Timing of computed tomography and prediction of vasospasm after aneurysmal subarachnoid hemorrhage

Background: The initial noncontrast computed tomography (CT) study of the head after an aneurysmal subarachnoid hemorrhage (SAH) is used to predict the risk of developing vasospasm. Changes in the extent of subarachnoid blood seen on CT images occur as a function of time after SAH, but there is no consensus on the time interval during which this study needs to be completed. Methods: Clinical and radiological information on adult SAH patients were reviewed. Patients were grouped based on the time elapsed from ictus to the initial head CT study. The amount of subarachnoid blood on CT was graded using the Hijdra sum score (HSS) and the modified Fisher scale (MFS). The relationship between the initial CT grading score and the risk of angiographic vasospasm was assessed for each group. Results: A total of 224 consecutive patients were identified (145 females, 65%). Initial CT was performed within 24 h of the event in 163 (Group 1, 73%) and after 24 h in 61 patients (Group 2, 27%). A total of 54 patients (24%) developed angiographic vasospasm. A statistically significant association between the extent of subarachnoid blood and subsequent development of vasospasm was observed only if the initial CT imaging study was performed within 24 h of aneurysmal rupture (P = 0.0001 and 0.02 for HSS and MFS, respectively). Conclusions: We propose that only CT scans obtained within 24 h of a subarachnoid bleeding event should be used to estimate the risk of vasospasm.