Coma (Medical)

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Bleeding (hemorrhage)

Bleeding within the brain (intracerebral hemorrhage) may be small, but also may cause associated swelling that may cause damage to the brain and result in coma. Blood is in the brain tissue is irritating and leads to inflammation with swelling. Many patients with small amounts of bleeding have the potential to recover very well.

Epidural, subdural, and subarachnoid hemorrhages

The lining of the brain has multiple layers, and these layers can act as potential spaces where bleeding can occur.

Epidural hematomas are located between the skull and the tissue that covers the brain (dura mater). These hematomas that are localized collections of loose blood are often associated with skull fractures and tears in arteries located near the fracture site.

Subdural hematomas are located beneath the dura mater and occur when the bridging veins from the skull to the brain are torn.

As the blood continues to accumulate, pressure builds within the skull and the brain is shifted away from the site of bleeding, compressing the brain against the skull. With both hemispheres of the brain compromised, loss of consciousness and coma may result. The more swelling, the higher the intracranial pressure, the deeper the coma.

Each brain is different and in older patients whose brains have atrophied and become smaller with age, there is more room in the skull to accommodate a small amount of swelling or bleeding. Each bleeding situation is different and each patient is assessed individually. However, being unconscious because of brain bleeding and/or swelling is associated with a poorer outcome than unconsciousness from drug toxicity, or seizures, etc.

Subarachnoid hemorrhage (bleeding beneath the arachnoid layer) occurs in the layer of the brain lining where cerebrospinal fluid (CSF) is located. CSF is produced in the ventricles that are located deep in the brain and is the nutrient fluid that bathes the brain and spinal cord. Bleeding here may cause few symptoms or it may cause significant problems like coma or stroke. Bleeding is often associated with a significant headache and neck stiffness.

Bleeding can occur within the skull or brain without trauma. Some medical causes of this form of bleeding include:

  • Hypertension (high blood pressure): when blood pressure is too high, and not controlled, blood vessels in the brain may not be able to tolerate the high pressure and may leak blood into the brain, subarachnoid space, or both.
  • Cerebral aneurysm, or an area in a blood vessel that is congenitally weak and ruptures. Some people are born with blood vessels that have a weak wall that can gradually balloon, like a weak spot in an inner tube. At some time in their life, or perhaps never, the weak spot gives way and blood is spilled into the subarachnoid space.
  • Arteriovenous malformations (AVMs) are abnormal blood vessels where arteries connect directly to veins and cause potential weak spots that can leak blood. Normally, arteries branch into smaller and smaller vessels until they form the smallest set of vessels called capillaries. Capillaries form meshes where chemicals, nutrients, oxygen and carbon dioxide are exchanged from the blood stream to individual cells. The capillaries then merge to form larger blood vessels, the veins. In AVMs, this relationship of artery to capillary to vein is abnormal and is at risk for bleeding.
  • Tumors, either benign or malignant, can be very vascular (composed of many arteries, veins, and capillaries) and have significant bleeding potential.

Picture of the brain and potentially brain injury areas

Picture of the brain and potentially brain injury areas


Just as blood takes up space within the skull and can cause coma, so may brain tumors. Brain tumors may be associated with localized swelling edema, inflammation and bleeding. Seizures, stroke-like symptoms, decreased mental status, and change in behavior may be the initial symptom. Most often, the symptoms have a gradual onset, but coma can progress quickly if bleeding or swelling occur.

Medically Reviewed by a Doctor on 3/11/2016
Next: Swelling

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