Perirectal injection of imaging materials for computed tomographic lymphography and near infrared fluorescent thoracoscopy in cats

For the treatment of chylothorax, the most common procedure is a thoracic duct ligation; however, recurrence of the issue is often common, generally due to the incomplete ligation of all thoracic duct tributaries. Therefore, accurate localisation of the thoracic duct tributaries is required to determine the ligation sites in each patient. The concept of the perirectal injection of the imaging materials, which provides a simple and minimally invasive approach, is investigated for computed tomographic (CT) lymphography and near infrared fluorescent thoracoscopy in cats. Three clinically healthy cats were used for the CT lymphography, and two clinically healthy cats were used for the near infrared fluorescent thoracoscopy. Iodine contrast agent for the CT or indocyanine green for the thoracoscopy was injected subcutaneously into the peri-anal tissue. The injection site was massaged for 5 min post-injection. However, in the indirect injection of the imaging materials, in three iohexol-administered cats, the abdominal lymphatics, cisterna chyle, and thoracic duct could be depicted by the CT lymphography; and in both indocyanine green-administered cats, the thoracic duct was depicted running alongside the aorta by the near infrared fluorescent thoracoscopy. The ideal imaging procedure for the thoracic duct ligation involves the pre-operative CT lymphography of the entire pathway of the lymphatic vessels in advance, followed by the direct visualisation using a thoracoscopy. A combined CT lymphography and thoracoscopy could be a reliable method for successful surgeries. Crucially, the subcutaneous peri-anal injection of a contrast/dye provides a simple and minimally invasive method for the pre-operative and intra-operative depiction of the lymphatic pathways.