Thyroid tumours in dogs
The U-Vet oncology service recently saw two dogs with thyroid tumours which illustrate some of the different ways these cancers can be diagnosed and treated.
In both cases, the owners noticed swelling the dog’s neck which prompted a visit to a general practitioner veterinarian. Samples were collected with a needle (fine needle aspirate) and in one case these confirmed a thyroid origin of the mass and in the other only blood was seen in the samples.
This result is quite common for thyroid tumours in dogs, as they have a large blood supply which can then obscure the tumour cells. In cases like this, diagnostic imaging (ultrasound or CT scan) is often recommended to try to determine whether the mass originated from the thyroid gland.
Larger biopsies of suspected thyroid tumours are generally avoided due to the risk of significant bleeding.
In both cases, we performed a CT scan of the neck and chest to gain a closer look at the mass and to determine if the tumour had spread to other parts of the body (metastases). In one case, although the primary tumour was very large and was pressing on the airway in the neck, there was no sign of metastases and the tumour was successfully removed.
In the other case, although only one tumour could be felt in the neck, the CT scan revealed that both the thyroid glands had tumour present (see image 1) and there was also a mass in the lung (see image 2).
A fine needle aspirate of the lung mass showed that it may have spread from the thyroid tumour or possibly an unrelated lung cancer. Although the thyroid tumours could be removed in this case, with cancer elsewhere in the body surgery was not recommended.
Image 1: CT scan of the head and neck area showing masses in both thyroid glands (denoted by red circles). In this image, it is like we are looking through the patient from the top down.
Image 2: CT scan of the lungs, showing mass in the right lung (denoted by red circle). The other grey circles in the lungs are normal blood vessels. In this image, it is as though we are looking through the patient from front to back.
In dogs with thyroid tumours, the swelling in the neck is usually what is first noticed. Whilst uncommon, thyroid tumours in dogs can produce excessive hormones which can cause signs such as increased appetite, behavioural change, and weight loss.
Surgery is usually the recommended treatment, though the tumours can become very large and not all can be removed.
In those cases, the next best treatment is radioactive iodine, and we are fortunate at U-Vet to be the only clinic licensed in Victoria to perform this treatment on dogs with thyroid tumours.
Chemotherapy is also an alternative treatment for thyroid tumours that have spread or are too large to remove.
Finding thyroid tumours when they are small means that they are less likely to have metastasised and are more likely to be removed successfully. For this reason, regular veterinary visits for thorough physical examinations are important especially in older dogs.