Chiari II Malformation

  • Etiology: Open lumbar spinal dysraphism leads to cerebrospinal fluid leakage through defect which leads to collapse of primitive ventricular system which leads to lack of expansion of rhomboencephalic vesicle which leads to small posterior fossa which leads to herniation of posterior fossa structures
  • Imaging MRI:
    — Classically: Interdigitation of gyri, tectal beaking, crowding of posterior fossa, enlargement of massa intermedia
    — Major intracranial findings: Small posterior fossa with hindbrain herniation, cerebellar tissue ectopia often asymmetric, effacement of subarachnoid space at cervicocranial junction
    — Minor intracranial findings: Tectal beaking, callosal dysgenesis, enlarged massa intermedia, migrational abnormalities (heterotopia), ventriculomegaly, fenestrated falx posteriorly, colpocephaly, lacunar skull
  • DDX:
  • Complications:
  • Treatment: Surgical closure of spinal dysraphism
  • Clinical: Majority of patients with Chiari II have open spinal dysraphism

Radiology Cases of Chiari II Malformation

Radiograph of lacunar skull in Chiari II malformation
Lateral radiograph of the skull shows a disordered arrangement of the inner table of the skull.
MRI of Chiari II malformation
Sagittal T1 MRI without contrast of the brain shows a small posterior fossa with downward cerebellar tonsil herniation and a small fourth ventricle. There is kinking of the spinal cord at the cervico-medullary junction. There is also agenesis of the body and rostrum of the corpus callosum.
MRI of Chiari II malformation and myelomeningocele
Sagittal T1 MRI without contrast of the brain (left) shows a small posterior fossa with downward cerebellar tonsil herniation and a small fourth ventricle. There is kinking of the spinal cord at the cervico-medullary junction. Sagittal (above right) and axial (below right) T2 MRI without contrast of the spine shows a low-lying conus medullaris with the spinal cord nerve roots terminating in a posteriorly located cerebrospinal fluid filled sac which is not covered by skin at the level of the L5-S1 vertebral bodies.