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Introduction: The formation of the occipital bone is intricate and has been extensively studied with many controversial conclusions, but with minimal effort being focused on the genes and molecular interactions necessary for its formation. A better understanding of this bone of the calvarial and skull base may shed light on pathologies where the occiput is often considered the offending entity., Methods: A review of the germane medical literature using textbooks and standard search engines was performed to gather information about previous conclusions as it pertains to the embryology and ossification of the occipital bone., Results: The occipital bone has both membranous and cartilaginous origin with ossification occurring as early as week 9 of fetal gestation. Its formations is dependent on complex interacts between genes and molecules with pathologies resulting from disruption of this delicate process., Conclusion: There has been much controversy in the past in regards to the development and ossification process necessary for occipital bone formation, which has only recently been clarified with documentation of the genes and molecular interactions necessary for its formation. Lastly, this improved knowledge might improve our understanding of such congenital derailments as the Chiari malformations.

Purpose: The clinical diagnosis of most common single-suture craniosynostosis is easily set, based on the stereotype of deformities and knowledge of the mechanisms of cranial deformations. However, synostosis of unilateral lambdoid suture, probably due to its lower incidence and similarity with other non-synostotic deformities affecting the posterior portion of the skull, makes its clinical diagnosis more difficult and imprecise. The aim of this study is to evaluate the most easily and accurate clinical characteristics to be recognized in the synostotic occipital plagiocephaly., Methods: This study consisted of clinical evaluation of eight patients with synostotic occipital plagiocephaly, whose diagnosis was further corroborated by computed tomography., Results: We identified the following: unilateral occipital flattening in eight out of eight patients (100 %), bulging of ipsilateral mastoid process in eight out of eight (100 %), "edge effect" of ipsilateral lambdoid suture in eight out of eight (100 %), inferior deviation of the ear in eight out of eight (100 %), "Dumbo" ears in eight out of eight (100 %), horizontal slant of the bimastoid line in seven out of eight (87.5 %), tilt of the head viewed from behind in seven out of eight (87.5 %), trapezoidal contour of the skull in top view in six out of eight (75 %), contralateral parietal bossing in six out of eight (75 %), and bossing of the contralateral forehead three out of eight (37.5 %)., Conclusions: The most important clinical features specific to the clinical diagnosis of synostotic occipital plagiocephaly, not present in the positional posterior plagiocephaly, were bulging of the ipsilateral mastoid process, edge effect of the synostotic lambdoid suture, tilt of the head, and slant of the bimastoid line viewed from behind, inferior deviation of the ear, and contralateral parietal bossing.

Background: The proatlas is derived from the fourth occipital sclerotome in human embryos. It usually fuses with the three upper occipital sclerotomes to form the occipital bone. However, this does not always occur. Manifestations of a partial proatlas structure may persist due to failure of fusion., Clinical Considerations: These embryological remnants can induce several symptoms in humans, ranging from mild to severe. On occasion, this structure can go unnoticed until a precipitating traumatic event results in symptoms. Proatlas segmentation abnormalities form bony masses at C1 and the foramen magnum. A number of surgical procedures have been devised to rectify the resulting neural compression and vascular compromise., Discussion: This paper will discuss the development of the proatlas and the resultant anomalies associated with its failure to merge with the occipital sclerotomes to form the occipital bone. In addition, some consideration of comparative anatomy and surgical techniques will be presented.

Background: The embryology of the bony craniovertebral junction (CVJ) is reviewed with the purpose of explaining the genesis and unusual configurations of the numerous congenital malformations in this region. Functionally, the bony CVJ can be divided into a central pillar consisting of the basiocciput and dental pivot and a two-tiered ring revolving round the central pivot, comprising the foramen magnum rim and occipital condyles above and the atlantal ring below. Embryologically, the central pillar and the surrounding rings descend from different primordia, and accordingly, developmental anomalies at the CVJ can also be segregated into those affecting the central pillar and those affecting the surrounding rings, respectively., Discussion: A logical classification of this seemingly unwieldy group of malformations is thus possible based on their ontogenetic lineage, morbid anatomy, and clinical relevance. Representative examples of the main constituents of this classification scheme are given, and their surgical treatments are selectively discussed.

