CENTRAL NERVOUSE SYSTEM

• Anencephaly


  Absence of the brain, rostral part of the brain (cerebral hemisphere) is absent or rudimentary and to varying degrees, the brain stem is preserved - prosencephalic hypoplasia
• Hydrocephalus


  Increased accumulation of the CSF either solely within the ventricular system space (communicating form) due to obstruction
• Forms of hydrocephalus


  • Non-communicating form
  • Communicating form
  • Hydrocephalus ex vacuo
• Non-communicating hydrocephalus


  • Results from obstruction within the ventricular system at or to the lateral apertures of the fourth ventricle
  • If congenital, associated with enlargement of the cranium caused by separation of the sutures prior to their fusion, and the enlarged head may cause dystocia
  • Most common in toy breeds and brachycephalic dogs
  • If acquired, associated with obstruction of the lateral aperture of the fourth ventricle, aqueduct, or interventricular foramen
• Causes of non-communicating hydrocephalus obstruction


  • Inflammation
  • Neoplasia
  • Cholesteatomas in the choroids plexus of horses (rare)
• Cholesteatoma


  An abnormal, noncancerous skin growth that can develop in the middle section of your ear, behind the eardrum. It may be a birth defect, but it's most commonly caused by repeated middle ear infections. A cholesteatoma often develops as a cyst, or sac, that sheds layers of old skin.
• Communicating hydrocephalus


  • Less common
  • Results from an obstruction preventing outflow of CSF into the venous system
  • Can occur following inflammatory or neoplastic involvement of the subarachnoid space, which interferes with the outflow of CSF through the arachnoid villi
• Lesions of non-communicating and communicating hydrocephalus

  • Prominent enlargement of the ventricular system proximal to the point of obstruction
  • White matter adjacent to the dilated lateral ventricles is reduced in thickness, although gray matter may retain a relatively normal appearance
  • Ependymal is generally not marked affected but may be focally discontinuous
  • Atrophy with fenestration of the interventricular septum (septum pellucidum)
  • Flattening of the surface gyri
  • Posterior or positioning of the brain with herniation of the cerebellum be accompanied by necrosis caused by circulatory obstruction
• Hydrocephalus ex vacuo


  Increased in size of the lateral ventricles secondary to absence or loss of cerebral tissue
• Hydranencephaly


  Characterized by a cavitation in the area normally occupied by the white matter of the cerebral hemispheres and results from lack of proper development of this part of cerebrum
• Lesions of hydranencephaly


  • Because of the lack of resistance, the ventricles may expand into this space, and the ependymal lining may remain relatively preserved or be variably defective
  • Cranium and meninges are generally unaltered
• Causes of hydranencephaly


  • Fetal viral infection
  • Nutritional copper deficiency
• Cranium bifidum


  Characterized by a midline cranial defect through which meningeal and brain tissue may protrude
• Spina bifida


  Spinal counterpart of cranium bifidum, frequently affects the caudal spine, characterized by a defect in the dorsal spinal column, through which there may herniation of either meninges (meningocele) or meninges and spinal cord (meningomyocele) into a sac covered with skin
• Animals affected by spina bifida

  • Horses
  • Calves
  • Sheep
  • Dogs (especially English bulldog)
  • Cats (particularly Manx breed)
• Syringomyelia


  A fluid-filled cavity within the spinal cord that is not lined by ependyma and may extend over several segments
• Syringomyelia


  • Described in humans and Weimaraner breed of dogs
  • Syrinx may communicate with the central canal
  • Cavity may contain fluid and is unlined, except for varying degrees of mural astrocytosis, which is usually very mild in the Weimaraner dogs
• Causes of syringomyelia


  • Presence of an anomalous pattern that results in a low-grade ischemia
  • Trauma
  • Infection
  • Neoplasia that can lead to parenchymal degeneration and cavitation
• Dysraphic anomalies


  Abnormal seam and usually refers to a defective closure of the neural tube during development
• Dysraphic anomalies


  • Defect may occur at any point along the tube, is exemplified by anencephaly and prosencephalic hypoplasia, cranium bifidum and spina bifida
• Lesions resulting from viral infection of the fetus

  • Viral effect on organogenesis
  • Viral effect on immature cells
  • Viral effects on differentiated cells
• Microencephaly


  Abnormally small brain, caused by influenza viral infection
• Myeloschisis


  Results from failure of the neural tube to close or rupture of a preformed neural tube, caused by NCD in young chicken embryo
• Parvoviral infection


