Chiari I malformation

Case contributed by Dr Bruno Di Muzio


Incidental finding while investigating possible vertebral artery dissection.

Patient Data

Age: 39
Gender: Male

CT Brain (selected series)

Chiari malformation with cerebellar tonsils extending 13 mm below the foramen magnum. There is an associated large syrinx within the cervical cord. This would be better evaluated on MRI.

No evidence of acute ischemia. No intra or extra-axial hemorrhage is seen.

The extracranial vessels, circle of willis and vertebrobasilar system opacity normally. No evidence of significant arterial stenosis, aneurysm or vascular malformation. No evidence of dissection.

Cervical spine alignment normal. No suspicious bone lesions. Lung apices clear.Conclusion

Chiari malformation with large syrinx. Further evaluation with MRI is recommended if this has not been previously diagnosed.


MRI Brain and Cervical spine

Low lying cerebellar tonsils (1.3 cm below the foramen magnum) again noted.

Posterior fossa normal in size.

Normal appearance of the midline structures, in particular the fourth ventricle and corpus callosum.Small focus of encephalomalacia in right cerebellar peduncle in keeping with established infarct in this location.Minor asymmetry of the occipital horns (right larger than left) is unchanged.

No evidence of hydrocephalus.No other abnormality of the brain parenchyma. No abnormal susceptibility related signal loss. No abnormal diffusion restriction.

Extensive syringhydroomyelia involving the cervical and thoracic cord, extending from just below the cervicomedullary junction to the level of T11-12. This abnormality is most marked between C2 and T3, where the cord is expanded and there is thinning of the cord parenchyma. There are multiple septations within the cervical and upper thoracic portion of the syrinx. It measures up to 1.3 x 0.9 cm in maximal axial dimensions.

Minor disc osteophyte complexes at C6-7

and T10-11 which do not cause significant spinal canal or foraminal stenosis.

Normal alignment in the cervical and thoracic spine.


Chiari 1 malformation with extensive cervical and thoracic syringohydromyelia as described above. No evidence of hydrocephalus.

Established infarct in right middle cerebellar peduncle.

Case Discussion

This case demonstrates typical radiologic features of a Chiari I malformation, wich is the most common variant of the Chiari malformations

The tonsillar herniation is assessed measuring its distance from the line that connects the inner margins of the foramen magnum (basion to opisthion). Above 5 or 6 mm is considered a Chiari I, values between 3 to 6 mm are indeterminate, and needs to be correlated with symptoms and presence of syrinx. 

Cervical cord syrinx is present in ~35% (range 20-56%) of patients with Chiari I. 


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Case information

rID: 40391
Published: 22nd Oct 2015
Last edited: 14th Aug 2019
Tag: rmh
Inclusion in quiz mode: Included

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