Clinical Presentation

A 14-year-old girl presenting with occipital headaches during Valsalva maneuver and anesthesia in both arms.

(A) Midsagittal T2-weighted image (WI) at the foramen magnum demonstrates a 12-mm descent of the tip of the cerebellar tonsils (arrow) below a line between the basion and the opisthion. A cervical syrinx is also noted. (B) Axial T2WI at the foramen magnum demonstrates ectopia of the cerebellar tonsils and effacement of the subarachnoid space. (C) Axial T2WI of the cervical spine shows a syrinx (arrow).

Differential Diagnosis