Thyroid Tumors in Horses
Key takeaways
Thyroid tumors arise from the cells of the thyroid gland, and are typically benign in horses.
- The tumors are noticeable as large masses near the throat of the horse
- Most tumors do not cause other symptoms, but in some cases difficulty swallowing or rapid breathing may be noted
- Diagnosis typically involves a physical examination, diagnostic imaging, and a biopsy of the mass
- Treatment depends on the type of tumor present, with some not requiring treatment, and others requiring surgical removal
- The prognosis for most thyroid tumors is excellent, even without surgical removal
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A closer look: Thyroid Tumors in Horses
The thyroid is a small gland which sits at the base of the neck. It is responsible for regulating hormones related to blood pressure, metabolism, and hormone responses. The thyroid affects the majority of organs in the body.
Thyroid tumors are often externally visually evident. Most thyroid tumors are benign with a favorable prognosis, but prompt veterinary examination is recommended to ensure the tumor is not a more aggressive form that may be life-threatening.
Risk factors
Thyroid tumors are uncommon in horses, but are more common in older horses over the age of 17.
Some thyroid tumors produce large amounts of thyroid hormone.
Possible causes
Thyroid tumors develop from normal thyroid gland cells that acquire mutations, allowing them to divide and grow uncontrolled. The underlying cause of thyroid tumors in horses is unknown, however they are most common in older horses over the age of 17. Thyroid tumors are typically benign, and do not metastasize or invade into local tissues.
Main symptoms
Typically, thyroid tumors cause no symptoms other than the presence of a large mass near the throat.
Testing and diagnosis
Identification of a thyroid tumor is usually based on a physical examination. An ultrasound of the mass may be used to determine whether it is invasive into surrounding tissues. Additional tests to support the diagnosis may include:
- Bloodwork, including measuring thyroid hormone levels
- Cytology of the mass
- Biopsy of the mass to confirm the type of tumor
Steps to Recovery
Treatment depends on the type of tumor present. As most thyroid tumors in horses are benign, some owners may choose to leave the tumor alone as long as it does not affect the horse’s quality of life. Otherwise, surgical removal of the tumor is typically curative, unless metastasis of the tumor has occurred to other organs. Surgical removal of large thyroid tumors can be very challenging due to the large number of vessels in the area, so referral to a board-certified veterinary surgeon may be necessary.
Most thyroid tumors have an excellent prognosis, regardless of whether they are removed, because they are usually benign. More aggressive cancers have a poor prognosis, particularly if the tumor has metastasized before it can be removed. Horses that have a large portion of the thyroid gland removed during surgery may require thyroid hormone supplementation for the rest of their lives.
Prevention
There are no known preventatives for thyroid tumors. Thyroid tumors are not contagious.
Are Thyroid Tumors in Horses common?
Thyroid tumors are uncommon in horses, and most commonly affect horses over 17 years of age.
Typical Treatment
- Benign neglect
- Surgical removal
