Oral food challenge unmasks porto-systemic shunting: a case report of a novel provocation test for congenital porto-systemic shunts.

Background: Congenital porto-systemic shunts (CPSS) are rare vascular malformations that may present with borderline haemodynamic significance under resting conditions, complicating decisions regarding intervention. Static, fasting-state assessments may underestimate the true physiological impact of these shunts. Case summary: A 9-year-old male with repaired total anomalous pulmonary venous connection (TAPVC) presented with progressive breathlessness. Cardiac computed tomography (CT) identified a residual anomalous venous connection between the left atrium and portal vein. Baseline phase-contrast magnetic resonance imaging (MRI) demonstrated a trivial left-to-right shunt not meeting conventional criteria for closure. An oral food challenge was performed to exploit the physiological increase in portal venous flow following feeding. Repeat MRI demonstrated reversal of shunt direction with net porto-systemic shunting, accompanied by a rise in serum bile acids above the upper limit of normal. The patient underwent successful percutaneous embolization. Discussion: This case introduces the oral food challenge as a novel, generalizable provocation test for CPSS, capable of unmasking physiologically significant porto-systemic shunting not apparent under fasting conditions. Dynamic assessment may inform intervention decisions even in the absence of conventional haemodynamic criteria.