To evaluate for stroke etiology, the patient underwent an extensive workup including hypercoagulable labs, CT chest, abdomen, and pelvis, telemetry monitoring, transthoracic and transesophageal echocardiograms, all of which resulted normal. 

Given high suspicion for cardioembolic source despite negative studies, a transcranial Doppler study was performed, which demonstrated multiple high-intensity transient signals (HITS) indicating high-grade right-to-left shunting. A Cardiac CT finally revealed a 2mm septal defect suspicious for patent foramen ovale, not previously seen. The patient was subsequently switched to anticoagulation and referred for PFO closure.

This case highlights the diagnostic value and the very high sensitivity of TCD ultrasound in evaluating arteriovenous shunting as a potential etiology of cryptogenic stroke in the setting of normal TTE and TEE. A positive TCD with negative TTE and TEE findings should prompt further diagnostic evaluation for an underlying right-to-left shunt. Cardiac CT is also an emerging study which will need further review for its ability to detect structural abnormalities such as PFO. This is also a minimally invasive test, making it especially valuable if TEE is significantly delayed or unable to be obtained.