1. eEdE-193
Brain MRI of Chiari II Malformation in the Era of Fetal Surgery Evolving from Fetal to Neonatal 
Eliana Bonfante
Katrina Hughes
Rajan Patel
Clark Sitton
Jennifer Johnston
Stephen Fletcher
Kenneth Moise
Anthony Johnson
Roy Riascos

2. Chiari II Malformation
Chiari II malformation is a complex developmental malformation of the central nervous system characterized by small posterior fossa and downward displacement of the cerebellum and brainstem through an enlarged foramen magnum.
Myelomeningocele (MMC) in the lumbar spine is almost always present and believed to be related to the pathophysiology of the intracranial changes.

3. Chiari II malformation Clinical implications in INFANTS
Infants and children younger than the age of 2 years present most frequently with cranial nerve and brainstem signs.
Respiratory difficulties:
Inspiratory stridor: vocal cord abduction paresis or paralysis from cranial nerve X dysfunction
PEAC (prolonged expiratory apnea with cyanosis)
Gastrointestinal disturbances :
Neurogenic dysphagia.
Chronic aspiration W
Para- or quadriparesis, hypotonia, opisthotonos, nystagmus, weak cry, and developmental delay.
Stenvensom KL NS focus
Stevenson. Chiari Type II malformation: past, present, and future. Neurosurg Focus 16 (2):Article 5, 2004 

4. Chiari II malformation Clinical implications in OLDER CHILDREN
Cervical myelopathy: Upper-extremity weakness and spasticity
Ataxia of both the upper extremities and trunk
Occipital headache and/or craniocervical pain
Syringomyelia
Hydrocephalus
Stevenson. Chiari Type II malformation: past, present, and future. Neurosurg Focus 16 (2):Article 5, 2004 

5. Myelomeningocele Consequences : Paraplegia Hydrocephalus
Chiari II malformation
Bowel and bladder dysfunction
Skeletal deformations
Neurocognitive impairment
Danzer et al. Fetal surgery for myelomeningocele: progress and perspectives. Dev Med Child Neurol. 2012 Jan;54(1):8-14

6. Myelomeningocele repair
Retrospective and prospective randomized studies suggest that fetal surgery of MMC before 26 weeks of gestation may
Preserve neuromotor function
Reverse hindbrain herniation
Reduce the need for ventriculoperitoneal shunting
Danzer et al. Fetal surgery for myelomeningocele: progress and perspectives. Dev Med Child Neurol. 2012 Jan;54(1):8-14

7. Fetal MRI Our Imaging Protocol
Small field of view images through the brain and spine in three planes
Single-shot fast epin echo (SSFSE)
Balanced steady-state free precession (bSSFP) for images with high signal fluid and soft tissue contrast
T1 gradient echo imaging for fat and blood
Diffusion-weighted imaging, echo planar images optional

8. Chiari II malformation Fetal MRI
MRI features of Chiari II malformation:
Small rounded cerebellum
Cerebellar herniation below the foramen magnum
Compression/obliteration of fourth ventricle and cisterna magna
Diffuse effacement of subarachnoid space
Callosal dysgenesis and subependymal heterotopias (common)
Bulas D. Fetal evaluation of spine dysraphism. Pediatr Radiol (2010) 40:1029–1037.

9. Crowded Posterior Fossa
Small rounded cerebellum wrapped around the brainstem (banana sign)
Near complete obliteration of the subarachnoid space
Sloping of the frontal bones (lemon sign)

10. Cerebellar Displacement
The cerebellar tonsils (white arrow) are displaced into the cervical canal. The fourth ventricle (yellow arrow) and cisterna magna are completely obliterated.
Postnatal ultrasound demonstrating a crowded posterior fossa (arrow) with no discernable fourth ventricle or cisterna magna.

11. Postnatal MRI Our imaging protocol
In patients that can cooperate with the exam or undergo general anesthesia a full pediatric MRI protocol including Sagittal T1, axial DWI, T2, FLAIR, and GRE, and coronal T2 is acquired.
Many of our patients receive a fast MRI protocol with axial, sagittal, and coronal propeller T2WI to avoid anesthesia. These images are adequate to make the diagnosis of Chiari II malformation and evaluate the hydrocephalus.

