NeuroradiologyBasilar impression
a mild form of craniovertebral junction anomaly characterized by an invagination (basilar invagination) of the margins of the foramen magnum upward into the skull. Basilar impression is the consequence of a range of variations in size, shape and orientation of the occipital condyles, clivus and petrous bones.
The radiological criteria are based on three lines drawn on AP and lateral tomograms: Chamberlains line, McGregor's line and the digastric line. In pronounced basilar impression the atlas may be surrounded by occipital bone; in Paget's disease the invagination may be considered as secondary to softening of the skull bone that bear the occipital condyles.
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