Ch 5 Malformations Flashcards
What develops the CNS?
Primitive neuroectoderm
The CNS develops from the primitive neuroectoderm during the process of neurulation.
What are the stages of neurulation?
Closure of the neural tube and separation of neural crest cells
The neural crest cells form neurons of peripheral autonomic ganglia and sensory nerve roots.
What is the role of immature neurons and glioblasts during CNS development?
Proliferation from subependymal germ cells and migration along radial glial processes
This process leads to functional cell maturation.
What is meant by functional cell maturation?
Formation of postmitotic neurons, astrocytes, and oligodendrocytes that form myelin
This process results in increased morphologic and functional complexity.
What is the consequence of normal apoptosis during CNS development?
Overabundance of neurons
Genetic abnormalities may lead to excessive cell death in specific populations, resulting in abiotrophy.
What are primary pathophysiological factors in CNS malformations?
Single point genetic mutations, chromosomal abnormalities, spontaneous or inherited factors
These factors can lead to various malformations.
What are secondary pathophysiological factors in CNS malformations?
Acquired from exposure to teratogens, transplacental infections, ionizing radiation, hyperthermia, toxic or therapeutic chemicals, hypothyroidism, vitamin deficiencies, plant toxins
These factors can contribute to the development of malformations.
When is the CNS most susceptible to teratogens?
During the 1st trimester
Post-natal myelination and neuronal cell trafficking can still be targets for teratogens.
What is the etiology of CNS malformations?
Most likely due to a combination of genetic and environmental factors
This multifactorial nature complicates the understanding of malformations.
What are the basic patterns of presentation for CNS malformations?
Immature animal and neurological signs immediately after birth or within the first few weeks or months
These signs are usually non-progressive or rapidly progressive.
What are the major categories of malformations?
- Defects of neural tube closure
- Defects of forebrain induction
- Neuronal migration disorders and sulcation defects
- Disorders of proliferation or size
- Encephaloclastic defects
- Cerebellar and spinal malformations
- Congenital hydrocephalus and cysts
Each category represents a different type of developmental defect.
What is dysraphism?
Failure to form the neural tube
It can lead to various conditions such as anencephaly and spina bifida.
What is anencephaly?
Complete lack of brain development
It is a severe defect associated with neural tube closure failure.
What is cerebral aplasia?
Absence of cerebral hemispheres
The diencephalon may be attached to haired skin rostrally.
What is cranium bifidum?
Osseous defect of cranial vault with possible eversion of meninges and brain
It usually occurs at the frontal midline.
What is spina bifida?
Absence of one or more segments of vertebral dorsal arch
It can occur with myelodysplasia in affected regions.
What is holoprosencephaly?
Failure in cerebral hemisphere separation
It can lead to facial defects such as cyclopia.
What is agyria?
Complete lack of normal number and thickness of cerebral gyri
It is associated with thickened cortex and reduced white matter.
What is megalencephaly?
Absolute increase in brain size/volume
This condition is rare in veterinary medicine.
What is porencephaly?
Single, cystic fluid-filled cavity in the wall of cerebral hemispheres
It may connect to a ventricle and is typically associated with white matter.
What is hydranencephaly?
Massive bilateral symmetric necrosis replaced by fluid-filled sacs
It results from a destructive process in pre-existing brain tissues.
What is Dandy-Walker Syndrome?
Midline defect of cerebellum with cystic dilation of the fourth ventricle
It is characterized by cerebellar vermal agenesis and enlargement of the caudal fossa.
What is myelodysplasia?
Umbrella term for spinal cord defects
It includes conditions like hydromyelia and syringomyelia.
What is hydrocephalus?
Enlargement of the ventricular system due to increased volume of CSF
It can be classified into internal and external types.
What are the main sites of obstruction in non-communicating hydrocephalus?
- Interventricular foramina
- Mesencephalic aqueduct
- Lateral foramina of the fourth ventricle
These sites can lead to intraventricular obstruction.
What is the definition of non-communicating hydrocephalus?
Obstruction of CSF at stricture point
What are the major sites of obstruction in non-communicating hydrocephalus?
- Interventricular foramina between lateral and 3rd
- Mesencephalic aqueduct
- Lateral foramina of 4th
What characterizes communicating hydrocephalus?
Bilateral and symmetrical
What is the difference between normotensive and hypertensive regarding CSF pressure?
- Normotensive – normal CSF pressure
- Hypertensive – increased CSF pressure
What causes acquired obstructive hydrocephalus?
- Neoplasia
- Inflammation
- Vitamin A deficiency
- Occipital bone hypoplasia
What is a potential consequence of vitamin A deficiency in beef calves?
Dural fibrosis that affects SA villi disrupts CSF absorption
What are the causes of acquired congenital hydrocephalus?
- Teratogens
- Neonatal tumors
What are examples of teratogens that can cause acquired congenital hydrocephalus?
- Transplacental infections
- Fetal aqueductal subependymal gliosis
- Stenosis
- Porencephaly
- Ependymitis
What is developmental obstructive hydrocephalus characterized by?
- Stenosis of mesencephalic aqueduct
- Malformation of mesencephalon
What is hydrocephalus ex vacuo?
Compensatory distension of ventricle into lesion site of cavitation
What are lesions secondary to hydrocephalus in young puppies?
- Rupture of ependyma
- CSF clefts and diverticula in parenchyma
- Hemorrhage
What is syringomyelia?
Cystic fluid filled cavity within the spinal cord extending over several segments
What condition is often associated with syringomyelia?
Chiari malformation
What is hydromyelia?
Focal or generalized dilation of central canal
What is the effect of increased intraventricular pressure?
Proximal strictures or occlusions of the central canal
What is syringobulbia?
Fluid-filled slit-like cavities in the medulla which usually communicate with the lumen of the 4th ventricle
What is a potential finding on necropsy related to arachnoidal and ependymal cysts?
Compressed spinal cord at site of cyst
True or False: Arachnoidal and ependymal cysts are true cysts.
False
Fill in the blank: Acquired obstructive hydrocephalus can be caused by _______.
[neoplasia, inflammation, vitamin A deficiency, occipital bone hypoplasia]
