Chiari malformation
Pronunciation: kee-AH-ree
Structural defect characterized by extension of cerebellar tonsils below the foramen magnum, potentially causing CSF flow obstruction.
Full Definition
Chiari malformation is a group of structural defects involving the cerebellum, brainstem, and skull base, with Type I being the most common form characterized by cerebellar tonsillar herniation below the foramen magnum. The condition can be congenital or acquired and may cause obstruction of cerebrospinal fluid flow, leading to syringomyelia, headaches, and neurological symptoms. Imaging diagnosis relies on sagittal MRI measurements showing tonsillar descent greater than 5mm below the McRae line. Associated findings may include syrinx formation, craniovertebral junction abnormalities, and hydrocephalus. Treatment may require posterior fossa decompression depending on symptomatology and associated complications.
Usage
Usage note: Specify type (I, II, etc.) when known; include measurement of tonsillar descent.
In Context
- "Sagittal T1-weighted images demonstrated Chiari I malformation with 8mm tonsillar herniation." — MRI report
- "The patient's syringomyelia was associated with underlying Chiari malformation." — Clinical correlation