4）Arnold-Chiari畸形：因小脑扁桃体、延髓及第四脑室疝入椎管内，使脑脊液循环受阻引起脑积水，常并发脊柱裂及脊膜膨出。
O O B-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis I-dis O O B-sym I-sym I-sym I-sym I-sym O B-sym I-sym O B-sym I-sym I-sym I-sym O O B-sym I-sym O O O B-sym I-sym I-sym O O O O O O B-dis I-dis I-dis O O O O B-dis I-dis I-dis O B-dis I-dis I-dis I-dis O