Brain abscess with dual rim sign


Dual rim sign is seen on T2/Flair/SWI, including 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.