Case contributed by A.Prof Frank Gaillard

Foramen magnum stenosis with significant compression of the cervico-medullary junction.


The clivus is short such that the tip of the odontoid is elevated to  the level of the posterior lip of foramen magnum. At this point, the AP diameter of the bony craniocervical junction measures only 7 mm. The cord fills the available subarachnoid space at this level, and there is impingement on the cord by the posterior lip of foramen magnum. Subtle T2 hyperintensity is shown in the medulla and in the upper cord down to the level of junction of odontoid with body of C2. Some T2 hyperintensity within or below the cruciform ligament raises a possibility of a little fluid but no evidence of ligamentous disruption is shown. 

The sagittal images show slight elevation of the anterior cerebellar tentorium. This is likely due to the relatively small posterior fossa. The pons and mid brain are unremarkable with plentiful room anteriorly. 
The third and lateral ventricles are mildly prominent as are the cortical subarachnoid spaces but there is no evidence of frank hydrocephalus. The grey and white matter signal intensities are normal.

The major venous sinuses are quite prominent within the cranium. There is a large midline occipital vein beneath the cerebellum which divides around the foramen magnum and I think the branches enter the jugular veins at the jugular canals . I believe the jugular foramina are patent and the upper most jugular veins are visible in the sagittal and axial images.

Case Discussion

Three month old child with achondroplasia.

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Case information

rID: 6251
Case created: 15th May 2009
Last edited: 30th Aug 2015
Inclusion in quiz mode: Included

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