.
What are the characteristics of epidural abscess on MRI?
- On T1-weighted images, it has the same intensity as spinal cord or neural elements.
- On T2-weighted images, it shows increased signal.
- On fat-saturated sequences, edema and soft tissue inflammation are clearly visible and bright.
- Contrast-enhanced images often show a peripheral rim of enhancement due to granulation tissue and hypervascularity.¹
What are the risk factors for this condition?
- Presence of hardware and instrumentation
- Repeated surgery
- Use of steroids
- Diabetes or other underlying medical problems such as renal failure, previous trauma, and urinary tract infections
- Intravenous drug abuse^3–5
What are the most common microorganisms involved in epidural abscesses in the immunocompetent patient?
- Gram-positive bacteria such as Staphylococcus (S.) aureus (reported in 60% of cases) or S. epidermidis^4,5
- Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa^4,5
What is the incidence of this condition in the postsurgical patient?
- The generally accepted incidence is less than 10%.
- The incidence is reportedly increased with higher complexity procedures. It is in the range of 0.6–3.7% after microdiscectomy and of 3.7–20% after instrumented lumbar cases.²
How do you manage this condition?
- Look for any discharge so it can be cultured before starting antibiotics.
- Explore the wound to see if you find a purulent collection or CSF.
- Drain the abscess, sampling tissue, and purulent material for culture.
- Perform a sharp debridement and lavage.³
- Place on broad-spectrum intravenous antibiotics until final culture results are available. Vancomycin for the gram-positive covering including methicillin-resistant Gram-positive cocci and cefepime for Gram-negative bacteria are among the most common medications used.⁴
- The closure of the wound is very important and can be done in different ways, but the key concept is the obliteration of the dead space caused by the removal of the infected tissue restoring the blood supply and postoperative drainage by outflow drain or suction/irrigation device.^6,7
How do you handle a dural tear in this specific setting?
- A tear in this specific condition can lead to a spreading of the infection in the subdural space because of the disruption of the normal dural barrier.⁸
- Suture with a 7–0 or 8–0 dural suture if accessible in a watertight fashion, using the Valsalva maneuver to confirm the closure.
- Cover with a dry piece of Gelfoam (Pfizer Pharmaceuticals, New York, NY) or collagen matrix.
- Cover with fibrin glue or hydrogel sealant.
- You may need to resect more bone to further the exposure and allow access to the whole tear.9
- Continue appropriate antibiotics.
Why do you not remove the instrumentation of the previous fusion?
- The infection on the MRI does not extend to the previously treated levels.
- The onset of symptoms is very recent as the surgery at the L3–L4 level was performed in the past 2 weeks. Therefore, the formation of the glycocalyx over the rod and other used material is improbable.^2,3
- Titanium materials have a porous surface that allows the penetration of antibiotics.⁶
- Good results have been shown when leaving the instrumentation in place, even in cases where the infection was involving those instrumented levels, if thorough debridement is performed and antibiotic therapy is well managed.^10,11
Why is the piece of facet detached?
- The bone is likely detached due to erosion from osteomyelitis.
What condition do you now worry about given the detached facet and how do you manage it?
- You worry about two entities:
  - Osteomyelitis and spread of the infection to bone
  - Instability and the possibility of spinal deformity
- Your management should now involve placing the patient in a brace postoperatively and obtaining flexion-extension lumbar spine radiographs.
- You may repeat radiographs in 2 to 4 weeks as osteomyelitic changes may become visible radiographically only after 2 to 3 weeks.³
- He may need a lumbar instrumented fusion once the infection has healed if instability is then demonstrated.¹²
- Treatment with antibiotics does differ in cases of osteomyelitis: he then needs 8–12 weeks of intravenous antibiotics instead of only 4–6 weeks (as in cases of simple epidural abscess with no bony involvement).⁵
- Hyperbaric oxygenation can help to promote host immune defense response and stimulate vascularization of the injured tissues.¹³