Can Imaging Mesenteric Lymph Nodes Save Horses' Lives?

If your horse is exhibiting signs of colic, weight loss, or diarrhea, your veterinarian might reach for an ultrasound probe to get a glimpse of what is going on inside the animal's abdomen. Some serious conditions, however, aren't easily visible on ultrasound.

Because lymphadenopathy (enlarged lymph nodes) is a common finding upon post-mortem examination of horses with infectious, inflammatory, or cancerous disease, Betsy Vaughan, DVM, assistant clinical professor of Large Animal Ultrasound at the University of California (UC), Davis, School of Veterinary Medicine, set out to determine if this condition could be identified on ultrasound, which might help veterinarians reach a conclusive diagnosis and implement treatment before horses are euthanized. She presented the results of her study at the 2013 American Association of Equine Practitioners convention, held Dec. 7-11 in Nashville, Tenn.

"Mesenteric lymph nodes are not often visualized by ultrasound because of their location deep within the horse's abdomen," Vaughan said. "The cecal mesentery (connective tissue attached to the cecum, part of the large intestine), however, is located adjacent to the body wall in the right flank region and can be readily visualized with ultrasound in most horses."

Therefore, she proposed that using ultrasound to evaluate this structure might reveal signs of lymphadenopathy and direct further diagnostic testing.

In Vaughan's retrospective study she reviewed the records of horses presenting to UC Davis from 1999 to 2007 for a complete abdominal ultrasound. She included in the study horses that had multiple cecal lymph nodes visible within the mesentery adjacent to the cecal artery and vein.

Vaughan identified 42 horses, aged 3 months to 26 years, with cecal lymphadenopathy. These horses had presented with signs of weight loss, fever, anorexia, lethargy, colic, and diarrhea, and she categorized them according to whether they were diagnosed with neoplasia (tumors, 14), inflammation (16), or infectious disease (12).

On ultrasound, Vaughan said the lymph nodes appeared oval to round in shape, variably sized, and were often too numerous to count. Other visible abnormalities included thickened intestine (90%), abdominal masses (29%), and abdominal abscessation (9.5%). She said 64% of the horses had more than one abdominal structure affected. Twenty-one horses (50%) were euthanized or died within six months of diagnosis.

Based on the study results, Vaughan determined that veterinarians can easily image the cecal mesentery from the right side of the horse to garner information that could lead to a lymphadenopathy diagnosis. She suggested they evaluate this structure as part of a complete abdominal ultrasound examination.

"Finding enlarged lymph nodes in this area suggests that something significant is affecting the horses abdomen," she said. "If found, concurrent ultrasound abnormalities can then help veterinarians better diagnose abdominal issues," and hopefully save more horses' lives.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.