Hematomas are a collection of blood, usually partially clotted, that tends to result from the breakage of a vein or blood vessel. Simple hematomas can be the result of minor trauma. A bruise is an alternate name for hematomas, but generally when doctors refer to hematomas, they are referring to hematomas from major traumatic injury or from surgery.

During surgery, damage to surrounding blood vessels can cause hematomas to form, which tends to slow down healing. In some cases, exceptionally large hematomas may need to be drained so that surgery sites are not impacted by the collection of partially clotted blood.

There are several severe types of hematomas that can cause problems or complicate healing. These are:

Epidural hematomas are usually related to head trauma and cause blood to pool between the skull and the exterior layer of the brain, the dura. These hematomas can create pressure on the brain resulting in loss of brain function. Blood may need to be removed surgically to reduce pressure.

Subdural hematomas occur between the brain’s dura and the middle layer of the brain, called the arachnoid layer. Frequently these are caused by trauma to the brain that has resulted in loss of consciousness, seizures or concussions. These hematomas are more difficult to remove. Larger ones may cause significant loss of brain function and may not be removable. Smaller subdural hematomas may be surgically removed with generally good recovery rates.

Subarachnoid hematomas are often caused by stroke, aneurysm, or extremely significant head injury. These are the most severe of hematomas, because of their location in the brain. They form between the arachnoid layer of the brain and the pia mater, which stretches into the cerebral cortex. These hematomas can cause death without immediate surgical intervention.

Other forms of hematomas can occur in soft tissues at surgical sites. Usually, keeping the stitches of surgical wounds slightly open can relieve pressure and allow any interior bleeding to be absorbed by bandages.