Dual rim sign of brain abscess
Young male with a severe headache and seizures since 2 weeks. No past medical history.
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MR demonstrates a well defined T1WI hypointense and T2WI hyperintense lesion in the left frontal subcortical white matter with extension to centrum semiovale, measured 40 x 37 x 34 mm. The lesion has a thick wall with dual rim sign best seen on T2WI, intensely enhancing on post contrast T1WI (ring enhancement). The lesion shows true restricted diffusion on DW images. There is marked perilesional edema.
The MRI findings are most suggestive of a brain abscess. A craniotomy was performed and the lesion was resected.
Granulation tissue with fibroblasts, macrophages with surrounding inflammatory necrotic tissue. No malignant cells were observed. Diagnosis: Pyogenic abscess
The imaging appearance of some cystic or necrotic glial tumors is similar to that of brain abscesses. DWI is very useful for the differential diagnosis between brain abscesses and cystic or necrotic brain tumors with the former typically demonstrating central diffusion restriction. The dual rim sign is the most specific imaging feature that is typically seen in pyogenic brain abscesses.