Female, 16 years old, with history of chronic intermittent headaches. Please evaluate for structural abnormality, especially the craniocervical junction. The right cerebellar tonsil demonstrates a pointed configuration and descends approximately 4 mm below the level of the foramen magnum. The CSF space is effaced around the right tonsil. The left cerebellar tonsil seems to terminate at the level of the foramen magnum and shows a normal round morphology.The remainder of the brain demonstrates normal morphology and signal characteristics. No restricted diffusion is seen. No parenchymal edema or mass effect is identified. There is no evidence of intracranial hemorrhage or any abnormal extra axial fluid collection. The ventricular system is normal.
Descent of the right cerebellar tonsil approximately 4 mm below the level of the foramen magnum is at least compatible with ectopia. Although the strict imaging criteria for a Chiari I malformation are not met, the fact that the tonsil is relatively pointed with effacement of the surrounding CSF space would nevertheless suggest the possibility of a Chiari I-type process.The remainder of the examination is unremarkable with no additional findings to account for the patient's headaches.