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Subdural Empyema

by John E. Greenlee, MD

A subdural empyema is a pocket of pus that develops under the top layer of tissue (dura mater) covering the brain, rather than in the brain itself.

A subdural empyema develops between the outer (dura mater) and middle (arachnoid mater) layers of the tissues that cover the brain (meninges).

A subdural empyema may result from a sinus infection, a severe ear infection, a head injury, surgery involving the head, or a blood infection. The same kinds of bacteria that cause brain abscesses (such as Staphylococcus aureus and Bacteroides fragilis) can cause subdural empyemas. In children younger than 5 years, a subdural empyema usually results from meningitis. Because meningitis is now uncommon in children, subdural empyemas are also uncommon in children.

Like a brain abscess, a subdural empyema can cause headache, sleepiness, vomiting, seizures, a stiff neck and other signs of brain dysfunction. The symptoms can evolve over several days, and without treatment, they progress rapidly to coma and death.

Diagnosis

To diagnose subdural empyemas, doctors use magnetic resonance imaging (MRI) done after gadolinium is injected intravenously. Gadolinium (an MRI contrast agent) makes empyemas easier to see on MRI scans. If MRI is not available, computed tomography (CT) is done after a radiopaque dye (which makes empyemas easier to see on CT scans) is injected.

A spinal tap (lumbar puncture) is of little help and may be dangerous. If a large empyema or another mass (such as an abscess) is present in the brain, removing spinal fluid during a spinal tap can cause the brain to shift down and be forced through a small natural opening in the tissue that divides the brain into compartments (called brain herniation—see Herniation: The Brain Under Pressure). The resulting damage can be fatal.

Treatment

In infants, a needle can sometimes be inserted directly into the empyema through a fontanelle (a soft spot between the skull bones) to drain the pus, relieve pressure, and help doctors make the diagnosis.

Subdural empyemas must be drained surgically. If the infection occurred because of an abnormality in the sinuses or middle ear, the surgeon may need to repair the abnormality at the same time.

Antibiotics are given intravenously. Anticonvulsants to control seizures and measures to reduce pressure within the brain may be needed. These measures include use of diuretics, which reduce the amount of fluid in the body, or corticosteroids, which reduce inflammation and swelling.