6. Neuro (Brain - Congenital)

Question 1

Congenital Malformations: Types (6)

Answer 1

Failure to form,
Failure to cleave,
Failure to migrate,
Normal forming but massive insult causes appearance of failure to form,
Herniation syndromes,
Craniosynostosis

Question 2

Failure to form types (5)

Answer 2

Corpus callosum agenesis/dysgenesis,
Anencephaly, Iniencephaly, Arhinecephaly
Rhombencephalosynapsis,
Joubert syndrome,
Dandy walker

Question 3

Corpus callosum hypoplasia - overview (3)

Answer 3

Corpus callosum forms front to back, then rostrum last.
Failure to form (hypoplasia) is usually absence of the splenium (with genu intact).
Commonly shown as asymmetric dilatation of the occipital horns (Colpocephaly) - which can be either Corpus callosum agenesis or Pericallosal Lipoma.

Question 4

Callosal dysgenesis/agenesis (8)

Answer 4

Associated with lots of other syndromes/malformations
- Lipoma,
- Heterotopias,
- Schizencephaly,
- Lissencephaly
“Most common anomaly seen with other CNS malformations”.
Colpoencephaly shown as “steer horn” appearance on coronal, or “Vertical ventricles, widely spaced” on axial.
Ventricles are widely spaced due to “Probst bundles”, which are densely packed white matter tracts, which can’t cross the corpus callosum because it isn’t there.
Instead they run parallel to the interhemispheric fissure.

Question 5

Intracranial Lipoma (4)

Answer 5

Associated with callosal dysgenesis.
50% found in the interhemispheric fissure.
CNS lipomas are congenital malformations, not true neoplasms.
Tubonodular type frequently calcifies.

Question 6

Anencephaly (5)

Answer 6

Neural tube fails to close on cranial end, causing reduced or absent cerebrum and cerebellum.
Hindbrain is present.
Not compatible with life.
Elevated AFP, polyhydramnios.
Antenatal US: polyhydramnios plus “frog eye” appearance on coronal plane, due to absent cranial bone/brain with bulging orbits.

Question 7

Iniencephaly (3)

Answer 7

Rare neural defect, with deficit of occipital bones.
Results in enlarged foramen magnum and deformed spines.
“Star gazing foetus”, due to neck contorted in a way that turns face upwards (hyper-extended cervical spine, short neck, upturned face)

Question 8

Arhinencephaly (2)

Answer 8

No olfactory bulbs and tracts.
Seen with Kallmann syndrome - hypogonadism, mental retardation

Question 9

Rhombencephalosynapsis (2)

Answer 9

Congenital anomaly of the cerebellum, vermis doesn’t develop and cerebellar hemispheres fuse together.
Classically a transverse oriented single lobed cerebellum.

Question 10

Joubert syndrome (4)

Answer 10

“Molar tooth” appearance of the superior cerebellar peduncles (elongated like roots of a tooth).
Small or aplastic cerebellar vermis, absence of pyramidal decussation.
Associated with retinal dysplasia and multicystic dysplastic kidneys.
When seen in combination with liver fibrosis, called COACH syndrome

Question 11

Dandy Walker (7)

Answer 11

Absent Vermis.
“Torcular-lambdoid inversion” - the torcular is above the level of the lambdoid due to abnirmally high tentorium.
Spectrum of morphologies (from most severe to least severe):

Ventriculocele DWM variant: Cystic dilatation of 4th ventricle, complete or partial agenesis of the vermis, enlarged posterior fossa PLUS erosion into the occipital bone –> encephalocele.

Classic DWM: Cystic dilatation of 4th ventricle, complete or partial agenesis of the vermis, enlarged posterior fossa, superiorly rotated vermian remnant.

Variant DWM: Partly obstructed 4th ventricle, variable hypoplasia of the vermis, posterior fossa NOT enlarged.

Persistent Blake pouch: cyst below and posterior to vermis, normal vermis, posterior fossa NOT enlarged, tentorium is elevated.

Mega cisterna magna: Retro-cerebellar CSF space >10mm. Normal cerebellum. Enlarged posterior fossa caused by enlarged cisterna magna

Question 12

Failure to cleave DDx (2)

Answer 12

Holoprosencephaly (HPE),
Anencephaly

Question 13

Holoprosencephaly (HPE) (5)

Answer 13

Midline cleaving problem, brain fails to cleave into 2 separate hemispheres.
Cleavage occurs back to front (opposite of the formation of corpus callosum), so milder forms, the posterior cortex is normal and anterior cortex is fused.
Spectrum:
Lobar (mild): right and left hemispheres are separate (anterior/inferior frontal still sometimes fused). May be limited to absent septum pellucidum. Pituitary problems are common.
Semi-lobar: basic structure present but fused at the thalami. Olfactory tracts and bulbs are gone.
Alobar (severe): single, large ventricle with fusion of thalami and basal ganglia. No falx, no corpus callosum.

