The thoracic duct and the Fontan patient

Background: Ultrasound imaging of adults with heart failure and increased central venous pressure (CVP) has shown significant thoracic duct (TD) dilation from impedance in lymphatic drainage. Elevated CVP and abnormal lymphatic drainage are implicated in severe Fontan complications, including protein losing enteropathy (PLE) and plastic bronchitis (PB). Systematic studies of TD and lymphatic circulation in children are limited, and their cervical TD normative values have not been established. Methods: Thoracic duct imaging was attempted prospectively during routine echocardiograms performed 7/2014–9/2016 in children 5–21 years old with normal cardiovascular physiology and Fontan palliation. TD insertion to the central venous system (lympho-venous junction) was assessed with an S12-4 MHz transducer. For the first 34 patients, only TD ostia were measured, but ostium shape variability at the lympho-venous junction led to including the TD arch 5–10 mm proximal to the ostium for the remaining cohort. Results: Seventy-nine total subjects were studied: 58 controls, 13 Fontan patients with normal systemic ventricular ejection fraction (EF) (>50%), and 8 Fontan patients with decreased EF (≤50%). Combined Fontan subjects had larger TD ostial diameters compared to controls when normalized by body surface area (median 2.6 mm/m² vs. 2 mm/m²) (P=.04). Conclusion: To our knowledge, this is the first systematic study of ultrasonographic TD imaging in children. Fontan patients have larger TD diameters, reflecting the impaired lymphatic circulation in patients with this physiology. Further research may provide important associations between sonographic TD features with the functional status of patients with Fontan circulation.