Metatarsal pad route improves feline CT lymphangiography
Bottom line
Version 1
A new American Journal of Veterinary Research study found that giving iohexol through the metatarsal pad produced better thoracic duct enhancement in cats undergoing CT lymphangiography than perirectal administration. The study used a randomized, cross-over design in healthy purpose-bred cats at a veterinary teaching hospital between August and October 2025, comparing how often the thoracic duct enhanced, how quickly it enhanced, and the overall image quality after each technique. The finding builds on earlier feline and canine work showing that metatarsal or metatarsal-region injection can be a practical route for thoracic duct imaging, while prior feline research had suggested perirectal iohexol administration was feasible but based on a very small sample. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinarians planning CT lymphangiography in cats, especially in chylothorax workups or pre-surgical mapping of thoracic duct anatomy, the study points toward a route that may improve consistency and diagnostic confidence. Better enhancement can make it easier to identify thoracic duct branches and anatomic variation before intervention, which matters because incomplete identification of tributaries is one reason thoracic duct ligation can fail. Earlier reports have described intrametatarsal pad CT lymphangiography as feasible in cats with chylothorax, with only mild, self-limited paw swelling reported in one case, and prior perirectal work showed the technique was simple and did not cause local adverse effects in its small experimental group. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next question is whether the metatarsal pad advantage seen in healthy research cats translates into better procedural planning and outcomes in client-owned cats with spontaneous chylothorax. (pubmed.ncbi.nlm.nih.gov)
Key facts
- Study
- American Journal of Veterinary Research study
- Species
- Cats
- Design
- Randomized, cross-over
- Population
- Healthy, purpose-bred cats
- Setting
- Veterinary teaching hospital
- Study period
- August to October 2025
- Intervention
- Iohexol via metatarsal pad or perirectal administration
- Main finding
- Metatarsal pad administration produced better thoracic duct enhancement than perirectal administration
- Outcomes compared
- Frequency of thoracic duct enhancement, time to enhancement, and image quality
Version 2
A new feline CT lymphangiography study in the American Journal of Veterinary Research suggests that where clinicians inject iohexol matters. In healthy cats, metatarsal pad administration outperformed perirectal administration for thoracic duct enhancement, a result that could help refine how referral centers image thoracic duct anatomy before surgery or in the workup of chylothorax. (pubmed.ncbi.nlm.nih.gov)
That question has been building for years. Thoracic duct imaging in cats has historically relied on more invasive or technically demanding approaches, including popliteal lymph node injection and other direct lymphatic techniques. A 2012 report described CT thoracic duct lymphography in cats by popliteal lymph node iohexol injection, and later studies expanded the field with alternative routes, including intrahepatic injection and intrametatarsal pad injection. In 2022, AJVR published a multicenter retrospective study showing intrametatarsal pad CT lymphangiography was feasible in cats with chylothorax. (onlinelibrary.wiley.com)
Perirectal administration also had some precedent, but the evidence base was thin. A 2019 experimental study reported that subcutaneous perirectal iohexol injection allowed visualization of abdominal lymphatics, the cisterna chyli, and the thoracic duct in three cats within five minutes, with visible enhancement persisting through later scans and no observed local adverse effects. The authors argued that the technique was simple, allowed larger contrast volumes than direct lymph node injection, and could be useful for CT lymphography and intraoperative fluorescence-guided thoracoscopy. (vetmed.agriculturejournals.cz)
The new AJVR study appears to move beyond feasibility and into head-to-head comparison. According to the abstract provided, investigators randomized healthy purpose-bred cats to metatarsal pad or perirectal iohexol administration in a cross-over design, then compared frequency of thoracic duct enhancement, time to enhancement, and enhancement quality. Based on the paper’s title, metatarsal pad administration yielded superior thoracic duct enhancement versus the perirectal route. That’s clinically meaningful because image quality and consistency, not just technical success, often determine whether CT lymphangiography is useful for case planning. (pubmed.ncbi.nlm.nih.gov)
There wasn’t much outside commentary available on this specific paper in the sources I could verify, but the broader specialty literature helps explain why the result matters. Reviews of chylothorax management note that surgical planning depends on accurately identifying thoracic duct anatomy and its branches, and prior veterinary reports have emphasized that better visualization can reduce the odds of missed tributaries during ligation. The earlier feline intrametatarsal pad study also suggested the approach was well tolerated, with only one cat developing mild, short-lived paw swelling and no lameness. (dvm360.com)
Why it matters: For veterinary radiologists and surgeons, this study may help standardize a CT lymphangiography protocol that is both practical and more diagnostically reliable. If metatarsal pad administration consistently produces stronger thoracic duct enhancement, clinicians may be better able to map anatomic variation, confirm the number and course of duct branches, and plan thoracic duct ligation or related procedures with more confidence. In referral practice, that could translate into fewer nondiagnostic scans and more actionable imaging in cats with suspected chylothorax. (pubmed.ncbi.nlm.nih.gov)
The study’s limits are also worth keeping in view. It was conducted in healthy purpose-bred cats, so performance in dyspneic, unstable, or client-owned cats with active chylothorax may differ. And while superiority for enhancement is an important imaging endpoint, it doesn’t automatically prove better surgical outcomes. The next step for the field will be to see whether this protocol is adopted in clinical cases and whether future studies tie improved enhancement to faster diagnosis, better operative planning, or lower recurrence after thoracic duct ligation. (pubmed.ncbi.nlm.nih.gov)