CONDITION
Brain Tumours
A brain tumour is an abnormal growth of cells within the skull — either arising from the brain tissue itself, the membranes around it, or spreading from elsewhere in the body. These growths can press on surrounding structures, disrupt normal signalling, or alter the environment in which the brain works. Owners often arrive at this question after noticing changes that seem to come from the head: seizures that begin in an older animal, shifts in behaviour or personality, changes in balance or coordination, or patterns that suggest something affecting how the brain interprets or sends information. The signs can be subtle at first, or they can appear more suddenly, and they tend to reflect which part of the brain is involved. This page explores what these changes can look like when they first appear, the mechanisms by which tumours affect the brain, how the picture is built through imaging and other investigations, and the range of approaches — from monitoring to surgery, radiotherapy, and supportive care — that exist depending on the tumour, its location, and the individual animal.
Why this matters now
Brain tumours tend to appear in middle-aged to older dogs and cats, with most cases diagnosed after seven years of age. Certain breeds show higher rates — boxers, golden retrievers, bulldogs, and Boston terriers among dogs; domestic shorthairs are most commonly affected among cats. The condition can also appear in younger animals, though this is less common, and some tumour types show stronger age or breed associations than others.
The way a brain tumour evolves depends on the type, location, and how quickly the cells are dividing. Some grow slowly over months or years, producing subtle changes that the owner may attribute to ageing or personality. Others progress more rapidly, with signs appearing or worsening over weeks. The progression often reflects increasing pressure within the skull, displacement of surrounding tissue, or growing disruption to the circuits that control movement, sensation, behaviour, or awareness.
Signals & patterns
Early signals
Seizures beginning in an older animal
A dog or cat with no previous history of seizures may begin having episodes after the age of five or six. The seizures can be generalised or more localised, and they often prompt investigation into what has changed in the brain.
Subtle changes in behaviour or temperament
The animal may seem less interested in usual routines, more withdrawn, or occasionally irritable in situations that previously caused no concern. These shifts can be gradual and easy to overlook at first.
Mild clumsiness or altered coordination
An owner may notice the animal misjudging jumps, drifting slightly to one side when walking, or seeming less sure-footed on stairs. The changes can be intermittent and mild enough to be dismissed as stiffness or age-related slowing.
Pressing the head against walls or furniture
The animal may stand with its head resting against a solid surface for longer than seems normal. This can reflect discomfort, altered awareness, or pressure inside the skull.
Changes in sleep or alertness patterns
The animal may sleep more during the day, seem slower to respond when called, or appear disoriented on waking. These patterns can be subtle and develop over weeks.
Later signals
Circling or compulsive pacing
The animal may walk repeatedly in one direction, often in tight circles, or pace without clear purpose. This typically reflects increasing pressure or involvement of areas controlling movement and spatial awareness.
Vision changes or apparent blindness
The animal may bump into objects, hesitate in familiar spaces, or show a reduced response to movement in one or both visual fields. This can occur when the tumour affects the pathways that process sight.
Weakness or paralysis on one side
One side of the body may become weaker or lose coordination, and in some cases the animal may be unable to rise or support weight evenly. This reflects involvement of the motor areas of the brain.
Increased frequency or severity of seizures
Seizures that were occasional may become more frequent, last longer, or occur in clusters. This often signals progression of the underlying process or increasing irritation of brain tissue.
Click to read about the biological mechanisms
How this is usually investigated
The investigation of a suspected brain tumour typically begins with a detailed history and physical examination, looking for patterns in the onset and progression of signs. Neurological examination can help localise the problem to a particular region of the brain, which in turn guides the choice of imaging and further tests. Advanced imaging is usually needed to visualise the mass itself, and additional tests may be used to assess overall health, rule out other causes, or guide decisions about intervention.
Neurological examination
Blood tests and biochemistry
Magnetic resonance imaging (MRI)
Computed tomography (CT)
Cerebrospinal fluid analysis
Options & trade-offs
Management of a brain tumour is usually tailored to the type and location of the mass, the rate of progression, the age and general health of the animal, and what feels workable for the household. Approaches often combine methods that address the tumour itself with those that manage the effects it is causing, such as swelling or seizures. Different combinations suit different situations, and there is variation in what owners find acceptable and what an individual animal tolerates.
Symptomatic management
This involves treating the signs caused by the tumour rather than the tumour itself. Medications to reduce brain swelling, such as corticosteroids, can relieve pressure and improve comfort or function in the short to medium term. Anti-seizure drugs are used when seizures are part of the picture. Some owners and vets choose this approach when imaging has not been pursued, when other interventions are not suitable, or as part of a broader plan alongside other treatments.
Trade-offs: Symptomatic treatment can improve quality of life and may extend functional time, but it does not slow tumour growth. Corticosteroids can have side effects with prolonged use, including increased thirst, appetite, and susceptibility to infection. The duration of benefit varies widely.
