SESSION TITLE: Medical Student/Resident Imaging Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: The differential diagnosis for right inferior hilar mass includes paratracheal malignancy, mediastinal lymphadenopathy, and on rare occasions, dilated vascular structures, primarily the Azygos vein. We present a 66-year-old man who was referred to us for biopsy of a right inferior hilar mass. On further evaluation and imaging, the mass structure was found to be a dilated Azygous vein. CASE PRESENTATION: A 66-year-old man with past medical history significant for essential hypertension, liver cirrhosis, and portal hypertension was admitted to tertiary care hospital for Acute Type 1 respiratory failure due to volume overload. Pulmonary service was consulted for possible Bronchoscopy with Endobronchial ultrasound (EBUS) of masslike consolidation along the right inferior hilar region that was apparent on Chest Xray(Figure 1). For further evaluation, the patient had a CT scan of the chest(Figure 2) during his hospitalization, which showed 4.5 x 3.4 cm right upper posteromedial chest mass positioned adjacent to the trachea and esophagus. This structure appeared to be continuous with an elongated structure extending through the posterior mediastinum adjacent to the esophagus. Given the patient history of portal hypertension and the connection of the mass to a tubular structure that was most likely venous in origin, ruling out dilated azygos vein as a possible diagnosis was mandatory. The patient underwent an MRI scan of his chest(Figure 3), which confirmed the mass to be a dilated Azygos vein, and Bronchoscopy was deferred. DISCUSSION: Right inferior hilar mass differential includes malignancy, whether primary or metastasis, mediastinal lymphadenopathy (inflammatory, neoplastic, or infectious in origin), and on rare occasions, dilated vascular structures, primarily the Azygos vein[1]. Our patient had a dilated Azygos vein presenting as a solid mass on Chest x-ray and CT chest. There are multiple causes of dilated Azygos vein, including congenital ( Superior or Inferior vena cava interruption or congenital portoazygos shunt ) and acquired causes (aortoazygos fistula, congestive heart failure, constrictive pericarditis, superior or inferior vena cava obstruction, or acquired portoazygos shunt)[2]. Our patient had an acquired portoazygos shunt due to portal hypertension as a cause for his dilated Azygos vein. Diagnosis based mainly on contrast-enhanced imaging with either CT scan or MRI, both of which can provide a detailed evaluation of the portal and systemic venous systems and the collateral pathways between them if present[3]. Ruling out the possibility of a dilated azygos vein is important to avoid any additional intervention. CONCLUSIONS: Although rare, physicians should be aware of the possibility of dilated azygous vein as one of the differential diagnoses of masses in the right inferior hilar region. Reference #1: Toma CL, Dumitrache-Rujinski S, Belaconi IN, et al. Unilateral pulmonary hilar tumor mass: is it always lung cancer? Maedica (Buchar) 2013;8 (1):30–33. Reference #2: Gebrael J, Yu H, Hyslop WB. Spontaneous Portoazygos Shunt in a Patient with Portal Hypertension. J Radiol Case Rep [Internet] 2013 [cited 2020 Mar 9];7 (7):32–36. Reference #3: Ishikawa T, Tsukune Y, Ohyama Y, Fujikawa M, Sakuyama K, Fujii M. Venous abnormalities in portal hypertension demonstrated by CT. AJR Am J Roentgenol 1980; 134 (2):271–276. DISCLOSURES: No relevant relationships by Ibrahim Haddad, source=Web Response No relevant relationships by Girendra Hoskere, source=Web Response No relevant relationships by Sajin Karakattu, source=Web Response No relevant relationships by Akesh Thomas, source=Web Response