Platybasia with Basilar invagination

MRI Mid sagittal section of CV junction shows:

• Platybasia (abnormal flattening of the skull base) evident by wide NTB (Nasion – Tuberculum – Basion) angle,
• Forward folding of the Clivus – Axis Angle (Angle of Wackenheim) causing lordotic tilt at CV junction, Elevated plane of the foramen magnum with retroflexed dens. 
• Basilar invagination evident by violation of Chamberlain’s (Hard palate - Ophisthion) line by the Dens. 
• Among two types of basilar invaginnation (Ventral and Paramesial), this is a Ventral variety of Basilar Invagination characterized by shortening of basiocciput due to short and horizontally placed clivus leading to forward facing plane of foramen magnum. 
• Abnormal sharp Clivus – Odontoid Angle causing exteme indentation over cervico medullary junction. However signal abnormality not very obvious in compressed medulla or cervico medullary junction.
• Normal Atlanto- Odontoid Distance. No obvious Atlanto Dental subluxation or dislocation. 

Imaging diagnosis : Platybasia with Basilar invagination.

Basal angle or NTB (Nasion – Tuberculum – Basion) angle. 

Chamberlain's line (Hard plate to Ophisthion)

Clivus – Axis Angle or ‘ Angle of Wackenheim’

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