Presentation
Sudden weakness on the right side of the body, fever.
Patient Data
The lesions demonstrate central restricted diffusion on DWI, ring enhancement on T1 C+, dual rim sign on FLAIR/T2 involving left parietal-occipital lobe and left temporal lobe in keeping with brain abscess.
There are peritumoral vasogenic edema and mass effect to compress adjacent brain parenchyma and left lateral ventricle.
Dual rim sign: the green arrow indicates the hyperintense inner rim, the red arrow indicates the hypointense outer rim overlapping the contrast-enhancing rim.
Case Discussion
Dual rim sign is seen on T2/FLAIR/SWI, comprising two concentric rims surrounding the abscess cavity, the outer one is hypointense, and the inner one is hyperintense.
Dual rim sign helps distinguish an abscess from a glioblastoma. The hypointense rim typically demonstrates a thin, complete, regular overlapping the contrast-enhancing rim in cerebral abscesses. In glioblastoma, the T2 hypointense line is inner to the contrast-enhancing rim and is irregular, incomplete.
On histopathology, the outer rim corresponds to the capsule abscess in which the production of paramagnetic free radicals by macrophages resulting in magnetic susceptibility 1. The granulation tissues between the necrotic center and capsule are responsible for the hyperintense inner rim 1,2.
In contrast, the random deposition of hemorrhagic products at the edge of the necrotic cavity glioblastoma causes the irregular, incomplete, hypointense margin on SWI 1,2.