Cat & Dog - Endocrine Tumours - Adrenal Medulla

These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout What is cancer. If not already performed your veterinary surgeon may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.

We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything, please do not hesitate to ask.

What are the adrenal glands?

The adrenal glands are located close to the kidneys. They are part of the body's endocrine (hormone) system, the glands of which also include the pituitary (in the brain), thyroid (in the neck), parathyroid (close to the thyroid) and Islets of Langerhans in the pancreas. Endocrine glands produce specialised chemicals called 'hormones'. These regulate and integrate many activities to maintain internal stability of the body. The hormones pass directly into the blood to affect target cells elsewhere. Hormones are also produced by many cells in other tissues.

Each of the two adrenal glands has two parts. The outer part (cortex) is controlled by a hormone (adrenocorticotrophic hormone, ACTH) from the pituitary gland. The cortex produces steroid hormones of several types.

The inner part (medulla) of the adrenal gland originates from the same cells that in the embryo form the nervous system, and therefore not surprisingly it produces neuroendocrine hormones (hormones which at on the nervous system) with effects similar to those of the sympathetic nervous system.

What are the tumours of the adrenal medulla?

Tumours of the medulla of the adrenal glands may be hyperplasias (non-cancerous cell overgrowths) or cancerous. Adrenal medullary tumours are rare but pheochromocytomas are the commonest type and are usually in middle aged to older dogs. Tumours of the nerve cells of the medulla are rare but benign adrenal ganglioneuromas occur in older animals and malignant adrenal neuroblastomas can develop in young animals. Few are diagnosed until late in the disease because, unlike tumours of the adrenal cortex, medullary tumours do not produce clinical signs. Approximately half spread to other parts of the body (metastasise).

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances which come together for the unfortunate individual.

We know little about the causes of tumours of the adrenal medulla.

Why has my animal developed this cancer?

Some animals have a greater tendency (genetic susceptibility) to cancer. Some breeds have far more cancers than others, often of specific types. Adrenal medullary pheochromocytomas are commonest in Boxer dogs.

How will these cancers affect my pet?

Small medullary pheochromocytomas usually have no clinical effect but approximately half are larger and invade the main vein (vena cava) returning to the heart. This impairs blood return from the hind legs. At least a quarter of the tumours spread to other organs, including the adjacent back bones. The tumours are occasionally functional (produce hormones) and induce high blood pressure, increased heart rate and enlargement of the heart. Medullary ganglioneuromas are usually benign but the neuroblastomas that develop in young animals and may spread through the body cavity.

How are these cancers diagnosed?

Cancer is often suspected from clinical signs. Radiographs (x-rays), ultrasound and MRI (magnetic resonance imaging) or CT (computerised tomography) scans may be useful in detecting the tumours, including metastases.

To identify the tumour type precisely, it is necessary to examine the tumour itself. This involves exploratory surgery, often with total removal of the tumour. The tissue samples are submitted for microscopic examination by histopathology. Specially prepared and stained tissue sections are made at a specialised laboratory where the slides are examined by a veterinary pathologist.

The histopathology report typically includes words that indicate whether a tumour is 'benign' (non-spreading, local growth) or 'malignant' (capable of spreading to other body sites). These, together with the origin or type of tumour, the grade (degree of resemblance to normal cells or 'differentiation') and stage (how large it is and extent of spread) indicate how the cancer is likely to behave.

The veterinary pathologist usually adds a prognosis (what will probably happen). This may include information on local recurrence or metastasis (distant spread).

What types of treatment are available?

Treatment for adrenal medullary tumours is surgical removal of the tumour.

Can these cancers disappear without treatment?

Cancer rarely disappears without treatment but as development is a multi-step process, it may stop at some stages. The body's own immune system can kill cancer cells but it is rarely 100% effective. Rarely, loss of blood supply to a cancer will make it die but this is rarely complete.

How can I nurse my pet?

After any surgery, you need to prevent your pet from interfering with the operation site and to keep it clean. Any loss of stitches or significant swelling or bleeding should be reported to your veterinary surgeon. You may be asked to check that your pet can pass urine and faeces or to give treatment to aid this. If you require additional advice on post-surgical care, please ask.

How will I know how the cancer will behave?

When histopathology is done, it will give your veterinary surgeon the diagnosis that also helps to indicate how a tumour is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread) for cancers.

When will I know if the cancer is permanently cured?

'Cure' has to be a guarded term in dealing with any cancer.

Most adrenal medullary tumours are large by the time they are diagnosed because few of them produce hormones and so there are no early clinical signs. Approximately half of these tumours will spread to distant organs (metastasise), metastatic cancers are rarely cured.

Are there any risks to my family or other pets?

No, these are not infectious tumours and are not transmitted from pet to pet or from pets to people.