From the Guidelines
Yes, a patient with syncope, collapse, and CT evidence of subarachnoid hemorrhage (SAH) can still have an aneurysm even if CT angiography (CTA) is negative.
Rationale
The most recent and highest quality study, 1, suggests that CTA may not detect aneurysms <3 mm in size, and the yield of repeat DSA studies in patients with an aneurysmal pattern of SAH and no etiology identified is around 10%.
Key Considerations
- CTA has a sensitivity of approximately 85-98% for detecting aneurysms, meaning some aneurysms may be missed 1.
- In cases of suspected aneurysmal SAH with negative CTA, further investigation with digital subtraction angiography (DSA) is strongly recommended, as it remains the gold standard with superior resolution for detecting small aneurysms (<3mm) 1.
- Some aneurysms may be obscured by adjacent bone structures, vasospasm, or thrombosis, making them difficult to visualize on CTA.
- The timing of imaging is also important, as vasospasm developing days after the initial bleed can mask an aneurysm.
Management
Management should include:
- Neurosurgical consultation
- Blood pressure control (typically maintaining systolic BP <140-160 mmHg) 1
- Close neurological monitoring
- Consideration of nimodipine 60mg every 4 hours for 21 days to prevent vasospasm complications 1
From the Research
Diagnosis of Aneurysm in Subarachnoid Hemorrhage
- A patient with syncope and collapse, and a computed tomography (CT) head scan showing subarachnoid hemorrhage, may still have an aneurysm even if the computed tomography angiography (CTA) is negative 2, 3, 4, 5, 6.
- Digital subtraction angiography (DSA) remains the gold standard for diagnosing the source of subarachnoid hemorrhage, and it can help to diagnose CTA-negative cases caused by unusual aneurysms 2, 3, 4.
- Studies have shown that DSA can identify a causative lesion in 4-13% of patients with CTA-negative subarachnoid hemorrhage, with most of the lesions detected being atypical aneurysms 2, 6.
- The pattern of subarachnoid hemorrhage may suggest the cause of hemorrhage, and aneurysms should specifically be sought with diffuse or perimesencephalic subarachnoid hemorrhage 6.
Yield of Digital Subtraction Angiography
- The yield of DSA among patients with CTA-negative subarachnoid hemorrhage is around 13%, including vasculitis/vasculopathy, aneurysm, arteriovenous malformation, and dural arteriovenous fistula 6.
- Repeat DSA may be needed to identify additional aneurysms or pseudoaneurysms, which can be identified in an additional 4% of patients 6.
- All patients with CT-negative subarachnoid hemorrhage should be considered for DSA, regardless of the pattern of hemorrhage 6.
Comparison of CTA and DSA
- CTA has a high sensitivity for aneurysms, but it may not be able to rule out aneurysmal subarachnoid hemorrhage in all cases 3, 5.
- DSA is more accurate than CTA in detecting aneurysms, especially in cases with diffuse or perimesencephalic subarachnoid hemorrhage 2, 6.
- CTA can be used as an initial screening tool, but DSA should be performed if the CTA is negative and the clinical suspicion of aneurysm is high 3, 5.