Cerebral edema (swelling of the brain) may arise for various reasons – as an inflammatory response to injury and infection, damage to the blood vessels which allows fluid and blood to leak into the brain tissue, impaired drainage of tissue fluid from the brain or an intracranial masses. Acute causes often hold the greatest danger as the various compensatory mechanisms to minimize the increase in intracranial pressure cannot respond in time. This compresses the brain tissue further compounding the damage and can even lead to death.
Causes of Cerebral Edema
There are a number of mechanisms that may cause swelling of the brain tissue.
Traumatic Brain Injury (TBI)
TBI is seen with trauma to the head and neck like in falls, motor vehicle accidents and assault where the impact causes the brain to collide with the surrounding skull bone. Inflammation sets in and is further exacerbated by the nature of the injury, especially if there is a fracture of the skull or sharp force trauma. Swelling is mediated by the inflammatory cells and chemicals and drainage of tissue fluid may also be compromised.
- Lacerations and contusions (brain)
- Shaken baby syndrome
Bleeding in the brain tissue may lead to a hematoma which compresses the brain tissue in a similar manner to swelling associated with tissue fluid accumulation. Rupture of a blood vessel may occur for various reasons, including trauma, a ruptured anuerysm or tearing of the blood vessel with high blood pressure. Apart from the swelling, the oxygen supply to the brain may also be affected (hypoxia) which leads to ischemia and inflammation.
- Hemorrhagic stroke
- Intracerebral hematoma
- Subarachnoid hemorrhage
Hypoxia and Ischemia
This may be associated with trauma and a hemorrhage. It is seen in cases like a stroke where a blood clot or reduced blood volume affects the oxygen supply to the brain tissue (hypoxia). Swelling occurs as a result of inflammation associated with hypoxia (ischemia).
- Cerebral ischemia
- Ischemic stroke – thrombotic, embolic
- Altitude sickness
Infections, Poisoning and Toxins
Various infections may arise in the brain and surrounding tissue with inflammation resulting in edema. This may be due to bacteria, viruses, parasites or rarely even fungi seen in immunocompromised patients like with HIV/AIDS and diabetics (mucormycosis). Apart from edema of the brain tissue (encephalitis) or meninges (meningitis), a collection of pus associated with an infection (abscess) and filling of cavities with pus (empyema) may also cause swelling and compression of the brain tissue.
- Viral and bacterial meningitis, encephalitis
Certain toxins, metals and even drugs can cause cerebral edema. This may be dosage-dependent. Cerebral edema may be vasogenic, cytotoxic, osmotic or hydrostatic in nature. Read more on types of cerebral edema.
- Lead poisoning
- Methanol poisoning
- Carbon monoxide poisoning
- Nitrous oxide
Tumors and Masses
Benign and malignant growths can cause cerebral edema as a result of compressing the tissue, blocking the blood flow, lymphatic drainage, CSF obstruction or leading to inflammation associated with tissue damage. Other intracranial masses, not related to overgrowth of tissue, may also be responsible – cysts (hydatid, arachnoid, colloid), schistosomiasis, tuberculoma and sarcoidosis (granulomas). Abscesses and hematomas are also intracranial masses discussed under infections and brain hemorrhage respectively. While these tumors and space-occupying masses compress the brain tissue thereby resulting in a host of symptoms, it is the ensuing inflammation and swelling that is true cerebral edema.