Synopsis
Choose and interpret CT angiography and catheter digital subtraction angiography after intracranial haemorrhage, recognising technical limits and acting when vascular anatomy does not explain the bleeding pattern.
- Non-contrast CT establishes the presence and distribution of acute blood; vascular imaging answers a different question: what vessel lesion caused it and how can it be treated?
- NICE NG228 says to offer head CTA without delay after confirmed subarachnoid haemorrhage to identify the cause and guide treatment.
- An aneurysm is the likely culprit only when it fits the blood pattern; if CTA is negative but suspicion remains, consider catheter DSA, or MRA when DSA is contraindicated.
Key red flags
A basal cisternal or focal arterial-territory pattern of subarachnoid blood with negative CTA retains a possible occult aneurysm and merits specialist consideration of DSA.
An aneurysm remote from the haemorrhage distribution may be incidental; securing the wrong lesion leaves the true rupture source untreated.
Falling consciousness, a new focal deficit, seizure or worsening headache during angiographic work-up may indicate rebleeding, hydrocephalus or ischaemia and requires immediate clinical reassessment and non-contrast CT.
Contrast allergy, renal impairment, pregnancy, anticoagulation and difficult arterial access alter risk and planning but do not justify abandoning time-critical vascular diagnosis without specialist alternatives.
Catheter angiography carries arterial injury, thromboembolism, access-site bleeding and contrast risks; new neurology during or after the procedure is an emergency.
A lesion whose side and arterial location do not fit the clot distribution may be non-culprit; an interventional neuroradiologist and neurosurgeon should review the mismatch without delay.
A negative CTA despite convincing aneurysmal SAH may reflect a very small, thrombosed or technically obscured aneurysm and is the key situation in which NICE advises considering DSA.
New focal deficit, severe headache, reduced consciousness, limb ischaemia or expanding access-site swelling after DSA requires immediate assessment for embolus, dissection, rebleeding or access haemorrhage.
Investigation priorities
Rapidly identify an aneurysm or other arterial cause and define anatomy for immediate specialist planning.
Provide the preferred specialist selective dynamic anatomy when aneurysm suspicion persists after negative or equivocal CTA.
Management branches
Non-contrast CT or CSF analysis has confirmed subarachnoid haemorrhage and a vascular cause must be defined.
- Discuss urgently with the specialist neurosurgical centre and review the non-contrast blood distribution, neurological state, renal function, allergy history and any previous aneurysm treatment.
- Offer CTA without delay and compare every lesion with the blood pattern; if CTA is negative but aneurysm suspicion persists, consider catheter DSA, or MRA when DSA is contraindicated.