Lymphography of the Thoracic Duct by Percutaneous Injection of Iohexol into the Popliteal Lymph Node of Dogs: Experimental Study and Clinical Application

To evaluate the efficacy of percutaneous administration of iohexol into the popliteal lymph node as a non-invasive technique for thoracic duct lymphangiography in dogs. Experimental study and clinical report. Normal adult dogs (n=4) and 1 dog with recurrent chylothorax. For the experimental study, 4 dogs (weight, 8.4-12.3 kg) had 5-10 mL iohexol injected percutaneously into 1 popliteal lymph node and then thoracic radiographs were taken. Popliteal lymph nodes were examined by histopathology 8 days later. One 25-kg dog with recurrent chylothorax had 25 mL iohexol injected into the right popliteal lymph node followed by thoracic radiography. In experimental dogs, the thoracic duct was best visualized on thoracic radiographs after administration of 10 mL iohexol. Clinically, no abnormalities were identified in the injected limb and except for 1 dog that had large numbers of siderocytes and erythrophagocytic macrophages in the injected lymph node, the histopathologic findings in the other injected popliteal lymph nodes were not different from contralateral nodes. In the clinical case, the thoracic duct was visualized, but there was leakage of iohexol around the node. The thoracic duct in dogs can be visualized by lymphography after percutaneous injection of iohexol (1 mL/kg at 2 mL/min) into the popliteal lymph node. Percutaneous popliteal lymph node administration of iohexol should be considered as an alternative to mesenteric lymph node injection for radiographic identification of the thoracic duct in dogs.