The Lymphatic System in the Fontan Circulation: Pathophysiology, Imaging and Therapeutic Interventions

The Fontan circulation, the definitive palliation for patients with univentricular hearts, produces a unique haemodynamic state characterised by chronically elevated systemic venous pressure, reduced cardiac output and the absence of a subpulmonary ventricular impulse. Because lymphatic drainage depends critically on the pressure gradient between the thoracic duct and the systemic veins, this physiology has profound consequences for the lymphatic system. Over the past decade, the lymphatic circulation has moved from being regarded as a passive bystander to being recognised as a central determinant of Fontan failure. Chronic systemic venous hypertension drives lymphatic overproduction and impaired central drainage, leading to progressive lymphatic congestion that manifests as chylothorax, protein-losing enteropathy (PLE), plastic bronchitis, lymphoedema and Fontan-associated liver disease. Advances in magnetic resonance (MR) lymphangiography, in particular dynamic contrast-enhanced MR lymphangiography and T2-weighted MR lymphangiography, now permit direct visualisation of abnormal lymphatic flow and precise planning of image-guided interventions. Percutaneous lymphatic embolisation and thoracic-duct decompression, together with surgical decompression procedures and, ultimately, heart transplantation, have shown clinically relevant efficacy in selected patients with complications refractory to medical therapy. This narrative review synthesises current knowledge on the pathophysiology, imaging and treatment of lymphatic complications in the Fontan circulation. Lymphatic involvement is frequent, under-diagnosed, and prognostically important; the integration of advanced lymphatic imaging and the consolidation of expertise in specialised percutaneous lymphatic intervention represent the most relevant advances of the last decade.