From the Guidelines
The diagnostic approach for subarachnoid hemorrhage (SAH) begins with a thorough clinical assessment, focusing on patients presenting with sudden, severe headache ("thunderclap headache"), often accompanied by nausea, vomiting, neck stiffness, photophobia, altered consciousness, or focal neurological deficits. Non-contrast computed tomography (CT) of the brain should be performed immediately, ideally within 6 hours of symptom onset when its sensitivity exceeds 95% 1. If the CT is negative but clinical suspicion remains high, a lumbar puncture should follow, looking for xanthochromia (yellow discoloration of cerebrospinal fluid) or red blood cells that don't clear in sequential tubes. CT angiography (CTA) or digital subtraction angiography (DSA) is then performed to identify the source of bleeding, typically cerebral aneurysms in 85% of cases. Magnetic resonance imaging (MRI) with FLAIR sequences may be useful in subacute cases when CT sensitivity decreases. Laboratory tests should include complete blood count, coagulation profile, and electrolytes to assess for coagulopathies or other contributing factors. This comprehensive approach is critical because SAH has high mortality (up to 50%) and morbidity, with early diagnosis significantly improving outcomes by enabling prompt neurosurgical or endovascular intervention before potential rebleeding occurs. Key considerations in the diagnostic workup include:
- Clinical presentation and history
- Imaging studies (CT, CTA, DSA, MRI)
- Laboratory tests (complete blood count, coagulation profile, electrolytes)
- Lumbar puncture for suspected SAH with negative CT scan The most recent guidelines from the American Heart Association/American Stroke Association 1 emphasize the importance of prompt and accurate diagnosis of SAH to improve patient outcomes. Given the high morbidity and mortality associated with SAH, it is essential to prioritize a thorough and timely diagnostic approach to ensure the best possible outcomes for patients. The diagnostic approach should be guided by the latest evidence-based recommendations, taking into account the patient's clinical presentation, imaging findings, and laboratory results. By following a comprehensive and evidence-based diagnostic approach, healthcare providers can improve the quality of care for patients with SAH and reduce the risk of complications and poor outcomes.
From the Research
Diagnostic Approach for Subarachnoid Hemorrhage
The diagnostic approach for subarachnoid hemorrhage involves several steps and modalities, including:
- Noncontrast cranial computed tomography (CT) scan: This is the initial imaging modality of choice for diagnosing subarachnoid hemorrhage, especially within 6 hours of hemorrhage 2.
- Lumbar puncture: This should be performed if the CT scan is negative and there is still a high suspicion of subarachnoid hemorrhage, as it can help detect blood in the cerebrospinal fluid 3, 2, 4, 5.
- Computed tomography angiography (CTA): This can be used to diagnose and treat cerebral aneurysms, and is slowly replacing digital subtraction angiography as the first-line technique 2.
- Digital subtraction angiography: This is still required in patients with diffuse subarachnoid hemorrhage and negative initial CTA 2.
Sensitivity of Noncontrast Cranial CT Scan
The sensitivity of noncontrast cranial CT scan for diagnosing subarachnoid hemorrhage is:
- 93% overall 3
- 94% for aneurysm or arteriovenous malformation 3
- 91% for patients presenting with headache and normal mental status who have a subarachnoid hemorrhage and vascular lesions 3
- 99.7% overall, with 100% sensitivity from day 1 to day 5 4
Role of Lumbar Puncture
Lumbar puncture is an important diagnostic tool for subarachnoid hemorrhage, especially when the CT scan is negative. It can help detect blood in the cerebrospinal fluid and confirm the diagnosis 3, 2, 4, 5. However, studies suggest that a negative CT scan may be sufficient to exclude subarachnoid hemorrhage in the first 3 days after ictus, and lumbar puncture may not be necessary in these cases 4.