Question 14

HPE associations (4)

Answer 14

Single midline eye,
Solitary median maxillary incisor (MEGA-incisor)
Nasal process overgrowth leading to pyriform aperture stenosis.
Meckel-Gruber syndrome:
- Triad of: Holoprosencephaly, Multiple renal cysts, polydactyly

Question 15

Failure to Migrate/proliferate - DDx (6)

Answer 15

Hemimegalencephaly,
Lissencephaly-pachygyria Spectrum,
Grey matter heterotopias,
Schizencephaly,
Porencephalic cyst
Hydrancephaly

Question 16

Hemiencephalencephaly (6)

Answer 16

Rare but unique malforation characterized by enlargement of all or parts of one cerebral hemisphere.
Likely due to abnormal neuronal differentiation and cell migration in a single hemisphere.
Affected hemisphere may have focal or diffuse neuronal migration defects, including areas of polymicrogyria, pachygyria and heterotopia.
Look at which side (big or little side) has ventriculomegaly:
Small side + big ventricle = atrophy, as may be seen with Rasmussen’s encephalitis)
Big side + big ventricle = Hemimegalencephaly.

Question 17

Lissencephaly-Pachygyria spectrum (4)

Answer 17

Spectrum of diseases that cause relative smoothness of the brain surface.
Includes agyria (no gyri), pachygyria (broad gyri) and lissencephaly (smooth brain surface)
Type 1: Smooth brain, due to arrest of migration. Buzzwords include “figure 8” “hour glass appearance” “vertically orientated shallow sylvian fissures”. Associated with band heterotopias.
Type 2: Cobblestone brain, results from over migration. Not band heterotopia and cortex is thinner than type I.

Question 18

Grey matter heterotopias (5)

Answer 18

“Normal neurons in abnormal locations”
Can be grouped and subgrouped many times.
Broadly speaking:
Nodular (Subependymal (most common), Subcortical) or Diffuse (BAnd “Double cortex”, Lissencephaly, Laminar)
Associated with other congenital neurologic conditions.
Often compared with Tubers of TS (Tubers are higher on T2 and more often calcified).

Question 19

Schizencephaly (5)

Answer 19

Migrational disorder resulting in grey matter lined cleft that will extend through the entire hemisphere.
Comes in 2 forms, Closed lip (20%) and open lip (80%).
Association with:
- Optic nerve hypoplasia (30%)
- Absent septum pellucidum (70%)
- Epilepsy (50-80%)

Question 20

Porencephalic cyst vs open lip schizencephaly (2)

Answer 20

Similar appearance, but schizencephalic cleft should be lined with grey matter, and is a true malformation.
Porencephalic cyst is a hole from a prior encpehaloclastic event (ischaemia).

Question 21

Hydranencephaly (4)

Answer 21

Destruction of cerebral hemispheres. Skull fills with CSF.
Secondary to vascular insult in utero (double MCA infarct).
Could be in setting of TORCH causing a necrotizing vasculitis (HSV).
Had a normal brain, so there is a falx, but the cortical mantle is gone

Question 22

Lots of CSF - DDx (3)

Answer 22

No cortical mantle: Hydranencephaly
Cortical mantle:
- Falx present: Hydrocephalus
- Falx absent: Holoprosencephaly

Question 23

Herniation syndrome DDx (2)

Answer 23

Cephaloceles
Chiari malformation

Question 24

Cephaloceles (3)

Answer 24

Herniation of contents through a defect in skull
Meningoencephalocele - brain + meninges
Meningocele - Just meninges

Question 25

Chiari malformation (2)

Answer 25

Occur due to a mismatch between size and content of the posterior fossa.
3 types

Question 26

Type 1 Chiari malformation (5)

Answer 26

Headaches.
Criteria is one cerebellar tonsol >5mm below the foramen magnum.
Often accompanied by crowding of the posterior fossa, should look for syringohydromyelia (seen in 50%).
Tonsils ascend with age, so 3mm below foramen magnum in a 90 year old is abnormal.
Several associations, most important is Klippel-Feil syndrome (congenital C-spine fusion).

