5.1 & 5.2-Congenital and developmental disorders. Metabolic and degenertative encephalopathies

Question 1

What is hydrocephalus?

Answer 1

an abnormal distension of the ventricular system of the brain related to inadequate
passage of CSF from its point of production within the ventricular system to its point of absorption.

Can be congenital (toy and brachycephalic breeds- genetic factors and in-utero exposure to toxins or infectious agents) or acquired ( secondary to CSF flow obstruction caused by neoplasia, mass lesions, intraventricular hemorrhage, meningoencephalitis).

Question 2

Clinical signs for hydrocephalus

Answer 2

failure to thrive, malformation of the skull, ventrolateral strabismus, abnormal behavior, cognitive dysfunction, ataxia, blindness, and vestibular dysfunction

Question 3

MRI findings in congenital hydrocephalus
may include:

Answer 3

Enlargement of the calvarium +/− open fontanelles.
Other congenital anomalies including meningomyelocele,
Chiari-like malformation, occipital dysplasia/
hypoplasia, syringohydromyelia, Dandy–Walker syndrome,
and cerebellar hypoplasia.

Question 4

Common MRI findings in cases of hydrocephalus
include:

Answer 4

Ventricular enlargement
Thinning of the cerebral cortices.

Less common: dilation of the olfactory recesses of the lateral ventricles and the infundibular recess. Periventricular edema resulting from trans ependymal
migration of CSF (best seen on T2-FLAIR images as
periventricular hyperintensity, and most common in
acute cases). CSF signal void in mesencephalic aqueduct on T2W
images attributed to high velocity or turbulent CSF
flow.

Question 5

What are some MRi findings that if you see it will mean that there is hydrocephalus instead of incidental ventriculomegaly?

Answer 5

A ventricle/brain index >0.6 on dorsal plane images.
(The ventricle/brain index is evaluated on dorsal T2
images and defined as the maximum continuous distance
between the internal borders of the ventricles
divided by the maximum width of the brain parenchyma
in the same image)
Elevation of the corpus callosum and dorso ventral
flattening of the interthalamic adhesion, best seen on
sagittal plane images.
Periventricular edema
Dilation of the olfactory recesses
Thinning of the cortical sulci and/or sub arachnoid
space.
Disruption of the internal capsule adjacent to the
caudate nucleus.

Question 6

what is meningocele and meningoencephalocele?

Answer 6

Protrusion of meninges alone or meninges along with
brain tissue through a calvarial defect respectively.

Question 7

Which feline breed has a genetic predilection for meningocele/meningoencephalocele?

Answer 7

Burmese cats

Question 8

MRI findings for meningocele/meningoencephalocele include:

Answer 8

Calvarial defect with herniation of meninges +/−
brain tissue in cases of superficial/parietal (meningo)
encephalocele.
Cribriform plate defect with herniation of meninges
+/− brain tissue in cases of nasal/ethmoidal (meningo)
encephalocele
Concurrent facial/calvarial deformity.
Meningeal enhancement of protruded tissue.
Porencephaly (in cases of parietal meningoencephalocele).

Question 9

What is Holoprosencephaly (HPE)?

Answer 9

failure of the forebrain to
sufficiently divide into two hemispheres, and is characterized
by absent or smaller midline prosencephalic
structures (corpus callosum, septum pellucidum, septal
nuclei, fornix, and optic nerves), incomplete separation of
normally paired forebrain structures (lateral ventricles,
cingulate gyri, and caudate nuclei), and hydrocephalus.

Question 10

HPE can be subdivided into?

Answer 10

alobar, semilobar, and lobar HPE

alobar: prosencephalic
cleavage fails, resulting in a single midline forebrain
with a primitive monoventricle. This condition is
usually associated with severe facial malformation
including a single cycloptic globe.

semilobar: the occipital lobes are distinct
while the rostral cerebral hemispheres fail to
separate.

lobar: the most rostral and ventral
portions of the cerebral hemispheres are fused.

Question 11

What is a very important MRI feature for HPE?

