What Is Subarachnoid Hemorrhage? Understanding Causes, Symptoms, and Diagnosis
Subarachnoid hemorrhage (SAH) is a serious and potentially life-threatening type of stroke characterized by bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater that surrounds the brain. This space normally contains cerebrospinal fluid, which cushions the brain and helps maintain intracranial pressure. When blood leaks into this region, it can lead to sudden neurological deterioration, severe headaches, and in some cases, coma or death if not treated promptly.
Understanding the Brain's Meningeal Layers
The human brain is protected by three distinct layers of meninges: the dura mater (outermost), the arachnoid mater (middle), and the pia mater (innermost). The subarachnoid space lies directly between the arachnoid and pia layers and houses a network of delicate blood vessels. Trauma to the head—such as from falls, car accidents, or blunt force injuries—can damage these vessels, resulting in bleeding within this space. This form of hemorrhage is often referred to as traumatic subarachnoid hemorrhage.
Spontaneous SAH: The Role of Aneurysms
In many cases, however, subarachnoid hemorrhage occurs spontaneously, without any external injury. The most common cause of spontaneous SAH is the rupture of a cerebral aneurysm—a weak, bulging spot on a brain artery wall. These aneurysms can develop over time due to factors like hypertension, smoking, genetic predisposition, or connective tissue disorders. When an aneurysm bursts, it releases blood rapidly into the subarachnoid space, triggering what patients often describe as "the worst headache of their life."
Recognizing the Symptoms
Symptoms of subarachnoid hemorrhage typically appear suddenly and dramatically. Common signs include:
- An explosive, severe headache (often described as thunderclap in nature)
- Nausea and vomiting
- Stiff neck (nuchal rigidity)
- Sensitivity to light (photophobia)
- Altered mental status or loss of consciousness
Because these symptoms can mimic other conditions like migraines or meningitis, timely diagnosis is critical to prevent complications such as vasospasm, hydrocephalus, or secondary ischemic strokes.
Diagnosing SAH with Imaging
Computed tomography (CT) scanning is the primary diagnostic tool used in emergency settings to detect subarachnoid hemorrhage. On a non-contrast CT scan, SAH appears as hyperdense (bright white) areas filling the cerebral sulci and fissures—particularly around the basal cisterns and interhemispheric fissure. In cases where the CT is inconclusive but clinical suspicion remains high, a lumbar puncture may be performed to analyze cerebrospinal fluid for the presence of blood or xanthochromia (a yellowish pigment indicating broken-down red blood cells).
Advanced Imaging and Follow-Up Tests
Once SAH is confirmed, further imaging such as CT angiography (CTA) or digital subtraction angiography (DSA) is typically conducted to identify the source of bleeding—most commonly, a ruptured aneurysm. These techniques allow neurosurgeons and interventional radiologists to plan appropriate treatment strategies, including surgical clipping or endovascular coiling.
Risk Factors and Prevention
Several modifiable and non-modifiable risk factors contribute to the development of aneurysms and subsequent SAH. Key risk factors include:
- Chronic high blood pressure
- Tobacco use
- Excessive alcohol consumption
- Family history of aneurysms
- Age (most common in adults aged 40–65)
- Polycystic kidney disease and other genetic syndromes
Lifestyle modifications such as quitting smoking, managing blood pressure, and regular health screenings can significantly reduce the risk of developing dangerous aneurysms.
Conclusion: Early Detection Saves Lives
Subarachnoid hemorrhage is a medical emergency requiring immediate attention. With advances in neuroimaging and neurosurgical techniques, outcomes have improved, but early recognition remains the key to survival and recovery. Public awareness about the warning signs—and the importance of seeking urgent care—can make a critical difference in reducing mortality and long-term disability associated with this condition.