Brain abscess medical therapy
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Treatment
Treatment is generally a team approach and most reliably depends on obtaining tissue via a stereotactic needle Bx. Although randomized, controlled trials have not been done, the consensus is that abscesses > 3cm should be drained (if accessible).
The treatment includes lowering the increased intracranial pressure and starting intravenous antibiotics (and meanwhile identifying the causative organism mainly by blood culture studies).
Surgical drainage of the abscess remains part of the standard management of bacterial brain abscesses. The location and treatment of the primary lesion also crucial, as is the removal of any foreign material (bone, dirt, bullets, and so forth).
There are a few exceptions to this rule: Haemophilus influenzae meningitis is often associated with subdural effusions that are mistaken for subdural empyemas. These effusions resolve with antibiotics and require no surgical treatment. Tuberculosis can produce brain abscesses that look identical to bacterial abscesses on CT imaging and surgical drainage or aspiration is often necessary to make the diagnosis, but once the diagnosis is made no further surgical intervention is necessary.
- Antibiotics: Brain abscesses are usually polymicrobial, with the most common bugs being microaerophilic streptococci (viridans) and anaerobic bacteria (bacteroides, anaerobic strep and fusobacterium).
- S. aureus, and enterobacteriacae are also seen.
- Bugs associated with trauma include S. aureus and clostridium sp.
- Empiric Rx usually starts with high-dose PCN (10 – 20 million units / d), metronidazole, +/- a 3rd gen cephalosporin.
- Even if the abscess is associated with a dental procedure and other organisms are considered (actinomyces sp.) they generally respond to the above Rx.
- If extending from an otitis, empiric Rx should also cover pseudomonas and enterobacteriacaea.
- If hematogenously spread, coverage depends on the original bug.
- The penetration of abx into an abscess does not necessarily equate with their penetration into the CSF (the blood-brain barrier is not the same as the blood-CSF barrier).
- Drugs like vancomycin, which have poor CSF levels (<10% of serum) have been shown to have good abscess levels (90% of serum).
- Most patients are treated parenterally for at least 8w.
- Some authors also recommend an additional 2 – 3 month course of oral abx to clear up any ‘residual’ infection and to prevent relapses.
- One study actually suggests that, when combined with surgical excision, 3w may be adequate.
- Other studies have reported good outcomes with abx alone in patients with small lesions (<2cm), in well vascularized areas (cortex), who were poor surgical candidates.
- There have not been any studies reporting benefit from intra-thecal or intra-abscess abx.
- There seems to be consensus on obtaining q 2 – 4w f/u CT/MRI scans to document resolution.
Adjuvants
- Although steroids have not been studies in well-designed trials, many authors use them in patients with elevated ICP.
- Some animal studies suggest interference with granulation tissue formation and bacterial clearance.
- Anticonvulsants are recommended prophylactically for the 1st 3m, though the data supporting this is lacking.