Diagnosing Brain Abscess: Imaging Approach
Brain MRI with diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) sequences, and T1-weighted imaging with and without gadolinium is the strongly recommended imaging modality for diagnosing brain abscess, achieving 92% sensitivity and 91% specificity. 1
Primary Imaging Modality
MRI is superior to CT for brain abscess diagnosis and should be the first-line imaging study whenever available. 1
MRI demonstrates characteristic findings: ring-enhancing lesion on post-contrast T1-weighted images, central hyperintensity on DWI, and corresponding low ADC values that distinguish abscess from other ring-enhancing lesions like tumors 1
Diagnostic accuracy from meta-analysis of 28 studies with 2,128 patients showed sensitivity 92% (95% CI 88-95%), specificity 91% (95% CI 86-94%), positive predictive value 88%, and negative predictive value 90% 1
The complete MRI protocol must include: DWI sequences, ADC sequences, and T1-weighted imaging both with and without gadolinium contrast 1, 2
Alternative Imaging When MRI Unavailable
Contrast-enhanced CT may be used only when MRI is not accessible, recognizing it has lower sensitivity and specificity than MRI. 1, 2
CT with contrast shows ring-enhancing lesions but cannot reliably differentiate abscess from necrotic tumors or other pathologies 3
CT improved brain abscess diagnosis significantly when introduced in the 1970s, but has been superseded by MRI for diagnostic accuracy 1
Critical Diagnostic Nuances and Pitfalls
MRI sensitivity decreases in specific clinical scenarios that require awareness:
Patients on prolonged antibiotic therapy (several weeks) may show reduced MRI sensitivity 1
Toxoplasmosis abscesses demonstrate lower MRI diagnostic accuracy 1
Post-neurosurgical abscesses are more difficult to identify on MRI 1
Confirmatory Diagnosis
Neurosurgical aspiration or excision provides definitive diagnosis through direct visualization and culture of purulent material. 1
Samples should be sent for aerobic and anaerobic cultures plus histopathological analysis 1, 4
Blood cultures are positive in 28% of cases and should be obtained in all patients 1, 4
Molecular-based diagnostics are recommended when available, especially with negative cultures 4
Additional Diagnostic Workup
Identify the source of infection through targeted imaging and testing:
Chest X-ray or CT thorax-abdomen-pelvis when infection source is unclear 1, 4
Transoesophageal echocardiography for bacteremic patients with monomicrobial streptococcal or staphylococcal abscess without other predisposing factors 1
HIV testing should be considered in all non-traumatic brain abscess cases 1, 4
ENT and maxillofacial surgery consultation for suspected sinus, ear, or dental sources 1
Common Pitfall to Avoid
Do not perform lumbar puncture in suspected brain abscess—it is relatively contraindicated due to herniation risk and provides low diagnostic yield. 1