1. Chiari Malformation

2.  Four types of Chiari malformations types I, II, III, and IV

3. Chiari 1 malformation

4. 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

6. 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.

7. 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,

8. CSF flow  During systole: increase cerebral flow craniocaudal displacement.  during diastole: elastic recoil reversal

9.  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

10. Normal anatomy Normally adult 5 mm Infant upto 6 mm

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

12. 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

16. 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

17. 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).5

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

20. 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.

23. Chiari II malformation

24. 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

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

27. LACUNAR SKULL

28. CONCAVE CLIVUS

29. Hypoplastic fenestrated falx

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

31.  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

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

33.  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.

34.  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

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

36.  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%)

37.  HeterotopiasDiastematomyeliaSegmentation anomalies (<10%),  incomplete C1 archMalrotation of the posterior arches of C1 and C2

38. (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.

47. Chiari III malformation

48.  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

49.  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 [