Brain

Changes in behaviour encompass alterations in alertness; loss of learnt commands; loss of house training; disorientation; decreased social interaction; altered personality. Behaviour is altered by general health: a common way of showing pain or illness is for an animal to withdraw from social contact.

Psychological disturbances, such as fear, anxiety, can also alter behaviour and can lead to the pet developing stereotypic activities, such as pacing in circles, head nodding, that mimic structural brain disease.

Cognitive dysfunction syndrome (“senility”) is recognised in elderly cats and dogs. It is important to rule out other causes of cerebral disease such as brain tumours and inflammation.

Neurologists are often called upon to assess animals for evidence of structural brain disease before the pet is diagnosed as having a psychological disturbance or is affected by senility. Behaviour changes can happen slowly and are therefore difficult for the pet owner to recognise. Consultation with a neurologist is a cost-effective way to determine if further investigations are required.

Hydrocephalus describes the enlargement of the cerebrospinal fluid-filled chambers (ventricles) within the brain. It may be caused by a congenital malformation, or it may occur secondarily to a tumour or inflammation blocking the outflow of the CSF. Treatment of congenital hydrocephalus is not required if the dog has normal behaviour and mentation.

An absence of thirst is an unusual problem in animals. It can lead to elevated sodium and this alters brain function. Agenesis of the corpus callosum is a rare congenital malformation in which a bundle of white matter fibres is missing. Affected dogs, often SBT and schnauzers, can present with tremors, seizures, or altered mentation as well as adipsia or hypodipsia.

Enlargement of the quadrigeminal cistern (“quadrigeminal cysts”) can be an incidental finding on MRI of the head. Knowledge of expected clinical signs and the ability to rule out other causes of those signs is vital to make a correct diagnosis.

MRI of the brain has increased our understanding of neurological disease in animals but it is important to always consider whether or not an abnormal structure has clinical relevance and requires intervention.

Brain tumour diagnosis and treatment has improved significantly in the last few decades.

“Primary” tumours (cancer) arise from uncontrolled multiplication of brain or meningeal cells. “Secondary” tumours are those that have spread (metastasized) from elsewhere in the body. Both types have a detrimental effect so it could be said that all brain tumours are “malignant”.

As the tumour enlarges, the pressure within the skull increases which leads to altered mental function. A sudden onset of “symptoms” is often due to secondary changes such as oedema (“tissue swelling”) and this may need emergency treatment before an MRI of the head is done.

Most brain tumours will be visible on an MRI. There are rare situations when this is not the case. Imaging the brain is done to exclude other causes of brain disease which have a different prognosis.

Palliative care, surgery, or radiation are the three chief treatments offered. With the exception of some feline meningioma patients, it is rare to “cure” a pet of a brain tumour. It is important to obtain a diagnosis in order to give the best advice to the client on how to manage their pet’s health.

Meningitis occurs when the covering of the nervous system (meninges) becomes inflamed. This is a painful condition. Typical signs include: fever, lethargy, depression, inappetence, an arched back and a reluctance to move the neck which gives the dog a stiff appearance. The signs may wax and wane.

Meningitis in dogs is not typically contagious ie it will not spread to other dogs in the household or to humans.

If the brain is also inflamed (meningoencephalitis) derangement of balance, alertness, behaviour, vision and gait can occur.

How is it diagnosed?

Cerebrospinal fluid (CSF) is collected and the cell counts, protein level and cytology are assessed. The procedure requires general anaesthesia and can be performed at the base of the spine (”lumbar tap”) or the back of the head (“cisternal tap”), or both.

Tests to check the pet for infections may be done on the blood, spinal fluid, or both. Certain tickborne diseases are becoming a problem within the UK.

MRI of the head and spinal cord is required in many cases.

How it is treated?

In some animals the underlying cause is an immune reaction. Finding the underlying trigger for this reaction is difficult and requires extensive testing.

Daily medication in tablet form is often required over several months. Each case is different and the care will be tailored to your pet’s needs.

What are seizures?

Seizures are the physical manifestation of excessive synchronous electrical discharge in the brain.

