Hydrocephalus

• Cause: may be congenital Hydrocephalus: congenital or acquired.
• Signs: paresis, blindness and seizures in kittens.
• Diagnosis: ultrasound, advanced imaging.
• Treatment: surgical shunting, anticonvulsants, corticosteroids.

• Depression/lethargy.
• Paresis develops in all limbs.
• Blindness and ventrolateral strabismus.
• Characteristic dome-shaped skull.

• Open fontanelle may be present.

• Seizures.

• Usually young cats for congenital disease.

• May develop at any age depending on cause.

• Siamese Siamese cats have a hereditary form of congenital disease.

• Surgical shunting from the ventricular system to peritoneal cavity.

• Corticosteroids to reduce cerebrospinal fluid (CSF) production, increase CSF absorption, and suppress any underlying inflammatory process.

General anesthesia

• Hypoxia due to seizure activity and compromise of the airway will lead to cytotoxic brain edema and possibly raised intracranial pressure.

• May occur as a consequence of inflammatory disease of the brain.
• Hydrocephalus can result from obstruction of the ventricular system, irritation of the ventricle (from inflammation or hemorrhage), increased size of the ventricles due to loss of brain parenchyma (hydrocephalus ex vacuo), be present without an obvious cause (congenital), or rarely, be the result of overproduction of CSF associated with a choroid plexus tumor Brain: neoplasia choroid plexus tumor.
• Ventricular obstruction can occur due to intraventricular or extraventricular obstruction.
• Diffuse ventricular enlargement suggests congenital ventricular dilation or obstruction at the level of the lateral apertures or foramen magnum.
• Focal ventricular enlargement suggests focal obstruction or parenchymal cell loss.
• It is not uncommon to have bilateral lateral ventricle enlargement that is asymmetric.
  Animals with asymmetric appearance of the ventricles should be critically evaluated for focal obstruction of, or impingement on, the ventricular system due to mass effect.
• Hemorrhage into the ventricular system can occur with head trauma , hypertension , and bleeding disorders Hemostatic disorders: acquired.
• Blood products Anemia: transfusion indications are irritating to the ependyma, and result in associated inflammation.

General

• Inflammatory disease of the brain.

• Usually caused by a disruption of CSF drainage from ventricular system (obstructive hydrocephalus).
• Hydrocephalus is the term commonly used to describe a condition of abnormal dilation of the ventricular system within the cranium.
• With the aid of modern imaging studies, diagnosis of the condition is usually not difficult, however, the clinical ramifications of intracranial ventricular dilation vary widely.
• For a better understanding of the pathophysiology of hydrocephalus, an understanding of normal cerebrospinal fluid physiology is advantageous:
  • The brain normally contains areas that are devoid of cells but filled with cerebrospinal fluid (CSF).
  • These areas are collectively known as the ventricular system.
  • From rostral to caudal the components of this system include the lateral ventricles, the third ventricle, the mesencephalic aqueduct, and the fourth ventricle.
  • The fourth ventricle is continued into the spinal cord via the central canal.
  • The ventricular system is lined by specialized columnar cells with microvilli known as ependymal cells.
  • These cells are important as a partial barrier between the CSF and the brain parenchyma.

• If the ventricular system is obstructed, CSF will be trapped behind the level of obstruction. This may also be referred to as a non-communicating hydrocephalus.
• As some, but inadequate, amounts of CSF may pass the level of the obstruction, this may not always be the most appropriate description of the pathophysiological state.
• Anatomically smaller areas of the ventricular system are common sites of obstruction. These include the interventricular foramen and the mesencephalic aqueduct.
• Obstruction can result from tumor, granuloma, hemorrhage or inflammation.

Neoplasia

• Tumors that have more commonly been associated with hydrocephalus include choroid plexus tumors Brain: neoplasia choroid plexus tumor, ependymomas Brain: ependymoma, and pituitary tumors Pituitary gland: neoplasia.

Infectious disease

• With infectious diseases that affect the ventricular system, the ependymal layer may be damaged predisposing the underlying parenchyma to be penetrated by the agent or associated products.
• An inflammatory reaction ensues, further damaging local tissues.
• The ependymal cells may be lost and replaced by subependymal microgliacytes or astrocytes.
• The end stage is a granular ependymitis.
• Feline infectious peritonitis   Feline infectious peritonitis  is the most common cause.

