Diffusion-Weighted Imaging of Intracranial Ring-Enhancing Lesions

Area of Science:

• Veterinary Radiology
• Neuroimaging
• Infectious Disease Imaging

Background:

• Ring-enhancing lesions on MRI present diagnostic challenges due to diverse etiologies like infection, neoplasia, and inflammation.
• Standard MRI sequences often struggle to differentiate these lesions effectively.
• Diffusion-weighted imaging (DWI) offers additional information for lesion characterization.

Purpose of the Study:

• To compare apparent diffusion coefficient (ADC) values of intracranial ring-enhancing lesions of infectious etiology with those of other causes.
• To evaluate the utility of ADC values in differentiating infectious from non-infectious ring-enhancing lesions.
• To determine if restricted diffusion on DWI is a reliable marker for specific types of infectious brain lesions.

Main Methods:

• Retrospective review of MRI studies with DWI and post-gadolinium T1-weighted imaging in animals with ring-enhancing lesions and definitive diagnoses.
• Generation of ADC maps and selection of regions of interest (ROIs) for lesional and contralateral brain tissue.
• Calculation of normalized ADC values (rADC = ADClesion/ADCbrain) for quantitative analysis.

Main Results:

• Intraparenchymal bacterial abscesses showed significantly lower median rADC (0.54) compared to gliomas (1.7) and non-infectious inflammatory lesions (1.7).
• Hemorrhagic lesions had similar rADC values (0.54) to bacterial abscesses, posing a potential diagnostic overlap.
• Extraparenchymal bacterial empyema (rADC 2.8) and fungal abscesses (rADC 1.2) did not consistently exhibit restricted diffusion.
• An rADC cutoff of 0.65 demonstrated high specificity (98%) and sensitivity (78%) for intraparenchymal bacterial abscesses when excluding hemorrhagic lesions.

Conclusions:

• Apparent restricted diffusion on DWI is a valuable indicator for identifying intraparenchymal bacterial abscesses among ring-enhancing lesions.
• However, extraparenchymal bacterial empyema and fungal abscesses may not display restricted diffusion, limiting the universal applicability of this finding.
• ADC values, particularly rADC, aid in differentiating infectious from neoplastic or inflammatory ring-enhancing lesions, with specific considerations for hemorrhagic and non-bacterial infectious etiologies.