title: Clinical and Anatomical Features as well as Pathological Conditions of Surgically Treated Adult Patients with Occipitalization of the Atlas.
abstract: BACKGROUND
  This paper intends to clarify clinical and anatomical features as well as pathological conditions of surgically treated adult patients with occipitalization of the atlas.
  
  
  METHODS
  The authors reviewed 12 consecutive adult patients with occipitalization of the atlas who underwent surgery for myleopathy in our hospital. Mainly using preoperative computed tomography and three-dimensional computed tomography angiography, we investigated their anomalies of the osseous structures and vertebral artery at the cervical spine including the craniovertebral junction (CVJ). We also developed a new classification system for occipitalization of the atlas.
  
  
  RESULTS
  Atlantoaxial subluxation (AAS) was detected in 9 patients (75%). The condition of AAS was irreducible in 7 patients. Among these 7 patients, deformity at the lateral atlantoaxial joints was detected in 2 patients. C2-3 fusion was detected in 6 patients (67%) among 9 patients with AAS. Anomalies of the VA were detected in 11 patients (92%). Occipitalization of the atlas was classified into three types according to their pathological conditions. In type 1 (2 patients) the medial atlantoaxial joint is semi-dislocated and the lateral atlantoaxial joints are severely deformed. Type 2 (7 patients) exhibits AAS but the lateral atlantoaxial joints are not deformed. Type 3 (3 patients) is not associated with AAS and therefore does not exhibit osseous stenosis at the CVJ. In type 3 the myelopathy was caused by another coexisting condition.
  
  
  CONCLUSIONS
  Occipitalization of the atlas is classified into three types. The main pathological condition in both types 1 and 2 is AAS. Reduction of AAS is essential in both; however, reduction of AAS in type 1 is more technically demanding than in type 2. The pathological conditions of type 3 are completely different from those of the others, so an accurate diagnosis must be made. The new classification system is a useful guide for surgeons when planning surgical strategies.
authors.affiliation: Yokohama Minami Kyosai Hospital, Yokohama, Kanagawa, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Tatara
authors.affiliation: Gunma Spine Center, Harunaso Hospital, Takasaki, Japan.
authors.forename: Takachika
authors.initials: T
authors.lastname: Shimizu
authors.affiliation: Gunma Spine Center, Harunaso Hospital, Takasaki, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Fueki
authors.affiliation: Gunma Spine Center, Harunaso Hospital, Takasaki, Japan.
authors.forename: Masatake
authors.initials: M
authors.lastname: Ino
authors.affiliation: Gunma Spine Center, Harunaso Hospital, Takasaki, Japan.
authors.forename: Naofumi
authors.initials: N
authors.lastname: Toda
authors.affiliation: Gunma Spine Center, Harunaso Hospital, Takasaki, Japan.
authors.forename: Tetsu
authors.initials: T
authors.lastname: Tanouchi
authors.affiliation: Gunma Spine Center, Harunaso Hospital, Takasaki, Japan.
authors.forename: Nodoka
authors.initials: N
authors.lastname: Manabe
keywords: atlantoaxial subluxation; craniovertebral junction; occipitalization of the atlas; vertebral artery