Brain tumours can occur in dogs, just as in people, and account for 2-5% of all canine cancers. When they happen, they can be devastating. As although there are many different types of tumour, most are eventually fatal, with or without treatment. Here we will cover some basics about brain tumours, which enable us to later navigate some of the difficulties associated with picking up the signs and diagnosing them.  

What are brain tumours?

A tumour is a growth of abnormal cells within a body tissue, in this case the brain. Tumours originating from the brain cells are known as primary brain tumours. Tumours that occur because of spread of cells from a tumour elsewhere in the body are called secondary brain tumours and are less common in dogs.  

Brain tumours are further categorised depending on the type of brain cells they originate from, how they appear under a microscope (histology), and how aggressively they behave. Some commonly occurring ones in dogs are;

  • Meningiomas, which are tumours originating from cells of the lining of the brain
  • Ependymoma, tumours that originate from the lining of part of the brain called the ventricle
  • Choroid plexus tumours, originating from the choroid plexus
  • Gliomas, tumours of the cells (glial cells) that create brain function itself
  • Pituitary tumours arising from pituitary cells

Brain tumours can occur in any breed, age, and sex of dog. However, they are seen more frequently in dogs over the age of 5, and in certain breeds. Short-nosed (brachycephalic) breeds more commonly suffer from glial and pituitary tumours. Meningiomas occur most frequently in long-nosed breeds. Breeds such as the boxer, golden retriever, Doberman pinscher, Scottish terrier, and old English sheepdog develop brain tumours more than other breeds.

Why does this all matter?

Signs occur with brain tumours for many reasons. Understanding that there are different types of tumour, affecting different functions of the brain. Equally, they can grow at a range of paces and in different parts of the brain. All of this helps us to understand why signs also vary. 

Abnormal tumour cells physically encroach on normal cells, reducing their function. New tissue may affect blood flow causing further cell death and function loss. Signs will depend on the function that cell should be playing. 

The limited space within the skull means pressure can build up as the tumour grows, leading to more cell death and potentially swelling of the brain tissues (cerebral oedema). Pressure can even cause hydrocephalus and herniation of the brain, further adding to signs. 

How the tumour behaves also affects what and when signs will occur. Primary brain tumours are often slow growing, giving the brain a chance to adapt to pressure changes. So, signs may be subtle at first, progressing rapidly when the brain can no longer compensate. With fast-growing tumours, the brain cannot compensate. These pets may skip the subtle signs, developing severe signs very quickly. 

How can I tell if my dog has a brain tumour?

You can now see that signs will vary depending on the type of cells affected (location), the size, and the speed of growth of a tumour. 

For many dogs, the signs will be so vague they will almost certainly go unnoticed. They may hide away more, be less active or not want to be handled. Signs like this are not likely to be noticed, or if noticed, could easily be attributed to having an off day, the weather, or a new baby in the house, for example. There are a thousand and one reasons why a pet’s behaviour can subtly change from day to day that wouldn’t involve brain tumours. 

Some dogs will have more obvious signs such as seizures. Seizures can be general, affecting the whole brain causing a classic ‘fit’, or focal, just affecting one part of the brain, thus one part of the body. An abnormal movement in a limb, for example. A brain tumour is just one possible cause for seizures. 

There might be signs specific to tumour location. Reduced sensation, weakness, loss of balance or staggering, visual impairment or blindness, and changes in sense of smell can happen. These signs may be subtle or severe. They could also be caused by other conditions. 

The tumour may have the secondary effect of increasing pressure in the brain and causing swelling. Dogs may show more obvious behaviour alterations, appear vacant, irritable, or lethargic. They might walk in circles compulsively or press their head against something. Because initial signs of brain tumours can be so vague, it’s often these secondary effects that alert dog-owners to take their pet to a vet. 

What will my vet do?

Your vet may notice abnormalities in a neurological examination, but that’s not always the case. If the signs and examination are suspicious, your vet may discuss referral to a neurologist for further testing, such as MRI/CT, under anaesthetic to rule it out. X-rays are not helpful for looking at the brain. 

Tumour location and size helps the vet guide you on the outlook and treatment options. A biopsy would increase the accuracy of this guidance further. 

What if my dog does have a brain tumour?

If the tumour is superficial, surgery may be an option. This would also allow for a biopsy and definitive diagnosis. Some tumours may respond to radiotherapy. A combination of surgery and radiotherapy may be used, alongside medical treatment to reduce symptoms.

The aim is increased lifespan and quality of life, not usually to cure. The increase in lifespan depends largely on the sort of tumour but is usually weeks and months rather than years. If surgery is possible, it’s often risky. Surgery or radiotherapy involves several vet trips and can be a financial burden, even with insurance.

Owners may choose to simply manage the signs for as long as possible, using anti-inflammatories and anti-seizure medications, until it’s sadly necessary to opt for euthanasia. Many owners opt out of having the diagnostic tests done in the first place given the costs involved, the anaesthetic risks and outlook if a tumour is confirmed. Unfortunately, whatever is done the outlook is sadly quite poor.

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