CT appearance

Early cerebritis

May be invisible.

Poorly marginated cortical or subcortical hypodensity with mass effect with little or absence of enhancement.

An ill-defined area of low density on plain CT corresponds to developing necrotic center in the cerebritis stage.

Late cerebritis

Irregular ring-enhancing lesion with a hypodense center, better defined than early cerebritis.

Early capsule

Well-defined rim-enhancing mass, an outer hypodense and inner hyperdense rim (double rim sign) is seen in most cases.

A slightly hyperdense, faint ring is seen surrounding a necrotic hypodense center [44] .

Late capsule

Rim-enhancing lesion with thickened capsule and diminished hypodense central cavity.

The capsule is seen as a ring in plain CT.