title: A morphometric study of the atlas occipitalization and coexisted congenital anomalies of the vertebrae and posterior cranial fossa with neurological importance.
abstract: OBJECTIVE
  Our study highlights the morphometry of the partial and complete atlas occipitalization (AOZ), its coexistence with fusions of the 2nd and 3rd cervical vertebrae and morphological and morphometric abnormalities of the posterior cranial fossa that are of paramount neurological importance.
  
  
  METHODS
  One hundred and eighty adult dry skulls, the atlas and axis vertebrae were examined.
  
  
  RESULTS
  Four skulls (2.2 %) showed AOZ. Two of them (1.1 %) presented a partial AOZ, one male skull (0.6 %) a complete AOZ and a female skull (0.6 %) had a fused left hemiatlas with the occipital bone and a fusion of the 2nd and 3rd cervical vertebrae. The inner anteroposterior and transverse diameters of the foramen magnum (FM) in the control group were 34.6 ± 3.46 and 29.3 ± 3.47 mm. Only the skull with the complete AOZ had a reduced outer anteroposterior diameter of the FM (29.8 mm), while no specimen was found with a reduced transverse diameter. A wide total decrease (range 13.1-50.9 %) in the surface area of the FM in skulls with AOZ was detected. Extracranial, the clivus length in two skulls with AOZ was smaller than the normal range. No skull was detected with a reduction in the intracranial length of the clivus. All skulls with the AOZ had a vermian fossa.
  
  
  CONCLUSIONS
  The study adds important morphometric details about the partial and complete AOZ and correlates the phenomenon of synostosis with the narrowing of the FM, particularly in the case of complete AOZ. Awareness of the AOZ and other fusions of the upper cervical vertebrae and their topographical relations and attendant problems are of paramount importance to surgeons, when operate to the craniocervical junction, or interpret imaging studies to plan a safe surgery for nerve or spinal tissue decompression.
authors.affiliation: Department of Anatomy, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, P.O. Box 300, 54124, Thessaloniki, Greece. natsis@auth.gr.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Natsis
authors.affiliation: Department of Anatomy, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, P.O. Box 300, 54124, Thessaloniki, Greece.
authors.forename: Christos
authors.initials: C
authors.lastname: Lyrtzis
authors.affiliation: Department of Anatomy, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, P.O. Box 300, 54124, Thessaloniki, Greece.
authors.forename: Trifon
authors.initials: T
authors.lastname: Totlis
authors.affiliation: Department of Anatomy, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, P.O. Box 300, 54124, Thessaloniki, Greece.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Anastasopoulos
authors.affiliation: Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens, 75 M. Asias Street, 11527, Athens, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Piagkou
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001269:Atlanto-Occipital Joint / Q000002:abnormalities* / Q000033:anatomy & histology; D001270:Cervical Atlas / Q000002:abnormalities* / Q000033:anatomy & histology; D002574:Cervical Vertebrae / Q000002:abnormalities* / Q000033:anatomy & histology; D003388:Cranial Fossa, Posterior / Q000002:abnormalities* / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000379:methods*; D012886:Skull / Q000033:anatomy & histology; D055815:Young Adult
keywords: Atlas assimilation; Atlas occipitalization; Fused vertebra; Hemivertebra; Occipitocervical synostosis