Canis ISSN: 2398-2942

Hydrocephalus

Contributor(s): Rodney Bagley

Introduction

  • Cause: may be congenital or acquired Hydrocephalus: congenital.
  • Typically seen in brachycephalic breeds.
  • Signs: paresis, blindness and seizures in puppies.
  • 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 (hydrocephalusex 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 Brain: trauma , hypertension Hypertension , and bleeding disorders Hemophilia A Hemostatic disorder: 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).
  • Impaired absorption of CSF is seen occasionally in Bull Mastiffs with familial ataxia Mastiff.
  • Hydrocephalus is the term commonly used to describe a condition of abnormal dilation of the ventricular system within the cranium.
  • Ventricular dilation occurs with some frequency in dogs due to a variety of intracranial disease processes.
  • 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 cell 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, ependymomas, and pituitary tumors.
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.
  • Distemper Canine distemper disease and parainfluenza Canine parainfluenza virus 2 infection are common causes.
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.
  • Many of these breeds have asymptomatic ventricular dilation which may not result in clinical disease.
  • Congenital malformations of the cerebellum are occasionally associated with hydrocephalus.
  • Caudal vermian hypoplasia is described, with some dogs having associated ventricular dilation.
  • Rarely, abnormalities of ependymal cilia function can result in ventricle dilation, probably due to poor or absent CSF flow. Immotile cilia syndrome and Kartagener's syndrome would be examples.
  • 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 to months.

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.
  • Rivers W J & Walter P A (1992) Hydrocephalus in the dog - Utility of ultrasonography as an alternative diagnostic imaging technique. JAAHA 28, 333-43 AGRIS FAO.
  • Hudson J A, Simpson S T, Buxton D F, Cartee R E et al (1990) Ultrasonographic diagnosis of canine hydrocephalus. Vet Rad 31 (2), 50-58 VetMedResource.
  • Spaulding K A & Sharp N J H (1990) Ultrasonographic imaging of the lateral cerebral ventricles in the dog. Vet Rad 31 (2), 59-64 VetMedResource.
  • Hudson J A, Cartee R E, Simpson S T & Buxton D F (1989) Ultrasonographic anatomy of the canine brain. Vet Rad 30 (1), 13-21 VetMedResource.
  • Simpson S T & Reed R B (1987) Manometric values for normal cerebrospinal fluid pressure in dogs. JAAHA 23 (6), 629-632 VetMedResource.
  • Kay N D, Holliday T A, Hornof W J & Gomez J (1986) Diagnosis and management of an atypical case of canine hydrocephalus, using computed tomography, ventriculoperitoneal shunting, and nuclear scintigraphy. JAVMA 188 (4), 423-426 PubMed.
  • Whittle I R, Johnston I H & Besser M (1985) Intracranial pressure changes in arrested hydrocephalus. J Neurosurg 62 (1), 77-82 PubMed.
  • Rosenberg G A, Saland L & Kyner W T (1983) Pathophysiology of periventricular tissue changes with raised CSF pressure in cats. J Neurosurg 59 (4), 606-611 PubMed.
  • Klemm W R & Hall C L (1971) Electroencephalograms of anesthetized dogs with hydrocephalus. Am J Vet Res 32 (11), 1859-1864 PubMed.
  • Gage E D (1970) Surgical treatment of canine hydrocephalus. JAVMA 157 (11), 1729-1740 PubMed.
  • Few A B (1966) The diagnosis and surgical treatment of canine hydrocephalus. JAVMA 149, 286-293 PubMed.
  • deLahunta A & Cummings J F (1965) The clinical and electroencephalographic features of hydrocephalus in three dogs. JAVMA 146, 954-964 PubMed.

Other sources of information

  • Greenberg M S (1991)Treatment of Hydrocephalus.In:Handbook of Neurosurgery. Lakeland, FL, 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 edn, 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.
  • Simpson S T & Reed R B (1987)Cerebrospinal fluid pressure in dogs -technique, normal values and meaning.Proceeding 5th ACVIM. pp 275-276.
  • deLahunta A (1983) In:Veterinary Neuroanatomy and Clinical Neurology. 2nd edn, Philadelphia: W B Saunders.


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