A subgaleal hematoma (SGH) is a collection of blood that accumulates in the space directly beneath the scalp’s main fibrous layer. While frequently discussed in newborns following complicated deliveries, its occurrence in adults is relatively uncommon. When it appears in an adult, it is typically the result of a significant traumatic event or a specific medical procedure. SGH is characterized by the potential for substantial blood loss, requiring prompt medical evaluation.
Anatomy and Definition of the Hematoma
The scalp consists of five distinct layers. The key layer involved in SGH is the fourth layer, the loose areolar connective tissue, which lies between the galea aponeurotica and the periosteum covering the skull. This area, known as the subgaleal space, is a “potential space” that is only loosely held together.
This unique anatomical arrangement allows the subgaleal space to expand significantly, permitting the accumulation of a large volume of blood. Bleeding occurs when emissary veins, which connect the scalp veins to the venous sinuses inside the skull, are torn or ruptured by shearing forces. Because the space is not compartmentalized by bony attachments, the hematoma can spread diffusely across the entire surface of the skull, often crossing the cranial suture lines. This characteristic spread distinguishes SGH from a cephalohematoma, which is confined by the periosteum to the surface of a single cranial bone.
Primary Causes in Adults
The primary cause of SGH in adults is typically a high-energy mechanism involving severe blunt force trauma to the head. Injuries sustained in motor vehicle accidents or significant falls create intense shearing forces that tear the blood vessels within the loose connective tissue of the scalp. This rapid movement of the scalp against the fixed skull ruptures the emissary veins.
SGH is also a recognized complication of neurosurgical procedures, particularly those involving a craniotomy. Beyond trauma and surgery, a notable risk factor is the use of anticoagulant or antiplatelet medications, which can cause minor trauma to result in substantial bleeding. Pre-existing conditions affecting blood clotting mechanisms significantly increase the risk for hematoma formation and expansion after injury.
Symptoms and Medical Assessment
The most recognizable symptom of SGH is the development of a diffuse, boggy, and fluctuating swelling of the scalp. This swelling can cover a large area of the head and feels wave-like upon palpation due to the liquid nature of the blood collection. A defining clinical feature is the swelling’s ability to extend across the coronal and sagittal suture lines of the skull.
The accumulated blood may also track downward into the facial tissues, potentially causing periorbital ecchymosis, sometimes called “raccoon eyes,” or extending into the neck. Medical assessment begins with a physical examination, but imaging is necessary to confirm the diagnosis and assess severity. A Computed Tomography (CT) scan is the preferred diagnostic tool, as it measures the volume and extent of the hematoma while ruling out associated skull fractures or intracranial injuries. Laboratory tests to check hemoglobin and hematocrit levels are conducted to quantify the extent of blood loss and monitor for potential hypovolemia.
Treatment and Recovery
Management is dictated by the size of the collection, its rate of expansion, and the patient’s overall clinical stability. For small, stable hematomas, the approach is conservative, prioritizing close observation and supportive care. This includes applying a pressure dressing or compression bandage and administering pain medication.
Interventional treatment is reserved for large, rapidly expanding, or symptomatic hematomas. The simplest intervention is needle aspiration, which removes the collected blood but carries a risk of reaccumulation or infection. More definitive management for massive cases involves surgical incision and drainage to fully evacuate the blood and secure any active bleeding points. A serious acute complication is hypovolemia, or hemorrhagic shock, due to the large volume of blood lost into the space. Most uncomplicated SGH resolve spontaneously over several weeks or months as the body reabsorbs the blood.