Brain abscess
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American Roentgen Ray Society Images of Brain abscess |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Historical Perspective
Pathophysiology
Epidemiology & Demographics
Risk Factors
Screening
Causes
Differentiating Brain abscess
Complications & Prognosis
Diagnosis
History and Symptoms | Physical Examination | Laboratory tests | Electrocardiogram | X Rays | CT | MRI Echocardiography or Ultrasound | Other images | Alternative diagnostics
Treatment
Medical therapy | Surgical options | Primary prevention | Secondary prevention | Financial costs | Future therapies
Differential Diagnosis
- Some studies suggest that indium scans can help differentiate abscess from CA, and thallium SPECT scans can distinguish CNS toxo from lymphoma.
- A CT scan with contrast will show a ring-enhancing mass that surrounds an area of hypodensity (necrosis or edema).
- The big differential is metastatic tumor: abscesses are often located in watershed regions, and tumors often enhance diffusely with contrast.
- Despite these differences, the true Dx is sometimes not made until biopsy.
- MRI is generally thought to be the imaging modality of choice and can more accurately stage the abscess and gauge the response to therapy.
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.
Surgery
Surgery has evolved dramatically over the last few decades.
- Once requiring open craniotomy and drainage / excision, most procedures are currently minimally invasive, closed, and performed under local anesthesia with conscious sedation and CT guidance.
- CT guidance is accurate to within 4 – 5mm.
- Stereotactic drainage can also be used if necessary, and is accurate to within 1 – 2mm.
- Open craniotomy with complete excision is usually reserved for patients with multiloculated abscesses or in cases due to more resistant pathogens (e.g. fungi and nocardia).
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.
Prognosis
Once an almost always fatal disease before the CT era. If the abscess is treated before the person goes into a coma then the death rate has been estimated from 5% to 20%.
Early treatment and the patients overall health has an effect on prognosis. Other factors include: antibiotic resistance or the abscess location. An abscess deep within the brain is more difficult to treat than others.
In general
- Mortality is currently quoted to range from 0 – 24%.
- Poor prognostic indicators include:
- Intraventricular rupture:
- 80% mortality rate, often treated with open drainage and debridement f/b ventriculostomy catheter for drainage and intrathecal abx
- Mental status and neurologic function at time of Dx:
- The most common sequellae is seizures, which develop in 35 – 70% of patients.
References
Additional Resources
Mathisen, G.E., Johnson, J.P., Brain abscess, Clin Infectious Disease 1997; 25: 763-781.