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

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.

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 

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 

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

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

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

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.

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)

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.

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.

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

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

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].

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

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

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

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

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

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

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.

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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