chiari malformation. four types of chiari malformations types i, ii, iii, and iv
TRANSCRIPT
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 [