Metatarsal pad iohexol administration in cats undergoing computed tomography lymphangiography yields superior thoracic duct enhancement versus perirectal administration.

Metatarsal pad iohexol administration provides superior thoracic duct enhancement on CT lymphangiography compared to perirectal administration in cats.

This prospective, randomized crossover study compared two iohexol administration sites—metatarsal pad (MTP) and perirectal region (PR)—for CT lymphangiography (CTLA) in cats, focusing on thoracic duct (TD) enhancement frequency, time to enhancement, enhancement quality, and post-procedural comfort. Seven purpose-bred healthy cats underwent two sedated CTLA sessions each, with administration sites assigned in randomized crossover fashion. Bilateral TD visualization was achieved in all seven cats regardless of technique. TD enhancement was achieved in 7/7 cats after MTP administration and 6/7 after PR administration. Critically, MTP administration produced significantly superior enhancement quality by both subjective grading (median grade 2 vs. grade 1) and objective Hounsfield unit measurement at T10–T12 (452.5 ± 130.4 HU vs. 91.17 ± 19.5 HU). Mild, self-resolving discomfort within 24 hours was noted in 5/7 cats after MTP and 3/7 after PR, suggesting a slightly higher but clinically acceptable discomfort rate with MTP. Both techniques were deemed safe and effective. The authors conclude that while PR administration is a viable alternative, MTP iohexol administration is the preferred route for preoperative TD mapping due to its superior contrast enhancement, which may improve surgical planning for conditions such as chylothorax. This study provides valuable evidence to guide clinicians selecting CTLA protocols in feline patients requiring thoracic duct surgery.

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