OCCIPITO-CERVICAL SYNOSTOSIS: ITS OCCURANCE AND EMBRYOLOGICAL BASIS Rakesh Kumar Diwan *, Deepshikha Kori, R.K Verma, A.K Pankaj, Garima Sehgal, Sushma Tomar. Department of Anatomy, King George’s Medical University, Lucknow, Uttar Pradesh, India.  Address   for   Correspondence:    Dr.    Rakesh   Kumar   Diwan,   Associate   Professor,   Department   of   Anatomy,   King   George’s   Medical   University,   Lucknow-   226003 Uttar Pradesh. India.Contact no. of corresponding author: +918005335622 E-Mail: dewanrakesh80@yahoo.com ABSTRACT Introduction:   Occipito-cervical   synostosis   is   a   rare   anomaly.   It   is   also   known   as   assimilation   or   occipitalization   of   atlas.   It   is   defined   as   a   congenital   fusion   of atlas   vertebra   with   the   base   of   occipital   bone,   it   may   be   complete   or   partial.   This   anomaly   results   due   to   failure   in   segmentation   and   separation   of   last occipital sclerotome and first cervical sclerotome during development of foetus. Material   and   Methods:   The   present   study   was   conducted   on   240   skull   bones   in   the   department   of   Anatomy   King   George   Medical   University,   Lucknow, India. We observed the synostosis of atlas vertebrae with basilar part of occipital bones. Results:   Among   240   bones   we   noticed   7   craniums   which   were   fused   with   the   first   cervical   vertebra   and   the   details   of   these   are   described   in   following article. Conclusion:   This   type   of   anomaly   may   alter   the   dimensions   of   foramen   magnum   and   may   compress   the   spinal   cord   and   vertebral   artery.   Therefore, improved    knowledge    on    the    fusion    of    atlas    with    the    occipital    bone    is    important    for    orthopedicians,    neurosurgeons,    radiologist,    anaesthetist, physiotherapist and anatomist, as it shows multiple variations and combinations. KEY WORDS: Atlas, occipital bone, synostosis, variation, sclerotome. References 1 . Basmajian   J.V.,   Slonecker   C.E.   Head   and   Neck,   Grant’s   Methods   of   Anatomy:   A   Clinical   problem   solving   approach.   1997,   11 th    ed.   BI   Waverly   Pvt   Ltd, New Delhi.  528. 2 . Standring   S.,   Borley   N.R.,   Collins   P.,   Corssman   A.R.,   Gatzoulis   M.A.,   Healy   C.,   Johnson   D.,   Mahadeved   V.,   Newell   R.L.M.,   Wigley   C.B.Gray’s   Anatomy-The Anatomical Basis of Clinical Practice. 40 th  ed. Churchill Livingstone, 2008: 419-420. 3 . Anu   vinod   Ranade,   Rajalakshmi   Rai,   Latha   Venkatraya   Prabhu,   Mangala   Kumaran,   Mangala   M.   Pai.   Atlas   Assimilation:   A   Case   Report,   Neuro   Anatomy. 2007;6:32-33 4 . Motabagani M.A., Surendra M. Total Occipitalization of the Atlas Vertebra. Anatom Scien Inter. 2006; 81:173-180. 5 . Sadler, T.W.Langman’s Essential Medical Embryology. 10 th  ed. Baltimore, Lippincott William and Wilkins. 2007:125-141. 6 . Jayanti V., Kulkarni R., Kulkarni R.N. Atlanto-occipital fusion-report of two cases. J Anat. Soc. India. 2003; 52(1):71-73. 7 . Nayak S, Vollala VR, Raghunathan D. Total fusion of atlas with occipital bone: A case report. Neuroanatomy.2005; 7(9):1835-1837. 8 . Vandana R, Ravikumar. Asymmetrical assimilation of atlas vertebra. J of evolution of medical and dental sciences 2013; 23(2):4102-4110. 9 . Ranade AV, Rai R, Prabhu LV, Kumaran M, Pai MM. Atlas assimilation: A case report. Neuroanatomy 2007; 6:32-33. 1 0 . Sani V, Singh R, Bandopadhyay M, Trapathi S, Shamal S. Occipitalization of the atlas: its occurrence and embryological basis. IJAV 2009; 2:65-68. 1 1 . Yochum T.R., Rowe L.J. Essentials of Skeletal Radiology. Volume 1, 2 nd  ed. Baltimore, Williams & Wilkins. 1987: 3. 1 2 . Jadhav S.D., Ambali M.P., Patil R.J., Doshi M.A., Roy P.P. Assimilation of Atlas in Indian dry Skulls. JKIMSU. 2012; 1(1):102-106. 1 3 . Hensinger R.N.1986.Osseous anomalies of the craniovertebral junction. Spine.11: 323-333. 1 4 . Greenberg A.D. Atlanto-axial dislocation. Brain. 1968; 91:655. 1 5 . Gholve   P.A.,   Hosalkar   H.S.,   Ricchetti   E.T.,   Pollock   A.N.,   Dormans   J.P.,   Drummond   D.S.   Occipitalization   of   Atlas   in   Children.   Morphologic   classification, associations and clinical relevance. J. Bone Joint Surg Am. 2007; 89:571-578.