CT Angiogram Timing in Confirmed Subarachnoid Hemorrhage
Once subarachnoid hemorrhage is confirmed on non-contrast CT, CT angiography should be performed immediately—without delay—to identify the bleeding source and guide urgent treatment planning. 1, 2
Immediate CTA After SAH Confirmation
Perform CTA as soon as SAH is confirmed on non-contrast CT, as this is a medical emergency with high early rebleeding risk (highest in first 24-48 hours) and mortality rates of 70-90% if rebleeding occurs. 1, 3
CTA has >90% sensitivity and specificity for detecting aneurysms and provides rapid, non-invasive vascular imaging that can guide immediate treatment decisions. 1, 4
The goal is to secure the aneurysm within 24-48 hours of hemorrhage, making immediate vascular imaging essential for treatment planning. 1
Why Timing Matters
Early rebleeding is the most preventable cause of death—approximately 25% of patients die after presentation, and urgent aneurysm identification allows for early securing (coiling or clipping) to prevent catastrophic rebleeding. 1
Patients should be transferred immediately to comprehensive stroke centers with neurosurgical expertise if not already at one, and CTA should be performed during or immediately after this transfer. 1, 3
The initial CT scan performed within 24 hours also helps predict vasospasm risk using the Hijdra sum score or modified Fisher scale—but this is secondary to the urgent need for vascular imaging. 5
CTA Limitations and Follow-up Strategy
CTA has reduced sensitivity for aneurysms <3 mm (approximately 61% sensitivity), and may miss small aneurysms adjacent to bone at the skull base. 1, 6
If CTA is negative but SAH is confirmed, proceed immediately to digital subtraction angiography (DSA) with 3D rotational imaging, which has >98% sensitivity and specificity and is the gold standard. 1, 3, 6
DSA identifies vascular pathology in 13% of patients with CTA-negative SAH, and repeat DSA may identify an additional 4% of aneurysms missed on initial angiography. 7
Critical Pitfalls to Avoid
Do not delay CTA to "stabilize" the patient—vascular imaging is part of the emergency evaluation and directly impacts immediate management decisions. 1, 3
Do not stop at negative CTA alone in diffuse or peripheral SAH patterns—these require catheter angiography as CTA misses small aneurysms that still require treatment. 1, 7
Perimesencephalic hemorrhage patterns may be adequately evaluated with CTA alone, but diffuse patterns mandate DSA if CTA is negative. 1
Ensure adequate arterial opacification on CTA (mean >500 HU in the internal carotid artery)—poor contrast timing significantly reduces sensitivity for aneurysm detection. 4