May Cause

Avascular intracranial mass

Avascular zone near the brain surface

Extra-axial lesion

Hypodense supratentorial lesion

Linear meningeal enhancement

Ring-enhancing intracranial lesion

May Be Caused by

 Common

Ethmoid sinusitis

Frontal sinusitis

Penetrating trauma

 Uncommon

Craniectomy

Mastoiditis

Meningitis

Middle ear infection

Osteomyelitis

Surgery