What causes a hematoma?

Trauma is the most common cause of a hematoma. When people think of trauma, they generally think of car accidents, falls, head injuries, broken bones, and gunshot wounds, etc.. Trauma to tissue may also be caused by an aggressive sneeze or an unexpected twist of a limb. When a blood vessel is damaged blood leaks into the surrounding tissue; this blood tends to coagulate or clot. The greater the amount of bleeding that occurs, the larger the amount of clot formation.

Blood vessels that are fragile may contribute to hematoma formation. For example, an aneurysm or weakening in a blood vessel wall may spontaneously leak.

There are many people who take blood thinners (anti-coagulation) medications. Examples include warfarin (Coumadin), aspirin, clopidogrel (Plavix) and prasugrel (Effient). These medications increase the potential for spontaneous bleeding and for hematomas to expand because the body cannot efficiently repair blood vessels and blood continues to leak through the damaged areas.

Occasionally, diseases may occur that decrease the number of platelets in the blood stream (thrombocytopenia) or their ability to function. The platelets are the cells that help initiate blood clot and fibrin formation.

All of the above situations may exist independently to cause a hematoma or they may occur together.

What are the types of hematomas?

Hematomas are often described based upon their location.

The most dangerous hematomas are those that occur inside the skull. Because the skull is an enclosed box, anything that takes up space increases pressure within that box and potentially impairs the ability of the brain to function.

Epidural hematomas occur because of trauma, often to the temple, where the middle meningeal artery is located. Bleeding accumulates in the epidural space, outside the 'dura' which is the lining of the brain. Because of the way the dura is attached to the skull, small hematomas can cause significant pressure and brain injury.

Subdural hematomas also occur because of trauma but the injury is usually to the veins in the brain. This causes a slower leak of blood, which enters the 'subdural' space below the dura. The space below the dura has much more room for blood to accumulate before brain function suffers. As people age, they lose some brain tissue and the subdural space is relatively larger. Bleeding into the subdural space may be very slow, gradually stop, and not cause acute symptoms. These 'chronic' subdural hematomas are often found incidentally on computerized tomography (CT) scans as part of a patient evaluation for confusion or because another traumatic incident occurred.

Intracerebral hematomas occur within the brain tissue itself. Intracerebral (intra= within + cerebrum=brain) hematomas may be due to bleeding from uncontrolled high blood pressure, an aneurysm leak or rupture, trauma, tumor or stroke.

Scalp hematomas occur on the outside of the skull and often can be felt as a bump on the head. Because the injury is to the skin and muscle layers outside of the skull, the hematoma itself cannot press on the brain. However, a scalp hematoma signals that there has been a head injury and it is important to assure that internal bleeding has not occurred within the skull. There are a variety of guidelines available to the health care practitioner to assist in accessing whether a patient will require further testing to explore any bleeding in the brain.

Aural or ear hematomas may occur if an injury causes bleeding to the outside helix or cartilage structure of the ear. Often called boxer's, wrestler's ear, or cauliflower ear, blood gets trapped between the thin layer of skin and the cartilage itself. Since the ear cartilage gets its blood supply directly from the overlying skin, a hematoma can decrease blood flow causing parts of the cartilage to shrivel and die. This scenario results in a bumpy, deformed outer ear.

Septal hematomas occur with nasal trauma. A septal hematoma may form associated with a broken nose. If not recognized and treated, the cartilage can break down and cause a perforation of the septum.

Orthopedic injuries are often associated with hematoma formation. Bones are very vascular structures since the marrow is where blood cells are made. Fractures are always associated with hematomas at the fracture site. Fractures of long bones such as the thigh (femur) and upper arm (humerus) can be associated with a significant amount of bleeding, sometimes up to one unit of blood or 10% of the body's blood supply.

Pelvic bone fractures can also bleed significantly since it takes a large amount of force to break these bones and it is very difficult to compress the area to decrease the amount of bleeding. Pelvic hematomas are hidden and the amount of blood loss may be difficult to assess.

Intramuscular hematomas can be very painful due to the amount of swelling and inflammation. Some muscles are surrounded by tough bands of tissues. If enough bleeding occurs, the pressure within these compartments can increase to the point that a 'compartment syndrome' can occur. In this situation, the blood supply of the muscle is compromised and the muscle and other structures such as nerves can be permanently damaged. This is most commonly seen in the lower leg and forearm.

Subungual hematomas are the result of rush injuries to the fingers or toes. Bleeding occurs under the fingernail or toenail and since it is trapped, pressure builds causing pain. Trephination, or drilling a hole through the nail to remove the blood clot, relieves the pressure and resolves the injury. A new nail grows over time.



Bruises and contusions of the skin (ecchymosis) are terms that describe subcutaneous hematomas. These occur due to trauma or injuries to the superficial blood vessels under the skin. Individuals who take anti-coagulant medication are more prone to subcutaneous hematomas.

Intra-abdominal hematomas and hemorrhage may be due to a variety of injuries or illnesses. Regardless of how the blood gets into the abdomen, the clinical finding is peritonitis (irritation of the lining of the abdomen). Hematomas may occur in solid organs such as the liver, spleen, or kidney. They may occur within the walls of the bowel, including the small intestine (duodenum, jejunum, ileum) or the large intestine (colon). Hematomas may also form within the lining of the abdomen called the peritoneum or behind the peritoneum in the retroperitoneal space (retro=behind).

Passing clots or hematomas is a common complaint when women menstruate. Blood can accumulate in the vagina as part of the normal menses and instead of flowing out immediately, it may form small blood clots. Passing blood clots after delivering a baby is also relatively common. However, vaginal bleeding and passing blood clots or hematomas while pregnant is not normal and should be a sign to seek medical attention.

Hematomas may occur anywhere in the body. Regardless of how a hematoma is described or where it is located, it remains a collection of clotted blood outside of a blood vessel.