A subdural hematoma involves a collection of blood that gathers on the surface of the brain, positioned beneath the dura mater, the outermost membrane covering the brain. This condition frequently develops following a head injury, even from seemingly minor trauma. When medical professionals suspect such an injury, a Computed Tomography (CT) scan of the head becomes the primary imaging tool for immediate detection in an emergency setting.
The Role of CT Scans in Diagnosis
A non-contrast head CT scan is widely recognized as the standard diagnostic procedure for individuals suspected of having a subdural hematoma. Its speed, typically completing in minutes, is particularly helpful in emergency situations where prompt diagnosis can significantly influence patient outcomes.
CT scanners are readily available in most emergency departments, making them accessible for immediate use. The technology also demonstrates a high sensitivity for detecting acute hemorrhage. While Magnetic Resonance Imaging (MRI) offers more detailed views, its longer scan time and lower accessibility make CT the initial and most practical step for rapid diagnosis in time-sensitive emergencies.
What a Subdural Hematoma Looks Like on a CT Scan
On a CT scan, a subdural hematoma typically presents with a distinctive crescent shape, appearing as a layer of blood conforming to the inner curve of the skull. The visual density of the blood collection on the scan changes significantly depending on how recently the bleed occurred.
When a subdural hematoma is acute, it appears bright white, or hyperdense, on the CT images. This is because fresh, clotted blood is dense and effectively blocks the X-rays used in the scan, resulting in a bright signal. As the blood ages, typically within a few weeks, the hematoma enters a subacute phase. During this stage, the blood begins to break down, and the collection may appear grayish, similar in density to the surrounding brain tissue.
Identifying subacute hematomas can sometimes be more challenging due to their similar density to brain tissue. Over weeks to months, a chronic subdural hematoma develops as the old blood continues to break down into a less dense, fluid-like substance. In this chronic phase, the hematoma appears dark gray or black, reflecting its lower density compared to brain tissue.
Interpreting the Scan’s Findings
Medical professionals interpret several aspects of the CT scan to gauge a subdural hematoma’s severity and guide treatment decisions. One important measurement is the size and thickness of the hematoma, quantifying the maximum width of the blood collection and estimating the volume of blood pressing on the brain.
Another finding is “mass effect,” which describes the degree to which the hematoma is compressing or pushing on adjacent brain structures. A particularly critical measurement is the “midline shift.” This occurs when the pressure from the hematoma is significant enough to displace the entire brain off-center from its normal position. A notable midline shift indicates dangerously high intracranial pressure and often signals an urgent need for medical intervention.
Follow-Up Imaging and Monitoring
After an initial diagnosis, CT scans play an important role in managing and monitoring subdural hematomas. For patients who undergo surgical intervention, post-operative CT scans are routinely performed to evaluate the surgical site. These scans help confirm that any residual blood has been removed and assess whether the brain has re-expanded to its normal position.
In cases where a subdural hematoma is managed non-surgically, repeat CT scans are performed periodically, often over days or weeks. These follow-up scans are used to monitor the hematoma’s progression, ensuring it is not enlarging and is slowly resolving on its own. The repeat imaging helps clinicians track the size and density changes, guiding decisions about continued observation versus potential intervention if the condition worsens.