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The animal may seem less interested in usual routines, more withdrawn, or occasionally irritable in situations that previously caused no concern.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
Options & trade-offs
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