ABSTRACT
INTRODUCTION The presence of a large patent (persistent) foramen ovale (PFO) is associated with an increased incidence of cryptogenic stroke (Chapter 3), some types of decompression illness,1,2 migraine with aura,3,4 and transient global amnesia.5 Compared with the general population, people who experience migraine with aura have an increased risk of ischemic stroke,6 decompression illness,7 and transient global amnesia.8 The increased risk of decompression illness in migraine sufferers is confined to those with a large PFO or another cause of large right-toleft shunt.9 The inter-relationships of these diseases suggest that they share a common etiological mechanism, which is that large right-to-left shunts allow venous blood and its contents (including thrombo-emboli, gas bubbles, or chemical agents) to circumvent the pulmonary capillary bed and reach the systemic circulation. Although approximately a quarter of the population have a PFO, the clinical syndromes associated with a PFO are confined to those with the largest right-to-left shunts.