Question 27

Type 2 Chairi malformation (7)

Answer 27

More complicated than type 1.
Hydrocephalus seen in 90%.
Other findings include:
- Myelomeningocele (lumbar spine)
- Towering cerebellum,
- Tectal plate beaking,
- Long skiny 4th ventricle (elongated craniocaudally, short in other dimensions). normal 4th ventricle may suggest shunt malformation
- Interdigitated cerebral gyri (most likely shown on axial CT, single image)

Question 28

Type 3 Chiari malformation

Answer 28

Type 2 + encephalocele (either high cervical or low occipital)

Question 29

Craniosynostosis (7)

Answer 29

Premature fusion of one or more cranial sutures, resulting in odd shaped head.
Scaphocephaly (Sagittal suture( is the most common subtype, often referred to as a dolichocephaly.
Brachycephaly (bilateral coronal and/or lambdoid) often assocuated with syndromes.
- Brachycephaly + fused fingers = Aperts.
- Usually Brachycephaly + first arch (maxilla and mandible hypoplasia) = Crouzons
- Brachycephaly + wormian bones + absent clavicles = Cleidocranial dysostosis.
Phagiocephaly: Due to unilateral coronal or lambdoid suture fusion (frontal or occipital plagiocephaly).
Ipsilateral coronal fusion can elevate the superior orbital wall and cause Harlequin eye.
Trigonocephaly: Metropic suture

Question 30

Craniosynostosis trivia (4)

Answer 30

Saggital suture craniosynostosis affects boys in 80%.
Coronal suture affects more girls.
Lambdoid craniosynostosis favours right side (70%)
Turricephaly (the tower) is from both coronal and lambdoid fusion.

Question 31

Enlarged extra-axial fluid spaces (5)

Answer 31

Extra-axial fluid spaces >5mm.
BESSI = Benign Enlargement of Subarachnoid Space in Infancy.
Due to immature villi, hence kids grow out of it.
Most common cause of macrocephaly.
Typically resolves around 2 years old with no Rx.
Increased risk of subdural bleed, spontaneously or with minor trauma.

Question 32

Choanal atresia (8)

Answer 32

Malformation of the choanal openings.
“Failure to pass NG tube” and “Respiratory distress while feeding” (neonates tend to breathe through noses).
Usually unilateral, can be bony (90%) or membranous (10%).
Appearance is unilateral or bilateral posterior nasal narrowing, with thickening of the vomer.
Associated with syndromes
- CHARGE,
- Crouzons,
- DiGeorge,
- Treacher Colins,
- Foetal alcohol syndrome

Question 33

Piriform aperture stenosis (2)

Answer 33

Can occur in isolation or with choanal atresia.
High association with hypothalamic-pituitary-adrenal axis dysfunction.

Question 34

MELAS (2)

Answer 34

Mitochondrial disorder, with lactic acidosis and stroke like episodes.
SPECT: increased lactate, decreased NAA.

Question 35

Leukodystrophies (2)

Answer 35

Affect white mater in kids. If white matter is affected on MRI in child, think of this.
All are untreatable and fatal

Question 36

Canavans (3)

Answer 36

• Large head, <1YO.
• SPECT shows elevated NAA.
• Diffuse bilateral subcortical U fibres involved.

Question 37

Alexanders: (2)

Answer 37

• large head, frontal white matter involvement, <1YO

Question 38

Metachromatic: (4)

Answer 38

• Most common, buzzword is Tigroid, dark spots or stripes within the T2 bright demyelinated periventricular white matter.
• Normal head size.
• Infantile form age 1-2, juvenile form age 5-7.
• Deficiency of enzyme arylsulfatase

Question 39

Adreno Leukodystrophy (3)

Answer 39

• Normal head size. 5-10 years old.
• Symmetric occipital and splenium of corpus callosum white matter involvement.
• Sex linked recessive (peroxisomal enzyme deficiency) only in boys.

Question 40

Leigh disease (3)

Answer 40

• Normla head, <5YO.
• Focal areas of subcortical white matter. Basal ganglia and periaqueductal grey matter involvement.
• Also called subacute necrotizing encephalomyelopathy. Mitochondrial enzyme defect

Question 41

High yield MR SPECT trivia (8)

Answer 41

Highest normal peak is NAA.
Choline is elevated in anything causing cell turnover (tumour, infarct, inflammation)
Lactate and lipid peaks superimpose, need an intermediate TE (140) to cause inversion of lactate peak to see it.
Lactate-lipid peak has characteristic double peak at long TE (around 280).
Normal adult head should not have a lactate peak (marker of anaerobic respiration)
- Seen in necrotic tumours (high grade) and infection (cerebral abscess)
Normal to see lactate elevated in first few hours of life
Choline, Creatine and NAA Are in ascending order, the dotted line between their peaks is Hunter angle.

Question 42

Tumour vs Radiation necrosis on SPECT (3)

Answer 42

High grade tumour = Choline raised, NAA down, Lactate and ipids Up
Low grade tumour = Choline down, NAA down, Inositol up.
Radiation necrosis = choline down, NAA down, lactate up.

Question 43

Dx specific SPECT (5)

Answer 43

Alanine elevation is specific for meningiomas.
Meningiomas do NOT have elevated NAA.
Myoinisitol is elevated in Alzheimers and low grade glioma.
Glutamine is elevated in hepatic encephalopathy.
NAA peak is elevated in Canavans.