Embryology of the craniocervical junction and posterior cranial fossa, part I: Development of the upper vertebrae and skull.

Although the embryology of the posterior cranial fossa can have life altering effects on a patient, a comprehensive review on this topic is difficult to find in the peer-reviewed medical literature. Therefore, this review article, using standard search engines, seemed timely. The embryology of the posterior cranial fossa is complex and relies on a unique timing of various neurovascular and bony elements. Derailment of these developmental processes can lead to a wide range of malformations such as the Chiari malformations. Therefore, a good working knowledge of this embryology as outlined in this review of its bony architecture is important for those treating patients with involvement of this region of the cranium. Clin. Anat. 31:466-487, 2018. © 2018 Wiley Periodicals, Inc.

Craniovertebral junction anomalies in inherited disorders: part of the syndrome or caused by the disorder?

Patterns of skeletal abnormality at the craniovertebral junction in the normal population and in syndromes such as Down, Morquio etc, are compared and the recent embryological data and comparative anatomy reviewed. The authors' view based on their own clinical and radiological experience is that the os odontoideum is the product of excessive movement at the time of ossification of the cartilaginous dens and is exactly analogous to the unfused Type II odontoid fracture. True hypoplasia of the odontoid peg is part of a wider segmentation defect associated with Klippel Feil, occipitalised atlas and/or basilar invagination; it is hardly ever associated with instability.

Cranio-cervical growth collision: another explanation of the Arnold-Chiari malformation and of basilar impression.

Analysis of neuro-cranio-spinal development suggests a cranio-cervical growth conflict as the cause of the Arnold-Chiari malformation and of basilar impression. The ascending course and elongation of the upper cervical nerves associated with the Arnold-Chiari malformation reflects the abnormal, caudo-cranially proceeding growth of the cervical spine. This is the opposite of the normal cranio-caudal direction of growth (which includes the brain) with downward slanting of the cervical nerve roots. The cervical growth reversal is a compensatory event related to the impairment of distal spinal growth at the level of the coexistent myelomeningocele. With the reversal of the cerical growth, the initial descent (uncoiling) of the primordial brain curvatures is compromised owing to the growth-collision with the ascending cervical spine. Their subsequent growth proceeds into the upper cervical spinal canal. The contents of the posterior cranial fossa are actively "sucked up", "devoured" by the latter. In contrast to the adaptively enhanced growth of the early cranio-cervical nervous structures in the Arnold-Chiari malformation, as an answer to the growth-shifts of the encasing skeleton, basilar impression is a postembryonic adaptation of the cervico-cranial skeleton to the inadequate growth of the nervous structures after the latter have lost their growth adaptability. Arnold-Chiari malformation and basilar impression are just two representatives of "osteo-neural growth pathology" encompassing some "dysplastic" disorders of the axial as well as of the limb skeleton such as platyspondyly, scoliosis, Scheuermann's kyphosis, achondroplasia-like conditions, congenital dysplasia of the hip etc.(ABSTRACT TRUNCATED AT 250 WORDS)