Hassanain Toma, MD

Kamalian S, Morais LT, Pomerantz SR, Aceves M, Sit SP, Bose A, et al. Clot Length Distribution and Predictors in Anterior Circulation Stroke: Implications for Intra-arterial Therapy. Stroke. 2013

In ischemic strokes, clot length impacts the effectiveness of IV tPA. Kamalian et al. sought to determine the distribution and predictors of clot lengths in consecutive anterior circulation proximal artery occlusions. They retrospectively analyzed thin-section non-contrast CT (NCCT) of anterior circulation strokes, involving the internal carotid (ICA), middle cerebral M1 and M2 arteries. Through multivariate analysis, they showed that occlusion location was the strongest predictor of clot length.  Clot length was >8mm in 94%, 73%, and 22% of ICA-terminus, M1, and M2 occlusions, respectively.

They concluded that 1) the majority of anterior circulation proximal occlusions are >8mm long, 2) ICA-terminus occlusion is an excellent marker for clot length >8mm, 3) Thin-section NCCT appears useful for patients with MCA occlusion due to the wide variability of clot lengths.

In essence, the authors have utilized NCCT to identify a biomarker for IV-tPA resistance in the setting of anterior circulation stroke. Although a hyperdense thrombus was reportedly visible in 96% of patients, their patient selection was unfortunately biased by excluding anterior cerebral artery strokes, albeit a small fraction. In addition, I’ve learned that “hyperdense” areas are not as synonymous with “clot length”.  It is expected that when an artery, such as proximal M1, is occluded then there will be static blood along its whole distal segment until it meets a collateralized branch. For this reason I raise the following question to the authors: How did they distinguish static blood from “clot” ?  Perhaps the location of occlusion is more meaningful. Nonetheless, this finding may have important implications in selecting appropriate patients for intravascular intervention such as intra-arterial tPA and thombectomy.