Complex Chiari

 “Bump” thought to represent aberrant clava, used as marker for cervicomedullary junction


image Abnormal tonsillar “pistoning” motion, reduced CSF flow around foramen magnum and cerebellar tonsils


• ± syringohydromyelia, ventral cervicomedullary compression

• ± odontoid retroflexion, small posterior fossa, clival anomalies, platybasia




Top Differential Diagnoses




• Chiari 1 malformation

• Chiari 2 malformation


Pathology




• Medullary pyramid decussation anatomic border between spinal cord, medulla oblongata
image Normal obex level is 10-12 mm above foramen magnum

image Obex displaced to or below foramen magnum level in CCM patients


Clinical Issues




• Headaches, myelopathy, bulbar symptoms, lethargy, failure to thrive


Diagnostic Checklist




• Consider CCM in context of cerebellar tonsillar herniation + low obex, dorsal medullary “bump”

• CCM considered subgroup of Chiari 1 malformation with more severe clinical phenotype

image
(Left) Sagittal T1WI MR shows classic features of a complex Chiari malformation, including marked cerebellar tonsil ectopia image and inferior displacement of the obex image. The 4th ventricle is in normal position.


image
(Right) Sagittal T2WI MR reveals characteristic tonsillar ectopia image and inferior displacement of the cervicomedullary junction, marked by position of the obex image below the foramen magnum. There is also mild retroflexion of the odontoid process image and mild clivus image foreshortening.

image
(Left) Sagittal T2WI MR (different patient) shows a prominent obex image and pointed, ectopic cerebellar tonsils image. The odontoid process image is retroflexed and the clivus image is foreshortened, with a reduced craniocervical angle with platybasia.


image
(Right) Sagittal T2WI MR (different patient) reveals striking odontoid image retroflexion. Note also severe cerebellar tonsillar ectopia image extending inferiorly to the C3 level and cervical syringohydromyelia image. The prominent, inferiorly displaced obex image confirms a complex Chiari malformation.


TERMINOLOGY


Abbreviations




• Complex Chiari malformation (CCM), Chiari 1.5


Synonyms




•  


Definitions




• Caudal cerebellar tonsil and brainstem herniation with dorsal cervicomedullary “bump”

• Frequently associated craniovertebral junction (CVJ) anomalies


IMAGING


General Features



Tags:
Oct 5, 2016 | Posted by in NEUROLOGICAL IMAGING | Comments Off on Complex Chiari

Full access? Get Clinical Tree
Get Clinical Tree app for offline access