Dual rim sign
On both susceptibility weighted imaging (SWI) and T2WI it consists two concentric rims surrounding the abscess cavity, one of which is hypointense (outer rim), and the other relatively more hyperintense (inner rim).
It has been postulated that granulation tissue lines the inner part of fibrocollagenous abscess capsule and together they form the histological basis of dual rim sign 1.
Cerebral abscesses tend to have low signal rims (capsule) seen best on SWI but also visible on T2/FLAIR. These are smooth (90%) and complete (75%).
In glioblastomas, the low signal rims (thought to represent haemorrhagic products at the outer region of necrotic core) are irregular (85%) and incomplete (85%) 1.
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 1.
On contrast enhancement, the ring enhancement corresponds to the T2 hypointense capsule in abscess, whereas it occurs peripheral to the T2 hypointense rim in glioblastoma.