Ch 5 - developmental abnormalities

Question 0

meningocele and meningoencephalocele and cranioschisis

Answer 0

meningocele = soft swelling containing meningeal tissue and covered by skin, located outside a defect in the skull

meningoencephalocele = if it also contains brain tissue

cranioschisis = the skull defect
- this is an inherited disorder in burmese cats, often associated with duplication of portions of the face

Question 1

choroid plexus and granulomas: normal and what goes wrong

Answer 1

normal: in the lateral, 3rd and 4th ventricles sometimes will form a specialized association with blood vessels known as the choroid plexus. it produces CSF that flows inside the ventricular lumen.

what goes wrong: in older horses, cholesterol crystals associated with crhonic bleeding accumulate in choroid plexus. if they get big enough they form cholesterinic granulomas that block CSF flow and increase intracranial pressure. these granulomas can be diagnosed using CT or MRI.

Question 2

exencephaly

Answer 2

brain tissue that protrudes outside the cranial vault and is covered only by meninges

• less common
• often involves cranioschisis

Question 3

duplication of the prosencephalon - dicephalus

Answer 3

dicephalus - associated with varying degrees of duplication of other portions of the head in addition to the brain.

• seen most often in calves
• probably associated with early splitting of the primitive streak.

Question 4

prosencephalic hypoplasia: normal and if it fails to occur

Answer 4

normal: the telencephalic vesicles develop as outpocketings of the neural tube near its cranial end
if it fails to occur: the result is prosencephalic hypoplasia. it is usually associated with a midline defect that can involve the neural tube and a localized region of the skull.

Question 5

hydranencephaly

Answer 5

the parenchyma of the cerebral neocortex is absent, leaving only meninges and ependyma dorsally.

• results from viral infection
• initial insult may be on vasculature supplying the hemisphere, thus only one side may be affected.
• the bluetongue virus can produce this lesion in cattle and sheep

Question 6

cerebellar malformations and abiotrophy

Answer 6

gross malformation of the cerebellum resulting in difficulty or inability to stand or walk, constant loss of balance, noticeable from first few weeks of life.

• abiotrophy = postnatal degeneration of purkinge cells. results in early normal standing and walking with later onset of progressive ataxia.
• usually only portions of the cerebellar cortex are affected.
• inherited condition

Question 7

lissencephaly and involvement of Lis-1

Answer 7

• cerebral hemispheres are not convoluted but appear smooth.
• clinical signs include difficulty with behavioral training, abnormal behavior, slow postural reactions, seizures common.
• Lis-1 is an autosomal gene that influences migration processes in the cerebral cortex. Lis-1 mutations interfere with microtubule cytoskeleton involved in normal migration processes. neuronal precursor cells migrate upward from ventricular zone but do not assume proper laminar locations

Question 8

DCX gene and its effects on males vs. females

Answer 8

doublecortin gene (DCX) - produces effects relatd to lissencephaly.

• the DCX gene is X-linked.
• in affected males, cortical development is like type 1 Lissencephaly.
• in females due to X-inactivation, half the neuronal precursors migrate but the other half remain in the ventricular zone and form subcortical band heterotopia = a collection of neurons in an abnormal location within the white matter. seizures are common in these cases.

Question 9

holoprosencephaly

Answer 9

the telencephalon develops but there is incomplete bilateralization into two hemispheres. its accompanied by a range of facial dysmoprhologies.

• known to occur in lambs after ingestion of the plant veratum californicum. it disrupts the sonic hedgehog signaling in the prechordal plate.
• facial malformations are probably secondary to underlying disorder of forebrain development and its associated with neural crest.

Question 10

cyclopia

Answer 10

single orbit; eyes may be fused

associated with holoprosencephaly

Question 11

hypotelorism or hypertelorism

Answer 11

hypo = eyes closer together than normal

hyper = eyes wider apart than normal

associated with holoprosencephaly

Question 12

ethmocephaly

Answer 12

proboscis located dorsally between narrow-set eyes

associated with holoprosencephaly

Question 13

facial malformations associated with holoprosencephaly

Answer 13

1. cyclopia
2. hypotelorism
3. hypertelorism
4. ethmocephaly
5. median cleft lip
6. single maxillary incisor

Question 14

what causes malformations of brain and face

Answer 14

the combination of the defects in the face and brain is due to abnormal signaling related to midline processes like splitting of the initially median eyefield primoridum into left and right fields

Question 15

regulation of brain development

Answer 15

regulated by signaling centers that lie outside the developing nervous system. these include the prechordal plate, hensen’s node, visceral endoderm, and epidermal ectoderm. these signals from non-neural centers cause local forebrain signaling centers to become established.