Abstract
Introduction: Atlanto-occipitalization(AOZ) is one of the congenital anomalies related to craniovertebral synostosis. The clear understanding of its anatomical features and cranial foraminal variants plays a critical role in finding the possible coping mechanism with its pathogenesis such as segmental instability or neurologic deficits.
 Objective: This study aimed to investigate the incidence of occipitalization of Atlas and related variant foramina, as the baseline awareness of these conditions among the Nepalese population is yet to be documented.
 Methodology: A retrospective study was performed for the total 86 dry skulls available in the department of Anatomy in Katmandu University of Medical Sciences, Institute of Medical Science, and B.P. Koirala Institute of Health Sciences. The skulls were examined thoroughly to evidence the occurrence of cranio-vertebral variations.
 Result: Out of 86 human adult skulls, 2 cases (2.32 %) were found with partial AOZ presenting posterior spina bifida close to the midline. Sphenoidal emissary foramen (SEF) was also observed in 17 skulls (19.76 %), an additional foramen lying anteromedial to the foramen ovale. Moreover, one of the skulls (1.16 %) was found with the presence of pterygospinous bar creating an additional foramen ‘foramen of Civinini’ in the lateral pterygoid plate of the sphenoid bone.
 Conclusion: The incidence of AOZ and pterygospinous bar seems to be quite low as compared to the cases of SEF. However, the knowledge of such variations and the presence of additional foramina carry great significance for orthopedists and neurosurgeons to have prognostic implications and an accurate surgical approach.
Highlights
Occipitalisa on of Atlas or the atlanto-occipital fusion is one of the skeletal varia ons where the adjacent part of the basiocciput gets fused with its succeeding first cervical vertebra (Atlas)
The incidence of atlanto-occipitaliza on (AOZ) and pterygospinous bar seems to be quite low as compared to the cases of Sphenoidal emissary foramen (SEF)
The failure of segmenta on between the cranial and caudal parts of the first cervical sclerotome leads to the AOZ since it gets assimilated with its preceding fourth occipital sclerotome
Summary
Occipitalisa on of Atlas or the atlanto-occipital fusion is one of the skeletal varia ons where the adjacent part of the basiocciput gets fused with its succeeding first cervical vertebra (Atlas). Lateral masses of the atlas form ellipsoid synovial ar cula ons with the occipital condyles. Since it is a biaxial joint, two movements are possible; one, around the transverse axis and the other, around the antero-posterior axis.[1] If there is the occurrence of atlanto-occipital assimila on, there will be no existence of the aforemen oned movements. The fusion could be par al[5] or complete,6which might cause a major risk in neurovascular injury during the surgical interven on In such cases, very careful examina on is required in regard to the 4th part of the vertebral artery and the first cervical nerve. Knowledge of the normal ossifica on pa erns is necessary to find the variant cle or foramina present in the skull.[8]
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