Congenital

• The cause of congenital hydrocephalus Hydrocephalus: congenital is not always apparent. Speculation suggests that this abnormality may be due to an obstruction of the ventricular system during a critical stage during development and subsequent damage to the vulnerable maturing nervous parenchyma.
• Congenital malformations of the cerebellum are occasionally associated with hydrocephalus.
• Feline cerebellar hypoplasia is caused by intrauterine panleukopenia infection which affects the external germinal layer of the cerebellum and prevents formation of the granular layer.
• Some affected cats have concurrent hydrocephalus and hydranencephaly.
• Hydrocephalus can result in clinical signs due to loss of neurons or neuronal function, alterations in intracranial pressure and associated pathophysiological effects of intracranial disease.
• Interstitial edema, for example, is increased water content of the periventricular white matter due to movement of CSF across the ventricular walls in instances of hydrocephalus.
• Periventricular white matter is reduced due to the disappearance of myelin lipids secondary to increases in white matter hydrostatic pressure or decreases in periventricular white matter blood flow.
• Increased CSF pressure may contribute to intracranial disease through alterations in intracranial pressure (consequences of increased intracranial pressure are described above).
• If formation of CSF equilibrates with absorption, a compensated hydrocephalic state may occur.
• In some instances, CSF production may decrease, possibly due to pressure damage to the choroid plexus or ependyma.

• Weeks, months, or years.

• Progressive neurological dysfunction in kittens.
• Signs may wax and wane with changes in intracranial pressure due to stress, concurrent illness, or physiological pressure changes (sneezing, coughing, or vomiting).

• Blindness.
• Depression.
• Seizures.

• Clinical signs of hydrocephalus reflect the anatomical level of disease involvement.
• Forebrain, vestibular, and cerebellar signs are most common.
• Severity of clinical signs is not necessarily dependent upon the degree of ventricular dilation, but rather on a host of concurrent abnormalities including the underlying disease process, associated intracranial pressure changes, intraventricular hemorrhage, and the acuity of ventricular obstruction.
• A ventral and/or lateral strabismus has been noted in humans and animals with hydrocephalus. This may be referred to as the "setting-sun sign". Confusion remains as to the underlying reason for this clinical findings. Some have suggested that this appearance is associated with the skull deformity and distortion of the orbits. Others suggest that because this abnormality can be improved with shunting on the lateral and third ventricles that this strabismus is associated with pressure on the mesencephalic tegmentum.
• As the forebrain structures are often involved with hydrocephalus, alterations in awareness and cognition are common.

Ultrasonography

• Ultrasound can be used to diagnosis hydrocephalus.
• This is most readily accomplished when a fontanelle is present providing an 'acoustic window' as ultrasound waves do not usually penetrate the skull well enough.
• If the bone is intact, a craniotomy defect can be created.
• Depending upon the size of the fontanelle, the lateral and third ventricles as well as the mesencephalic aqueduct are usually easily identified.

Other

• Computed Tomography (CT):
  • Computed tomography, as a non-invasive intracranial imaging modality, is often useful in defining ventricular size.
  • As CSF has a lower CT number than brain parenchyma, the ventricular system is usually readily identified due to its relative blackness in comparison to parenchyma.
• Magnetic resonance imaging (MRI):
  • Magnetic resonance imaging also affords evaluation of the ventricular system.
  • This modality provides for better parenchyma resolution than CT, and is especially useful for evaluation of the infratentorial structures.

Radiography

• Survey radiographs of the skull Radiography: skull (basic) may suggest the presence of hydrocephalus, but are usually not helpful for definitive diagnosis:
  • Findings associated with congenital hydrocephalus include loss of gyral striations, separation of cranial sutures (diastasis), and persistent fontanelles.
  • If hydrocephalus is acquired after the skull has formed, radiographic abnormalities are rarely encountered

Other

• Electroencephalography (EEG):
  • Electroencephalography has been used to diagnosis hydrocephalus, primarily prior to advanced imaging.
  • Classically, slow frequency, high voltage (amplitude) activity is noted.
  This pattern can be seen with other encephalopathies that destroy cortical parenchyma. So, EEG is rarely used as the sole means of diagnosis of hydrocephalus.

• The gyri and sulci may be flattened and cortex may appear soft.
• If CSF inadvertently leaks from the brain, the cerebral hemispheres may collapse.
• On transverse section, enlargement of the ventricles is present.

• The ventricular space is enlarged.

• Periventricular inflammation, hemorrhage or tumor may be noted with acquired hydrocephalus.

• Portosystemic shunts Congenital portosystemic shunt (CPSS).
• Trauma.

• In young cats (<1 year of age), other considerations for intracranial disease include:
  • Encephalitis .
  • Other congenital brain defects.
  • Inherited degenerative diseases, eg abiotrophies and storage diseases Storage disease.
• In middle-aged to older cats:
  • FIP Feline infectious peritonitis.
  • FIV Feline immunodeficiency virus disease.
  • Brain tumors.
  • Encephalitis.

• The choice of treatments is generally dictated by physical status, age of the animal, and cause of the hydrocephalus if known.
• Medical treatment may include general supportive care, and medications to limit CSF production and reduce intracranial pressure.
• Surgical treatment is designed to provide drainage of CSF from the brain to another site for absorption.

