A case of embolic stroke of undetermined source with large intrapulmonary arteriovenous anastomosis associated with interstitial pneumonia

A 67-year-old male with a history of interstitial pneumonia presented with embolic stroke of undetermined source (ESUS) in the right middle cerebral artery territory. Initial workup revealed a large right-to-left shunt (RLS) suggestive of patent foramen ovale (PFO) due to bubble inflow occurring within three heartbeats after releasing the Valsalva maneuver. However, PFO was ruled out when guidewire passage through the atrial septum failed, and pulmonary angiography showed no evidence of pulmonary arteriovenous fistula or malformation. Ultimately, intrapulmonary arteriovenous anastomoses (IPAVA) were considered as the source of the RLS. It was hypothesized that numerous small IPAVA combined to form a large RLS, which, despite its size, could not be the embolic source. This case highlights the importance of thorough evaluation of RLS in patients with lung diseases, as even large shunts may originate from IPAVA rather than from intracardiac shunts such as PFO.