Felis ISSN 2398-2950

Hydrocephalus

Contributor(s): Carley Abramson, Rodney Bagley

Introduction

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

Pathogenesis

Etiology

  • 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.

Predisposing factors

General

  • Inflammatory disease of the brain.

Pathophysiology

  • 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

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.

Timecourse

  • Weeks, months, or years.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

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.


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