Editorial–A New Method to Classify the Collateral Patterns in the Posterior Circulation

Several studies have reported on collaterals in anterior circulation arterial occlusion seen in patients with acute ischemic stroke (1–4). The presence of collateral flow in basilar artery occlusion has been recognized in small studies (5,6). Moscow and Newton (5) reported nine cases of basilar artery occlusion located proximal to the origins of the superior cerebellar artery. The posterior cerebral and superior cerebellar arteries filled in all nine patients via collateral flow either through the posterior communicating artery (n=7) or pial anastomoses from the middle cerebral arteries to the posterior cerebral arteries (n=2). Subsequently, Archer and Horenstein (6) provided more in-depth data regarding frequency and type of collaterals on the surface of the cerebellum in 20 patients with basilar artery occlusion and three patients with bilateral vertebral artery occlusions. Drake (7) reported that three of the seven patients in whom basilar artery was surgically occluded to treat intracranial aneurysm survived with minimal deficits presumably due to collateral formation. Such observation highlighted that collateral flow can develop and adequately supply the posterior circulation distribution in the event of basilar artery occlusion.

Numerous studies have found that a large proportion of patients with basilar artery occlusion have a poor outcome despite recanalization following intravenous or endovascular thrombolytic treatment (8–11). This observation has prompted the investigators to look for factors such as collateral circulation that are associated with patient outcomes. Brandt et al. (11) determined the variables affecting recanalization and clinical outcome in 51 patients with basilar artery occlusion who were treated with either intra-arterial or intravenous thrombolysis. The initial collateral state was graded as follows: 0, no collaterals; 1 (minimal), anterograde or retrograde collaterals with partial or slight filling; 2 (moderate), anterograde or retrograde collaterals with filling of the superior cerebellar arteries; and 3 (maximal), collateralization with anterograde and retrograde channels or maximal bilateral filling of the superior cerebellar arteries. Collateral circulation was moderate or maximal in 32 patients and was associated with lower mortality independent of recanalization. However, collaterals that form over the surface of the cerebellum are not accounted for by this method.