What is the recommended workup and treatment for a brain abscess?

Brain Abscess Workup and Treatment

Brain MRI with diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) sequences, and T1-weighted imaging with and without gadolinium is the strongly recommended first-line imaging modality, followed by neurosurgical aspiration or excision as soon as possible, with empirical treatment consisting of a 3rd-generation cephalosporin combined with metronidazole for 6-8 weeks intravenously. 1

Diagnostic Imaging

MRI is superior to CT and should be obtained first whenever available, achieving 92% sensitivity and 91% specificity for diagnosing brain abscess. 2 The characteristic findings include:

• Ring-enhancing lesion on post-contrast T1-weighted images 2
• Central hyperintensity on DWI with corresponding low ADC values that distinguish abscess from tumors 2
• If MRI is unavailable, contrast-enhanced CT is acceptable but has lower diagnostic accuracy 1

Critical pitfall: Never perform lumbar puncture in suspected brain abscess—it is relatively contraindicated due to herniation risk and provides minimal diagnostic yield. 1, 2

Microbiological Workup

Obtain blood cultures in all patients (positive in 28% of cases) before initiating antibiotics. 1, 3

Withhold antimicrobials until neurosurgical aspiration or excision in patients without severe disease (no sepsis, imminent rupture, or impending herniation) if surgery can be performed within 24 hours of radiological diagnosis. 1 This approach maximizes culture yield and pathogen identification.

Send abscess pus samples for:

• Aerobic and anaerobic cultures 1
• Histopathological analysis 1, 3
• Molecular-based diagnostics if cultures are negative 1
• Ziehl-Nielsen stain and tuberculosis PCR in endemic areas or based on clinical presentation 1

Additional Diagnostic Studies

HIV testing should be considered in all patients with non-traumatic brain abscess. 1, 3, 2

Obtain targeted imaging to identify the infection source:

• Chest X-ray or CT thorax-abdomen-pelvis when source is unclear 1, 3
• Transoesophageal echocardiography for bacteremic patients with monomicrobial streptococcal or staphylococcal abscess without other predisposing factors (endocarditis diagnosed in 5% of cases) 1, 2
• ENT and maxillofacial surgery consultations for suspected ear-nose-throat or dental infections 1

Neurosurgical Management

Neurosurgical aspiration or excision should be performed as soon as possible in all patients whenever feasible (excluding toxoplasmosis). 1, 3 This is pivotal for source control and provides both diagnostic and therapeutic benefits. 1

Aspiration is the preferred procedure in most cases, with approximately 20% requiring re-aspiration or secondary excision. 1

Excision should be considered for:

• Abscesses caused by difficult-to-treat pathogens (fungi, Nocardia species) 1, 3
• Superficial abscesses in non-eloquent areas 1, 3
• Posterior fossa location 1, 3
• Abscesses ≥2.5 cm in diameter (reduces mortality from 24% to 9%) 3

Empirical Antimicrobial Therapy

For community-acquired brain abscess, strongly recommend a 3rd-generation cephalosporin (cefotaxime or ceftriaxone) combined with metronidazole. 1, 3, 4

Add vancomycin if:

• Meticillin-resistant Staphylococcus aureus is suspected 4
• Post-neurosurgical abscess 4
• Penetrating head trauma 4

For severely immunosuppressed patients (transplant recipients):

• Add voriconazole AND trimethoprim-sulfamethoxazole or sulfadiazine to cover Toxoplasma and fungi 4

Duration of Antimicrobial Therapy

Administer 6-8 weeks of intravenous antimicrobials for aspirated or conservatively treated brain abscesses. 1, 3

A shorter duration of 4 weeks may be considered for patients treated with complete excision. 1

Do not use oral consolidation therapy after 6 weeks of IV antimicrobials (excluding permanent neuroanatomical defects, tuberculosis, nocardiosis, toxoplasmosis, and fungal brain abscess). 1

Adjunctive Therapies

Corticosteroids (dexamethasone) are strongly recommended for severe symptoms due to perifocal edema or impending herniation. 1, 3 However, reduce the dose as soon as intracranial pressure is controlled, as steroids may retard abscess capsule formation and decrease antibiotic concentrations. 5

Primary prophylaxis with antiepileptics is conditionally recommended against in most patients with brain abscess. 1

Follow-up Imaging Schedule

Perform imaging every 2 weeks after aspiration or excision in clinically stable patients until clinical cure is evident. 6, 3

Obtain immediate imaging for any clinical deterioration (worsening neurological status, increased headache, altered mental status, new focal deficits). 6, 3

Expected radiological evolution:

• Abscess volume typically stationary or only slightly diminished at 2 weeks (normal finding) 6, 3
• Lack of regression by 4 weeks is unusual and warrants repeat intervention 6, 3
• Residual contrast enhancement may persist for 3-6 months; do not prolong antimicrobials based solely on this finding 6, 3

Indications for Repeat Neurosurgical Intervention

Perform repeated aspiration or excision when:

• Clinical deterioration occurs despite appropriate therapy 6, 3
• Abscess enlargement documented on imaging 6, 3
• No reduction in abscess volume by 4 weeks after initial aspiration (almost always requires repeat intervention) 1, 6, 3

Critical Complications

Abscess rupture carries 27-50% mortality and occurs in 10-35% of cases, particularly with close proximity to ventricles. 3 This warrants earlier surgical intervention regardless of size.

Long-term sequelae occur in approximately 45% of patients at 6 months, including focal neurological deficits and neurocognitive impairment, necessitating referral to specialized neurorehabilitation. 3