Medical Treatment

• Medical therapy usually does not provide long-term resolution of the clinical signs.
• Treatment is generally used for peri-operative stabilization of the patient and for management of cases with limited financial resources.
• Medications are grouped into two categories: glucocorticoids, and diuretics.

Diuretics

• Acetazolamide Acetazolamide, a carbonic anhydrase inhibitor, reduces CSF pressure by decreasing CSF production:
  • Therefore, this diuretic is especially useful for short-term management of animals with elevated intracranial pressure.
  • A dose of 10 mg/kg is given orally every 6 to 8 hours.
  • Electrolyte status should be monitored closely because acetazolamide, especially when used with corticosteroids, may cause potassium depletion.
• Mannitol Mannitol is an osmotic diuretic which decreases CSF production and reduces intracranial pressure:
  • A dose of 1-2 mg/kg is given intravenously over 15 or 20 minutes and may be repeated 2-4 times over the following 48 hours.
  • The patient should be monitored closely for dehydration.

Glucocorticoids

• Glucocorticoids are used to decrease CSF production, thereby, limiting intracranial pressure and further neurologic injury.
• Prednisolone Prednisolone:
  • At 0.25-0.5 mg/kg is given orally twice daily.
  • The dose is gradually reduced at weekly intervals to 0.1 mg/kg every other day.
  • This dose is continued for at least one month.
  • Then the medication is discontinued if possible.
• Alternatively, dexamethasone Dexamethasone may be given:
  • Orally at 0.25 g/kg every 6 to 8 hours.
  • The dose can be gradually reduced over two to four weeks.
• Some animals can be adequately managed with long-term glucocorticoid administration at low doses.
• If no clinical benefits are observed within two weeks, or if side effects develop, other forms of therapy should be tried.

Surgical Treatment

• CSF drainage is generally required for those animals that do not improve within 2 weeks, or if deterioration occurs during corticosteroid therapy.
• The surgical procedures are designed to provide controlled CSF flow from the ventricles of the brain to either the peritoneal cavity or the right atrium.
• Shunt systems which have been designed for use in humans seem to work well for animals.
• The shunts have not been proven to be more effective than medical management, but only surgical treatment offers the possibility of long-term control of the clinical signs.
  Ventriculoatrial (VA) and ventriculoperitoneal (VP) shunts are both effective, but VP shunts are technically easier to install and are most commonly used in human neurosurgery.
• Complications include infection, shunt occlusion (ventricular or abdominal), and inflammatory reaction in surrounding tissues.

• For improving demeanor.
• Repeat imaging studies may be performed but do not correlate well with the clinical condition.
• Radionuclide shuntography:
  • Requires injection of 0.5 to 3 mCi of 99m-Tc (Technetium pertechnetate), in 1 ml of fluid, into the shunt reservoir while occluding distal flow.
  • The patient is scanned immediately to verify flow into the ventricles which establishes patency of the ventricular catheter.
  • If spontaneous flow into the abdomen is not seen within 10 minutes, the patient is held vertically and re-scanned.
  • If flow is not seen after 10 minutes the reservoir is pumped to encourage flow.
  • If this is ineffective the distal catheter is probably completely occluded.

Monitoring

• Usually based on clinical response.
• Follow up imaging may also be appropriate.

• Good: the clinical signs are adequately controlled.
• Poor: there is no resolution of the profound neurological deficits, the disease may be terminal.

• Improving clinical demeanor.
• Medical treatment will only provide temporary relief of signs.

• Medical management unlikely to be successful in long-term.
• Undershunting due to blockage or disconnection of catheter.
• Complications associated with shunt, eg infection.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Whittle I R, Johnston I H & Besser M (1985) Intracranial pressure changes in arrested hydrocephalus. J Neurosurg 62 (1), 77-82 PubMed.
• Bruinsma D L (1983) Acquired hydrocephalus in an adult cat. Vet Med Small Anim Clin 78 (12), 1857-1858 VetMedResource.
• Rosenberg G A, Saland L & Kyner W T (1983) Pathophysiology of periventricular tissue changes with raised CSF pressure. J Neurosurg 59 (4), 606-611 PubMed.

Other sources of information

• Greenberg M S (1991) Treatment of Hydrocephalus. In: Handbook of Neurosurgery. Ed: F L Lakeland, Greenberg Graphics. pp 200-218.
• Adams R D & Victor M (1989) Disturbance of cerebrospinal fluid circulation, including hydrocephalus and meningeal reactions. In: Principle of Neurology. 4th ed, New York: McGraw Hill. pp 501-515.
• Simpson S T (1989) Hydrocephalus .In: Kirk R W, ed: Current Veterinary Therapy X. Philadelphia, W B Saunders. pp 842-847.
• deLahunta A (1983) In:Veterinary Neuroanatomy and Clinical Neurology. 2nd edn, Philadelphia: W B Saunders.