Ch17 Craniospinal anomalies Flashcards
What proportion of Chiari 1 malformations are associated with a syrinx?
30-70%(Guinto G et al. 2004 Part 1 Contemp Neurosurgery)
What proportion of patient with Chiari 1 and syrinx have hydrocephalus?
7-9%
What proportion of patients with Chiari 1 are asymptomatic?
15-30%
What abnormalities of the C-spine are associated with Chiari 1?
Anterior indentation at FM e.g. Basilar invagination
Klippel-Feil
Occipitalisation of atlas
Hypermobility of craniocervical junction
What is the commonest presenting symptom in Chiari 1 malformation?
Occipital headache (69%)
What is the most characteristic finding on eye examination in Chiari?
Downbeat nystagmus
What are the main signs associated with Chiari 1?
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
Hydrocephalus and raised ICP
How much herniation is most often cited to diagnose Chiari 1?
5mm. Although this is not diagnostic nor essential.
What is meant by Chiari zero malformation?
Patients with syringohydromyelia without hindbrain herniation that responded to p-fossa decompression
Which patients are most likely to benefit from surgical intervention in Chiari 1?
Cerebellar syndrome responds well, as do headaches.
Symptoms lasting less than 2 years also do better than those that are >2 years
What features are associated with Type 2 (Arnold)-Chiari malformation?
Myelomeningocoele (almost always)
Hydrocephalus
Beaking of tectum
Enlarged interthalamic adhesion (massa intemedia)
Low attachment of tent / torcula
Syringomyelia
Bony abnormalities - platybasia - Klippel-Feil - assimilation of atlas microgyria
Hypoplasia of falx
What are the recommended indications for post fossa decompression in Chiari 2?
Neurogenic dysphagia
Stridor
Apneic spells
Always make sure patient has a working shunt first!
What is the commonest cause of mortality in Chiari 2?
Respiratory arrest.
What is the Lemire Classification?
Proposed classification system for neural tube defects - splitting them into pre neurulation (open) and post neurulation (closed) 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
What are the different forms of lissencephaly?
Agyria: completely smooth surface
Pachygyria: few broad and flat gyri with shallow sulci
Polymicrogyria: small gyri with shallow sulci. May be difficult to diagnose by MRI and may be confused with pachygyria
What are the different forms of migration defect?
Lissencephaly
Heterotopia - arrest of radial migration
Cortical dysplasia - a deep cleft that doesn’t communicate with the ventricle
Schizencephaly - cleft that communicates with the ventricle
What are the 2 different forms of schizencephaly?
Open lipped - communicates with cortical surface
Closed lipped - outpouching from the ependyma that does not communicate with cortical surface
How do you differentiate between schizencephaly and a porencephalic cyst?
InSchizencephaly the wall of the cyst is lined with cortical grey matter (usually abnormal, may have polymicrogyria), porencephalic cysts are lined by white matter.
What classically causes hydranencephaly?
Bilateral ICA infarcts (post neurulation defect)
How can you differentiated between hydranencphaly and hydrocephalus?
EEG - No cortical activity in hydranencephaly
MRI/CT/US - loss of anterior circulation but PCA distribution intact
Angiography - confirms no flow from ICAs bilaterally
What causes cyclopsia?
severe holoprosencephaly - failure of the telencephalic vesicle to cleave into two hemispheres
What is holoprosencephaly associated with?
80% association with a trisomy (predominantly 13 and to a lesser extent trisomy 18)
What happens embryologically in holoprosencephaly?
Telencephalic vesicle fails to fully cleave into 2 hemispheres.
What is MCAP?
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)
What are the risk factors for the development of NTDs?
Folate deficiency, Cocaine, Heat in 1st trimester, Obesity, Valproic acid
What is a neuroenteric cyst?
CNS cyst lined by epithelium resembling that of the GI, or less often, respiratory tract.
Where in the CNS are you most likely to have a neuroenteric cyst?
Lower cervical/upper thoracic spine
What is the mechanism of forming a neuroenteric cyst?
As a result of the persistence of the neuroenteric canal, a temporary duct between the notochord and the primitive gut (amniotic and yolk sacs) formed during week 3 of embryogenesis by the breakdown of the floor of the notochordal canal.
Where are intracranial neuroenteric cysts likely to be found?
P-fossa (CPA, Midline anterior to brainstem or cisterna magna)
Supratentorial locations are mainly suprasellar
Supratentorial neurenteric cysts, colloid cysts and Rathke’s may all arise from what?
