Subdural Empyema

What happens in subdural empyema

The brain is wrapped in three layers. The dura is the tough outer layer attached to the skull. Below it lies the arachnoid. The space between them, the subdural space, has no internal barriers, so pus that gets in spreads quickly over the surface of the brain and into the groove between the two hemispheres.

Infection usually reaches this space through tiny veins that pass through the skull from the sinuses or middle ear. These can become clotted and infected, carrying bacteria inward. Less often, infection spreads directly through bone affected by osteomyelitis.

Pus presses on the brain, causes swelling, and can clot the veins that drain the brain's surface. This is what leads to seizures, weakness and reduced consciousness.

Causes

• Sinusitis: the most common cause, especially frontal and ethmoid sinusitis in adolescents and young men. The frontal sinuses are still growing in the teenage years and have a rich network of veins.
• Ear infections: chronic otitis media and mastoiditis.
• Head trauma: especially open skull fractures.
• After neurosurgery or sinus surgery.
• Meningitis in infants: subdural empyema can complicate bacterial meningitis in babies.
• Infection of an existing subdural hematoma, rarely.

Usual organisms include streptococci (especially the Streptococcus anginosus group), anaerobic bacteria and Staphylococcus aureus, often in combination. After surgery or trauma, staphylococci and gram-negative bacteria are more common.

Symptoms

Symptoms often progress over days and can worsen rapidly:

• Severe headache, often on one side, becoming generalized
• Fever
• Vomiting
• Stiff neck
• Confusion, drowsiness or reduced consciousness
• Seizures, often focal, in a large share of patients
• Weakness on one side (hemiparesis), facial droop, or difficulty speaking
• Swelling of the forehead or around the eye from the underlying sinus infection

Antibiotics given for the sinus infection can partly mask symptoms, delaying diagnosis.

How it is diagnosed

• MRI of the brain with contrast: the best test. Diffusion-weighted imaging clearly shows pus and distinguishes empyema from sterile fluid. It also shows brain swelling and vein clots.
• CT scan with contrast: often done first in the ER. It can miss small or early collections, so a normal CT does not rule out empyema if suspicion is high.
• CT of the sinuses and temporal bones to identify the source.
• Blood tests and blood cultures.
• Lumbar puncture is usually avoided, because pressure in the skull can be raised and the test is risky and rarely helpful.
• Culture of pus collected at surgery identifies the bacteria and guides antibiotics.

Treatment

Subdural empyema is treated as a neurosurgical emergency.

Surgery

• Drainage of the pus as soon as possible. A craniotomy (removing a section of skull bone temporarily) generally allows more complete drainage than burr holes and has lower rates of re-operation.
• Burr holes may be used in very ill patients or for small, localized collections.
• Repeat surgery is sometimes needed if pus re-collects.

Treating the source

ENT surgeons often drain the infected sinuses or mastoid at the same time or shortly after, to remove the source of infection.

Antibiotics

• IV antibiotics start immediately, before culture results, typically a combination covering streptococci, anaerobes and staphylococci, such as a third-generation cephalosporin plus metronidazole, with vancomycin when MRSA is possible.
• Treatment usually continues for 3 to 6 weeks, guided by cultures and follow-up imaging.

Supportive care

• Antiseizure medicines.
• Management of raised pressure in the skull.
• Treatment of any vein clots, decided case by case.
• Intensive care monitoring when needed.

Complications

• Brain abscess and brain swelling
• Cortical vein and venous sinus thrombosis
• Long-term epilepsy
• Weakness, speech or cognitive problems
• Hydrocephalus (fluid buildup)

Outlook

Before modern imaging and surgery, subdural empyema was often fatal. Today most patients survive, with death rates around 10% or lower in many series. The outcome depends heavily on consciousness level at diagnosis: people who are alert when treated usually recover well, while those in coma have much worse outcomes. Some survivors have ongoing seizures or neurological deficits and need rehabilitation.

Prevention

• Seek medical review for sinus infections that are severe, worsening after initial improvement, or causing forehead swelling or eye symptoms.
• Treat ear infections fully, and see an ENT specialist for chronic ear discharge.
• Get prompt care for fever or headache after head injury or brain surgery.

Frequently asked questions

What causes subdural empyema?

Most cases spread from a sinus infection, especially frontal sinusitis in teenage boys and young men. Other causes include ear and mastoid infections, skull fractures, brain or sinus surgery, and meningitis in infants. Bacteria travel through small veins from the infection into the space around the brain.

What are the symptoms of subdural empyema?

The main symptoms are severe headache, fever and vomiting, often during a sinus infection. Within days these can progress to a stiff neck, confusion, drowsiness, seizures, weakness on one side and difficulty speaking. These are emergency warning signs.

How is subdural empyema treated?

It is treated with emergency surgery to drain the pus, usually by craniotomy, combined with 3 to 6 weeks of IV antibiotics. The infected sinus or ear is often drained too. Antiseizure medicines and intensive monitoring are also commonly needed.

Is subdural empyema the same as a brain abscess?

No. A subdural empyema is pus on the surface of the brain, beneath the dura. A brain abscess is a pus collection inside the brain tissue itself. Both can come from sinus or ear infections, can occur together, and both need urgent treatment.

Can you fully recover from subdural empyema?

Many people do, especially those diagnosed and operated on early while still alert. Some are left with seizures, weakness, speech or memory problems that improve with rehabilitation over months. Delayed treatment and coma at diagnosis are linked to worse outcomes.