Whole-Brain Susceptibility-Weighted Thrombus Imaging in Stroke: Fragmented Thrombi Predict Worse Outcome

BACKGROUND AND PURPOSE:The prevalence and clinical importance of primarily fragmented thrombi in patients with acute ischemic stroke remains elusive. Whole-brain SWI was used to detect multiple thrombus fragments, and their clinical significance was analyzed.MATERIALS AND METHODS:Pretreatment SWI was analyzed for the presence of a single intracranial thrombus or multiple intracranial thrombi. Associations with baseline clinical characteristics, complications, and clinical outcome were studied.RESULTS:Single intracranial thrombi were detected in 300 (92.6%), and multiple thrombi, in 24 of 324 patients (7.4%). In 23 patients with multiple thrombi, all thrombus fragments were located in the vascular territory distal to the primary occluding thrombus; in 1 patient, thrombi were found both in the anterior and posterior circulation. Only a minority of thrombus fragments were detected on TOF-MRA, first-pass gadolinium-enhanced MRA, or DSA. Patients with multiple intracranial thrombi presented with more severe symptoms (median NIHSS scores, 15 versus 11; P = .014) and larger ischemic areas (median DWI ASPECTS, 5 versus 7; P = .006); good collaterals, rated on DSA, were fewer than those in patients with a single thrombus (21.1% versus 44.2%, P = .051). The presence of multiple thrombi was a predictor of unfavorable outcome at 3 months (P = .040; OR, 0.251; 95% CI, 0.067–0.939).CONCLUSIONS:Patients with multiple intracranial thrombus fragments constitute a small subgroup of patients with stroke with a worse outcome than patients with single thrombi.

Little is known about the proportion of acute ischemic strokes caused by multiple intracranial thrombi. Rarely, distal thrombus fragments that are separate from the primary occluding thrombus can be detected on DSA. Incomplete vessel occlusion by the primary thrombus with distal passage of contrast is required for this observation. Therefore, the true prevalence of multiple intracranial thrombi in the stroke population and the implications for clinical outcome remain unknown.Advanced gradient-echo-based MR imaging sequences, such as SWI, are highly sensitive in distinguishing structures that have different susceptibility values than their surroundings (eg, deoxygenated blood, hemosiderin, ferritin, or calcium).¹ SWI offers the possibility to directly visualize thrombotic material, commonly referred to as the susceptibility vessel sign (SVS), independent of the presence of blood flow or contrast media.^2–4 Recent studies confirmed that 1.5T and 3T SWI is a fast, robust, and highly sensitive imaging technique in acute stroke without relevant image interference following gadolinium application.^5,6 We performed SWI, covering the whole brain in patients with acute ischemic stroke of the anterior or posterior circulation to determine the prevalence of multiple intracranial thrombi before thrombolytic treatment and to study the associations between the presence of fragmented thrombi and baseline clinical and imaging characteristics, stroke etiology, and clinical outcome.