Discussion

Modifications of the Fontan operation can provide excellent palliation for many patients with various forms of single-ventricle physiology. In appropriately selected candidates, early and late survival rates may reach 95–97%. ^{Reference Driscoll4} However, because Fontan physiology relies on chronically elevated systemic venous pressure, it creates a nonphysiological circulation. Over time, this venous hypertension can impair lymphatic drainage and lead to Fontan-associated lymphatic dysfunction, which in turn predisposes patients to serious complications such as protein-losing enteropathy, chylothorax, and, more rarely, plastic bronchitis. ^{Reference Kołcz, Adamczyk, Rudek-Budzyńska and Skalski5}

Managing this rare complication can be extremely challenging in day-to-day practice. As a first step—consistent with standard paediatric cardiology practice—we initiated medical therapy and pursued transcatheter interventions to optimise Fontan haemodynamics. Accordingly, although distal extracardiac conduit stenosis was relieved with stent implantation and the fenestration was enlarged to improve Fontan decompression, the patient experienced only transient symptomatic improvement. This clinical course supports the interpretation that lymphatic dysfunction—rather than residual Fontan pathway obstruction alone—was the dominant driver of disease. Given the early recurrence of symptoms, we reassessed the patient with follow-up cardiac magnetic resonance imaging, which demonstrated a type 4 lymphatic perfusion pattern, placing him within a severe and likely refractory spectrum of Fontan-associated lymphatic disease. Type 4 perfusion has been associated with diffuse mediastinal and pulmonary lymphatic leakage and is generally reported to respond poorly to medical and catheter-based therapies. ^{Reference Ghosh, Griffis and Glatz6} In this context, and recognising the limited durability of conventional measures, we proceeded to the next step and considered surgical options that more directly target lymphatic decompression.

Catheter-based lymphatic interventions, including selective lymphatic embolisation, have emerged as an important therapeutic option for Fontan-associated lymphatic failure. Potential advantages include a less invasive approach and the ability to directly target abnormal lymphatic pathways responsible for airway or enteric leakage. However, these procedures require specialised infrastructure and a highly experienced multidisciplinary team, including advanced lymphatic imaging for accurate anatomic/physiologic mapping and confident target selection, and they may necessitate staged or repeat interventions. In critically ill patients, prolonged procedural time and the uncertainty of identifying the culprit channels can be limiting. Surgical thoracic duct decompression (Hraska procedure) is more invasive because it requires redo sternotomy, yet it offers a more direct and potentially durable reduction in lymphatic outflow pressure and can be combined with Fontan pathway revision when structural/hemodynamic contributors (e.g., conduit restriction) are also present. *As an alternative,* transcatheter innominate vein decompression has theoretical appeal as a less invasive option, but it is technically challenging, not widely standardised, and may be constrained by anatomic suitability and concerns regarding durability and thrombotic risk. In our patient—who remained clinically fragile after catheterisation, demonstrated severe lymphatic perfusion abnormalities, and had an indication for concomitant Fontan conduit enlargement—we favoured a definitive surgical strategy that addressed both lymphatic decompression and Fontan pathway optimisation in the same setting.

Surgically, thoracic duct decompression offers a targeted approach by redirecting thoracic duct drainage to a lower-pressure atrium. In our patient, rerouting the innominate (brachiocephalic) vein to the right atrium using a bovine pericardial conduit—performed alongside extracardiac conduit patch augmentation—was followed by marked clinical improvement, with regression of plastic bronchitis symptoms and an increase in oxygen saturation. This outcome aligns with the proposed mechanism: persistently elevated systemic venous pressures increase thoracic duct pressure, promoting protein-rich lymphatic leakage into the airways through the pulmonary lymphatic network and subsequent cast formation. From this perspective, although optimising Fontan haemodynamics remains essential, it may be insufficient once lymphatic disease is advanced. Therefore, in patients with severe lymphatic perfusion abnormalities, strategies that directly reduce lymphatic outflow pressure may offer meaningful benefit, particularly in medically and interventionally refractory plastic bronchitis.

In follow-up, we continued pulmonary hypertension–targeted therapy and maintained anticoagulation with warfarin, given the markedly slow flow within the conduit and the associated concern for thrombosis. The patient’s sustained symptomatic improvement made us reluctant to discontinue these medications, as ongoing pharmacologic support may have contributed to clinical stability. Nevertheless, it remains uncertain whether the favourable course would have been maintained without continued therapy, or whether some agents could have been safely tapered over time. At present, experience is limited regarding standardised post–thoracic duct decompression management, and further clinical experience and longer-term data are needed to define the optimal duration and intensity of adjunct medical therapy in this setting.