Brain tumours in dogs: symptoms, tests and treatment

Overview

Brain tumours are a group of different diseases with varying growth rates and treatment options. Meningioma, a tumour of the membranes around the brain, is the most common primary brain tumour in dogs. It accounts for about 45% of primary canine brain tumours. Gliomas, arising from the brain's supporting cells, are also common.

Meningiomas usually grow slowly, but aggressive forms also occur. Even a tumour classified as benign on tissue examination can be life-threatening within the skull's confined space. The exact cell type is confirmed from a tissue sample.

Primary brain tumours are usually solitary masses. Tumours in the brain may also arise from the pituitary gland or the choroid plexus within the brain's ventricles.

Causes

A tumour can start inside the skull or spread there

The exact cause of most canine brain tumours is unknown. A primary tumour arises from cells of the brain or its surrounding structures. A glioma grows from the brain's supporting tissue. A meningioma originates in the meninges outside the brain tissue itself.

A secondary tumour may be a metastasis that has spread through the blood from elsewhere. In dogs, haemangiosarcoma is one example of a cancer that can spread to the brain. A tumour can also extend directly into the skull from the nasal cavity or adjacent tissues.

Some tumours of the brain's ventricles can spread through cerebrospinal fluid to other parts of the central nervous system. Spread of a primary central nervous system tumour outside that system is rare.

Symptoms arise from the tumour and its surroundings

A tumour may invade nerve tissue or compress nearby structures. Swelling can develop in the surrounding brain. A tumour can obstruct cerebrospinal fluid circulation and cause hydrocephalus. The skull's bones confine the space, so a growing mass cannot expand freely.

A tumour can also disrupt local blood flow in the brain. Local tissue death may develop in the tumour area. Widespread swelling and pressure effects can mask signs of a localised lesion.

Risk factors

Brain tumours are found particularly in middle-aged and older dogs. Median age at onset is about 9 years. Meningiomas occur most often in dogs over 7 years old. However, a young dog can also have a tumour.

Short-skulled dogs have an increased risk, particularly of gliomas. Meningiomas are found more often in large dogs with long skulls. No clear overall sex predisposition to nervous system tumours has been established.

Post-mortem studies have found tumours inside the skull in about 2–5% of dogs examined. This figure describes dogs examined after death, rather than the chance of disease in all living dogs. Gliomas can occur in dogs as young as 6 months.

Typical symptoms

Symptoms may develop slowly or start suddenly, and their severity can fluctuate. They usually progress as the tumour grows.

• Your dog has a seizure, or previous seizures recur.

• Learned routines are forgotten, interest in the surroundings decreases or behaviour changes.

• Your dog circles compulsively or wanders restlessly.

• Vision or awareness of one side deteriorates, and your dog bumps into obstacles.

• Balance worsens, your dog tilts its head or falls sideways.

• Steps become unusually high or exaggerated and the body sways.

• Swallowing, voice or eye movements may change.

A forebrain tumour may initially cause seizures alone. Cerebellar damage may cause poor coordination despite normal muscle strength. Brainstem damage can impair both balance and strength on one side of the body.

Appetite and drinking may increase or decrease when forebrain function is disrupted. A cerebellar head tremor may worsen as your dog reaches for food and disappear when it relaxes. Balance problems may include involuntary back-and-forth eye movements, known as nystagmus.

Complications and consequences

Pressure, swelling and associated problems

Raised pressure inside the skull can displace brain tissue, causing herniation. Severe brainstem damage can progress to paralysis, coma and death. Swallowing difficulties increase the risk of food or water entering the airways and causing aspiration pneumonia.

A prolonged seizure can cause a rise in body temperature and oxygen deficiency. Finding a brain metastasis means cancer has spread from its original site.

The outlook also depends on tumour location

Median survival in dogs given treatment to relieve brain tumour symptoms has been 69 days. In another group receiving symptomatic care, median survival was 2 months from the imaging diagnosis. In a study comparing locations, median survival for tumours in the brainstem and cerebellar region was 28 days. The corresponding median for tumours in the cerebral hemispheres was 178 days.

Diagnosis at the vet

Examination locates the source of symptoms

The vet assesses alertness, movement, awareness of limb position and cranial nerve function. This helps locate the part of the nervous system causing symptoms. Other diseases damaging the same area can cause similar signs.

Blood cell counts, biochemistry and urinalysis help rule out other diseases and assess anaesthetic risk. Chest imaging and abdominal ultrasound look for tumours or metastases elsewhere in the body.

A brain tumour should be considered as a cause even when a first seizure starts after 4 years of age.

MRI shows the mass and surrounding tissue

Brain MRI is the first-choice imaging method. Dogs undergo it under general anaesthesia. Images assess the tumour's location, size and margins, as well as swelling and disrupted fluid circulation.

Ordinary skull X-rays do not usually show soft tissue tumours. CT can help assess bone changes in particular. MRI generally shows brainstem and cerebellar changes better than CT.

Contrast may show tumour margins and internal details more clearly. A glioma can also resemble a brain infarct, haemorrhage or immune-mediated inflammation on images. Well-defined margins or contrast uptake therefore do not, by themselves, establish cell type.

