An epidural abscess is q collection of pus (infected material) between the outer covering of the brain and spinal cord and the bones of the skull or spine. The abscess causes swelling in the area.

Epidural abscess is a rare disorder caused by infection in the area between the bones of the skull or spine, and the membranes covering the brain and spinal cord (meninges). This infection is called an intracranial epidural abscess if it is inside the skull area, or a spinal epidural abscess if it is found in the spine area. Nine out of 10 cases are located in the spine.

The infection is usually caused by bacteria (Staphylococcus aureus is common), but may be caused by fungus. It can be due to other infections in the body, or germs that spread through the blood. However, in up to one-third of patients, no source of infection is found.

In the case of an intracranial epidural abscess (within the skull), risk factors include:

• Chronic ear infections
• Chronic sinusitis
• Head injury
• Mastoiditis
• Recent neurosurgery

A spinal epidural abscess may be seen in patients with:

• A history of back surgery or other invasive procedures involving the spine
• Bloodstream infections
• Boils
• Bone infections of the spine (vertebral osteomyelitis)

People who inject drugs are also at increased risk.