Chiari 1 malformation with basilar invagination

Case contributed by Ahmed Abdrabou


Recurrent headache, numbness and weakness of both hands.

Patient Data

Age: 17 years
Gender: Male

MR spine revealed cystic syringohydromyelia involving all the cervical and dorsal cord from the medulla oblongata superiorly to the conus medullaris inferiorly.

Small posterior fossa with downward herniation of the cerebellar tonsils are noted. No hydrocephalic changes.

Horizontal orientation of the clivus associated with posterior tilt and superior migration of the odontoid process.

Annotated image

The tonsillar herniation is estimated to be 7 mm below the foramen magnum

The dense projects 9 mm above the chamberlain line and 11 mm above the McGregor line.

Case Discussion

Chiari I malformation consists of downward tonsillar herniation and syringomyelia. As an association with this syndrome there is also basilar invagination as shown by flat basioccipt (platybasia) and upward odontoid projection. Normally the dens should project up to 3 mm above Chamberlain line and 5 mm above Mc Gregor line.

How to use cases

You can use Radiopaedia cases in a variety of ways to help you learn and teach.

Creating your own cases is easy.

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.