Idiopathic epilepsy is the term used to describe spontaneous seizures without an identified cause. In some dogs the underlying fault is genetic but in many breeds a DNA mutation has not been proven.

It isn’t usually possible to determine the cause of a seizure from its appearance. Typically, there is a loss of consciousness or an altered responsiveness to the environment and autonomic (i.e. involuntary “visceral”) signs often occur e.g. excessive drooling; dilated pupils; passing urine or faeces. Filming of abnormal events by owners helps us better define what is going on. In some cases a loss of balance, pain, severe weakness, tremor disorders, or even extreme itchiness can be mistaken for a seizure.

How does the specialist discover the cause of the seizures?

Abnormal function of the brain can be altered by diseases elsewhere in the body such as a low blood sugar, high blood pressure, abnormal liver function, and abnormal electrolyte concentrations. Your local vet usually performs blood tests prior to referral. Sometimes these need to be repeated as underlying disease can worsen or be difficult to find on the more routine tests.

Why is the neurological exam so important?

Examination of the pet’s nervous system assesses its normal functions and requires careful observation and experience in performing the various tests and interpreting the results. Looking at the pupils, assessing vision, movement, and spinal reflexes as well as checking for pain and weakness all takes time. The length of the consultation allows this to be done without rushing the pet and causing unnecessary stress.

How is MRI useful?

MRI is an imaging technique with the ability to look within the skull and create finely detailed images of the brain and surrounding tissues. This allows the neurologists and radiologists to check for diseases such an inflammation, meningitis, tumours, bleeding, infarction (“strokes”) and malformation. It is possible for animals to have abnormal changes seen on MRI that are not clinically important and so experience in this modality is vital to plan future treatment.

Will my pet need anticonvulsant medication?

The neurologist will make that decision together with you, based on the frequency and nature of the seizures. Side effects and benefits of medication are discussed. Monitoring of drug levels and future management decisions are done in concert with you and your local vet.

Syringomyelia is the abnormal formation of fluid-filled channels within the spinal cord. It is caused by an abnormality in circulation of the cerebrospinal fluid (CSF).

How is it diagnosed?

MRI is used to detect changes within the spinal cord. Different MRI settings (“sequences”) are used to differentiate between fat, fluid, blood, spinal cord. Syringomyelia is secondary to an abnormality and so MRI of the spinal cord and brain are required to find the underlying cause.

In some cases CT scans and radiographs may be required if a malformation of the vertebrae at the back of the head is suspected. CT scans take cross-sectional images and are particularly good at finding abnormalities with bone.

What causes syringomyelia?

Interruption of the normal cranial to caudal flow of CSF can cause syringomyelia. This interruption may be due to congenital malformations at the back of the dog’s head or where the head joins the neck. This is common in brachycephalic breeds.

It may occur after spinal cord trauma, intervertebral disc extrusion, or be caused by neoplasia of the spinal cord or the brainstem.

What is vestibular syndrome?

The vestibular system controls the balance. Derangement of balance shows up as an inability to walk a straight line: affected animals can fall backwards, forwards or sideways, roll, lean, or stumble. The head can be held on one side (head tilt) and the eyes can flick spontaneously (nystagmus). A loss of balance can cause the pet to vomit and to be distressed by an inability to stand.

What causes vestibular syndrome?

The balance is detected by “peripheral vestibular” structures within the inner ear. The nerve pathways then enter the brain (“central vestibular”). Damage to the peripheral or central structures may cause the same “symptoms”.

Inflammation of the brain commonly results in a loss of balance. Ear infection, use of certain antibiotics, tumours, hypothyroidism, “strokes” in the brain, and old age change to the balance receptors can also damage the vestibular apparatus.

The neurologist will discuss your pet’s recent health with you and perform a neurological examination in order to make a judgement on where the problem lies and what possible causes (“differential diagnoses”) may be happening.

Will my pet recover?

The chance of recovery (prognosis) can be excellent. This is important to remember as the initial stages of balance loss are often distressing to see. Further tests (blood tests; MRI of the head; spinal fluid analysis) may be required for diagnosis.