Craniocervical developmental anatomy and its implications.

INTRODUCTION: Congenital and developmental osseous abnormalities and anomalies that affect the craniocervical junction complex can result in neural compression and vascular compromise and can manifest itself with abnormal cerebrospinal fluid dynamics. An understanding of the development of the craniocervical junction is essential to recognize the pathological abnormalities.
MATERIALS AND METHODS: Atlas assimilation, segmentation failures, os odontoideum, basilar invagination, and the various syndromes that affect the craniocervical junction have been analyzed. The natural history provides an added insight into its treatment.
RESULTS: Proatlas segmentation abnormalities surrounded the foramen magnum and the posterior arch of C1. Hindbrain herniation was associated in 33 of the 90 children involved. Spastic quadriparesis presented in 80% and lower cranial nerve abnormalities in 33%. Vertebrobasilar dysfunction was observed in 40% and trauma presentation seen in 60% of individuals. Atlas assimilation was present in 550 individuals who were evaluated for craniovertebral junction abnormalities. Hindbrain herniation occurred in 38%. Segmentation failure of C2 and C3 vertebrae compounded the abnormal dynamics resulting in atlantoaxial instability. This was a reducible instability with formation of pannus around the odontoid process until it became irreducible at approximately 14 years of age. Unilateral atlas assimilation caused torticollis in children. Os odontoideum was investigated regarding craniocervical trauma at a young age.
CONCLUSION: The conclusion was that os odontoideum was associated with an unrecognized fracture in children below the age of 5 with a previously normal odontoid structure as observed in our series. Atlas and axis abnormalities were reviewed in this series. This large database has provided an understanding of the natural history of many entities and allowed treatment protocols to be established that have stood the test of time.