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cerebellar tonsillar herniation
Displacement of cerebellar tonsils through the foramen magnum, indicating increased intracranial pressure.
Full Definition
Cerebellar tonsillar herniation occurs when the cerebellar tonsils are pushed downward through the foramen magnum due to increased intracranial pressure or mass effect. This is a critical finding requiring immediate clinical attention as it can compress the medulla and result in respiratory compromise. On imaging, tonsillar descent greater than 5mm below the foramen magnum is considered abnormal. This condition can be congenital (as in Chiari malformation) or acquired due to mass lesions or cerebral edema.
Usage
Usage note: Always specify measurement in millimeters when describing tonsillar descent.
In Context
- "The radiologist noted 8mm of cerebellar tonsillar herniation on the sagittal T1-weighted images." — MRI report
- "Signs of cerebellar tonsillar herniation were absent despite the large frontal mass." — CT interpretation
Also known as
tonsillar descent
Chiari herniation
Don't confuse with
cerebellar ectopia
Chiari malformation