Posterior Intercostal Arteriovenous Malformation Mimicking a Pleural Mass: A Diagnostic Pitfall.

Intercostal arteriovenous malformations (AVMs) are rare, particularly in congenital cases. We report a 29-year-old man with no history of chest trauma who presented with left-sided chest pain for 3 months. Initial routine contrast-enhanced chest computed tomography (CT) revealed a pleural mass-like lesion. Ultrasound-guided biopsy was initially considered. However, pre-biopsy chest ultrasound revealed pulsatile vascular flow within the lesion, raising suspicion for a vascular malformation. Subsequent CT angiography (CTA) demonstrated tortuous vessels supplied by multiple intercostal arteries with venous drainage into the intercostal veins and azygos system, confirming a congenital posterior intercostal AVM. Given persistent symptoms and surgical complexity, transarterial embolization with Onyx and N-butyl cyanoacrylate (NBCA) resulted in marked shunt reduction and symptomatic improvement. This case reminds clinicians to consider intercostal AVMs in the differential diagnosis of pleural-based lesions and reports our experience with endovascular embolization.