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* Hydrocephalus may also be hidden and detected later in life.
* Hydrocephalus may also be hidden and detected later in life.
[[Category:Nervous System - Pathology]]
[[Image:hydrocephalus.jpg|thumb|right|150px|Hydrocephalus in situ]] [[Image:hydrocephalussection.jpg|thumb|right|150px|Hydrocephalus. Image courtesy of BioMed Archive.]] [[Image:aqueductstenosis.jpg|thumb|right|150px|Aqueduct stenosis. Image courtesy of BioMed Archive.]]
* Hydrocephalus is an increased accumulation of fluid in the cranial cavity.
* There are several different types of hydrocephalus relating to where the fluid is located within the cavity.
** '''Internal''' hydrocephalus - fluid is within the <u>ventricles</u>
*** The most common type.
*** There is unilateral or bilateral dilation of the ventricles.
** '''External''' hydrocephalus - fluid is within the <u>arachnoid space</u>
** '''Communicating''' hydrocephalus - fluid is within the <u>ventricles and arachnoid space</u>
** '''Hydrocephalus ex vacuo''' - the <u>ventricle is dilated secondary to loss of cerebral tissue</U>
*** Also known as compensatory hydrocephalus.
[http://w3.vet.cornell.edu/nst/nst.asp?Fun=F_KSsrch&kw=HYDROCEPHALUS View images courtesy of Cornell Veterinary Medicine]
===Causes===
* Hydrocephalus may be '''congenital'''.
** Congenital hydrocephalus is common in brachycephalic and small breed dogs.
*** It occurs sporadically in cattle.
** Obstructive lesions are often not found.
** Amalformed mesencephalic aqueduct may be involved.
** The cranium may be abnormal, for example, doming.
* '''Acquired''' hydrocephalus is the result of obstruction, usually due to inflammation or compression.
** Space-occupying lesions include :
*** Neoplasms
*** Abscesses
*** Cholesteatomas
** Inflammation of meninges and/or ependymal cells can lead to hydrocephalus.
*** For example, FIP causes ependymitis which can obstruct flow if it affects the mesencephalic aqueduct.
* Hydrocephalus may also arise with:
** Increased ventricle size due to loss of brain parenchyma.
** Overproduction of CSF
*** Rare
*** Associated with choroid plexus tumours.
===Breed predisposition===
* Some breeds are predisposed to hydrocephalus.
** Chihuahua, pomeranian, yorkshire terrier, english bulldog, lhasa apso, toy poodle, cairn terrier, boston terrier, pug, pekingese, maltese terrier.
** Hydrocephalus has also been described in
*** Bullmastiffs, in association with cerebellar ataxia.
*** Siamese cats, as an autosomal recessive trait.
===Clinical Signs===
* Clinical signs are the result of:
** Loss of neurons or neuronal function
** Alterations in intercranial pressure
** Pathophysiological effects of intracranial disease
* Signs reflect the anatomical level of disease involvement.
** Rostrotentorial, vestibular and cerebellar signs are most common.
* Signs are not related to the degree of ventricular dilation. They are more associated with other damage caused by the disease proces:
** Intracranial pressure changes
** Intraventricular haemorrhage
** Speed of ventricular obstruction
* Hydrocephalus may contribute to abnormalities of skull development, where it is a congenital disease.
** Thinning of the bone structure
** Dome-shape head
** Persistent fontanelles
* Ventral or lateral strabismus may occur, although the reason for this is unknown.
** May be related to distortion of the orbits, due to skill deformity.
** May be realted with pressue on the mesencephalic tegementum.
===Diagnosis===
* Diagnosis is by a variety of imaging and electrophysiologic methods.
** MRI allows examination of the ventricular system, and give better resolution of the brain parenchyma than CT.
===Treatment===
* Prognosis is generally poor.
* Medical treatment:
** General supportive care
** Medications to limit CSF production and reduce intracranial pressure.
* Surgical treatment:
** Aims to allow drainage of CSF from the brain to another site for absorption.
[[Category:Central Nervous System - Congenital Abnormalities]]