Chiari Malformation

Four types of Chiari malformations types I, II, III, and IV

Chiari 1 malformation

Important features Small posterior cranial fossa herniation of the cerebellar tonsils through

the foramen magnum into the cervical spinal canal

Distention CSF of the central canal of spinal cord (ie, hydromyelia) or paracentral cavities (ie, syringomyelia) in 25%

not directly associated with other congenital brain malformations

Pathophysiology mesodermal disorder Underdevelopment of the occipital somites of

the para-axial mesoderm produces overcrowded (PCF).

Tonsillar herniation occurs secondarily as a result of mechanical factors.

Causes May have genetic basis its association with

known genetic disorders such as achondroplasia and Klippel-Feil syndrome

some families suggest an AD Acquired CMI is reported to develop after

lumboperitoneal or ventriculoperitoneal shunt placement,

CSF flow During systole: increase cerebral flow

craniocaudal displacement. during diastole: elastic recoil

reversal

remain asymptomatic for prolonged periods aged 10-30 years

arachnoidal adhesions may increase the compression of the hindbrain and spinal cord and further interfere with CSF flow at the foramen magnum and thus cause symptoms

Normal anatomy

Normally adult 5 mmInfant upto 6 mm

Intracrainial findings CT FINDINGS: Obliterated cisterna magna Hydrocephalus Flattened spinal cord Tonsillar ectopia Peglike cerebellar tonsils Normally positioned fourth ventricle

MRI FINDINGS Displacement of cerebellar tonsils

below the level of the foramen magnum

Pointed and/or peglike tonsils Narrow PCF Elongation of the fourth ventricle,

which remains in the normal position Hindbrain abnormalities Obstructive hydrocephalus syringomyelia

EXTRA CRANIAL FINDINGS Platybasia, basilar invagination (25-50%) Atlantooccipital assimilation (1-5%) Klippel-Feil syndrome (5-10%) Incomplete ossification of C1 ring (5%) spina bifida at the C1 level Retroflexed odontoid process (26%) Scoliosis (42%) Kyphosis Increased cervical lordosis Cervical ribs Fused thoracic ribs

Platybasia, basilar invagination abnormal flattening of the skull base When platybasia is associated with basilar

invagination, or the inward and upward migration of the cervical spine through the foramen magnum, signs and symptoms of compression of the brainstem and upper cervical cord can result (5).

Atlantooccipital assimilation The union of the atlas with the occipital bone constitutes the anomaly. There may be partial

or complete union

Klippel feil syndrome They described patients who had a short,

webbed neck; decreased range of motion (ROM) in the cervical spine; and a low hairline.

classified the syndrome into 3 categories:

Chiari II malformation

THEORIES HYDRODYNAMIC THEORY: posterior fossa

herniation was related to supratentorial hydrocephalus

TRACTION THEORY:tethered spinal cord near the myelomeningocele may pull the cerebellum and medulla into the cervical canal

complex deformity of the calvarium, dura, and hindbrain, and it is almost always associated with myelomeningocele

LACUNAR SKULL

CONCAVE CLIVUS

Hypoplastic fenestrated falx

Cerebellar peg: Protrusion of vermis and hemispheres through the foramen magnum (90%) results in craniocaudal elongation of cerebellum behind the spinal cord

Medullary kink: The medulla is kinked inferiorly (75%) and lies dorsal to the spinal cord, which is unable to descend because of competent dentate ligaments

Towering cerebellum or vermian pseudotumor: The cerebellar hemispheres and vermis also extend above the incisura of the tentorium

Tubelike elongated fourth ventricle: The fourth ventricle is elongated craniocaudally, narrowed transversely, and decreased in anteroposterior diameter

The cerebellopontine cistern and the cisterna magna are obliterated.

Beaked tectum: Variable degrees of fusion of the colliculi and tectum result in prominent beaking and inferior displacement of the tectal plat

Hydrocephalus Colpocephaly: The occipital horns and atria

are often mildly enlarged because of maldeveloped occipital lobes

Prominent massa intermedia: A prominent massa intermedia, herniation of the third ventricle into the suprasellar cistern, and an enlarged suprapineal recess are often seen

Associated anomalies Myelomeningocele (88-100%) Dysgenesis of corpus callosum (80-90%) Obstructive hydrocephalus following closure

of myelomeningocele (50-98%) Syringohydromyelia (50-90%) Aqueductal stenosis (70%) Absence of septum pellucidum (40%) Contracted, narrow gyri (stenogyria; 50%)

HeterotopiasDiastematomyeliaSegmentation anomalies (<10%),

incomplete C1 archMalrotation of the posterior arches of C1 and C2

(1)Colpocephaly;) 2 (beaked tectum;

) 3 (cascade of an inferiorly displaced vermis behind the medulla;

) 4 (elongated, tubelike fourth ventricle ;

)5 (low-lying torcular herophili ;)6 (cerebellar hemispheres

wrapping around the brainstem anteriorly;

) 7 (concave clivus ;)8 (medullary spur; and

)9 (medullary kink.

Chiari III malformation

Incompatible with life This condition always comprises of high

cervical and low occipital encephalocele Encephaloceles contain varying amounts of

brain i.e. cerebellum, occipital lobes, ventricles and sometimes pons and medulla

Herniated lesion may be strikingly abnormal and often nonfunctioning because of necrosis, gliosis, fibrosis and the presence of heterotropias

Associated anomalies include petrous and clivus scalloping, over/undergrown cerebellar hemisphere, tonsillar herniation, deformed midbrain, hydrocephalus, dysgenesis of corpus callosum, posterior cervical vertebral agenesis, spinal cord syrinx [