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What Happens When a Brain Bleeds? Jeffrey Bazarian, MD, BrainLine

I've been hearing about bleeding in the brain after a TBI. Can you explain how this happens and why it's so dangerous? What exactly is a subdural hematoma?

Let's start with the basics. A hematoma is a tumor-like collection of blood, usually clotted, located outside a blood vessel. The subdural space is located between the dura mater (the outermost, toughest, and most fibrous of the three membranes covering the brain and spinal cord) and the arachnoid membrane (the middle of these three membranes). The epidural space is located on or outside the dura mater.

Now, to answer your question, a subdural hematoma is basically bleeding into the space between the brain cover (dura mater) and the brain itself. More specifically, there are blood vessels running through the brain and in the spaces between the outside of the brain and the inside of the skull. During a brain injury, any of these vessels can tear and bleed. Ruptured vessels running in the subdural space — typically veins — cause subdural hematomas. Ruptured vessels running through the epidural space — typically arteries — cause epidural hematomas. Both types of bleeding take up space in the skull and in so doing squeeze down on the brain. Because arteries are under pressure, epidural hematomas leak quickly and compress the brain rapidly while subdural hematomas leak much more slowly.

Because the brain is enclosed within the rigid skull, it gets compressed by this leaking blood. With enough bleeding, the brain gets compressed so much that oxygen-rich blood is prevented from flowing into the brain tissue. This lack of oxygen causes additional brain swelling. This brain swelling, added to the blood leaking from the torn vessel, forces the brain down through the small hole at the base of the skull called the foramen magnum. The parts of the brain that come in direct contact with the bone around this opening get so compressed that they stop working. Because these brain areas control breathing and heart rate, death can result.

Getting to the hospital quickly is the best way to diagnose and treat this bleeding, which usually requires surgery to remove the blood and relieve the pressure on the brain.

 

Click here to go to About Ask the Expert.

Jeffrey Bazarian, MD, Dr. Bazarian is an emergency physician with a strong research interest in traumatic brain injury. He is associate professor of Emergency Medicine, Neurology, and Neurosurgery at the Center for Neural Development and Disease, University of Rochester Medical Center.

He graduated from Brown University and from the University of Rochester School of Medicine. He completed his residency training in Internal Medicine and has a Masters of Public Health. Dr. Bazarian was one of the first emergency physicians to be awarded a five-year Career Development Award from the National Institute of Neurologic Disorders and Stroke. The focus of his research was traumatic brain injury epidemiology and outcomes.

Over the years, Dr. Bazarian's research interest shifted to finding better ways to diagnose traumatic brain injury, especially concussion. He assembled a diverse group of researchers within the University to tackle this problem, creating a truly translational research team. These efforts earned him an R01 award in 2007 from the National Institutes of Child Health and Human Development to develop a blood test for brain injury, making him one of only a handful of emergency physicians nationally to have such a grant.

Dr. Bazarian has served on several TBI-related task forces and panels for the Centers for Disease Control and Prevention, the National Institutes of Health, and the National Science Foundation. He is currently involved in an Institute of Medicine panel attempting to determine the long-term health consequence of head injuries among American troops serving in Iraq and Afghanistan.

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