Subarachnoid Hemorrhage: Key CT Imaging Features and Clinical Implications

Subarachnoid hemorrhage (SAH) is a critical neurological emergency that requires prompt diagnosis and intervention. One of the most reliable methods for early detection is non-contrast computed tomography (CT) scanning of the brain. In typical cases, SAH presents with distinct hyperdense (bright white) areas visible in specific regions of the brain, making it identifiable in the initial imaging phase.

Classic CT Findings in Subarachnoid Hemorrhage

The hallmark radiological sign of SAH is the presence of high-density blood accumulation within the subarachnoid spaces. These areas include the cerebral sulci, interhemispheric fissures (longitudinal fissure), sylvian fissures (lateral fissures), ambient cisterns, and pre-pontine cistern. Blood pooling in these cerebrospinal fluid-filled spaces appears bright on CT scans due to its higher attenuation compared to surrounding brain tissue.

Blood Distribution Patterns on CT

In many patients, the bleeding extends into the ventricular system, leading to intraventricular hemorrhage, which can be clearly visualized as dense signals within the lateral, third, or fourth ventricles. In more severe cases, clot formation may occur, resulting in localized hematomas that exert mass effect on adjacent brain structures. The distribution pattern often provides clues about the source of bleeding—such as aneurysmal rupture near major vascular junctions.

Common Causes Behind Subarachnoid Bleeding

The primary cause of spontaneous SAH is the rupture of an intracranial aneurysm, typically located at branch points in the Circle of Willis. These weakened vessel walls balloon over time and eventually burst under pressure, spilling blood into the subarachnoid space. The second most frequent etiology includes vascular malformations such as arteriovenous malformations (AVMs) and cavernous angiomas, which are abnormal tangles of blood vessels prone to hemorrhage.

Although less common, tumor-related hemorrhage—also known as tumor apoplexy—can also lead to SAH. Certain brain tumors, particularly glioblastomas or metastatic lesions with rich vascularity, may bleed suddenly, mimicking aneurysmal SAH both clinically and radiologically.

Importance of Early Vascular Imaging

Given the potentially life-threatening nature of SAH, rapid identification of the underlying cause is essential for effective management. After confirming the diagnosis via CT, clinicians strongly recommend performing a cerebral angiogram—either through digital subtraction angiography (DSA), CT angiography (CTA), or MR angiography (MRA). DSA remains the gold standard for detecting small aneurysms and complex vascular abnormalities.

Identifying the exact source allows neurosurgeons and interventional neuroradiologists to tailor treatment strategies, whether endovascular coiling, surgical clipping, or radiosurgery for vascular malformations. Timely intervention not only prevents rebleeding but also reduces the risk of complications like vasospasm, hydrocephalus, and delayed cerebral ischemia.

Conclusion and Clinical Outlook

Recognizing the classic CT appearance of subarachnoid hemorrhage is crucial for emergency diagnosis and immediate care planning. Hyperdensity in basal cisterns, cortical sulci, and ventricles should raise strong suspicion for SAH, prompting urgent vascular imaging. With advances in neuroimaging and minimally invasive treatments, patient outcomes have significantly improved when care is delivered swiftly and accurately based on precise etiological diagnosis.