CNS Congenital Abnormalities - Pathology

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.

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 in situ

Hydrocephalus. Image courtesy of BioMed Archive.

Aqueduct stenosis. Image courtesy of BioMed Archive.

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.

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 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 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.

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.