FINDINGS Figure 71-1. Sagittal T1WI through the fourth ventricle. There is inferior descent of the pointed cerebellar tonsils (arrow) below the foramen magnum. The fourth ventricle (star) is in normal position. There is a subtle kinking at the junction of the medulla and the spinal cord (chevron). Midline supratentorial structures are normal without obvious hydrocephalus. Figure 71-2. An axial FLAIR through the level of the foramen magnum. There is obliteration of the cisterna magna by the cerebellar tonsillar ectopia (arrows).
DIFFERENTIAL DIAGNOSIS Chiari I malformation (CIM), idiopathic intracranial hypertension, low-lying tonsils, transforaminal herniation.
DIAGNOSIS Chiari I malformation (CIM).
DISCUSSION
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