Samples refine the presumptive diagnosis

Imaging may suggest the likely tumour type, but an abscess or other inflammation can look similar. A biopsy or sample taken during surgery confirms cell type and helps assess malignancy. Cerebrospinal fluid may contain increased protein or inflammatory cells. Tumour cells are only rarely found in the fluid.

Fluid collection is planned only after imaging, as a pressure change can cause brain herniation. Biopsy also carries risks, including seizures or neurological deterioration.

A meningioma may be classified on tissue examination as grade I, benign; grade II, atypical; or grade III, malignant. The grade can help assess its likely behaviour.

Treatment

Symptom relief is part of every treatment approach

The vet plans treatment according to tumour location, type and your dog's overall condition. Symptomatic care aims to control seizures, pressure, inflammation and pain. Corticosteroids can reduce swelling around the tumour. Seizure medicines may include phenobarbital or, in an acute situation, diazepam.

Surgery and radiotherapy

Surgery aims to remove the whole tumour or reduce it as safely as possible. Normal brain tissue is preserved because damage can cause significant permanent deficits. Complete removal of a canine meningioma can be difficult when it invades surrounding tissue.

Radiotherapy can be used alone or alongside surgery. It may suit tumours that cannot be removed safely. Risks include repeated anaesthesia and delayed radiation damage to brain tissue.

Surgery also provides a tissue sample and may reduce symptoms caused by the mass even if some tumour remains. With gliomas, microscopic tumour cells may remain in tissue after the visible mass has been removed. Stereotactic radiotherapy targets radiation very precisely to a defined area.

Possible surgical complications include uncontrolled seizures and air accumulating inside the skull. Radiotherapy can also cause skin and eye effects, such as permanent hair loss or cataracts.

Chemotherapy and investigational treatments

Medicines used for gliomas include temozolomide and lomustine. Hydroxycarbamide has been used for meningiomas, but there are no large canine studies of its effectiveness as the sole treatment.

Delivering treatment directly into brain tissue can bypass the blood–brain barrier's restrictions on drug entry.

Other research includes immune treatments directed at the tumour and methods using viruses that destroy tumour cells.

Survival figures apply to particular patient groups

Median survival of about 7 months has been reported for dogs undergoing meningioma surgery. A summary of reports on surgery for different brain tumours gave a median of 312 days. Median survival after combined surgery and radiotherapy for meningioma has ranged from 11–28 months. For tissue-confirmed meningiomas treated with radiotherapy alone, medians were 11.5–19 months.

Across all brain tumour types treated with radiotherapy, reported medians ranged from 139–906 days. The summary median of these reports was 351 days. Chemotherapy effectiveness is limited partly by the blood–brain barrier, which makes it harder for a drug to reach its target.

Prevention

There is no known way to prevent a brain tumour from developing. The causes of most tumours remain unclear. Once disease is diagnosed, prevention focuses on complications such as seizures and raised pressure inside the skull. Abruptly stopping seizure medication can increase seizures or trigger a cluster.

Addressing swallowing difficulties is part of managing aspiration risk.

Changes to seizure medication are planned with the vet; independent adjustments are not recommended. Medication management includes monitoring adverse effects and regularly reassessing the response.

Important for dog owners

Keep a diary of seizures, walking, balance, vision, eating and behaviour. Record when a change began and how it progressed. Bring a video of an everyday abnormality if you can record it safely.

For seizures, record the time, duration and your dog's condition before and afterwards.

Agree with the care team which changes require contact and how to assess your dog's abilities at home. Note good days as well, so the overall picture includes more than individual difficult moments.

Follow-up includes regular examinations and repeat imaging when appropriate.

Assess whether your dog can rest, eat and move normally at home. Record situations in which it needs help, along with any restlessness or changes in interaction. This helps relate treatment goals to your dog's own daily life and abilities.

Frequently asked questions

Does a first seizure mean my dog has a brain tumour?

No: other structural brain diseases, poisoning or low blood sugar can also cause seizures, for example. A first seizure in a dog over 5–6 years old is a reason to investigate a possible tumour too. Blood tests also help investigate diseases elsewhere in the body.

Can a benign brain tumour be dangerous?

Yes: even a benign tumour growing inside the skull can compress the brain and raise pressure. A growing meningioma can therefore cause severe neurological damage or death. Treatment options also depend on tumour location. Swelling may additionally develop in the brain tissue around the tumour.

Does MRI confirm the tumour type?

MRI may create a strong suspicion, but the exact cell type is confirmed from a tissue sample. Inflammatory lesions can resemble tumours on images. Examining the sample also provides information about malignancy. Biopsy safety is assessed individually because sampling can worsen neurological signs.

How long can a dog live with a brain tumour?

In a group receiving symptomatic care, median survival was 69 days. For meningiomas treated with combined surgery and radiotherapy, medians of 11–28 months have been reported. Tumour type, location and tissue damage affect the outlook. A median is the middle survival time in a patient group; it does not determine an individual dog's remaining time.

Can diet prevent a brain tumour?

There is no known way to prevent brain tumours. The causes of most remain unclear. If a tumour is diagnosed, treatment goals include removing or reducing it and controlling swelling and pressure. Seizures are treated with separate medication when needed, according to the vet's plan.