TOPIC: Procedures TYPE: Medical Student/Resident Case Reports INTRODUCTION: Pulmonary arteriovenous malformations (PAVMs) are rare vascular abnormalities in which arterioles connect directly to venules without passing through a capillary bed. Up to 95% of all PAVMs are associated with hereditary hemorrhagic telangiectasia (HHT). HHT is an autosomal dominant disease characterized by AVMs most notably affecting the pulmonary, hepatic, and cerebral circulations. Idiopathic PAVMs have a greater propensity to present as solitary malformations. We present the case of a patient with six incidentally discovered PAVMs. Further evaluation, including genetic testing not consistent with HHT, made this an unusual case of multiple presumed idiopathic PAVMs. CASE PRESENTATION: A 34-year-old female with a history of recent left ankle fracture was referred to the pulmonary clinic after an emergency department evaluation revealed six PAVMs on CT pulmonary angiogram following the diagnosis of a left lower extremity deep vein thrombosis. The largest PAVM (2.4 cm) was located in the right upper lobe and was classified as complex, having multiple segmental feeding arteries with a dominant draining vein. The remaining five were classified as simple AVMs, having a single feeding artery and draining vein. She endorsed a history of epistaxis, family history of stroke, and persistent borderline hypoxemia. An anatomic shunt study was performed with arterial blood gas measurements on room air and while breathing 100% oxygen with a calculated shunt fraction of 28%. Transthoracic echocardiogram showed normal pulmonary and central venous pressures. MRI brain revealed multiple punctate foci of enhancement most consistent with small vascular malformations. She underwent genetic testing for HHT (including ACVRL1, ENG, EPHB4, GDF2, RASA1, and SMAD4 genes) which was negative. The patient was referred to Interventional Radiology for coil embolization of the two largest PAVMs given her clinically significant right-to-left shunt. DISCUSSION: PAVMs cause impairment in gas exchange, filtration, and processing of systemic venous blood with a spectrum of clinical manifestations including life-threatening hemorrhage and paradoxical embolism. Although PAVMs are commonly asymptomatic, their unique complications include hypoxemia, dyspnea, hemoptysis, pulmonary hypertension, brain abscess, seizure, and stroke. There is evidence to suggest that idiopathic PAVMs act similarly to HHT-related PAVMs with comparable symptoms and plausible clinical complications. CONCLUSIONS: Clinical presentation may vary widely, however, PAVMs are important to recognize and evaluate for need for intervention, even if asymptomatic, given their potential for serious sequelae if left untreated. REFERENCE #1: Shovlin, CL. Pulmonary Arteriovenous Malformations. Am J Respir Crit Care Med 2014; 190 (11): 1217-28. REFERENCE #2: Wong HH, Chan RP, Klatt R, Faughnan ME: Idiopathic pulmonary arteriovenous malformations: clinical and imaging characteristics. Eur Respir J 2011; 38: 368-75. REFERENCE #3: Kroon S, van den Heuvel DAF, Vos JA, et al. Idiopathic and hereditary haemorrhagic telangiectasia associated pulmonary arteriovenous malformations: comparison of clinical and radiographic characteristics. Clin Radiol. 2021;76(5):394. DISCLOSURES: No relevant relationships by Sarah Kemp, source=Web Response No relevant relationships by Patrick Kicker, source=Web Response