  • Gross: reduction in size of the cerebellum that varies in severity depending on the age when the host is infected; have affinity for and destroy cells undergoing mitosis
  • Loss of external granular layer, primarily infects cells of the external granular early neonatal periods. Necrosis of these cells prevents their normal migration to form the internal granular layer
• Bovine viral diarrhea


  • Primarily lesion: cerebellar hypoplasia-atrophy
  • Others: prosencephaly, hydranencephaly (associated with early inflammation) and dysmyelination
• Aminoacidopathy


  Characterized by errors of amino acid metabolism
• Maple syrup disease


  Occurs in young polled Hereford
• Bovine citrullinemia


  Rare, inborn error of metabolism of the cycle that results in a pronounced accumulation of citruline in the body fluids due to a failure of normal synthesis of arginosuccinic acid by the enzyme arginosuccinate synthetase
• Lesions of bovine citrullinemia

  • Gross: pale yellow-ochre colored liver, normal appearance and weights of brain
  • Microscopic: brain - mild to moderate, diffuse, astroglial swelling in the cerebrocortical gray matter; liver - mild to severe hepatocellular hydropicchange
• Lysosomal storage disease


  Cellular alteration in which an increased amount of material that is normally degraded accumulates within lysosomes of cells, often eventually resulting in cell death
• Mechanisms involved in lysosomal storage disease

  • Synthesis of catalytically inactive proteins resembling active normal enzyme
  • Defects in post translational processing of enzyme protein destined for the lysosome
  • Lack of enzyme activator or protector protein
  • Lack of substrate activator protein
  • Lack of transport protein that is required for elimination of the digested material from lysosomes
• Affected neurons in lysosomal storage disease

  • Foamy (finely vacuolated) or granular-appearing cytoplasm, myelin formation and maintenance, and accumulation of globoid cells
• Anatomic differences in susceptibility of CNS to trauma

  • In animals, the percentage of brain mass in relation to skull size is much less than for primates
  • In some species (e.g. bovine and porcine), the cranial cavity is additionally protected by prominent dorsal frontal sinuses
  • Birth trauma, important in human beings, is insignificant to animals because in the latter the shoulder and, particularly, the pelvis rather than the head are likely to be compressed in the birth canal. Exception include brachycephalic breeds of dogs
• Amount of space between the spinal cord and the wall of the vertebral canal


  • Important in determining the degree of injury following swelling (e.g. edema) or compression (e.g. disk herniation)
  • Space is greater in the cervical area (e.g. dog) than at the thoracolumbar level, causing disk herniation at the latter area to often result to more severe spinal cord injury
• Functional factors in susceptibility of CNS to trauma

  • Brain of a freely movable head is much more susceptible to injury than that of the stationary, supported head
  • Mass and velocity of the object striking the head - trauma following impact of large blunt object can create marked brain movement and tissue damage, while a small but fast-moving object (bullet) may cause less head movement and a smaller but deeper area of tissue damage
• Factors involved in the protection of the brain

  • Rigidity of cranium (depends on age)
  • Round shape of the dorsum of the skull
  • Structure of the cranial bone (diploe), suture, sinuses, ridges in the floor of the cranial cavity, meninges and CSF
• Factors involved in the protection of the spinal cord

  • Vertebral column which is surrounded by soft tissues (e.g. adipose tissue and muscle)
  • Intervertebral disk and cancellous bone of vertebrae (absorbs shock)
  • Vertebral ligaments - maintain alignment of vertebral column
  • Denticulate ligaments - helps maintain proper position of spinal cord
  • Meninges and CSF - help cushion against trauma
• Concussion


  Clinical designation characterized by a temporary loss of consciousness with recovery that follows head injury, part of a spectrum referred to as diffuse brain injury
• Diffuse brain injury


  • Severity depending on the degree of trauma can range from a very mild, reversible concussion, without loss of consciousness, to severe injury that axonal degeneration, and result in a permanent neurologic deficit or even death
  • Involves widespread or global disruption of neurologic function that is usually not associated with gross lesions
  • Results primarily from rotational forces that cause shear, tensile and compressive strains throughout the brain
  • Microscopic lesions: central chromatolysis, axonal degeneration, and cell loss
• Contusion


  Localized area of hemorrhage, and it may, like concussion, result in unconsciousness and death