An epidural abscess is 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.

An epidural abscess is caused by infection in the area between the bones of the skull or spine, and the outer meninges (the membranes covering the brain and spinal cord). 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.

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

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

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

A spinal epidural abscess may be seen in patients with bone infections of the spine (vertebral osteomyelitis), boils, bloodstream infections, and after back surgery or other invasive procedures involving the spine. People who inject drugs are also at increased risk.

Epidural abscess is a rare disorder. Nine out of ten cases are located in the spine. The infection may spread into the bones of the spine or skull (osteomyelitis). It may also spread into the spinal fluid and cause meningitis, or lead to a brain or spinal cord abscess.

Spinal epidural abscess:

• Fever and back pain
• Bowel or bladder incontinence
• Difficulty urinating (urinary retention)

Intracranial epidural abscess:

• Headache
• Fever
• Lethargy
• Nausea and vomiting
• Pain at the site of recent surgery that gets worse (especially if fever is present)

Neurological symptoms depend on the location of the abscess and may include:

• Weakness
• Paralysis
• Decreased ability to move any part of the body
• Loss of sensation in any area of the body or abnormal changes in sensation

The health care provider will perform a physical exam and a neurological exam to look for a loss of functions such as movement or sensation.

Tests such as CT (cat scan) or MRI are frequently needed to confirm the presence of an epidural abscess.

To determine what is causing the infection, a sample of the abscess is usually necessary.