Chiari I Malformation

  • Etiology: Abnormality of dorsal induction where cerebellar tonsils extend below the foramen magnum and cause obstructive symptoms
  • Imaging: What to look for:
    — What is position of cerebellar tonsils
    — Is cerebrospinal fluid flow restricted
    — Is there hydrocephalus
    — Is there spinal cord syrinx
  • Imaging MRI:
    — Normal volume cerebellum,
    — Small posterior fossa in most
    — Cerebellar tonsils extend greater than 5 millimeters below foramen magnum (tonsillar ectopia)
    — Tonsillar pointing or peg-shaped
    — Effaced subarachnoid space at cervicocranial junction
    — Spinal cord syrinx in 50-60%
    — Can also see platybasia, clival hypoplasia, dental retroversion
  • DDX:
  • Complications: Obstructive symptoms
  • Treatment: Posterior fossa decompression if symptomatic
  • Clinical: Present with headaches

Radiology Cases of Chiari I Malformation

CT of Chiari I malformation
Sagittal midline 2D reconstruction of CT without contrast of the brain shows the cerebellar tonsils to be herniating > 5 mm beneath the foramen magnum.
Radiograph and MRI of abnormal adolescent idiopathic scoliosis
AP radiograph of the spine (left) shows thoracic scoliosis convex left (levoscoliosis) with a compensatory lumbar scoliosis convex right, thus this is an atypical scoliosis curve for adolescent idiopathic scoliosis. Sagittal T1 MRI without contrast of the cervical spine (above right) shows the tip of the cerebellar tonsils over 10 mm beneath the foramen magnum. Sagittal and axial T2 MRI of the thoracic spine (below right) show a large syrinx in the center of the thoracic spinal cord.