This European multicenter observational study aims to evaluate the real-world use, timing, and outcomes of lymphatic interventions in patients with congenital heart disease and/or primary lymphatic disorders. The study will examine the effectiveness of diagnostic imaging and interventional techniques, such as lymphatic embolization, in improving clinical symptoms, biomarkers, and fluid-related complications. The central question is whether early diagnosis and targeted intervention can lead to clinically meaningful improvements and reduced need for reintervention. Data collected retrospectively and prospectively from participating centers will help identify predictors of outcome, assess disease severity, and inform standardized diagnostic and therapeutic pathways across Europe.

This is a prospective, multicenter observational study with retrospective components. The study population includes patients who have undergone or are undergoing lymphatic imaging diagnostics and lymphatic interventions at participating centers across Europe. Patients are included both retrospectively (from medical records) and prospectively as part of their routine clinical care.

Inclusion Criteria:

• Patients of any age with a confirmed central lymphatic disorder, either in the context of CHD or as a primary lymphatic disorder, verified through lymphatic diagnostics (e.g. lymphatic imaging or relevant biomarkers).
• Patients who have undergone, or are undergoing, diagnostic lymphatic imaging and/or interventional procedures for their lymphatic disorder.
• Patients who are receiving, or have received, conservative (non-interventional) management for their lymphatic disorder.

Exclusion Criteria:

• Patients with isolated peripheral lymphatic disorders not involving the central lymphatic system.
• Patients with acute postoperative iatrogenic chylothorax (<3-4 weeks duration and not requiring intervention).
• Patients without sufficient clinical documentation to confirm diagnosis, treatment, or follow-up.
• Patients who decline, or whose legal guardians decline, to provide informed consent (for prospective inclusion).

Participants will be identified from pediatric and adult congenital cardiology and lymphatic referral centers across Europe. The study population includes patients of any age with congenital heart disease (CHD) and associated central lymphatic complications (such as plastic bronchitis, protein-losing enteropathy, or chylothorax), as well as patients with primary central lymphatic disorders. Patients are included from tertiary care institutions that perform lymphatic imaging and/or interventions and will be enrolled retrospectively from existing clinical records and prospectively during routine care.