What is the recommended initial evaluation and acute management for a patient with suspected subarachnoid hemorrhage (SAH)?

Initial Evaluation and Acute Management of Suspected Subarachnoid Hemorrhage

Immediate Diagnostic Approach

Obtain a noncontrast head CT scan immediately upon patient arrival—this is the cornerstone diagnostic test for SAH and must never be delayed. 1, 2

CT Scan Specifications and Timing

• The scan must cover from below the foramen magnum to above the circle of Willis and middle cerebral artery bifurcation 3
• CT sensitivity is 98-100% when performed within the first 6 hours of symptom onset, declining to 93% at 24 hours and 57-85% by day 6 3, 2
• Never use contrast-enhanced CT as the initial study—it obscures blood detection 2

When to Perform Lumbar Puncture

The decision to perform LP depends critically on timing and CT quality:

• LP is NOT required if CT is performed ≤6 hours after headache onset AND interpreted by an experienced neuroradiologist using third-generation (or newer) CT scanner 2, 4
• LP is mandatory if CT is performed >6 hours after symptom onset, regardless of CT result 2, 4
• LP is also required when high clinical suspicion persists despite negative CT, when no experienced neuroradiologist is available, when using older-generation CT scanners, or when the patient has altered consciousness 2

Lumbar Puncture Technique

• Perform LP >6 hours after the most recent symptom onset to allow xanthochromia to develop 2
• CSF analysis must include: cell count with differential, spectrophotometric xanthochromia analysis (sensitivity 100%, specificity 95.2%), protein, and glucose 1, 2
• Visual inspection for xanthochromia is insufficient—spectrophotometric analysis is essential 2

Common Pitfall: The 2018 Yale study found that LP in neurologically intact, CT-negative patients had a 13% false positive rate for xanthochromia and 4% complication rate, yet identified zero cases of aneurysmal SAH 5. However, this finding applies only to patients scanned within 6 hours by experienced neuroradiologists—do not extrapolate this to patients scanned later or in less optimal conditions.

Clinical Recognition

Key Presenting Features to Identify

• Thunderclap headache: sudden onset reaching maximum intensity within 1 hour, often described as "worst headache of my life" (present in 80% of cases) 1, 4
• Meningismus (neck stiffness) occurs in approximately 35% 2
• Witnessed loss of consciousness or onset during exertion 1
• Seizures occur in up to 20% of patients, most commonly within the first 24 hours, particularly with intracerebral hemorrhage, hypertension, and middle cerebral or anterior communicating artery aneurysms 3, 2

Sentinel (Warning) Hemorrhages

• Occur in 19.4-43% of patients, typically 2-8 weeks before major rupture 2, 4
• Present as milder headache lasting hours to days, often with nausea/vomiting but uncommon meningismus 3
• Missing a sentinel bleed increases mortality nearly 4-fold and rebleeding risk 10-fold 3, 4
• The most common diagnostic error is failure to obtain noncontrast CT, resulting in a 12% misdiagnosis rate 3

Vascular Imaging After Confirmed SAH

Immediately proceed with CT angiography (CTA) once SAH is confirmed on CT to identify the bleeding source. 1

CTA Performance and Limitations

• Overall sensitivity of 96.5% for all aneurysms, with 85-100% sensitivity for aneurysms ≥5mm 3
• Sensitivity drops to 61% for aneurysms <3mm 3, 2
• Interpretation must be based primarily on source images, with 3D reconstructions used only to clarify specific questions 3

When to Proceed to Digital Subtraction Angiography (DSA)

• If diffuse SAH pattern in basal cisterns and Sylvian fissures is present but CTA is negative, proceed immediately to DSA 1, 2
• DSA remains the gold standard with >98% sensitivity and specificity and is required for definitive treatment planning 2
• DSA is indicated for any aneurysm not definitively identified by noninvasive imaging 2

Acute Management Priorities

Blood Pressure Control

Control hypertension using titratable agents with a target systolic BP <160 mmHg for unsecured aneurysms to balance rebleeding risk against maintaining cerebral perfusion pressure. 1, 4

• Early rebleeding occurs in 4-13.6% of patients within the first 24 hours, with one-third occurring within 3 hours 2
• Rebleeding peaks within the first 2-12 hours and is associated with catastrophic outcomes 2

Nimodipine Administration

Administer oral nimodipine 60mg every 4 hours immediately upon diagnosis and continue for 21 consecutive days to improve neurological outcomes and reduce delayed cerebral ischemia. 1, 4

• Must be started within 96 hours of symptom onset 4
• This is the only pharmacologic intervention with proven benefit for preventing delayed cerebral ischemia 6, 7

Hydrocephalus Management

• Manage acute hydrocephalus with CSF drainage via external ventricular drain or lumbar drain 1
• Maintain euvolemia to prevent delayed cerebral ischemia 1, 7

Seizure Monitoring

• Monitor for seizures, which occur in up to 20% of patients, most commonly in the first 24 hours 1
• Consider anticonvulsants, particularly for patients with intracerebral hemorrhage, hypertension, or middle cerebral/anterior communicating artery aneurysms 3, 7

Urgent Consultation and Transfer

Patients with aneurysmal SAH require immediate evaluation by physicians with stroke expertise and urgent neurosurgical consultation. 2, 4

• Patients presenting to low-volume hospitals (<10 SAH cases/year) should be transferred early to high-volume centers (>35 cases/year) with multidisciplinary neuro-intensive care 2
• Surgical clipping or endovascular coiling should be performed as early as feasible (within 24-48 hours) to reduce rebleeding rate 2, 4
• When an aneurysm is amenable to both techniques, endovascular coiling should be considered 2, 4

Critical Pitfalls to Avoid

• Do not skip lumbar puncture after negative CT if >6 hours from onset—CT sensitivity declines significantly after this window 1, 2
• Do not rely on CTA alone if diffuse SAH pattern is present but CTA is negative—proceed to DSA due to limited sensitivity for small aneurysms 1, 2
• Do not delay neurosurgical consultation—rebleeding risk is highest in the first hours and mortality exceeds 40% within 30 days without proper management 2, 4
• Do not use MRI as the first-line test in acute settings due to limited availability, difficulty scanning critically ill patients, motion artifacts, longer study time, and higher cost 3, 2
• Do not dismiss severe headache as benign based solely on normal CT when clinical suspicion remains high—1.4% of SAH patients are diagnosed only after vascular imaging despite normal CT and CSF findings 2