Background: Magnetic resonance imaging (MRI) of ring-enhancing lesions results from various diseases, including infection, neoplasia, inflammation and vascular etiologies. Differentiation based on standard MRI sequences can be challenging. Hypothesis: Diffusion-Weighted Imaging (DWI) of ring-enhancing infectious disease will be highly restricted and allow differentiation from other ring-enhancing etiologies. Animals: 18 infectious, 54 non-infectious cases.
Methods: Retrospective study. Records were reviewed for MR studies with DWI and post-gadolinium T1-weighted ring-enhancing lesions with histopathological diagnoses or a microbiological diagnosis of brain infection. Apparent diffusion coefficient (ADC) maps were generated. Normalized ADC values (rADC) were calculated using ADC values from lesional and contralateral brain (CB) regions of interest (rADC=ADClesion/ADCCB).
Results: Histopathological diagnoses of abscess were made in 16 cases. Two infectious cases had microbiological diagnosis only. Median rADC was significantly lower for intraparenchymal bacterial abscesses (0.54, n=9) compared to ring-enhancing gliomas (1.69, n=18; p<0.0001), non-infectious inflammatory lesions (1.53, n=12; p=0.001), and other types of neoplasm (0.91, n=12; p=0.01). There was no significant difference between rADC for intraparenchymal abscess and intraparenchymal hemorrhage (0.55, n=12; p=0.73). Median rADC was significantly lower for intraparenchymal bacterial abscesses (0.54, n=9) compared to extraparenchymal bacterial abscesses (2.5, n=6; p=0.002), and intraparenchymal fungal abscesses (1.2, n=3; p=0.01). With exclusion of hemorrhagic lesions, an rADC of 0.61 had a sensitivity/specificity of 78%/90% for bacterial abscess.Conclusions and clinical importance: DWI may differentiate bacterial abscess from other common ring-enhancing lesions and abscess of fungal origin. Some uncommon neoplasia and hemorrhagic lesions may mimic intraparenchymal bacterial abscess on DWI.