Remnants of Seesel’s pouch - a transient endodermally derived diverticulum of the cranial end of the embryonic foregut
How would you investigate a patient with a Chiari 1 malformation?
MRI brain - tonisillar decent, brain stem compression, hydrocephalus, empty sella, associated conditions
MRI C- spine for syrinx and bony abn; CISS sequence for arachnoid web
CT skull base for posterior fossa volume, assimilation and skull base abn (platybasia etc)
Cine MRI - demonstrates CSF flow at FM
(CT myelogram if a contraindication to MRI)
What is the most commonly performed condition for Chiari 1?
Posterior fossa decompression through suboccipital craniectomy and C1 laminectomy
Size of craniectomy should be 3cm x 3cm. If too large causes cerebllar ptosis (sagging).
Y-shaped durotomy (note the torcula may be low!)
+/- dural expanstion graft
+/- tonsillar bipolar / adhesiolysis
What are craniolacunia?
Rounded defects in the skull associated with sharp borders. Found in Chiari 2. Not associated with hydrocephalus.
What is the outcome of p-fossa decompession for Chiari?
70% near resolution of symptoms; 20% no difference
What is Chiari 1.5?
Severe case of Chiari 1 with obex below the FM. Associated with platybasia.
What is Chiari 3?
Controversial if exists but is cerebellar herniation with occipital encephalocele.
What is Chiari 4?
Cerebellar hypoplasia with small p-fossa.
How would you perform an FMD?
Informed Consent
GA / Prone / Mayfield pins / head elevated
Midline incision inion to C2
Suboccipital craniectomy 3x3 cm and C1 arch removal
USS for CSF flow.
If no flow then Y-shaped durotomy +/- expansion graft +/- adhesiolysis +/- tonsillar shrinkage
What happens if the suboccipital craniectomy is too large following FMD?
Cerebellar ptosis (sagging)
What abnormality is commonly associated with a Schizencephaly?
Absent septum pellucidum
What the types of holoprocencephaly?
Lobar, semi lobar and alobar
What is microcephaly?
Head circumferences <2 S.D. from the mean
What are the causes of microcephaly?
- Infections (TORCH / Zika etc)
- Malnutrition
- Toxins - maternal ETOH / Cocaine
What serum marker suggests the presence of a neural tube defect?
AFP. If raised at 20 weeks suggests a 250x risk of NTD.
What are the different types of holoprosencephaly?
Alobar - complete failure of separation with a single cerebrum
Semilobar - Frontal and parietal lobes fused but posterior interhemispheric fissure present
Lobar - Only frontal lobes fused
Syntelencephaly - Middle hemipshere fusion only
Arrhinencephaly - Absent olfactory bulbs, olfactory tracts and gyrus rectus
In cerebral palsy, which part of the brain is most affected?
The periventricular WM as this is a watershed area in the neonatal period due to the increased metabolic demand of myelinating white matter. Causes periventricular leukomalacia.
What genetic syndrome is associated with porencephalic cysts?
COL4A1 mutation. Note porencephalic cysts are lined by WM whilst schizencephaly is lined by GM.
Proboscis - snout like protrusion from the forehead
Cyclopsia
Cleft lip/palate
Hypotelorism
Solitary median maxillary central incisor
How can lobar holoprosencephaly and septo-optic dysplasia be differentiated?
Snake under the skull sign: The ACA is anteriorly displaced in lobar holoprosencephaly to under the frontal bone due to failure of cleavage of the frontal lobes. Of note, septo-optic dysplasia does not demonstrate fusion fo the frontal lobes or fornices and there is hypoplasia of the optic nerves.
What are the features of alobar holoprosencephaly?
Thalami are fused with a single fused posteriorly located ventricle
What are the features of semilobar holoprosencephaly?
The cerebral hemispheres are fused anteriorly and at the thalami. The olfactory tracts are missing. Agenesis or hypoplasia of the corpus callosum.
Least severe type characterised by presence of the falx and interhemispheric fissure along the entire midline. The hemispheres are present but subtle fusion abnormalities are seen between parts of the lobes e.g. frontal horns, fusion of the fornices, absence of the septum pellucidum / callosal hypoplasia and fused fornix.
What are the features of septo-optic dysplasia?
Part of the holoprosencephaly spectrum with:
Optic nerve hypoplasia
Absence of the septum pellucidum
Hypothalamic/pituitary dysfunction in ⅔