12. Chiari II malformation Postnatal MRI
Most reliable MRI features of Chiari II malformation: Downward herniation cerebellum below the foramen magnum Downward displacement of the medulla oblongata, pons and fourth ventricle Medullary kinking Abnormally shaped fourth ventricle Hypoplastic tentorium Beaked mesencephalic tectum
Geerdink et al. Essential features of Chiari II malformation in MR imaging:
an interobserver reliability study—part 1. Childs Nerv Syst (2012) 28:977–985

13. Downward herniation cerebellum below the foramen magnum
The foramen magnum is measured from basion to opisthion. The parasagittal images demonstrate to a better extent the amount of herniated tissue
Visualizing the cerebellar tonsils and the dens in the same axial image usually indicates downward displacement
At times the cerebellar tonsils appear detached from the cerebellum

14. Downward herniation cerebellum below the foramen magnum
In follow up studies the herniated cerebellar tonsils undergo atrophy and the caudal extension appears to decrease. Patient with history of fetal repair at 26 weeks, with post natal imaging at 2 days [left] and 11 months [right].

15. Downward displacement of the medulla oblongata, pons and fourth ventricle
Stretching of the pons which appears elongated, with diminished AP diameter
Downward displacement of the medulla oblongata, which appears compressed by the herniated tonsils and crowded spinal canal

16. Medullary kinking
Kink of the medulla dorsal to the upper cervical spinal cord

17. Abnormally shaped fourth ventricle
NS focus
The fourth ventricle, which is typically small and poorly visualized, frequently displaced into the cervical canal along with its choroid plexus

18. Hypoplastic tentorium
Underdeveloped tentorium with abnormally low insertion at the occipital bone

19. Beaked mesencephalic tectum
In the axial images the quadrigeminal plate appears deformed as a pointed or bulbous mass
The cerebral aqueduct is rarely visible. The quadrigeminal plate appears thickened due to fusion of the colliculi

20. CSF space at the foramen magnum
We have observed outpouching of the CSF near the inferior margin of the foramen magnum in Chiari II patients following repair of the myelomeningocele

21. Conclusion
We present a pictorial essay of the imaging findings in 14 patients with fetal and neonatal MRI who underwent fetal repair of MMC. Fetal MRI imaging findings include downward displacement of the cerebellum, compression of the fourth ventricle and cisterna magna, and effacement of the subarachnoid space. Post natal MRI most frequently demonstrates downward herniation cerebellum below the foramen magnum; downward displacement of the medulla oblongata, pons and fourth ventricle; medullary kinking; abnormally shaped fourth ventricle; hypoplastic tentorium; and beaked mesencephalic tectum. In our experience a fast protocol with T2WI in the Sagittal, Axial, and Coronal planes is useful to depict the relevant findings of Chiari II malformation and allows evaluation of the hydrocephalus.

22. References
Sutton, L. N. et al. Improvement in hindbrain herniation demonstrated by serial fetal magnetic resonance imaging following fetal surgery for myelomeningocele. JAMA 1999; 282:1826–1831
Geerdink, N. et al. Interobserver reliability and diagnostic performance of Chiari II malformation measures in MR imaging--part 2. Childs Nerv. Syst. ChNS Off. J. Int. Soc. Pediatr. Neurosurg. 2012;28:987–995
Geerdink, N. et al. Essential features of Chiari II malformation in MR imaging: an interobserver reliability study--part 1. Childs Nerv. Syst. ChNS Off. J. Int. Soc. Pediatr. Neurosurg. 2012;28:977–985
Grant, R. A. et al. Morphometric analysis of posterior fossa after in utero myelomeningocele repair. J. Neurosurg. Pediatr. 2011;7: 362–368
Danzer et al. Fetal surgery for myelomeningocele: progress and perspectives. Dev Med Child Neurol. 2012 Jan;54(1):8-14
Stevenson. Chiari Type II malformation: past, present, and future. Neurosurg Focus 16 (2):Article 5, 2004
Bulas D. Fetal evaluation of spine dysraphism. Pediatr Radiol (2010) 40:1029–1037.

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