A hematoma is a collection of blood outside of a blood vessel. Hematomas form when blood vessels are damaged and leak blood into surrounding tissues. The blood pools and coagulates, forming a bloody mass. So in short, yes, a hematoma is filled with blood.
What is a Hematoma?
A hematoma, also called a blood tumor or blood cyst, is a pooling of blood in tissues, organs, or spaces. It occurs when a blood vessel wall ruptures, allowing blood to seep out into surrounding areas. As the blood leaks out, it begins to clot and coagulate. The pooled blood appears as a bruise, bump, or swollen area.
Hematomas can occur in any vascularized tissue in the body. Common sites include under the skin, in muscles, and inside organs. Hematomas range in size from tiny petechial spots to large masses. They may be superficial or deep within the body.
Causes of Hematomas
Hematomas are caused by disrupted blood vessels that allow blood to escape. Possible causes include:
- Trauma – Blunt force, penetrating injuries, falls, collisions
- Surgery – Surgical procedures that cut blood vessels
- Medical procedures – Blood draws, IV placements, injections
- Spontaneous rupture – Weak blood vessels spontaneously burst
- Blood disorders – Clotting disorders, leukemia, hemophilia
- Medications – Blood thinners, chemotherapy, corticosteroids
When a blood vessel wall is damaged, typical healing events are activated. However, if the rupture is large enough, blood escapes the vessel before clotting can occur. The greater the damage, the more blood pools in surrounding tissues.
Types of Hematomas
Hematomas can occur nearly anywhere in the body. The composition and effects depend on their location. Common types include:
- Subcutaneous – Under the skin, causes bruising
- Intramuscular – Within muscles, causes swelling
- Retroperitoneal – Behind the abdominal cavity, compressing organs
- Subungual – Under fingernails or toenails, causing nail bed discoloration
- Subdural – Between the dura mater and brain, increased intracranial pressure
- Epidural – Outside the dura mater in the spine, compressing the spinal cord
Hematoma Composition
The contents of a hematoma depend on its age and include:
- Whole blood – Freshly leaked blood that has yet to clot
- Clotted blood – Gelatinous mass of coagulated red blood cells and fibrin
- Serosanguineous fluid – Pinkish fluid from lysed red blood cells and inflammatory exudate
- Cholesterol crystals – Crystals that develop over time in chronic hematomas
Right after a blood vessel ruptures, active bleeding fills the space with whole, unclotted blood. Platelets soon activate the clotting cascade, crosslinking fibrin to form an insoluble clot. The clot stops further bleeding and seals in the blood.
Over hours to days, the clot progressively liquefies from proteolytic enzymes in the blood. Red blood cells lyse and release hemoglobin, imparting a reddish-brown color. This serosanguineous fluid contains breakdown products from the clotted blood.
Over weeks to months, chronic hematomas develop granulation tissue and fibrous capsules. Cholesterol crystals and calcification may be deposited over time.
Hematoma Stages
Doctors often characterize hematomas by their stage or age:
- Acute – Within first hours to days, whole blood and clotted blood
- Subacute – 1-7 days old, clot retraction occurs
- Chronic – Weeks to months old, liquefied with cholesterol crystals
- Resolving – Weeks to months, fibrotic tissue replaces hematoma
The composition and appearance of a hematoma change over time. An acute hematoma contains unclotted bright red blood that gradually clots and retracts. Over weeks, it liquefies and develops cholesterol deposits and a fibrous wall. Knowing the stage and contents helps guide appropriate treatment.
Hematoma Color Changes
As a hematoma evolves, it progresses through a spectrum of color changes. These correspond to what is happening inside the lesion:
- Red – Unclotted blood or ruptured small vessels within the hematoma
- Blue – Deoxygenated blood from intact deeper vessels
- Purple – Mixture of oxygenated and deoxygenated blood
- Green – Biliverdin from hemoglobin breakdown
- Yellow – Bilirubin from further hemoglobin breakdown
- Brown – Proteinaceous fluid with hemoglobin metabolites
Bright red indicates recent bleeding or re-bleeding. Blue tones suggest intact deeper blood vessels. Eventually hemoglobin breaks down into colorful byproducts that turn the region yellow or green.
Changes Over Time
Here is a typical timeline of a hematoma’s color progression:
- Day 1 – Purple/red, unclotted blood
- Day 2 – Blue/purple, clotted blood
- Day 3+ – Green/brown, hemoglobin breakdown
- Week 2+ – Yellow, further breakdown
- Month 1+ – Brown, proteinaceous fluid
These color changes reflect the hematoma’s evolving contents. Following the color patterns helps track its age and stage.
Do Hematomas Contain Blood Cells?
Yes, hematomas contain the formed elements of whole blood, mainly red blood cells. Other blood cells like white blood cells and platelets are also present.
Red blood cells are by far the most abundant cell type in blood. When a vessel ruptures, the red cells leak out and make up the majority of the hematoma’s initial volume. Many of the red cells eventually rupture and release hemoglobin.
