# Understanding thromboembolus transport patterns in the brain for stroke in the presence of carotid artery stenosis

## TL;DR

This study uses computer models to show how blood clots from carotid artery blockages can travel unexpectedly in the brain, complicating stroke diagnosis.

## Contribution

The study introduces a patient-specific computational model to demonstrate non-intuitive embolus transport patterns in the brain due to carotid stenosis.

## Key findings

- Thromboemboli from left and right carotid sources can travel contralaterally in the brain.
- Cardiogenic thromboemboli do not show distinct transport preferences based on stenosis severity.
- Contralateral stenosis can lead to emboli crossing the Circle of Willis, causing diagnostic ambiguity.

## Abstract

Deciphering the source of an embolism is a common challenge encountered in stroke treatment. Carotid stenosis is a key source of embolic strokes. Carotid interventions can be indicated when a patient has greater than 50% stenosis in the carotid ipsilateral to the cerebral infarction, which is designated as the symptomatic carotid. However, there are often a significant number of cases where carotid emboli travel contralaterally, leading to ambiguity regarding which carotid is symptomatic. We use a patient-specific computational embolus-hemodynamics interaction model developed in prior works to conduct an in silico experiment spanning 30 heart-to-brain arterial models with differing combinations of bilateral severe and mild stenosis degrees. We used these models to study source-to-destination transport of thromboemboli released from left/right carotid disease sites, and cardiogenic sources. Across all cases considered, thromboemboli from left and right carotid sources showed non-zero contralateral transport. We also found that cardiogenic thromboemboli do not have an altered hemisphere distribution or distinct transport preference dependent on stenosis degree, thus potentially making the underlying etiology more cryptic. In patients with carotid stenosis or chronic occlusion ipsilateral to the area affected by stroke, we have demonstrated that the presence of contralateral stenosis can cause emboli that travel across the Circle of Willis (CoW) which can potentially lead to ambiguity when deciding which carotid is truly symptomatic.

Here we investigate how varying degrees of carotid artery stenosis can lead to non-intuitive transport of thromboemboli in the brain, complicating stroke diagnosis and treatment. Using computer simulations of embolus transport and embolus-hemodynamics interactions across 30 patient image-derived vascular models, we show that emboli from both carotid and cardiogenic sources can have non-intuitive source-to-destination distribution via the Circle of Willis, especially trans-hemispheric distribution in cases of asymmetric or severe stenosis. Our findings highlight the need for more nuanced risk stratification in stroke patients for revascularization therapies, particularly in Embolic Strokes of Undetermined Source (ESUS).