Transcranial color Doppler ultrasonography: methodology and usefulness for the study of patent foramen ovale in cryptogenic stroke

Non-invasive Doppler ultrasonographic study of cerebral arteries (transcranial Doppler, TCD) has been extensively applied on both outpatient and inpatient settings. It is performed placing a low-frequency (≤2 MHz) transducer on the scalp of the patient over specific acoustic windows, in order to visualize the intracranial arterial vessels and to evaluate the cerebral blood flow velocity and its alteration in many different conditions. Nowadays a valid indication for TCD in the outpatient setting is the research of right-to-left shunting, responsible for the so-called "paradoxical embolism", most often due to patency of foramen ovale, which is responsible for the majority of cryptogenic strokes occurring in patients younger than 55 years. TCD also allows to classify the grade of severity of such shunts using the so-called "microembolic signal grading score". Therefore, TCD is an essential cardiological exam for the detection of patent foramen ovale, assuming an important role as a first-level examination to guide the subsequent diagnostic-therapeutic management. In addition, TCD has found many useful applications in neurocritical care practice. It is useful for the identification of intracranial vascular stenosis and for the assessment of critical conditions including vasospasm in subarachnoid hemorrhage, traumatic brain injury and brain stem death. It is also used to evaluate cerebral hemodynamic changes after stroke, to investigate cerebral pressure autoregulation, and for the clinical evaluation of cerebral vasomotor reactivity.