Can you do a lymphangiogram on a cat?

VRU 2012

Namsoon Lee 1, Sungjun Won, Mihyun Choi, Junyoung Kim, Kangjae Yi, Dongwoo Chang, Mincheol Choi, Junghee Yoon

Background
The study investigates a minimally invasive technique for imaging the thoracic duct in cats using computed tomographic (CT) lymphography. Traditional methods, such as direct lymphangiography, are invasive and carry higher risks. The authors aimed to develop a reliable protocol involving ultrasound-guided administration of iohexol into the popliteal lymph node to assess the thoracic duct anatomy and guide surgical interventions, particularly in cases like chylothorax.

Methods
Eight healthy adult cats underwent percutaneous injection of iohexol (300 mgI/ml) into the popliteal lymph node under ultrasound guidance. Three dosages (1.0, 1.5, and 2.0 ml) were tested. Serial CT scans were performed at 2-minute intervals to measure lymphatic vessel attenuation in Hounsfield Units (HU) across five anatomical regions of interest (L3, T13, T8, T4, and T1). Helical CT imaging was also conducted. Statistical analyses were performed to determine the optimal dose, and inter- and intraobserver reliability were assessed.

Results
The optimal dose of iohexol was determined to be 1.5 ml, providing sufficient attenuation without excessive leakage. The lymphatic vessels were delineated effectively, with attenuation values peaking at 1 minute post-injection and gradually decreasing. Helical CT revealed thoracic duct anatomy, which varied in branching and termination but consistently entered the venous system at the cervical level. In a clinical case of chylothorax, CT lymphography identified a dilated and tortuous thoracic duct with contrast medium leakage.

Limitations
The study's sample size was small (eight cats), and findings may not fully represent the anatomical variability across a broader population. Extranodal leakage was a concern at higher doses, and the technique's reliability in clinical settings may require further validation.

Conclusions
Ultrasound-guided percutaneous injection of 1.5 ml iohexol into the popliteal lymph node is a simple and reliable method for CT imaging of the thoracic duct in cats. This protocol facilitates detailed anatomical visualization, aiding in surgical planning, particularly for conditions like chylothorax. Helical CT scans should be performed immediately after iohexol administration to maximize diagnostic value.

Ultrasonographic images of popliteal lymph nodes after injection of 1.0 ml (B), 1.5 ml (C), and 2.0 ml (D) of iohexol. (A) During the injection, lymph nodes are increased in size and echogenecity compared to before injection. The hyperechoic line (short white arrows) is the needle tip. Extranodal leakage of iohexol is seen as anechoic fluid around the lymph node (long arrows)

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