However, enlarged ventricles alone do not establish the cause of symptoms or persistently raised pressure. Some animals have enlargement without noticeable symptoms. Assessment combines neurological findings, imaging and investigation of other brain diseases.
When to see a vet urgently
Go to an emergency vet immediately if your cat develops any of the following:
- reduced consciousness or failure to respond normally to the surroundings
- repeated seizures without recovery between them
- sudden loss of the ability to stand or walk
- balance problems or unusual behaviour after a head injury
Find an emergency vet near you and contact them. A cat with a head injury needs urgent assessment and should be moved as little as possible during transport.
Overview
Cerebrospinal fluid normally circulates through the brain's ventricles and subarachnoid space, providing nutrients and protecting brain cells. When fluid outflow is impaired or production becomes excessive, the ventricles enlarge and nervous tissue is damaged.
The ventricles are fluid-filled cavities inside the brain. The subarachnoid space lies between membranes surrounding the brain. Fluid passage can be blocked at a narrow point, enlarging the ventricles upstream of the obstruction. Impaired fluid absorption can also contribute to accumulation.
Loss of surrounding brain tissue can also enlarge the ventricles. In that situation, enlargement of a fluid cavity on imaging does not involve the same mechanism as blocked fluid pathways. Establishing this distinction affects whether surgery to improve fluid drainage can help that cat.
Causes
Hydrocephalus may be:
- Congenital: due to developmental abnormalities of the brain and skull, more common in short-skulled, or brachycephalic, breeds.
- Acquired: developing, for example, from the following:
- Head injuries.
- Brain tumours.
- Inflammation, such as encephalitis or meningitis.
- Consequences of parasitic infection.
- Abnormal skull development.
Encephalitis means inflammation of brain tissue, while meningitis affects the surrounding membranes. Neurological feline infectious peritonitis (FIP) is a particularly relevant underlying cause to investigate in cats. Inflammation can damage ventricular surfaces and fluid pathways. In some cases, no cause is identified despite investigation; this is called idiopathic hydrocephalus.
Congenital does not automatically mean a proven inherited disease associated with a single genetic defect. Harmful influences during foetal development can also be involved in central nervous system abnormalities. Investigating the cause therefore requires, where possible, information about the mother's pregnancy and littermates' health as well as the kitten's symptom history.
Risk factors
- Kittens with inherited abnormalities.
- Brachycephalic breeds, such as Persians.
- Animals with previous brain trauma or inflammation.
An extremely short-skulled appearance in Persian cats has been associated with larger ventricles and skull abnormalities. However, risk is not identical in every Persian, and breed name alone does not confirm diagnosis. Studies have distinguished severely brachycephalic individuals from those with a more moderate skull shape.
Information about general risk factors for feline hydrocephalus is limited. Family information from even a symptom-free kitten can help breeding assessment, but does not replace examination of a cat with symptoms.
Symptoms
Hydrocephalus symptoms depend on the amount of fluid:
- increased head size in kittens
- episodes and seizures
- ataxia, or an unsteady gait
- circling and disorientation
- blindness or impaired vision
- behavioural changes, such as aggression or apathy
- reduced consciousness and, in severe cases, coma
Severity is not inferred from fluid amount alone: the underlying cause, brain tissue damage and disease development also matter. An adult cat may have a normal external skull shape despite enlarged ventricles. The absence of a domed head does not rule out the disease.
At home, changes may appear as aimless circling, reduced responsiveness or altered movement. The eyes may deviate outwards and downwards. These signs cannot be used as a home test, however, because a brain tumour, inflammation and other central nervous system diseases can look similar.
A kitten's coordination problems may also be caused by cerebellar underdevelopment. Trembling and clumsiness in that condition may remain fairly unchanged during growth, whereas symptoms associated with hydrocephalus may worsen. Investigations distinguish them because watching the gait alone does not confirm either diagnosis.
Possible complications
Without treatment, hydrocephalus can lead to:
- chronic neurological disorders
- permanent blindness
- seizures
- delayed kitten development
- death in severe cases
Permanent damage may limit recovery even if fluid passage is corrected. Conversely, not every case progresses in the same way, and a list of complications cannot predict an individual cat's future. Changes in symptoms and treatment response are essential to prognosis assessment.
Small outcome studies have been published, often involving both dogs and cats. They describe both clear improvement after surgery and serious complications. A combined percentage must not be interpreted as a guaranteed recovery prognosis for your own cat.
Veterinary investigations
Diagnosis uses:
- neurological examination
- brain ultrasound through open fontanelles in kittens
- CT or MRI
- laboratory tests to exclude infectious causes
What does imaging investigate?
Neurological examination assesses consciousness, movement and cranial nerve function, for example. Findings help locate the disorder. An ordinary blood test does not show ventricle size, but investigations are needed to look for other diseases causing neurological symptoms.