Surgical removal
Surgery to remove or reduce the size of a brain tumour is possible in some cases, depending on location, tumour type, and accessibility. The procedure is carried out by a specialist neurosurgeon and involves opening the skull to access the mass. Removal can reduce pressure, improve signs, and in some cases provide tissue for definitive diagnosis.
Trade-offs: Surgery carries risks associated with anaesthesia, bleeding, infection, and the potential for damage to surrounding brain tissue. Not all tumours can be fully removed, and some locations are not accessible. Recovery can be prolonged, and surgery is often combined with other treatments such as radiotherapy.
Radiotherapy
Radiation therapy uses targeted beams to damage tumour cells while attempting to spare surrounding normal tissue. It is typically delivered in multiple sessions over several weeks and may be used after surgery, as the sole treatment, or to manage tumours that cannot be surgically removed. Some tumour types respond more predictably than others.
Trade-offs: Radiotherapy requires repeated anaesthesia, access to specialist facilities, and referral. Side effects can include skin changes, fatigue, and delayed effects on surrounding brain tissue. The response varies with tumour type, and the treatment may extend functional time rather than provide long-term control.
Chemotherapy
Chemotherapy involves drugs that target dividing cells, and it is used for certain tumour types, particularly lymphoma involving the brain. It may be given alone or alongside other treatments. The blood-brain barrier limits which drugs reach effective concentrations in the brain, so protocols are chosen with this in mind.
Trade-offs: Not all brain tumours respond to chemotherapy, and the approach is more commonly used for specific tumour types. Side effects vary by drug and can include nausea, bone marrow suppression, and effects on other rapidly dividing cells. The treatment requires monitoring and may involve repeated visits.
Monitoring and supportive care
Some owners choose a period of close observation, particularly when signs are mild or when investigations have not yet been pursued. Adjustments to the home environment, activity levels, and feeding routines can help maintain comfort and safety. This approach may be combined with symptomatic medications or may be the sole plan when other interventions are not pursued.
Trade-offs: Monitoring allows time to observe the pattern and pace of change, but it does not alter the course of the tumour. Signs may progress during this period, and decisions about further intervention can become more complex as function declines.
Common misconceptions
"If a brain tumour is found, nothing can be done."
There are several approaches that can improve quality of life, reduce signs, and in some cases extend functional time. The range includes surgery, radiotherapy, medications to manage swelling and seizures, and combinations of these. The suitability of each depends on tumour type, location, and the individual animal, but the presence of a tumour does not mean all options are closed.
"Seizures in an older animal always mean a brain tumour."
Seizures beginning in middle age or later can have many causes, including brain tumours, but also metabolic disturbances, liver or kidney disease, inflammatory conditions, infection, and sometimes no identifiable structural cause. Imaging and other tests are needed to build a fuller picture, and many animals with late-onset seizures do not have a tumour.
"Behavioural changes in older pets are just part of ageing and not worth investigating."
Ageing can bring changes in behaviour, but new or progressive shifts — particularly if one-sided, accompanied by other neurological signs, or changing over weeks rather than years — can reflect an underlying problem that may be manageable. Brain tumours, cognitive decline, pain, metabolic disease, and other conditions can all present with behavioural change, and distinguishing between them often requires investigation.
Related conditions
Glioma in Dogs
Glioma is one specific type of brain tumour that arises from the supporting cells within the brain tissue itself, rather than from the surrounding membranes or other structures. When a brain tumour is identified on imaging, determining whether it is a glioma often requires consideration of its location, appearance, and sometimes biopsy findings.
Meningioma
Meningioma is another common type of brain tumour in dogs and cats, but it arises from the protective membranes surrounding the brain rather than from brain tissue itself. The distinction between meningioma and other brain tumours can influence decisions about surgery and prognosis, as meningiomas tend to be more accessible and, in many cases, slower-growing.
Pituitary Macroadenoma
A pituitary macroadenoma is a growth at the base of the brain that can produce signs similar to those of other brain tumours, particularly when it becomes large enough to press on surrounding brain tissue. Both conditions may present with changes in behaviour, vision, or coordination, and imaging is often needed to distinguish between them.
Vestibular Disease
Vestibular disease can produce sudden changes in balance and coordination that may initially raise the question of a brain tumour, particularly in older animals. While vestibular signs often arise from problems in the inner ear or nerve pathways rather than from a mass within the brain, imaging is sometimes needed to rule out a tumour affecting the vestibular system.
Granulomatous Meningoencephalomyelitis (GME)
Granulomatous meningoencephalomyelitis is an inflammatory condition of the brain that can present with signs very similar to those caused by a brain tumour, including seizures, behaviour changes, and altered coordination. Distinguishing between inflammation and a tumour typically requires advanced imaging and, in some cases, analysis of cerebrospinal fluid or tissue samples.
Understanding how a brain tumour fits within the broader picture of an ageing nervous system can be useful, particularly when thinking about what else might explain similar signs or what other changes might appear over time. The pages on seizures and cognitive changes explore overlapping territory, and the longevity section of this resource offers context on the balance between investigation, intervention, and quality of life as animals grow older. These are conversations that often evolve over time rather than being settled in a single appointment.