Background and Purpose--Right-to-left shunt (RLS) due to patent foramen ovale is a well-established risk factor for cryptogenic stroke and is highly prevalent in cases of migraine, cluster headache, and obstructive apnea. It can be diagnosed by gaseous-contrast transcranial Doppler, yet in a small percentage of cases it cannot be done owing to an insufficient temporal window. The aim of the study was to compare transtemporal with transoccipital approaches for gaseous-contrast transcranial Doppler for RLS diagnosis.

Methods--We evaluated 183 subjects with a standard protocol for RLS diagnosis by simultaneously monitoring the right middle cerebral and vertebrobasilar circulations.

Results--Vertebrobasilar recording reached high specificity (100%) and good sensitivity (83.72%) for the diagnosis of RLS after the Valsalva maneuver. For only medium and large shunts, both sensitivity and specificity reached 100%. Time to bubble appearance after injection was higher in the vertebrobasilar circulation (4.36±1.7 vs 6.77±2.5 seconds; P<0.001). There was a positive correlation between the number of bubbles in the right middle cerebral and vertebrobasilar circulation (=0.97).

Conclusions--Transcranial Doppler with vertebrobasilar monitoring is highly sensitive and specific in detecting RLS, particularly when medium or large. It can be proposed for subjects with an insufficient temporal bone window.