LAUSR

Percutaneous diagnosis and intervention in the arterial space is a mature field, due to the prevalence of arteriosclerosis and the availability of tools for treatment. The same is increasingly true of venous interventions especially for thrombotic disorders. By comparison, the lymphatic system has been very poorly studied due to a lack of imaging and interventional options to date. To review the basic anatomy, the thoracic duct is the main conduit for 80% of the body's lymphatic drainage including from the liver, lower extremities, and intestine. Its primary function is to transfer interstitial fluid to the left subclavian vein. Thoracic duct obstruction (TDO) or narrowing can result in impaired lymphatic circulation, resulting in lymphatic flow disorders (LFDs) including chylothorax, proteins‐losing enteropathy, lymphatic plastic bronchitis, and chylous ascites. The diagnosis of TDO has been facilitated by the recent development of the intranodal lymphangiogram and dynamic contrast‐enhanced magnetic resonance lymphangiography (DCMRL). Intranodal lymphangiography is performed by inserting a 25‐gauge needle directly into the center of the inguinal lymph nodes under ultrasound guidance, and injecting oil‐based contrast material (Lipiodol; Guerbet). DCMRL is performed by placing a needle in the lymph node, then injecting gadolinium contrast with a power injector. DCMRL has higher spatial resolution and three‐dimensional acquisition, so is typically the first‐line modality. While somewhat technically and logistically challenging, lymphatic imaging can help identify the location of obstructions and leaks in the thoracic duct and guide percutaneous or surgical interventions. Percutaneous interventions can be performed in a retrograde fashion across the lympho‐venous junction at the left subclavian, or antegrade through a trans‐abdominal approach. In this issue of Catheterization and Cardiovascular Interventions, Srinivasan et al. characterize the features of TDO using imaging, invasive lymphangiography, and measurement of the lympho‐venous pressure gradient (LVPG). TDO was defined as a visible narrowing on DCMRL or narrowing and stasis of contrast on lymphangiography. This retrospective study was performed with 11 young patients from 2016 to 2021 who were known to have lymphatic obstruction with LFD despite medical therapy. Ten patients underwent both direct lymphangiography and DCMRL, while one patient had lymphangiography alone. The subject patients presented with pleural effusions (8/11), ascites (8/11), and both in 5/11 patients. Protein‐losing enteropathy was seen in 5 patients. The majority of patients (8/11) had congenital heart disease in which most had idiopathic obstruction at the site of the thoracic