Severe angiographic vasospasm is a major determinant of risk of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage, and therefore a key decisional marker for considering intensive therapies such as vasospasm angioplasty in many centers. Although CTA has been reported to be well correlated with DSA for vasospasm assessment, its indications remain unclear. We aimed to determine the accuracy of CTA compared to DSA and propose a screening algorithm of severe angiographic vasospasm using CTA.

A severe angiographic vasospasm was defined as a vasospasm ≥50% on DSA. Contemporaneous CTA and DSA imaging performed in patients at baseline and during acute vasospasm were analyzed. Vasospasm of the anterior circulation vasculature was blindly quantified up to the end of 2nd segments of both anterior and middle cerebral arteries. Two readers retrospectively analyzed 210 arterial segments in 20 consecutive patients. Skin and lens radiation doses were prospectively measured in 6 patients.

Segment-based CTA/DSA correlation strongly depended on reader experience, imaging quality, and the absence of metallic artifact (Pearson ≤0.86). For the most experienced reader, patient-based certainty for excluding or confirming severe angiographic vasospasm was respectively obtained on CTA for threshold<30% (Sensitivity=100%, Specificity=50%) and ≥40% (Sensitivity=87%, Specificity=100%) (Fig. 1). Skin radiation doses were 3-time lower with CTA. Lens radiation doses were identical between the two modalities Table 1.

Vasospasm determination on CTA remains difficult. However, with optimized imaging and experienced analysis, CTA can reliably and non-invasively rule out or confirm clinically relevant vasospasm, keeping in mind it should be performed in selected cases to prevent inutile lens radiation and contrast toxicity.