Heart and Carotid Artery Tumors in Dogs

Symptoms vary depending on whether the tumor is located in the heart or carotid artery, but may include heart failure, trouble breathing, coughing, vomiting, and fatigue. Treatment relies on reducing the size of the tumor, with complete removal being the ultimate goal, though this is difficult to achieve. Surgery or radiation may be used to treat chemodectomas. Continued monitoring is necessary to ensure there is no recurrence, though the prognosis for survival is grim in malignant tumors. Breeds that are more likely to develop chemodectomas include brachycephalic breeds (breeds with a short skull and nose) such as Boxers and Boston Terriers, as well as German Shepherds.

Chemodectomas are tumors of the chemoreceptors, which are responsible for detecting changes in chemical levels in the blood. These tumors occur primarily in the heart and carotid artery, though tumors of the heart are most prevalent in dogs. Brachycephalic breeds are predisposed to the development of these tumors.

Chemodectomas are non-functional, meaning they don’t output hormones into the blood. Associated symptoms result primarily from their growth and imposition on other areas of the heart and carotid artery, causing functional disturbances. Symptoms will differ depending on whether the tumor is affecting the heart or carotid artery. Tumors affecting the carotid artery primarily affect swallowing and the neck region, while tumors affecting the aorta affect the functions of the heart and produce signs consistent with other types of cardiac disease. Symptoms may include:

• Heart failure
• Inadequate blood circulation
• Trouble swallowing
• Shortness of breath
• Coughing
• Edema (an excess of watery fluid collecting in cavities under the skin of the neck, causing swelling)
• Hemorrhages
• Pericardial effusion (fluid around the heart)
• Dyspnea (labored breathing)
• Hydrothorax (fluid in the pleural cavity of the lungs)
• Hydropericardium (accumulation of fluid in the pericardial cavity, near the heart)
• Fatigue
• Weight loss
• Vomiting
• Vena Cava syndrome (obstruction of the superior vena cava, a vessel carrying circulating blood into the heart)

Types

Benign adenomas 

• A benign adenoma is a tumor that is non-cancerous and doesn’t spread through the body. Most of the time, chemodectomas are benign. In the aorta, small benign adenomas are typically attached to the adventitia of the pulmonary artery and ascending aorta or in the tissue between vascular trunks. Larger benign adenomas in the aorta may be found near the atria and partially surround the arterial trunks at the heart’s base.

Malignant carcinomas 

• A malignant carcinoma is a tumor that is cancerous and can spread. Approximately 30% of malignant chemodectomas metastasize (spread) to other sites of the body. Malignant carcinomas of the aorta are typically larger in size than benign adenomas. Carcinomas in the aorta may be found in the wall of the pulmonary artery. It is unusual for malignant carcinomas of the aorta to spread to the lungs and liver in dogs. Malignant carcinomas in the carotid artery are larger than benign adenomas. 

As with most cancers, direct causes of development are not altogether known. Genetics play some role in the susceptibility of certain breeds, particularly those that are brachycephalic (having a short skull and nose). It is believed that these breeds are more susceptible to development of chemodectomas because of low oxygen concentrations and genetic mutations. This theory is further supported by higher prevalence of chemodectomas in people who live at higher altitudes. While these tumors are rare in dogs, they are more common in short-nosed breeds and affected dogs are normally eight years or older and males are more likely to develop these tumors than females. In dogs, tumors are most common in the aorta.

Chemodectomas are tumors of the tumors of the chemoreceptors (sensory extensions of the peripheral nervous system in the blood vessels that detect changes in the blood chemical levels, such as carbon dioxide, oxygen, and blood pH). These include both benign (non-cancerous) and malignant (cancerous) tumors, and develop primarily in the aortic (heart) area and carotid artery. In animals, chemodectomas are more common in the heart, while chemodectomas in the carotid artery are more common in humans.  Based on this known information, your veterinarian will diagnose after the following steps are taken.

• Physical exam
• Blood tests
• Serum chemistry profile
• Urinalysis
• X-Rays of the chest
• Electrocardiogram
• Echocardiography
• Histopathology (microscopic exam of tumor tissue)

As with most cancers, chemodectomas are difficult to treat, and the prognosis is not good. While surgical removal and additional therapies can be attempted, it’s always difficult to tell if the entirety of the tumor has been removed. In most cases, whether the tumor is benign or malignant, removal or shrinking of the tumor will be necessary to avoid continued functional disturbances. Options for relief of functional disturbances include:

• Radiation
• Surgical removal of the tumor

If surgery is completed, your pet will need to be kept from messing with the incision site and this site will need to be regularly cleaned and kept dry. Any lost stitches, significant swelling, or excessive bleeding should be reported to your veterinarian. Your dog will need to be routinely evaluated to monitor healing, in addition to checking for potential recurrence or spread of the cancer. In addition, if the tumor is benign and some remains after surgical removal or radiation, monitoring may be required to ensure no further functional disturbances occur.