A hematoma and a blood clot are related but not the same thing. A hematoma is a pool of blood that has leaked out of a damaged blood vessel and collected in surrounding tissue. A blood clot, in the way most people use the term, refers to a solid clump that forms inside a blood vessel and can block circulation. The confusion makes sense because the pooled blood in a hematoma does clot as it sits in tissue, but the two conditions form differently, pose different risks, and require different responses.
How Each One Forms
A hematoma starts when a blood vessel breaks open, usually from an injury, surgery, or a hard bump. Blood escapes into the surrounding space and, because it has nowhere to drain, fills a pocket in the tissue. As that blood sits outside the vessel, it naturally begins to clot and thicken. So technically, a hematoma contains clotted blood, but the problem is the escaped blood pressing on tissue, not a blockage inside a vessel.
An intravascular blood clot (the kind people worry about) forms inside a vein or artery while blood is still circulating. Sluggish blood flow, vessel wall damage, or a clotting disorder can trigger platelets and clotting proteins to build up and form a plug right where blood is supposed to be moving. The clot narrows or blocks the vessel, reducing blood supply to whatever lies downstream.
Why the Distinction Matters
The biggest practical difference is the type of danger each one poses. A blood clot inside a deep vein, known as deep vein thrombosis, can break loose and travel to the lungs. That complication, called a pulmonary embolism, is life-threatening. A hematoma cannot do this because the blood has already left the circulatory system. It sits in tissue rather than flowing through vessels, so there is no pathway for it to travel to the lungs or brain.
Hematomas carry their own risks, though. Because pooled blood takes up space, a hematoma can press on nerves, organs, or other structures. A hematoma inside the skull is especially dangerous: even a modest amount of blood trapped between the brain and skull can increase pressure rapidly and cause neurological symptoms. Hematomas elsewhere in the body, like in a muscle or under the skin, are far less concerning but can still cause significant pain and swelling.
What a Hematoma Looks and Feels Like
Most hematomas near the surface look like a severe bruise. The skin turns dark red, deep purple, or black and blue, and the area is painful and tender to the touch. You may feel a firm lump under the skin where blood has collected. A small bruise on your shin after bumping a table is technically a minor hematoma, but the term usually refers to larger collections of blood that form a distinct, palpable mass.
Deeper hematomas, like those in muscle or around organs, may not show visible discoloration at all. Instead, you might notice swelling, stiffness, or deep aching in the area. Hematomas inside the skull can cause headaches, confusion, weakness on one side of the body, or drowsiness that worsens over time.
Common Types by Location
- Subdural hematoma: Blood collects between the brain and its outer covering, usually after a head injury. This is one of the most serious types because rising pressure can damage brain tissue quickly.
- Epidural hematoma: Blood pools between the skull and the brain’s outer membrane, often from a skull fracture. Symptoms can develop within hours.
- Intramuscular hematoma: Blood fills a space within a muscle after a direct blow or strain. Common in contact sports and after falls.
- Subungual hematoma: Blood trapped under a fingernail or toenail after a crush injury. Painful due to pressure in a small, enclosed space, but rarely dangerous.
How Hematomas Heal
Most hematomas outside the skull resolve on their own as the body gradually reabsorbs the trapped blood. Depending on the size and location, this takes anywhere from 1 to 4 weeks. You’ll see the skin shift through a familiar bruise palette: dark red or purple at first, then greenish, then yellow-brown as the body breaks down the blood pigments. Applying ice in the first 24 to 48 hours helps limit swelling, and keeping the area elevated reduces further blood flow to the site.
Larger or deeper hematomas sometimes need medical attention. If a hematoma keeps growing, feels increasingly tense, or causes numbness or loss of function nearby, a doctor may need to drain it. For subdural hematomas in the skull, patients with significant symptoms, generally those with a hematoma thicker than about 10 mm or enough pressure to shift brain structures more than 5 mm, are typically considered for surgical drainage. When someone’s neurological condition is deteriorating, emergent drainage becomes the standard approach.
How Each Is Diagnosed
Surface hematomas are usually diagnosed by physical exam alone. For deeper collections, CT scans are the most reliable way to confirm a hematoma and measure its size. Brain imaging guidelines call for a CT or MRI within 25 minutes of hospital arrival when a brain bleed is suspected. For soft tissue hematomas in the abdomen or limbs, contrast-enhanced ultrasound offers a faster, bedside alternative that avoids radiation and is especially useful when a patient is too unstable to be moved to a scanner.
Blood clots inside veins are diagnosed differently. Ultrasound of the legs is the go-to tool for suspected deep vein thrombosis, while a CT scan of the chest is used to check for a clot that has reached the lungs. The imaging looks for blockages within vessels rather than blood collections outside them.
When a Hematoma Does Involve a Clot Problem
There is one important overlap: people who take blood-thinning medications are at higher risk for both conditions. Blood thinners make it harder for blood to clot, which means a minor injury can produce a much larger hematoma than it normally would. At the same time, stopping blood thinners abruptly to manage a hematoma can raise the risk of forming dangerous clots in blood vessels. Managing this balance is one of the trickiest aspects of treating hematomas in people on anticoagulant therapy, particularly when the hematoma is inside the skull.
People with clotting disorders, liver disease, or those recovering from surgery also face higher risk of hematomas because their blood doesn’t clot efficiently enough to seal off damaged vessels quickly. In these cases, what starts as a small leak can expand into a large blood collection.