Answer 11

Agenesis or dysgenesis of the corpus callosum is a feature of HPE (may also occur as an isolated abnormality)

Adipsia/hypodipsia (associated with hypernatremia) is the most common presenting complaint

Question 12

Which breeds appear predisposed to HPE and agenesis or dysgenesis of corpus callosum?

Answer 12

Staffordshire Bull Terriers and Miniature Schnauzers

Question 13

What’s is the most likely diagnosis?

Answer 13

agenesis corpus callosum (consider HOLOPROSENCEPHALY as well)

p.164 for normal MRI findings

Question 14

What is lissencephaly? What breed is this codition hereditary?

Answer 14

disorder of cortical neuronal migration is characterized by paucity, absence, and/or hypoplasia of cerebral gyri (pachygyria) and thickening of the cerebral cortex.

Lhasa Apsos

Question 15

MRI finidings for lissencephaly include:

Answer 15

A smooth cerebral surface and a thick neocortex with absence of the corona radiata

Less commonly, concurrent anomalies such as cerebellar hypoplasia, corpus callosum abnormalities, ventriculomegaly, or arachnoid cysts

Question 16

What is the most likely diagnosis?

Answer 16

Lissencephaly (notice the abscene of gyri and sulci)

Question 17

What is polymicrogyria? Which breed is this condition thought to be hereditary?

Answer 17

a disorder of cerebrocortical development resulting in an increased number of small, disorganized gyri in the dorsal and lateral cerebral cortex.

Standard Poodles

Question 18

MRI findings for polymicrogyria?

Answer 18

Increased numbers of disorganized shallow gyri in the occipital lobes, most easily visualized on dorsal plane T2W images

Less common MRI findings include ventriculomegaly/ hydrocephalus63 and thinning of the subcortical white matter in the occipital lobes

Question 19

What is your most likely diagnosis?

Answer 19

polymicrogyria

Question 20

What is Dyke–Davidoff–Masson-like syndrome? What are MRI findings?

Answer 20

intrauterine or early childhood loss of unilateral brain parenchyma and subsequent asymmetric changes to the cranium.

Hypoplasia/partial absence of a cerebral hemisphere.

Changes in the overlying cranium including hyperostosis and expansion of the diploic space.

Question 21

What is your most likely dx?

Answer 21

Dyke-Davidoff-Masson-like syndrome

Question 22

What is cerebellar aplasia and hypoplasia?

Answer 22

Cerebellar aplasia/agenesis is defined as complete absence of cerebellar tissue.

Cerebellar hypoplasia is characterized by uniform shortage of cerebellar tissue.

In kittens, this is most commonly observed following inutero infection with the panleukopenia virus

Question 23

MRI findings for crebellar aplasia and hypoplasia

Answer 23

An absent or abnormally small cerebellum with CSF filling the space normally occupied by cerebellar parenchyma.

This is particularly visible on T2W images due to the hyperintensity of the surrounding CSF.

Less commonly, concurrent anomalies such as lissencephaly and hydranencephaly are seen.

Question 24

What is Dandy-Walker malformation complex? What dog breed is genetically predisposed?

Answer 24

Primarily involve the cerebellum and adjacent tissues. Cases of cerebellar vermian aplasia or hypoplasia with or without associated cystic dilation of the fourth ventricle have been reported in dogs.

Eurasier dogs

Question 25

Common MRI findings dor Dandy-Walke malformation include:

Answer 25

Hypoplasia/agenesis of the cerebellar vermis.

Cyst-like dilation of the fourth ventricle.

Enlargement of the caudal fossa.

Question 26

What is your most likely dx?

Answer 26

Dandy-Walker malformation complex

Question 27

What is your dx?

Answer 27

Chiari-like malformation

Question 28

Chiari-like malformation classification

Answer 28

Question 29

What is chiari-like malformation?

Answer 29

characterized by a mismatch in size between the brain (which is too large) and the skull (which is too small).

Question 30

What are lysosomal storage diseases? Examples?

Answer 30

characterized by the intracellular accumulation of one or more products of an interrupted metabolic pathway.

Flucosidosis and Alpha-mannosidosis