How to Diagnose Subarachnoid Hemorrhage: Modern Imaging and Clinical Evaluation

Diagnosing subarachnoid hemorrhage (SAH) has become significantly more accurate and efficient thanks to advances in modern medical imaging and clinical assessment. SAH, a life-threatening type of stroke caused by bleeding into the space surrounding the brain, requires prompt detection to improve patient outcomes and reduce complications.

Recognizing the Key Symptoms

One of the hallmark signs of subarachnoid hemorrhage is a sudden and severe headache, often described by patients as "the worst headache of my life." This abrupt onset of pain is typically accompanied by other neurological symptoms such as nausea, vomiting, sensitivity to light (photophobia), and neck stiffness—also known as nuchal rigidity. These physical signs point toward meningeal irritation, which plays a crucial role in early clinical suspicion of SAH.

Primary Diagnostic Tool: Non-Contrast CT Scan

The first-line diagnostic method for suspected SAH is a non-contrast computed tomography (CT) scan of the head. In fact, this imaging technique can detect over 95% of acute subarachnoid bleeds, especially when performed within the first 6 to 12 hours after symptom onset. The widespread availability of CT scanners—even in rural and community hospitals—has made rapid screening accessible and highly effective.

When CT Results Are Negative But Suspicion Remains

In cases where the CT scan does not show evidence of bleeding but clinical symptoms strongly suggest SAH, further investigation is essential. A lumbar puncture (LP) becomes the next critical step. During this procedure, cerebrospinal fluid (CSF) is collected and analyzed. If the CSF appears xanthochromic (yellowish due to broken-down red blood cells) or contains red blood without trauma from the needle insertion, it supports a diagnosis of SAH, particularly in delayed presentations.

Identifying the Underlying Cause

Once SAH is confirmed, identifying the source of bleeding is vital for proper treatment planning. The most common cause is a ruptured cerebral aneurysm, but arteriovenous malformations (AVMs), trauma, or other vascular abnormalities may also be responsible.

Advanced Imaging for Cause Detection

To pinpoint the origin of the hemorrhage, advanced vascular imaging techniques are used. CT angiography (CTA) is widely preferred due to its speed, non-invasive nature, and high accuracy in detecting aneurysms and other vascular irregularities. In some cases, especially when CTA results are inconclusive, a digital subtraction angiography (DSA) may be performed. DSA remains the gold standard for evaluating cerebral vasculature and provides detailed images that guide neurosurgeons or interventional radiologists in planning treatment.

MRI's Role in Diagnosis

While CT remains the go-to initial test, magnetic resonance imaging (MRI) and its associated sequences—such as gradient echo (GRE) or susceptibility-weighted imaging (SWI)—can also detect evidence of prior or minor bleeds. These modalities are particularly useful in patients with atypical presentations or when diagnosing chronic or small-volume hemorrhages that might be missed on early CT scans.

In summary, diagnosing subarachnoid hemorrhage involves a combination of clinical evaluation, neuroimaging, and sometimes lumbar puncture. Early recognition of symptoms, immediate CT scanning, and follow-up vascular studies ensure timely intervention. With current technology available even in smaller medical centers, accurate diagnosis and effective management of SAH are increasingly achievable, significantly improving survival rates and long-term recovery.