CNS Congenital Abnormalities - Pathology

()Map NERVOUS SYSTEM (Map)

Introduction

• Congenital malformations may involve the spinal cord, brain, meninges, calvaria or vertebral column.
• Abnormalities typically result from defects in neural tube development.
• Congenital malformations are present at or before birth, and manifest as either:
  • Morphological problems
  • Functional problems
    • Tend to arise as biochemical abnormalities, such as the lysosomal diseases or leukodystrophies.
• Causes of congenital abnormalities include:
  • Environmental causes
    • For example, these may be toxic, infectious, nutritional, or physical (e.g. radiation)
    • This is by far the most common cause.
  • Inherited traits.

Meningoencephalocoele

• A defect in the cranium allows protrustion of the brain and meninges.
  • There is alwaus crania bifida (a split skull).
• Meningoencephalocoele may be inherited in pigs and cats.

Hydrocephalus

Hydrocephalus in situ

Hydrocephalus. Image courtesy of BioMed Archive.

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 ventricles
    • The most common type.
    • There is unilateral or bilateral dilation of the ventricles.
  • External hydrocephalus - fluid is within the arachnoid space
  • Communicating hydrocephalus - fluid is within the ventricles and arachnoid space
  • Hydrocephalus ex vacuo - the ventricle is dilated secondary to loss of cerebral tissue
    • Also known as compensatory 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.

Cerebellar Defects

• Cerebellar defects include:
  • Cerebellar hypoplasia
  • Cerebellar abiotrophy