The Role of Transcranial Doppler in Patients with Cryptogenic Stroke

Abstract

Identifying the stroke mechanism is crucial for secondary prevention of ischemic stroke. However, approximately 20% to 30% of patients with ischemic stroke do not display a discernible cause after standard diagnostic evaluation and are classified as having cryptogenic stroke. Most cryptogenic strokes are believed to be of embolic origin, referred to as embolic stroke of undetermined source. Several potential causes, including occult atrial fibrillation, aortic arch atheroma, non-stenotic atherosclerosis, coagulopathy, and patent foramen ovale (PFO), are significant contributors to cryptogenic stroke. Among these, PFO-associated strokes often manifest as small cortical lesions in the posterior circulation and are associated with fewer traditional risk factors. Ischemic stroke is considered a high risk if there is a large PFO with significant shunting or the presence of an atrial septal aneurysm. Although transesophageal echocardiography is regarded as the gold standard for diagnosing PFO, its invasiveness, high cost, and challenges in certain stroke patients necessitate alternative approaches. Recently, transcranial Doppler (TCD) has emerged as a valuable screening tool for detecting high-risk PFOs, as supported by recent research. Accurate determination of the culprit PFO responsible for ischemic stroke remains crucial for guiding appropriate treatment decisions. This article provides a comprehensive review of the different modalities used to diagnose PFO, strategies for assessing the risk of PFO causing paradoxical embolism, and the role of TCD in patients with cryptogenic stroke caused by other etiologies.