Q: My 20-year-old Arabian gelding has a hard, bony, fingerlike growth deep in a pectoral (chest) muscle. It doesn't seem to bother him. I noticed it about two months ago. Could it be an old puncture that encapsulated? It's probably about two inches long and about the width of a finger, sitting straight back into the muscle. --Denise Gilseth, via email

A: Based on your description, your suspicion of an "encapsulated old wound" is a possibility. This is referred to as a "granuloma," and it develops when the horse’s body attempts to wall off a foreign object or infection from the body. The granuloma's location might determine whether it can lead to a health problem for the horse. In many cases, a granuloma located on the surface of or just underneath the skin poses few health concerns, but can become a cosmetic nuisance. You might have your veterinarian ultrasound the area to provide additional information on the structure, location, and extent of the mass. Surgical removal might also be possible, but again this may depend on the granuloma's location and your veterinarian's recommendation after evaluating the mass. Other possibilities include:

1) Mineralized soft tissue This often occurs following a traumatic event, such as a kick from another horse.
2) Sarcoid A benign tumorlike growth possibly caused by a papillomavirus.
3) Previous injection site reaction Similar to a granuloma in that the body develops an atypical reaction to a medication or vaccine.
4) Cancer/Neoplasia Although uncommon, cancers such as melanoma, fibrosarcoma, or squamous cell carcinoma can develop in the horse.
5) Manubrium A normal protrusion of bone on the front of the sternum that serves as a muscle attachment site. This is more easily located on thinner conditioned horses or in breeds with less-defined muscle mass in their pectoral regions, such as Arabians. It is located in the center of the chest or pectoral region of the horse about one hand's width below where the neck connects to the chest.

Your veterinarian might also recommend collecting a biopsy of the mass for further identification. Specially trained veterinary pathologists are often consulted to determine the type and nature of a mass and together with your veterinarian can help determine an appropriate management or treatment option for your horse.

About the Author

Casey Gruber, DVM

Casey Gruber, DVM, is an associate veterinarian at Moore Equine Veterinary Centre in Calgary, Alberta, Canada, where he specializes in podiatry and emergency and sport horse care. He’s a graduate of Colorado State University.

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