Background: A surgical technique of posterior calvarial augmentation without the use of plates or screws and avoiding the formation of free bone flaps is described., Discussion: Three infants with strong occipital flattening successfully underwent the procedure in their first year of life. There were no intra- or postoperative complications; the amelioration of the head shape and the cosmetic results in all three cases were convincing also in the long term., Conclusion: The proposed surgical technique is both feasible and effective; it is recommended for infants with marked flat deformation of the posterior calvaria in the first year of life.

Purpose: We describe the case of a patient with a split medulla associated with multiple closed neural tube defects., Case Report: This 13-year-old female initially presented to our service at just over a year of age for neck abnormalities and a congenital midline occipital dermal sinus. MRI and CT scans showed the presence of multiple cervical vertebral segmentation abnormalities, a bony spur at the level of the craniocervical junction, split medulla, split cervical spinal cord, and a midline occipital dermal sinus. Since the patient's neurological course had remained stable during follow-up for over 11 years, the only surgical procedure undertaken was excision of the dermal sinus to prevent infection., Conclusions: The constellation of abnormalities indicates that the notochord was split early during gestation, both rostral and caudal to the cervicomedullary junction. Surgical intervention to treat the other malformations needs to be considered only if the patient develops a progressive neurological deficit.

Purpose: When linear lucency is present in the occipital bone on radiographs throughout childhood, differential diagnosis becomes important because some primary sutures are similar to fractures. The authors here chronicled the normal development of ossification centers, sutures, and synchondroses in the chondrocranium by radiographic examination., Methods: One hundred and twenty-seven children, aged from newborns to 6 years and without any skull base deformities, were referred to for radiographs of Towne's projection., Results: In the occipital bone at birth, three primary sutures could be identified. At the age of 0-3 years, occipital and innominate sutures started to fuse, this being complete by 4 years, whereas mendosal sutures persisted until 6 years of age, after which no primary sutures could be seen., Conclusion: The complex process of skull base development features a step-wise process sutural closure for which radiographic standards allow differential diagnosis from fractures with judgment of the timing.

Chiari malformations are brain stem anomalies with or without spinal canal involvement. The combination of brain stem and cerebellar anomaly with a cervical cele is named Chiari III malformation. Patients with this extremely rare defect frequently present with severe neurological defects and can have a poor prognosis. Following a report on a newborn child with a Chiari III malformation that took a fatal but typical course the literature is reviewed.

The discovery of a craniocervical junction malformation requires management in three steps: (1) The patterns must be recognized using tomographic measurements (Chamberlain's line, Wackenheim's line). Dynamic flexion-extension studies are necessary to assess stability or instability. Stable patterns range from platybasia to basilar invagination, with gradual deformation, and are frequently associated with Chiari malformation. Unstable patterns characterized by odontoid instability are the equivalent of an odontoid fracture. The origin is malformative (hypoplasia, aplasia of the dens, os odontoidum), but the last may be difficult to distinguish from an old odontoid fracture. They are found in many syndromes (Down, Morquio, etc.). Unstable atlantoaxial patterns with atlas assimilation are hardly reducible; they evolve toward progressive instability. (2) The neurological consequences must be defined from the clinical features of the spinal cord and the cranial nerves. Both static and dynamic MRI scans must be performed; in this way identification of the neural abnormalities (hydromyelia, Chiari, etc.) and of the osseous compression is possible. (3) The most appropriate operative procedure must be selected: stable platybasia with a nervous compression by Chiari is cured only by posterior decompression; odontoid instability is cured by reduction and posterior fixation, using hooks and autologous bone grafts on the posterior arches of C-1 and C-2. Sometimes a transarticular screw fixation of C1-2 is necessary if there is a defect on the C-1 posterior arch. Craniocervical dislocations with assimilation of the atlas require posterior occipito-vertebral bony fixation with grafts and external halo immobilization or internal fixation with hooks or screws, with anterior transoral decompression in a second step.

A case of monochorionic/monoamnionic twin with discordant occipital developmental malformations is presented. One female twin appeared to have an occipital meningocele with cerebellar aplasia and died immediately after birth. The other twin presented with signs and symptoms of raised intracranial pressure at the age of 7 months. Severe hydrocephalus was present due to an infected intracerebellar dermoid tumor with a contiguous occipital dermal sinus. The clinical and pathological characteristics are described and the different theories concerning twinning, embryogenesis, and dysmorphology in relation to neural tube defects are discussed. Analysis of the features of these monozygotic twins indicates that a meningocele is not a post-neurulation disorder but results from deficient neurulation, probably due to mesodermal insufficiency.