We will provide an educational pictorial review with cases from a large teaching hospital, performing nearly 500 computed tomography angiogram (CTA) examinations per year, in order to: provide a structured approach to the assessment of CTA following atraumatic subarachnoid haemorrhage (aSAH) to identify causative lesions. demonstrate the range of vascular causes that can lead to aSAH. illustrate unusual CTA appearances which have the potential to be missed.

Atraumatic SAH causes between 3-6% of all strokes. Although the prevalence is low, a ruptured aneurysm is disastrous, ending in between 25-50% mortality. The surviving patients often suffer from disabling neurologic deficits. Thus, recognition of haemorrhage and the causative lesion is essential in guiding management, most importantly in preventing further rupture and vasospasm. The timing of non-enhanced CT after ictus is essential as it is positive for SAH in 98% of cases within 12 hours of onset but reduces to less than 75% by the...

Common causes and (a)typical appearances Saccular aneurysm rupture causes approximately 85% of aSAH. They are likely caused due to shear forces – commonly located where a straight vessel curves and produces branches. Endothelial damage, fragmentation of the internal elastica and thinning of the tunica media creates these aneurysms. Although anterior circulation rupture is more prevalent, causing 90% of bleeds, 20% of patients presenting with aSAH have multiple aneurysms. The bleed patterns on CT vary according to the site of aneurysmal rupture. Although haemorrhage is typically...

CTA is an excellent tool, both in sensitivity and specificity and timing in helping to identify the cause of an aSAH. However, it requires a thorough interpretation and in light of a negative CTA – strong clinical suspicion should lead to catheter angiography.

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