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 classified as intracranial epidural abscess if it is located in the skull area, or as a spinal epidural abscess if it is found in the spine area.

The infection is usually caused by bacteria (staphylococcus is common), but some may be caused by fungus. Infected material (pus) frequently includes destroyed tissue cells, white blood cells, and live or dead microorganisms which may wall off into an abscess. There is often inflammation of the tissues around the abscess in response to the infection.

Most symptoms are due to enlargement of the abscess and surrounding inflammation which can lead to compression of tissues in the brain and spinal cord.

The infection can result from the spread of nearby infections or it may be caused by microorganisms that spread from distant locations via the bloodstream. However, in up to one-third of patients, there is no identified source of infection.

In the case of intracranial epidural abscess (within the skull), risk factors include: chronic ear infections, mastoiditis, chronic sinusitis, in addition to head injury and recent neurosurgery.

Spinal epidural abscess may be seen in patients with bone infections of the vertebral column (vertebral osteomyelitis), skin infections such as 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 (spinal epidural abscess). 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 abscess, or a spinal cord abscess.

Spinal epidural abscess:

• Fever and back pain (the back pain may be confined to the spine or may radiate to the extremities, the arms or legs)
• Bowel or bladder incontinence
• Difficulty urinating (urinary retention)

Intracranial epidural abscess:

• Headache, fever, lethargy, nausea & vomiting (if associated with sinusitis or chronic ear infections, there may be localized pain in those areas)
• Progressive pain at the site of recent surgery (neurosurgery) especially if accompanied by fever
• Neurological symptoms depending on the location of the abscess which can be varied and include:
  • Weakness or decreased movement of any area of the body
  • A decrease in sensation of any area of the body

Persistent back pain with fever or headache with fever should lead to medical evaluation including a neurological exam to look for focal neurological deficits (loss of neurologic functions such as movement or sensation).

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

To establish a diagnosis of the underlying infection causing the abscess, sampling of the abscess is usually needed.

• Recurrence of infection (common even if the disorder is treated)
• Spread of infection
• Brain abscess
• Spinal cord abscess
• Meningitis
• Permanent neurological damage if diagnosis and treatment are delayed

Call your health care provider if fever, persistent headache, back pain, or other symptoms of epidural abscess develop, particularly if there is a known risk for the disorder.

An epidural abscess is a medical emergency. Early diagnosis and treatment greatly improve the chance of a good outcome. Once neurologic symptoms occur (such as weakness, paralysis, or sensation changes) the chances of recovering lost function are diminished.