OCCIPITALISATION OF ATLAS VERTEBRA AND ITS CLINICAL FRAMES OF REFERENCE- AN ANALYSIS

 

Dr. Neelima. P ¹, Dr. Ravi Sunder. R ²

 

¹ Professor and HOD, Anatomy, NRIIMS, Visakhapatnam-531162, Andhra Pradesh, India

² Professor and HOD, Physiology, GIMSR, GITAM deemed to be University, Visakhapatnam-530045, Andhra Pradesh, India

 

1. INTRODUCTION

Vertebral column is a part of axial skeleton with 33 vertebrae forming the vertebral canal to protect spinal cord. Medulla oblongata, which is a part of rhombencephalon or hind brain, leaves the cranial cavity through foramen magnum and continues as spinal cord at the level of outer border of atlas, the first cervical vertebra. Assimilation of atlas in forming the cranial base is termed as occipitalisation. This is the most common malformation at the cranio vertebral junction. This can be radiologically diagnosed by lateral teleradiography as discussed by Kahouadji et al. (2013). Neurosurgeons or radiologists should be conscious about this variant anatomy at the cranio vertebral junction while diagnosing myelopathies or nerve compression syndromes. Khamanarong et al. (2013) evaluated the neurovascular symptoms of this congenital malformation. Surekha Jadhav et al. (2012) demonstrated the assimilation of atlas in Maharastra region. As stated by Srisopark (1974), the incidence was found to be 0.08-3%. Though studies on occipitalisation of atlas insist on the clinical symptomatic presentations of neurological sequelae, a study by Gholve et al. (2007) explains the asymptomatic scenario observed in children. Wackenhein (1974) states that assimilation of atlas is variable in its tposition as it may involve any aspect of atlanto occipital articulation. In the present study, a skull with almost complete occipitalisation of atlas except at posterior arch was analysed and clinically correlated.

 

2. MATERIALS AND METHODS

On routine examination of dried skulls at the occipital region, one skull was found to show incomplete assimilation of atlas. Photographs were taken and compared with normal skull.

 

3. RESULTS

One dried skull exhibited incomplete occipitalisation of atlas. The anterior arch of atlas was completely fused. Posterior arch was found to be splitted with a gap in the center. The styloid process was long, and its tip was found close to the fused atlas. This is represented in the following pictures.

 

Figure 1

Figure 1 Norma Basalis Showing Occipitalisation of Atlas

 

 

      

 

Figure 2

Figure 2 Lateral Views of Skull

 

Figure 3

 

Figure 3 Comparison with Normal Skull

 

4. DISCUSSION

Assimilation of atlas is due to the fusion of caudal fourth occipital somite with proximal first cervical somite. Somite is a paraxial mesoderm derivative which is developed during 4th week of intrauterine life. 44 pairs of somites are formed on either side of the developing neural tube extending from cranial to caudal areas of the embryo. Each somite forms sclerotome, myotome, and dermatome where the entire vertebral column is derived from the sclerotome component. 4 occipital somite’s form the skull base called the occiput. Normally, occipital somites and cervical somites’ remain separate. Occipitalisation of atlas occurs when the last occipital somite fuses with the first cervical somite. Sween et al. (2014) demonstrated three skulls with occipitalisation of atlas. Nayak et al. (2005) put forth complete assimilation of atlas in their study. The main concern of such type of variant anatomy at the cranio vertebral junction is the wide spectrum of presenting symptoms. Howard and Simpson (1994) elaborated on the symptoms of paraesthesia’s, numbness, impairment of 2-point discrimination, loss of vibration sense etc due to compression of dorsal columns. Kassim et al. (2010) analysed the myelopathies due to the compression. The wide range of neuro vascular complications due to such an anatomical variation should be borne in the minds of neurosurgeons or radiologists while dealing with such presentations. This study analyses the occipitalisation of atlas and its clinical frames of reference.

 

5.  CONCLUSION

Incomplete occipitalisation of atlas with bifid posterior arch has been reported. This may lead to myelopathies or compression syndromes as vital structures like lower medulla becoming spinal cord, vertebral artery, cervical spinal nerves are related.

 

CONFLICT OF INTERESTS

None. 

 

ACKNOWLEDGMENTS

None.

 

REFERENCES

Gholve, P. A. Hosalkar, H.S. Ricchetti, E.T. Pollock, A.N. Dormans, J.P. Drummond, D.S. (2007). Occipitalization of Atlas In Children. Morphologic Classification, Associationsand Clinical Relevance. J. Bone Joint SurgAm, 89, 571-578.    

Howard, S. Simpson, J. (1994). Surgery of The Cervical Spine. London : CRC press, London.  

Jadhav, S. Ambali, M.  Patil, R.  Doshi, M.  Roy, P. (2012). Assimillation of Tlas In Indian Dry Skulls. JKIMSU, 1, 102-106.

Kahouadji E, Lucas O, Khonsari RH, Longis J, Hamel O, Corre P. (2013). Occipitalisation de l'atlas. Diagnostic Radiologique Et Implication Clinique [Occipitalization of the Atlas. Radiological Diagnosis And Clinical Significance]. Rev Stomatol Chir Maxillofac Chir Orale.114(3),187-91.  

Khamanarong, k. et al. (2013). Occipitalization of the Atlas : Its Incidence And Clinical Implications. Acta Medica Academica, 42(1),41-45.

Kassim, N.M. Latiff, A.A. Das, S.Ghafar, N. A. Suhaimi, F.H. Othman, F. et al. (2010).  Atlanto-Occipital Fusion : An Osteological Study With Clinical Implications. Bratisl Lekárske Listy, 111(10), 562–5.

Nayak, S. Vollala, V.R. Raghunathan, D. (2005). Total fusion of Atlas With Occipital Bone : A Case Report. Neuroanatomy. (2), 39-40.

Srisopark, S. (1974). Occipitalization of the Atlas. JDentistry Association Thailand, 245(5), 294-299.  

Sween, W.  Modi, B. S. Puri, N. Patnaik, V. V. G. (2014). Occipitalization of Atlas. Int J Anat Res, 2(4) :781-784.

Wackenhein, A. (1974). Roentgen Diagnosis of The Craniovertebral Region.  Newyork ; Springer-Verlag, 360-362.