Tumours are the abnormal growth of cells and can occur anywhere in the body. Brain tumours are rare, with an incidence of 0.0035, and account for 2.2% of all tumours [1]. They can be benign or malignant, primary or secondary. A benign tumour does not invade neighbouring tissue or spread to other parts of the body and has well-defined boundaries. Malignant tumours have poorly defined boundaries and in most cases, can spread to other parts of the body or invade neighbouring tissue. While brain tumours don’t spread to other parts of the body, like most malignant tumours, they can spread to other parts of the brain and spinal cord.
- Primary tumours are just that, a tumour that has developed at the site it is located, in this case, the brain or lining of the brain (meninges).
- A secondary tumour is a tumour that has originated elsewhere in the body and spread. Melanomas, hemangiosarcoma and mammary carcinomas are the most common causes of secondary brain tumours.
Approximately 70% of brain tumours are primary.
Brain tumours occur most often in cats over nine years of age, and there is a higher incidence in short-coated male cats.
Types of brain tumour
The brain is an incredibly complex structure with many types of cells, all of which can potentially develop tumours. Types of brain tumour include the following:
Meningioma – The most common type of brain tumour in cats, meningiomas are benign tumours that originate from the meninges, which is the membrane that surrounds the brain.
Ependymoma – A primary tumour originating from the ependyma cells which line the ventricles of the brain and the central part of the spinal cord.
Glioma – Benign or malignant tumour originating from the glial cells, which are supporting cells of the central nervous system which are made up of astrocytes, oligodendrocytes and microglia.
Choroid plexus tumour – A benign or malignant tumour arising from the choroid plexus, which are cells responsible for the production of cerebrospinal fluid.
Medulloblastoma – A rare tumour that originates in the external germinal layer of the cerebellum.
Olfactory neuroblastoma – An aggressive tumour of the immature neuroblast cells, which are the precursor of neurons.
Brain tumours can develop in cats of all ages; however, they are seen most often in older cats.
Causes
- Genetics
- Dietary
- Environmental
- Viral infections
In most cases, it is not possible to identify the cause.
Symptoms
Brain tumour symptoms can vary depending on the size, type, and location of the tumour while other symptoms will be the same for different tumours. Tumours affect the brain in several ways; they destroy brain tissue, compress normal tissue and increase pressure within the brain, which of course is encased in the hard skull.
Some symptoms can be specific to the particular part of the brain affected, but it is also important to remember that as a tumour increases in size, it can push on other areas of the brain which can lead to the development of additional symptoms.
Brainstem:
The brainstem is the region of the brain that connects the cerebrum with the spinal cord and controls the flow of messages from the brain to the rest of the body and controls autonomic functions such as respiration, heartbeat, digestion and pupil dilation and constriction.
- Muscle weakness
- Loss of balance
- Vision disturbances
- Droopy eyelids
- Dilated pupils
- Difficulty swallowing
- Nausea
- Vomiting
- Lethargy
- Seizures
- Change in voice
Cerebrum:
The cerebrum is the large, outer part of the brain located in the front of the skull and made up of two hemispheres that are connected by the corpus callosum. It controls thoughts, senses (visual, auditory, somatosensory, gustatory, and olfactory) and conscious movements.
- Behavioural changes
- Seizures
- Weakness
- Vision changes
Cerebellum:
The smaller region in the lower part of the brain, the cerebellum receives input from sensory systems of the spinal cord and coordinates voluntary movement such as walking, balance, and vocalisation.
- Loss of coordination (ataxia)
- Wide based stance
- Difficulty swallowing
- Head tremors
- Abnormal eye movements
- Change in vocalisation
General symptoms:
- Behavioural changes
- Seizures
- Head tilt
- Circling
- Loss of coordination (ataxia)
- Muscle weakness
- Nausea
- Vomiting
- Vision problems (walking into walls and furniture)
- Dilated (enlarged) pupils
- Change in appetite (eating less or more)
- Lethargy
If the tumour has spread to the sinuses, nasal cavity or eye, additional symptoms can include:
- Nasal discharge
- Eye swelling
- Nasal distortion
Diagnosis
Your veterinarian will perform a complete physical and neurologic examination of your cat and obtain a medical history from you including symptoms you have observed and how long they have been occurring.
Diagnostic workup:
Baseline tests: Complete blood count, biochemical profile and urinalysis to evaluate the overall health of your cat.
Computed tomography (CT) or magnetic resonance imaging (MRI) scans: These advanced imaging techniques evaluate the brain for tumours. Both procedures are performed under general anesthetic. In most cases, these will be at a specialist veterinary centre.
Chest and abdominal X-rays: To determine if the tumour has spread to the lungs or abdomen.
Biopsy: A biopsy of the tumour will be necessary to evaluate the type of cells the tumour is made up of as well as grade the tumour. Grading helps your veterinarian determine how advanced the tumour is.
Treatment
There are three primary treatments for brain tumours. The size, type, and location of the tumour all play a factor in the type of treatment your cat will receive as well as caregiver finances. Larger, and aggressive tumours have a poorer outcome as do cats with severe symptoms.
Surgery: To remove the tumour entirely or reduce the size of the tumour, which will alleviate symptoms. Unfortunately, not all tumours can be removed due to their location deep within the brain. Meningiomas are the easiest tumour to surgically remove due to their location on the brain surface and have a high success rate.
Radiation therapy: This procedure uses a high-energy radiation beam to specifically target tumours, shrinking and killing them. It is the treatment of choice for gliomas which are located deep within the brain. Radiation therapy is performed under general anesthesia in several small doses over several days.
Chemotherapy: A less common treatment for brain tumours as most chemotherapy agents cannot cross the blood-brain barrier. Those agents which can target brain tumours can be toxic to healthy brain tissue. Carmustine and lomustine are the most frequently used chemotherapy agents for brain tumours.
Supportive care: Corticosteroids such as prednisone to reduce inflammation, anti-seizure medications such as Phenobarbitol and analgesics to relieve pain.
Palliative care: The goal is to alleviate symptoms and improve the quality of life but not provide a cure.
Treatment can extend the life of the cat as well as relieve suffering, but in most cases, it is not curative.
Home care
Administer medications as prescribed by your veterinarian.
Make modifications to the home to make life easier. Install ramps, use baby gates to prevent accidents and screen all windows.
It is highly recommended the cat remain indoors or provide access to a safe cat enclosure.
Food, water, and comfortable beds should be within easy access of the cat.
Keep stress to a minimum.
Monitor your cat’s symptoms as well as food intake, if you notice any changes, speak to your veterinarian.
Prognosis
The prognosis will depend on the type of tumour, its location and treatment.
Median survival time means 50% of cats have survived past the time, and 50% have died.
Meningiomas have an MST of 2 years or more.
The MST of other tumours can vary greatly depending on the type and the location but can range from weeks or months to over a year.
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