A hematoma is a localized collection of clotted blood that forms outside of blood vessels, usually resulting from trauma that causes blood to leak into surrounding tissues. This pooling of blood is distinct from a simple bruise (ecchymosis) because it involves a larger volume that often forms a mass or lump. While most hematomas resolve quickly, the body’s ability to clear the collected blood depends heavily on its size, location, and biological processes.
How Hematomas Normally Resolve
The body clears collections of blood through a natural biological process. Following the initial injury, the leaked blood coagulates, forming a solid clot. Over the next few days or weeks, specialized white blood cells called phagocytes migrate to the site to break down the debris.
The main component processed is hemoglobin, the oxygen-carrying protein in red blood cells. As hemoglobin breaks down, it changes color (visible as the shifting hues of a bruise), converting into bilirubin and then hemosiderin. These breakdown products are gradually reabsorbed into the bloodstream and carried away for final disposal. For smaller hematomas, this process leads to complete resolution, typically within days to a few weeks.
The Biological Reasons for Persistence
A hematoma persists when the body’s reabsorption mechanism fails to fully clear the blood mass. One primary reason is “organization,” where the body attempts to isolate the blood by forming a fibrous layer around it. This tissue growth leads to encapsulation, creating a tough, non-absorbent membrane or pseudocapsule that walls off the clot from healthy tissue.
Encapsulation and Re-bleeding
The newly formed capsule often contains delicate, abnormal blood vessels, known as neovasculature. These fragile vessels are prone to repeated, small bleeds, which continuously add fresh blood products to the encapsulated space. This cycle of microbleeding and inflammation prevents the clot from shrinking, leading to a chronic, often expanding, hematoma.
Calcification
In some instances, the blood products within a long-standing hematoma break down into mineral deposits, a process called calcification. This calcified tissue hardens the hematoma, turning it into an inert, long-term mass that may remain indefinitely.
Clinical Types of Long-Term Hematomas
The persistence of a hematoma depends on its location and the specific biological response it triggers.
Chronic Subdural Hematoma (CSDH)
CSDH forms between the brain’s surface and its outer protective layer. It usually begins weeks after a head injury and can persist for months or years, especially in older adults. The persistence is due to a fragile membrane that forms around the collection, which continues to weep fluid and blood, maintaining or expanding the collection.
Chronic Expanding Hematoma (CEH)
CEH occurs in soft tissues, such as the thigh or calf muscles. It is characterized by a slowly enlarging mass that can last for years, sometimes up to a decade, and may mimic a soft-tissue tumor. This expansion is sustained by repeated hemorrhage from the neovasculature within the fibrous capsule.
Calcified Hematoma
A hematoma can persist indefinitely if it undergoes calcification. A calcified chronic subdural hematoma, sometimes called an “armored brain,” is a rare outcome where the periphery of the clot hardens into a mineralized shell. While these lesions can be asymptomatic, they may cause neurological symptoms, such as seizures, years after the initial event.
Monitoring and Treating Persistent Hematomas
The management of a persistent hematoma is determined by its clinical presentation and location.
Watchful Waiting
Small, stable, or calcified hematomas that cause no symptoms are often managed with “watchful waiting.” This involves regular imaging, such as CT or MRI scans, to monitor for changes in size or mass effect. This non-invasive approach is preferred when the risks of intervention outweigh the benefits of removal.
Surgical Intervention
Intervention becomes necessary when a persistent hematoma causes symptoms, such as neurological deficits, severe headaches, or local pain and swelling. For symptomatic CSDH, surgical drainage is the standard treatment, often performed through a burr-hole craniostomy (a small hole in the skull). Placing a drain after the procedure reduces the rate of recurrence.
For Chronic Expanding Hematomas in soft tissue, the treatment of choice is complete surgical excision of the mass, including the surrounding fibrous capsule. Incomplete removal of the capsule can leave behind fragile vessels responsible for re-bleeding, increasing the risk of the hematoma returning. Emerging medical therapies, such as tranexamic acid, are also being explored as non-surgical or adjunct treatments for CSDH.