Neck Nuisances

Q:My 27-year-old mare has a growth on the right side of her neck that is now the size of a small Nerf football. We first noticed this mass in 2003, but I was told that because of her age there would be no point in removing it. Now Cassie is 27 and appears to be very healthy in every other way except for the growth still on her neck.

Her growth/tumor is finally to the size that it inhibits her ability to flex her head back to her chest. She doesn't flinch at all when I touch the growth, but it is very hard and I assume it is becoming uncomfortable.

My questions are, 1) What do you think this growth is? and 2) Is there any way to remove, treat, or shrink this mass?   

Kimberly Lewis, via e-mail

A:There are several causes of swelling in this area, and it's not clear from looking at the picture exactly which one is most likely. Possibilities to consider include some sort of thyroid gland abnormality. These are usually benign growths, but occasionally they can be malignant tumors. The thyroids are paired plum-shaped structures that usually sit under the "strap muscles" around the throatlatch area. In older horses they can become more palpable as the attachments loosen with age, but they should not become larger.

An active thyroid tumor can secrete excess hormones and affect the horse's metabolism, leading to weight loss, high heart rate, and skin and coat abnormalities. However, many thyroid growths do not secrete excessive thyroid hormones. Additionally, this area of the neck also contains salivary gland tissue, the deeper retropharyngeal lymph nodes, and the guttural pouches, which are large, air-filled structures associated with the ear's Eustachian tube. Problems with any of these can result in swelling, indicating an abscess, tumor, or infection and inflammation within the tissue itself.

Finally, we occasionally see large fluid-filled swellings in older horses' necks/throat areas that are due to an abnormal structure forming during embryonic development. These branchial remnant cysts are benign, but they can impede swallowing or breathing if they get particularly large.

My advice would be to obtain a thorough veterinary examination, including a good physical examination, some baseline blood tests to look for evidence of infection or inflammation, and thyroid testing if indicated by the exam findings. To determine the exact cause and treatment, though, a vet with specialties in ultrasonography might perform an ultrasound examination of the mass. If indicated, the vet can take samples of the mass with ultrasound guidance to make a definitive diagnosis and construct a treatment plan.

Several of the conditions listed above can be treated surgically by removing the mass, but many are best left alone and monitored every six months, as the area has numerous essential structures that make the surgical approach quite challenging.

Best of luck with this lovely older horse; she's lucky to have an owner who cares so much about her welfare.

About the Author

Rose Nolen-Walston, DVM, Dipl. ACVIM

Rose Nolen-Walston, DVM, Dipl. ACVIM, is an assistant professor of large animal internal medicine at the University of Pennsylvania School of Veterinary Medicine’s (Penn Vet) New Bolton Center, in Kennett Square. She graduated from the University of Georgia College of Veterinary Medicine in 2001, and then completed an internship and residency in large-animal internal medicine at Tufts University, in North Grafton, Massachusetts. She spent a subsequent year at Tufts doing research in adult stem-cell biology in mice. She joined the Penn Vet faculty in 2007, where she won the university’s 2013-2014 Lindback Award for Distinguished Teaching.

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