Calcified clot challenge 2

Calcified cerebral embolus challenge

Calcified cerebral emboli (CCE) pose a significant challenge in reperfusion therapy for acute ischemic stroke , with an incidence rate of approximately 3% to 5.9%. These emboli primarily originate from the aortic valve, mitral valve, aortic arch, and cervical arteries, and approximately 14% are iatrogenic afterinvasive procedures. Calcified emboli are particularly difficult to recanalize due to their resistance to intravenous thrombolytic agents, which can only dissolve the thrombus attached to the surface of the emboli, potentially causing distal embolization. Their hard, irregular, and sharp-edged nature also complicates mechanical thrombectomy, leading to low recanalization rates and an increased risk of vessel wall injury.

At the CLOTS 7.0 Summit, experts reached a consensus on eight types of challenging thrombi encountered during thrombectomy, including white-colored clots, calcified clots under histology and imaging, stiff clots, sticky/adherent clots, hard clots, difficult to pass clots and clots that are resistant to pulling. These thrombi often require alternative or salvage strategies due to the failure of initial 2~3 attempts.

Calcified emboli are sometimes difficult to cross with microcatheters or even microwires due to their lack of deformability, which also hampers effective contact with the distal tip of aspiration catheters. However, large-bore aspiration catheters (0.088 inches) may be a game changer to maintain high FPE. Blood flow control using a balloon guide catheter (BGC) is an essential strategy to prevent embolus escape. Stent retrievers with interlinked cage-like configurations, such as NeVa and ERIC, can enhance the capture of calcified emboli and prevent their rolling and escape. For medium or distal vesselocclusions, starting with combined techniques such as the SWIM technique combined with microcatheter “pining,” double stent technique, or dual aspiration using a microcatheter and an intermediate catheter (MAT) may improve recanalization rates.

Calcified emboli may exhibit a “waist sign” when the stent retriever is deployed. After mechanical thrombectomy, residual calcified emboli can cause stenosis that closely resembles intracranial atherosclerotic stenosis. If multiple thrombectomy attempts fail, timely switching to rescue stenting may be considered to restore blood flow and prevent excessive vascular wall damage. Pre-dilatation with a small-diameter balloon to achieve suboptimal angioplasty can avoid vessel perforation by the hard embolus. Post-stenting VasoCT can further differentiate between calcified emboli and in-situ stenosis. Intensive antiplatelet therapy may be appropriate for patients with emergency stenting, massive vascular wall injury after thrombectomy, or significant residual stenosis to prevent reocclusion.

On non-contrast CT, calcified emboli have higher CT values than red thrombi (median 327, range 150–1200HU), and they show significant contrast attenuation on CTA. During DSA procedure, high-density embolus may be visible. CTA can also reveal calcified plaques in the aortic arch and carotid arteries as potential sources of emboli. Due to the irregular shape of the emboli, the affected vessels may be subocclusive, and CTP may show hypoperfusion lesion patterns. In the future, AI-based analysis of thrombus composition may assist in surgical planning and device suggestion. Synthetic thrombi mimicking human calcified tissue can be placed in silicone neurovascular models to develop thrombectomy devices and specific techniques for calcified emboli.

Reference

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