Pathology: Congenital and other Malformations Flashcards
What is a Primary Malformation of the nervous system?
A spontaneous or inherited single point gene mutation or chromosomal abnormality
What is a Secondary Malformation of the nervous system?
An acquired malformation from exposure to known teratogens e.g.: Transplacental viral infections Ionizing radiation Hyperthermia Known toxic or therapeutic chemicals Hypothyroidism Vitamin, trace element deficiencies Plant toxins etc.
What are the general features we look for when trying to diagnose a Congenital Malformation?
- Immature animal with neurological signs occurring immediately after birth or within first weeks or months of life
- Signs are usually non-progressive, but may on occasion progress rapidly
- Deviation from obvious normal anatomy
- Certain types of gross malformations occur as a result of interference with normal sequential development
What are the most common Malformation Categories seen in domestic animals?
- Defects of neural tube closure
- Defects of forebrain induction
- Neuronal migration disoder and sulcation defects
- Disorder of proliferation and size
- Encephaloclastic defects
- Cerebellar and Spinal malformations
- Congenital hydrocephalus and cysts
During what trimester of gestation do neural tube closure defects occur?
- First Trimester
Give examples of Neural tube defects
- Anencephaly: uncommon, but documented in pups and calves. Complete lack of brain and no cranium
- Spina bifida: absence of one or more segments of the dorsal arch, usually lumbosacral
Spina bifida occulta – skin covering, no herniation
Spina bifida aperta – defective closure in skin, spinal cord visible
Meningocele – arachnoid and dura mater lined fluid filled sac protrudes.
Myelomeningocele – includes spinal cord. Calves, lambs, foals and English bulldogs
Give examples of Forebrain induction defects
- Holoprosencephaly – failure in cerebral hemispheric sagittal cleavage resulting in a small monoventricular cerebrum
- Cerebral aplasia/ prosencephalic hypoplasia;
the cerebral hemispheres are absent, but components of the
brainstem (midbrain, pons, medulla) are formed - Cyclopia: resulting in a midline facial abnormality. In lambs its due to the dam being exposed to the plant Veratum californicum
Give examples of Neuronal Migration Disorders and Sulcation defects
- Pachygyria: fewer and wider gyri
- Polymicrogyria: excessive cortical folding resulting in increased numbers of small gyri. Animals are often blind.
- Lissencephaly: complete lack of the normal number and thickness of cerebral hemispheric gyri. Bilateral hydrocephalus is common. Reported in Lhaso Apso dogs.
note: rodents and rabbits naturally lack gyri on their brain
Give examples of Disorders of proliferation or size
- Microencephaly: congenital defect resulting in a brain smaller than usual size and weight – lacks both white and grey matter – mainly cerebrum – can be caused by teratogenic viruses.
- Megalencephaly: absolute increase in size of brain
- Megaloencephaly: enlargement of head irrespective of cause
Give examples of Encephaloclastic Defects
Note: These are secondary malformations due to an acquired destructive process in the pre-existing brain tissue e.g. viral infections
- Porencephaly; characterized by cysts or fluid-filled cavities within the cerebral hemisphere
- Hydranencephaly; severe form of porencephaly, a condition in which the brain’s cerebral hemispheres are absent to a great degree and the remaining cranial cavity is filled with cerebrospinal fluid
Viral Infections include:
- Arboviruses, such as Akabane virus, Bluetongue virus, Schmallenberg virus
- Pestiviruses such as BVD and Border disease
- Swayback due to in utero copper deficiency
- Foetal hyperthermia in last two trimesters in ewes
- Feline parvovirus in cats.
Give examples of Cerebellar and Spinal Malformations
- Cerebellar Hypoplasia: most commonly associated with feline and canine parvovirus, BVD, Border Disease Virus and Classical swine fever virus
- Equine Cerebellar Hypoplasia and dysplasia: occurs as a genetic cause in Arab and Arabian cross foals
- Syringomyelia: a cyst or cavity forms within the spinal cord. This cyst, called a syrinx, can expand and elongate over time, destroying the spinal cord and blocking vascular and CSF flow to and from the brain. CKCS dogs
Give example of Congenital hydrocephalus
- Hydrocephalus: Most common congenital CNS abnormality in domestic animals (especially in dogs). It is when there is an abnormal accumulation of CSF in the ventricular system (internal) or in the subarachnoid space (external)
Causes; in utero viral infection (parainfluenza dog, feline panleukopenia), developmental abnormalities in the ependyma or ventricular system, infection and subsequent blocking of the ventricular system
Genetic predisposition in some dog breeds (toy and brachycephalic breeds)
Most frequent in Lhaso apso, Chihuahua, toy poodle
What is the difference between Non-communicating and Communicating Hydrocephalus?
Non-communicating Hydrocephalus: due to obstruction to normal flow within the ventricular system (most common)
Communicating Hydrocephalus: occurs when the flow of CSF is blocked after it exits the ventricles and enters the subarachnoid space, where it can accumulate
What is acquired hydrocephalus?
Acquired hydrocephalus occurs after birth when a tumor, injury or disease blocks the absorption of cerebrospinal fluid in the brain e.g. meningitis, abscess, cyst
note: Hydromyelia is a focal or generalized dilation of the central canal (most commonly found in the lumbar segment) that is a result of hydrocephalus
What are the teratogenic viruses that can cause neural malformation ?
- Feline panleukopenia virus (parvovirus)
- Canine parvovirus
- Classical swine fever virus (pestivirus)
- Bovine viral diarrhoea virus (pestivirus)
- Border disease virus (pestivirus)
- Akabane virus, Cache Valley virus, Schmallenberg virus (orthobunyavirus)
- Bluetongue virus (Orbivirus)
