DIFFUSION-WEIGHTED MRI FOR DIFFERENTIATING PYOGENIC, TUBERCULOUS, AND FUNGAL BRAIN ABSCESSES: A RADIOLOGICAL-MICROBIOLOGICAL CORRELATION STUDY

Abstract

Background: Pre-culture diagnosis of a brain abscess is clinically significant as the treatment of bacterial, antitubercular, and antifungal brain abscesses varies significantly and the ring-enhancing appearance is common in both conventional contrast-enhanced MRI and in the majority of bacterial and tuberculous brain abscesses. Objective: To assess the ability of diffusion-weighted imaging (DWI) patterns and apparent diffusion coefficient (ADC) measurement to differentiate pyogenic, tuberculous and fungal brain abscesses and to correlate with microbiological findings. Method: This was an observational radiological-microbiological correlation study involving 86 patients with brain abscesses (46 pyogenic, 23 tuberculous, and 15 fungal). Pre-treatment or early-treatment 3-T MRI with DWI and ADC mapping were performed in all patients. The following parameters were compared between groups: central cavity ADC, normalized ADC ratio, distribution of restricted diffusion, intracavitary projections, multiplicity, and wall morphology. Results: Mean central ADC was lowest in pyogenic abscesses (0.58 ± 0.14 × 10⁻³ mm²/s), intermediate in tuberculous abscesses (0.76 ± 0.18 × 10⁻³ mm²/s), and highest in fungal abscesses (1.02 ± 0.27 × 10⁻³ mm²/s; p < 0.001). Pyogenic lesions were more likely to have homogeneous central restriction (82.6%) compared to fungal abscesses, which were more likely to have heterogeneous peripheral or intracavitary projection restriction (73.3%; p < 0.001). An ADC threshold of ≤0.67 × 10⁻³ mm²/s was found to be 80.4% sensitive and 78.9% specific for the diagnosis of pyogenic abscess. The combined DWI model with central ADC and restriction pattern and intracavitary projections yielded a three-class diagnostic accuracy of 82.1% (κ = 0.71). Conclusion: DWI is a valuable etiological stratification tool if used as a pattern-based technique, not just based on central diffusion restriction. The quantitative ADC assessment can be used to assist with earlier targeted microbiological investigation and antimicrobial decision making, when used in conjunction with lesion morphology.