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UC Davis Veterinarian Pioneers Near-Infrared Imaging

VMTH “Case of The Month” – July 2014
Cutting-Edge Procedure Helps Surgeons See Through Tissue

Atlas, a 3-year-old male mastiff, was experiencing a decreased energy level and his respiratory rate was increasing more than normal, even on the easiest of walks. His owners were concerned enough to bring him to their veterinarian, who diagnosed him to have a build-up of a milky white fluid called chyle (which leaks from the thoracic duct) in his chest, a condition known as chylothorax. As this can be deadly if not treated properly, Atlas’ veterinarian referred him to the specialists at the UC Davis Veterinary Medical Teaching Hospital.

Atlas was saved using a cutting-edge procedure, pioneered at UC Davis, that allows surgeons to see through tissue.

Once at UC Davis, Atlas was immediately seen by the Emergency Service who removed almost 2,000 milliliters of fluid from his chest. The removal of fluid helped Atlas temporarily feel better, but the cause of the chylothorax needed to be determined.

A number of things can cause chylothorax, including: tumors in the chest cavity, heart disease, trauma to the chest causing damage to the thoracic ducts and fluid leakage, heartworm disease, and idiopathic chylothorax (in which no known underlying cause is identified). The Emergency Service recommended a follow-up visit with the Internal Medicine Service to help determine the possible causes. Chest radiographs, an echocardiogram, and a thoracic ultrasound ruled out any structural or functional abnormalities that could have caused the chylothorax. Given that all other diagnostics were otherwise normal, the Internal Medicine Service determined that Atlas had idiopathic chylothorax. Mastiffs are among certain breeds that are over represented for idiopathic chylothorax.

Atlas’ thoracic ducts are not clearly visible to the naked eye.

Veterinarians discussed several options with Atlas’ owners, including a plan for medical therapy that involved medications and an alteration of Atlas’ diet, as well as a surgical option that involved thoracic duct ligation. As medical therapy is not generally very successful in resolving the chylothorax, Atlas’ owners chose to have him undergo thoracic duct ligation. This procedure is often done via an open surgical approach, but UC Davis is able to offer thoracoscopic thoracic duct ligation, a minimally invasive surgery to correct the problem. The surgery has shown similar success rates (80 – 85%) compared to typical, more invasive thoracotomy. The advantage to the minimally invasive option to the patient is a quicker recovery and less discomfort.

To prepare for the surgery, Atlas underwent general anesthesia for a CT lymphangiogram performed by the Diagnostic Imaging Service, which outlines the number and position of the thoracic ducts that carry chyle in the chest and helps the surgeons plan which side of the chest should be approached. Drs. Philipp Mayhew and Michele Steffey, of the Soft Tissue Surgery Service, were then able to proceed with the thoracoscopic thoracic duct ligation. This minimally invasive approach to chylothorax is used in human medicine and at a few veterinary schools, but what sets UC Davis’ approach apart is the use of intraoperative near-infrared imaging offered by Dr. Steffey to make the lymphatic vessels more visible to the human eye during surgery. The thoracic ducts that carry the chyle are very small, and often difficult to see at surgery under normal illumination, as they are buried in fat and other tissue. However near-infrared imaging uses different wavelengths of light that is not visible to the human eye without special imaging systems. A special medical dye is injected into a lymph node, which gets carried by the lymphatic vessels that ultimately collect in the chest to form the thoracic ducts. The dye is generally not visible by eye, and therefore does not distort the appearance of tissues or inhibit the surgeon’s dissection. However, when surgeons switch from a normal view to the near-infrared view through the scope, the near-infrared dye within the ducts allows them to see the position of the thoracic ducts very clearly, enabling the dissection and minimizing any chance of missing the ducts. The near-infrared wavelengths travel through tissue better, so surgeons can see the dye through several millimeters of tissue/fat in the near-infrared spectrum, whereas the naked eye can only see the surface of the tissue.

Atlas’ thoracic ducts are easily visible using UC Davis’ new near infrared imaging technique.

This approach enabled surgeons to easily locate where Atlas’ thoracic duct was leaking chyle into his chest cavity, and stop the leakage. The near-infrared approach, pioneered at UC Davis by Dr. Steffey for this disease, may soon become the optimal protocol for these types of cases. Other schools of veterinary medicine have taken notice, with a few recently purchasing the equipment to start using the near-infrared method.

Atlas remained hospitalized for two days after the operation, but because the surgery was minimally invasive, he was back to his old self within a week with only oral pain medication to help his recovery. After successful one-week and one-month recheck examinations, Atlas was given a clean bill of health, and continues to do well nearly a year after the surgery.

About the Veterinary Medical Teaching Hospital

The William R. Pritchard Veterinary Medical Teaching Hospital at the University of California, Davis—a unit of the School of Veterinary Medicine—provides state-of-the-art clinical care while serving as the primary clinical teaching experience for DVM students and post graduate veterinarian residents. The VMTH treats more than 47,000 animals a year, ranging from cats and dogs to horses, cows and exotic species. To learn more about the VMTH, please go to www.vetmed.ucdavis.edu/vmth. Timely news updates can be received on its Facebook (www.facebook.com/ucdavisvetmed) and Twitter (www.twitter.com/ucdavisvetmed) pages.

Rob Warren
VMTH Communications & Marketing Officer
rjwarren@ucdavis.edu
530-752-2363

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