Dual rim sign (brain abscess)
On both susceptibility weighted imaging (SWI) and T2WI it consists of two concentric rims surrounding the abscess cavity, outer one of which is hypointense, and the inner one relatively more hyperintense.
It has been postulated that granulation tissue lines the inner part of the fibrocollagenous abscess capsule and together they form the histological basis of the dual rim sign .
Cerebral abscesses tend to have low signal rims (capsule) seen best on SWI but also visible on T2/FLAIR. These are typically smooth (90%) and complete (75%).
In glioblastomas, the low signal rims (thought to represent hemorrhagic products at the outer region of the necrotic core) are irregular (85%) and incomplete (85%) .
In cerebral abscesses on SWI, immediately internal to the low-intensity rim, is a high-intensity line (granulation tissue). This is known as the dual rim sign .
On contrast enhanced sequences, the ring enhancement corresponds to the T2 hypointense capsule in abscess, whereas it occurs peripheral to the T2 hypointense rim in glioblastoma.