Figure 1.

(A-C): MRI sagittal midline T1-weighted images of three different patients with scoliosis. The reference lines (BO-lines) connect the basion (B) and opisthion (O). (A) 16 years old boy with IS and no cerebellar ectopia. The cerebellar tonsils are above the BO-line. (B) 16 years old girl with IS showing descent of cerebellar tonsils 4 mm below the BO-line (tonsillar ectopia). (C) 14 years old girl with scoliosis, and Chiari I malformation showing cerebellar tonsils 8 mm below the BO-line (Chiari malformation).