White blood cells enter the hematoma as part of the inflammatory response. They help clear debris and fight infection. Platelets initiate the clotting cascade to stop the bleeding.
In essence, all the cellular components of blood are present in a freshly formed hematoma. The cells provide clues about the timing of the bleeding event and the body’s healing response.
Cellular Contents
Specifically, these formed elements are found inside hematomas:
- Red blood cells
- White blood cells
- Neutrophils
- Lymphocytes
- Monocytes
- Eosinophils
- Basophils
- Platelets
- Fibrin strands
Examining a hematoma’s architecture reveals blood vessels, the fibrin meshwork, inflammatory cells, and remnants of ruptured red blood cells. Doctors may analyze the cellular contents to determine the timing of injury.
Do Old Hematomas Still Contain Blood?
Old hematomas generally do not contain liquid blood, but do contain the breakdown products of blood. As the hematoma ages, the typical timeline is:
- 1-3 days – Clotted blood, serosanguineous fluid
- 1-2 weeks – Liquefied with cholesterol crystals
- 2+ weeks – Increasingly fibrotic, calcification
In the first days after forming, the hematoma contains clotted blood and fluid from red cell lysis. Later, cholesterol crystals accumulate as the blood contents liquefy.
Over several weeks, the liquefied blood is gradually replaced by fibrotic scar tissue. In chronic hematomas, mostly fibrotic tissue remains with scattered cholesterol deposits and calcium.
So while old hematomas do not contain liquid blood, they do contain the residual breakdown products of ruptured blood vessels, namely iron, cholesterol, and calcium.
Re-Bleeding Risk
Re-bleeding into a chronic hematoma can occur if new vessels grow into the lesion. This again fills the cavity with fresh liquid blood.
Sudden expansion of an old hematoma likely represents renewed bleeding. However, most chronic hematomas do not contain significant liquid blood.
Can a Hematoma Resorb Over Time?
Yes, small stable hematomas can spontaneously resorb over time. The body is able to gradually clear the leaked blood, allowing complete resolution.
Resorption depends on the hematoma’s size and location. Small, superficial hematomas have the greatest chance for complete resolution without intervention.
The inflammatory healing process removes the damaged tissue and residual blood breakdown products. Macrophages and fibroblasts remodel the area until no visible signs remain.
Large or expanding hematomas are less likely to fully resorb. Portions may liquefy and be reabsorbed, but fibrotic tissue usually persists.
Resorption Factors
Factors that promote hematoma resorption include:
- Small size
- Superficial location
- No active bleeding
- Intact coagulation
- Good lymphatic drainage
- Healthy tissue perfusion
With optimal conditions, the body can gradually clear small hematomas over days to weeks without intervention. Larger lesions may resorb partially.
Can a Hematoma Become Infected?
Yes, hematomas can become infected, especially if they are open to the outside environment. Signs of an infected hematoma include:
- Expanding size
- Fluid leakage
- Foul odor
- Redness
- Warmth
- Fever
Bacteria have an easier time entering hematomas that rupture through the skin. Open skull fractures or peri-implant hematomas are at greater risk.
Immunocompromised patients and those with diabetes are also more prone to complications like infected hematomas. IV drug users can introduce skin flora into blood-filled spaces.
Treating Infected Hematomas
Small infected hematomas may be treated with antibiotics and local wound care. Larger lesions often need surgical drainage or debridement.
Cleaning out the infected material reduces the bioburden and allows antibiotics to work better. Irrigation with sterile saline may be used.
Rarely, severe infections cause such extensive tissue damage that reconstructive surgery is required after source control.
Can a Hematoma Cause Long-Term Damage?
Yes, hematomas, especially large ones, can cause permanent damage to tissues. Complications include:
- Skin necrosis
- Nerve compression
- Muscle/tendon fibrosis
- Organ dysfunction
- Calcification
- Cosmetic defects
Pressure from expanding blood can compress and ischemia tissues. The pressure disrupts capillary beds, reducing oxygen supply.
Ischemic necrosis leads to replacement with non-functional fibrotic scar tissue. Nerves are very sensitive to compression injury.
Preventing Damage
Prompt hematoma drainage helps reduce lasting damage. Elevating the affected area may improve venous return and tissue perfusion.
Early range of motion exercises prevent contractures after muscle/tendon hematomas. Physical therapy may improve outcomes.
However, large hematomas often cause some degree of permanent injury even with appropriate treatment.
Conclusion
In summary, hematomas form when blood vessels rupture and leak blood into tissues. The blood initially pools as a liquid before clotting. Over time, the hematoma liquefies again as red blood cells lyse. The end result is a fluid-filled cavity encapsulated by fibrous tissue.
Hematomas contain all the formed elements of blood, mainly red blood cells. As the blood breaks down, it progresses through color changes reflecting the hematoma’s age. Small stable hematomas may fully resorb over time.
However, hematomas can become infected or cause significant tissue damage. Rapid treatment is needed for large hematomas to prevent permanent dysfunction. So while most resolve spontaneously, some hematomas lead to lasting deficits.