Before the appointment, gather information on whether symptoms began suddenly or gradually and how they have changed. Your vet examines the whole cat, rather than just the head. Limb postural reactions and reflexes help distinguish disorders affecting different parts of the nervous system.
Examining eye movements and responses assesses nerves involved in vision and head functions. Bumping into objects is not always due to the eye itself because processing of visual information can also be impaired in the brain. Blood samples can look for metabolic disturbances associated with neurological signs.
A fontanelle is a gap between skull bones. If open, it allows ultrasound to show enlarged ventricles. However, the investigation does not always describe the whole brain structure adequately. MRI is generally more detailed than CT for assessing brain tissue and concurrent abnormalities.
Images look for a possible obstruction and assess surrounding brain tissue. If inflammation is suspected, a neurologist plans further investigations. FIP is considered before symptoms are interpreted solely as a congenital fluid circulation disorder or shunt surgery is planned.
Treatment and follow-up
Treatment aims to relieve symptoms and reduce harm to the brain. Medicines may be used to manage acute deterioration and seizures, for example. Medication does not remove a structural obstruction, and treatment targeting fluid production may have only limited or temporary effects. Medicines are selected by your vet.
Surgery can place a shunt, a thin tubing system that carries fluid from a brain ventricle under the skin into the abdominal cavity for absorption. Suitability depends on symptoms, the underlying cause and images. The goal is improved function; existing nervous tissue damage does not always recover.
A shunt can become blocked, displaced or infected. Excessive fluid drainage can also cause a serious complication. If previously improved neurological signs return, reassessment is needed rather than automatically assuming the original disease has simply worsened. Sometimes the tubing system needs surgical repair.
After surgery, neurological follow-up and any necessary imaging are agreed. Monitoring is particularly important early on because many problems in studies occurred soon after surgery. Recovery is assessed from functional ability: alertness, walking and use of vision can change at different rates.
Safety at home
If vision is impaired, keep feeding places and the litter tray in the same positions. Keep familiar routes clear and prevent stair access until movement is safe. Do not lift a visually impaired cat onto a high surface from which it could fall. A safe indoor environment or protected outdoor access reduces accidents.
Record how your cat moves and responds in daily life for the appointment. Unusual circling, new balance problems or reduced responsiveness are reasons to contact the treating vet. Follow emergency instructions if there is sudden deterioration.
Prevention
- Exclude animals with congenital hydrocephalus from breeding.
- Prevent head injuries.
- Maintain vaccinations and treat infections promptly.
- Provide particular care and monitoring for susceptible breeds.
Vaccines do not prevent congenital structural hydrocephalus. They form part of general infection prevention, but protection against every fluid circulation disorder cannot be promised. Avoiding an extremely brachycephalic appearance in breeding is also justified by the associated skull and brain structural abnormalities.
What it means for owners
Hydrocephalus in cats is rare but serious and needs early recognition. It is important to know:
- Congenital forms usually appear in kittens during the first months.
- Acquired hydrocephalus can develop after injuries and infections.
- Any neurological symptoms are reasons to contact a veterinary neurologist immediately.
This material is for information and does not replace veterinary care. Contact a vet immediately if your cat develops symptoms.
Frequently asked questions
Can a cat have hydrocephalus without a large head?
Yes. Particularly in disease diagnosed later, external skull shape may not change. Diagnosis is based on symptoms, neurological examination and imaging together, rather than head size.
Does every finding of enlarged ventricles need surgery?
Not automatically. The first step is to assess whether symptoms relate to that finding or to concurrent inflammation, for example. Distinguishing a symptom-free finding from disease needing treatment requires veterinary assessment.
Does a shunt cure the cat completely?
A shunt can relieve symptoms and improve function, but does not repair every injury. Agreed follow-up is needed after treatment, and returning symptoms may indicate a shunt system problem.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
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- Surgical management of primary and idiopathic internal hydrocephalus in dogs and cats, Frontiers in Veterinary Science, accessed 2026-11-03.
- Outcome of ventriculoperitoneal shunt implantation for treatment of congenital internal hydrocephalus in dogs and cats: 36 cases (2001-2009), Journal of the American Veterinary Medical Association / PubMed, accessed 2026-11-03.
- The Relationship between Brachycephalic Head Features in Modern Persian Cats and Dysmorphologies of the Skull and Internal Hydrocephalus, Justus-Liebig-Universität Gießen / Journal of Veterinary Internal Medicine, accessed 2026-11-03.
- Neurological Disorders, Cornell University, accessed 2026-11-03.
- Blind Cats, Cats Protection, accessed 2026-11-03.
- The Neurologic Evaluation in Cats, Merck Veterinary Manual, accessed 2026-11-03.