Type II Abernethy Malformation with Hepatopulmonary Syndrome: Single-Stage Endovascular Occlusion of an SMV–IVC Communication — A Case Report

Background: Congenital extrahepatic portosystemic shunts (Abernethy malformations) can be associated with hyperammonemia and hepatopulmonary syndrome (HPS). Endovascular closure requires careful assessment of shunt anatomy and portal venous drainage. Case presentation: A 12-year-old girl presented with progressive exertional dyspnea, central cyanosis, clubbing, and room-air SpO₂ of 74%. Serum ammonia was 103 µmol/L, while liver biochemistry was within the reference ranges. Echocardiography showed no structural cardiac cause for the cyanosis and agitated saline bubble echocardiography showed delayed appearance (6 cardiac cycles) of bubbles in the left atrium. CT pulmonary angiography demonstrated distal pulmonary vascular dilatation and subpleural telangiectatic vessels, consistent with HPS. The preprocedural ABG on room air showed pH 7.45, PaCO₂ 31 mmHg, PaO₂ 62 mmHg, HCO₃⁻ 22 mEq/L, and A–a oxygen gradient of 49 mmHg; the follow-up ABG normalized. The baseline SpO₂/PaO₂ discrepancy remained unresolved. Abdominal CT angiography showed a side-to-side communication between the superior mesenteric vein (SMV) and infrarenal inferior vena cava (IVC), with tortuous collateral channels and normal, patent intrahepatic portal branches. During temporary balloon occlusion, portal pressure rose from 7 to 17 mmHg, and contrast opacified the intrahepatic portal branches and hepatic parenchyma. The primary communication was occluded with a 12-mm Amplatzer Vascular Plug II, with adjunctive gelfoam embolisation of collateral channels. Outcome: Doppler ultrasound demonstrated hepatopetal portal flow during early follow-up. At 3 months, room-air SpO₂ was 94%, central cyanosis had resolved, serum ammonia had decreased to 46.8 µmol/L, and the follow-up ABG normalized. Conclusion: This case highlights the role of cross-sectional vascular mapping and temporary balloon occlusion assessment before single-stage endovascular closure of a congenital portosystemic shunt.