17 Primary craniospinal anomalies

Question 1

What proportion of Chiari 1 malformations are associated with a syrinx?

Answer 1

30-70%

Guinto G et al. 2004 Part 1 Contemp Neurosurgery

Question 2

What proportion of patient with Chiari 1 and syrinx have hydrocephalus?

Answer 2

7-9%

Question 3

What proportion of patients with Chiari 1 are asymptomatic?

Answer 3

15-30%

Question 4

What abnormalities of the C-spine are associated with Chiari 1?

Answer 4

anterior indentation at FM e.g. Basilar invagination
Klippel-Feil
occipitalisation of atlas
hypermobility of craniocervical junction

Question 5

What is the commonest presenting symptom in Chiari 1 malformation?

Answer 5

Pain (69%)

Question 6

What is the most characteristic finding on eye examination in Chiari?

Answer 6

Downbeat nystagmus

Question 7

What are the 3 main patterns of signs?

Answer 7

foramen magnum compression syndrome (22%): ataxia, corticospinal and sensory deficits, cerebellar signs, lower cranial nerve palsies. 37% have severe H/A

central cord syndrome (65%): dissociated sensory loss (loss of pain & temperature sensation with preserved touch & JPS), occasional segmental weakness, and long tract signs (syringomyelic syndrome). 11% have lower cranial nerve palsies

cerebellar syndrome (11%): truncal and limb ataxia, nystagmus, dysarthria

Question 8

How much herniation is most often cited to diagnose chiari 1?

Answer 8

5mm. Although this is not diagnostic nor essential.

Question 9

What is meant by Chiari zero malformation?

Answer 9

Patients with syringohydromyelia without hindbrain herniation that responded to p-fossa decompression

Question 10

Which patients are most likely to benefit from surgical intervention in Chiari 1?

Answer 10

Cerebellar syndrome responds well, as do headaches.

Symptoms lasting less than 2 years also do better than those that are >2 years

Question 11

What features are associated with Type 2 (Arnold)-Chiari malformation?

Answer 11

Myelomeningocoele (almost always)
hydrocephalus
Beaking of tectum
enlarged interthalamic adhesion (massa intemedia)
low attachment of tent

syringomyelia
bony abnormalities 
    - platybasia
   - Klippel-Feil
   - assimilation of atlas
 microgyria
hypoplasia of falx

Question 12

What are the recommended indications for post fossa decompression in Chiari 2?

Answer 12

Neurogenic dysphagia
Stridor
Apneic spells

Always make sure patient has a working shunt first!

Question 13

What is the commonest cause of mortality in Chiari 2?

Answer 13

Respiratory arrest.

Question 14

What is the Lemire Classification?

Answer 14

Proposed classification system for neural tube defects - splitting them into neurulation (open) and post neurulation (closed)

neurulation defects = non closure of neural tube e.g. craniorachischisis, anencephaly or myelomeningocoele in the spine.

post neurulation (migration disorders) e.g. microcephaly, hydranencephaly, lissencephaly, porencephaly, diastematomyelia, diplomyelia, syringomyelia, DWM

Question 15

What are the different forms of lissencephaly?

Answer 15

agyria: completely smooth surface
pachygyria: few broad & flat gyri with shallow sulci
polymicrogyria: small gyri with shallow sulci. May be difficult to diagnose by CT/MRI, and may be confused with pachygyria

Question 16

What are the different forms of migration defect?

Answer 16

Lissencephaly
Heterotopia
Cortical dysplasia
Schizencephaly

Question 17

What are the 2 different forms of schizencephaly?

Answer 17

can be open lipped or closed lipped.

Question 18

How do you differentiate between schizencephaly and a porencephalic cyst?

Answer 18

in Schizencephaly wall of the cyst is lined with cortical grey matter (usually abnormal, may have polymicrogyria)

Question 19

What classically causes hydranencephaly?

Answer 19

Bilateral ICA infarcts

Question 20

How can you differentiated between hydranencphaly and hydrocephalus?

Answer 20

EEG - No cortical activity in hydranencephaly
MRI/CT/US
Angiography

Question 21

What causes cyclopsia

Answer 21

severe holoprosencephaly

Question 22

What is holoprosencephaly associated with?

Answer 22

80% association with a trisomy (predominantly 13 and to a lesser extent trisomy 18)

Question 23

What happens embryologically in holoprosencephaly?

Answer 23

Telencephalic vesicle fails to fully cleave into 2 hemispheres.

Question 24

What is MCAP?

Answer 24

megalencephaly-capillary malformation syndrome (MCAP): an overgrowth syndrome with megalencephaly (often with hydrocephalus, Chiari malformation, polymicrogyria and seizures) and capillary malformations in the skin (usually on the face)

Question 25

What are the risk factors for development of NTD?

Answer 25

folate deficiency, Cocaine, heat in 1st trimester, obesity, valproic acid

Question 26

What is a neuroenteric cyst?

Answer 26

CNS cyst lined by epithelium resembling that of the GI, or less often, respiratory tract.

Question 27

Where in the CNS are you most likely to have a neuroenteric cyst?

Answer 27

Lower cervical/upper thoracic spine

Question 28

What is the mechanism of forming a neuroenteric cyst?

Answer 28

occurs as a result of persistence of the neuroenteric canal (temporary duct between the notochord and the primitive gut (amniotic and yolk sacs) formed during week 3 of embryogenesis by breakdown of the floor of the notochordal canal).

Question 29

Where are intracranial neuroenteric cysts likely to be found?

Answer 29

P-fossa (CPA, Midline anterior to brainstem or cisterna magna)

Question 30

supratentorial NEC, colloid cysts and Rathke’s may all arise from what?

Answer 30

remnants of Seesel’s pouch - a transient endodermally derived diverticulum of the cranial end of the embryonic foregut