Comparative popliteal and mesenteric computed tomography lymphangiography of the canine thoracic duct

Thoracic duct computed tomography (CT) lymphangiograms were performed on seven clinically normal dogs. The appearance of the thoracic duct system was compared following administration of contrast medium through a mesenteric lymphatic vessel vs. ultrasound guided percutaneous injection into a popliteal lymph node using helical and sequential CT acquisition modes. The number of visible thoracic duct branches and the largest thoracic duct branch cross-sectional area and mean Hounsfield units (HU) were determined from thoracic vertebra 9 to lumbar vertebra 1. Procedural time and patient discomfort were also assessed. Popliteal administration produced a successful thoracic duct lymphangiogram in eight of 11 dogs (73%) after two attempts, while mesenteric administration was successful in eight of 10 dogs (80%) after a single attempt. Popliteal lymphography required 46% of the time and was associated with less patient discomfort than mesenteric lymphangiography. The number of thoracic duct branches seen was not significantly different for either administration technique (P=0.256) or CT acquisition mode (P=0.417). However, the cross-sectional area and mean HU of the largest thoracic duct branch were greater with mesenteric administration (P<0.001), and helical image acquisition (P<0.001). The thoracic duct branch number, size, and location were highly variable between dogs. Percutaneous popliteal lymphography appears to be an acceptable alternative to mesenteric lymphangiography for the detection of thoracic duct branches in the dog when using either helical or sequential CT acquisition modes.