Cerebral Edema (Brain Swelling)

What cerebral edema is

The brain sits inside a rigid skull together with blood and cerebrospinal fluid (CSF), the clear fluid that cushions it. If any one of these increases, the others have little room to move. When brain tissue takes on extra water, pressure inside the skull rises. High pressure reduces blood flow to the brain and, in severe cases, pushes brain tissue out of place. This shifting is called herniation and can compress the brainstem, which controls breathing and consciousness.

Swelling can be localized, for example around a tumor or a stroke, or affect the whole brain, as after a cardiac arrest or severe traumatic brain injury.

Types of brain swelling

Doctors describe several mechanisms. More than one often happens at once.

This matters for treatment. Steroids work well for vasogenic edema around tumors but do not help, and can harm, after head injury or stroke.

Causes of cerebral edema

• Head injury: bleeding and bruising of the brain trigger swelling that often peaks 2 to 4 days after the injury.
• Ischemic stroke: a large stroke can cause swelling that peaks around days 2 to 5. Large strokes in the middle cerebral artery territory carry the highest risk.
• Bleeding in the brain: a brain hemorrhage causes swelling around the blood clot.
• Brain tumors: both primary brain tumors and cancer spread from elsewhere commonly cause vasogenic edema.
• Infections: meningitis, encephalitis and brain abscess.
• Low blood sodium: a rapid fall in sodium (hyponatremia), for example from drinking very large amounts of water during endurance events, draws water into brain cells.
• High altitude: high-altitude cerebral edema (HACE) is the most severe form of altitude sickness, usually above about 2,500 m (8,200 ft).
• Metabolic and toxic causes: acute liver failure, diabetic ketoacidosis in children, carbon monoxide poisoning and some drug overdoses.
• Lack of oxygen: after cardiac arrest, near-drowning or choking.

Symptoms of brain swelling

Symptoms depend on how fast swelling develops and where it is. They often worsen over hours.

• Headache: often worse lying flat, on waking, or with coughing and straining.
• Nausea and vomiting, sometimes without much nausea beforehand.
• Drowsiness, confusion or a change in behavior.
• Vision problems: blurred or double vision. Swelling of the optic nerve at the back of the eye (papilledema) may be seen by a doctor.
• Seizures.
• Focal signs: weakness, numbness, speech difficulty or clumsiness, depending on the area affected.
• Late signs of dangerous pressure: a pupil that is large and does not react to light, slow pulse with high blood pressure, irregular breathing and loss of consciousness.

How cerebral edema is diagnosed

1. Neurological exam: level of consciousness (often scored with the Glasgow Coma Scale), pupils, strength, speech and reflexes.
2. CT scan of the head: fast and widely available. It shows swelling, bleeding, midline shift and compressed fluid spaces.
3. MRI: more detailed, and better at showing the type of edema and small lesions.
4. Blood tests: sodium, glucose, kidney and liver function, blood gases and infection markers to find the cause.
5. Intracranial pressure monitoring: in intensive care, a thin probe placed through the skull measures pressure continuously, mainly after severe head injury.

A lumbar puncture (spinal tap) is avoided until a scan has ruled out significant swelling, because removing fluid from below can make herniation more likely.

Treatment for cerebral edema

Treatment happens in hospital, often in intensive care. It has two aims: lower the pressure now and treat the cause.

Measures to lower pressure

• Positioning: raising the head of the bed to about 30 degrees and keeping the neck straight helps blood drain from the head.
• Osmotic therapy: mannitol or concentrated (hypertonic) saline given into a vein pulls water out of brain tissue.
• Oxygen and breathing support: keeping oxygen and carbon dioxide at target levels. Brief controlled over-breathing on a ventilator may be used as a temporary bridge.
• Controlling temperature, blood sugar and sodium, and treating seizures promptly.
• Sedation to reduce the brain's demand for oxygen.
• Steroids: dexamethasone reduces vasogenic edema around tumors and abscesses, often within a day or two.

Surgery

• Draining CSF through a tube placed into a fluid space of the brain (external ventricular drain).
• Decompressive craniectomy: removing part of the skull so the swollen brain can expand. It is used for large strokes and some severe head injuries.
• Removing the cause: a tumor, blood clot or abscess.

Specific causes

High-altitude cerebral edema is treated with immediate descent, oxygen and dexamethasone. Hyponatremia is corrected carefully, because raising sodium too fast can cause a different brain injury (osmotic demyelination).

Complications and outlook

The outlook depends on the cause, how severe the swelling is and how quickly it is treated. Mild swelling around a tumor often settles completely with steroids. Swelling from a large stroke or severe head injury can cause lasting problems with movement, speech, memory or thinking, and herniation can be fatal.

People who recover may need rehabilitation with physical, occupational and speech therapy. Recovery can continue for months to a year or more.

Prevention

• Wear helmets for cycling, riding motorcycles and contact sports, and use seat belts.
• Control blood pressure, diabetes and atrial fibrillation to reduce stroke risk.
• At altitude, ascend gradually (above 3,000 m, no more than about 300 to 500 m of sleeping altitude a day) and descend if symptoms worsen.
• During long endurance events, drink to thirst rather than forcing large volumes of water.

Frequently asked questions

What causes swelling of the brain?

The most common causes are head injury, stroke, bleeding in the brain, brain tumors and infections such as meningitis. Low blood sodium, lack of oxygen after cardiac arrest, liver failure and high altitude can also cause it. In each case fluid builds up in or around brain cells, raising pressure inside the skull.

What are the first signs of cerebral edema?

Early signs are a headache that keeps getting worse, nausea or vomiting, and feeling drowsy or confused. Blurred vision, a seizure or new weakness can follow. After a head injury or stroke, any increase in drowsiness is a warning sign that needs emergency assessment.

Can you recover from brain swelling?

Yes, many people do, especially when swelling is mild or treated early. Swelling around a tumor often improves within days on steroids. Recovery after severe swelling from head injury or stroke depends on how much brain tissue was damaged, and may need months of rehabilitation.

How long does it take for brain swelling to go down?

Swelling after a head injury or stroke usually peaks within 2 to 5 days and then gradually settles over 1 to 2 weeks. Vasogenic swelling around a tumor often improves within 24 to 72 hours of starting steroids. The timing varies with the cause and size of the injury.

Is cerebral edema the same as hydrocephalus?

No. Cerebral edema is excess fluid within brain tissue. Hydrocephalus is a build-up of cerebrospinal fluid in the brain's fluid spaces (ventricles), usually from a blockage. Both raise pressure in the skull, and hydrocephalus can push fluid into the tissue, but they are treated differently.