Understanding the difference between a hematoma and blood loss
A hematoma and true blood loss, or hemorrhage, are related but distinct medical conditions. The primary difference lies in the location and state of the blood. A hemorrhage is characterized by active, profuse bleeding from a damaged blood vessel, which can be either internal or external. If this bleeding is significant and causes a reduction in the body's total blood volume, it is classified as blood loss.
A hematoma, on the other hand, is the result of a hemorrhage, a collection of blood that has escaped from a vessel and has clotted and pooled in the surrounding tissues. A bruise is a common, minor example of a subcutaneous hematoma, where the collected blood is visible just beneath the skin. A hematoma does contain blood that has left the circulatory system, but it is not typically 'lost' from the body. Instead, it is sequestered in one place. A large or internal hematoma, however, can represent a clinically significant volume of sequestered blood, which can have systemic effects.
How the body processes a hematoma
For most minor hematomas, the body's natural healing process takes care of the issue over time. This involves the gradual reabsorption of the clotted blood back into the body. This process is why bruises change color—from red-purple to blue-black, then to green, and finally yellow, as the body breaks down the hemoglobin and removes the blood products. During reabsorption, the components of the blood are recycled and returned to the system. The time it takes for a hematoma to reabsorb varies depending on its size, location, and the individual's overall health. While a small superficial hematoma may fade in a couple of weeks, a deeper or larger one can take months to fully resolve.
When a hematoma can lead to significant blood loss symptoms
Although the blood in a hematoma is not lost from the body, a sufficiently large hematoma can lead to a state of internal hypovolemia. This is where a large volume of blood is no longer circulating within the vascular system. This can lead to a drop in overall blood volume, which in turn can reduce blood pressure and potentially lead to symptoms of shock. In addition, the blood sequestered within the hematoma is not available to the body's erythropoiesis (red blood cell production) process. For chronic or very large hematomas, this can lead to anemia, a condition where the body has a lower-than-normal number of red blood cells. Several studies have shown a link between larger hematoma volumes and poorer outcomes, which can be partially mediated by anemia. This is particularly dangerous for intracranial hematomas, where the pressure exerted by the pooled blood can cause severe neurological damage.
Types of hematomas and their severity
Hematomas are classified based on their location, with severity largely dependent on size and placement.
Subcutaneous Hematoma
This is a superficial hematoma located just under the skin, commonly known as a bruise or contusion. They are typically minor, non-threatening, and resolve on their own.
Intramuscular Hematoma
This type occurs within the muscle tissue, often from a muscle strain or trauma. They can be quite painful and cause significant swelling and restricted movement.
Subdural and Epidural Hematomas
These are types of intracranial hematomas, located inside the skull, but in different layers. These are potentially life-threatening due to the pressure the pooled blood exerts on the delicate brain tissue.
Retroperitoneal Hematoma
This hematoma occurs in the retroperitoneal space, behind the abdominal cavity. These can be difficult to detect and may indicate serious internal bleeding from trauma or surgery.
Hematoma vs. Hemorrhage Comparison
| Feature | Hematoma | Hemorrhage |
|---|---|---|
| Definition | A contained, localized collection of blood, often clotted, outside of a blood vessel. | Active, ongoing, and potentially profuse bleeding from a damaged blood vessel. |
| State of Blood | Clotted and pooled in a specific area. | Actively flowing out of a ruptured vessel. |
| Location | Can be superficial (bruise) or deep (intracranial, retroperitoneal). | Can be internal (into a body cavity) or external (visible bleeding). |
| Urgency | Varies. Small ones often resolve on their own, but large or critical ones (e.g., in the brain) require urgent medical attention. | Typically requires immediate medical attention to stop the bleeding and address potential shock. |
| Risk of Anemia | Possible with large or chronic hematomas due to sequestration of blood volume. | Direct cause of blood loss that can quickly lead to anemia or hypovolemic shock. |
When to seek medical attention for a hematoma
While a minor bruise or superficial hematoma is rarely a cause for concern, there are instances where a medical evaluation is crucial. Seek immediate medical care if you suspect a serious hematoma, especially after a head injury. Warning signs include a sudden, severe headache, confusion, weakness, unequal pupil sizes, seizures, or loss of consciousness. Other reasons to see a doctor include a hematoma that grows rapidly, doesn't improve after several weeks, causes severe pain, or is accompanied by signs of infection like increased redness, warmth, or pus.
Conclusion
In summary, while a hematoma is not considered systemic blood loss, it is a localized collection of blood that has escaped from circulation. Most resolve naturally, but large or deep hematomas, especially those in critical areas like the brain, can cause complications related to pressure and sequestered blood volume. Understanding the distinction between a hematoma and an active hemorrhage is important for proper assessment and management. For more information on this topic, consult authoritative medical resources like the Cleveland Clinic on hematoma.
