Anatomic and radiologic appearance of several variants of the craniocervical junction.

Skull Base 02/1996; 6(2):83-94. DOI: 10.1055/s-2008-1058649
Source: PubMed

ABSTRACT Four typical manifestations of the occipital vertebra are described from both an anatomic and a radiologic point of view; the basilar process, the condylus tertius, the paracondylar process, and the isolated prebasioccipital arch. The clinical importance of the described variants is discussed.

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    ABSTRACT: Minor variations in the ossicles, foramina and ridges of the cranium have aroused the curiosity of anatomists for many decades. These non-metric variants help us to study the genetic relationships among ancient populations. Since these traits show considerable frequency differences in different populations, they can be used as anthropological characters in epidemiological studies. These variants indirectly reflect the part of underlying genotype of a given population thus implying their usefulness in biological comparisons of related groups. They can be used for the assessment of the existence of the parental structures within a community or as taxonomic indicators. For anthropological studies, the traits should be genetically determined, vary in frequency between different populations and should not show age, sex, and side dependency. The present study was conducted on hundred dry adult human skulls from Northern India. They were sexed and studied for the presence of hyperostotic traits (double hypoglossal canal, jugular foramen bridging, and paracondylar process). Sexual and side dimorphism was observed. None of the traits had shown statistically significant side and sexual dimorphism. Since the dimorphism is exhibited by none of them, it can be postulated that these traits are predominantly under genetic control and can be effectively used for population studies.
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    ABSTRACT: The Nariokotome boy skeleton KNM-WT 15000 is the most complete Homo erectus fossil and therefore is key for understanding human evolution. Nevertheless, since Latimer and Ohman (2001) reported on severe congenital pathology in KNM-WT 15000, it is questionable whether this skeleton can still be used as reference for Homo erectus skeletal biology. The asserted pathologies include platyspondylic and diminutive vertebrae implying a disproportionately short stature; spina bifida; condylus tertius; spinal stenosis; and scoliosis. Based on this symptom complex, the differential diagnosis of spondyloepiphyseal dysplasia tarda, an extremely rare form of skeletal dysplasia, has been proposed. Yet, our reanalysis of these pathologies shows that the shape of the KNM-WT 15000 vertebrae matches that of normal modern human adolescents. The vertebrae are not abnormally flat, show no endplate irregularities, and thus are not platyspondylic. As this is the hallmark of spondyloepiphyseal dysplasia tarda and related forms of skeletal dysplasia, the absence of platyspondyly refutes axial dysplasia and disproportionate dwarfism. Furthermore, we neither found evidence for spina bifida occulta nor manifesta, whereas the condylus tertius, a developmental anomaly of the cranial base, is not related to skeletal dysplasias. Other fossils indicate that the relatively small size of the vertebrae and the narrow spinal canal are characteristics of early hominins rather than congenital pathologies. Except for the recently described signs of traumatic lumbar disc herniation, the Nariokotome boy fossil therefore seems to belong to a normal Homo erectus youth without pathologies of the axial skeleton. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.
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    ABSTRACT: The "condylus tertius" or the "third occipital condyle" is an embryological remnant of the proatlas sclerotome. Anatomically, it is attached to the basion and often articulates with the anterior arch of the atlas and the odontoid apex; hence, it is also called the "median occipital condyle". It is a rare anomaly of the cranio-vertebral junction (CVJ) that can lead to instability and compression of important surrounding neurovascular structures. We report a case of a 16-year-old boy who presented with suboccipital neck pain, torticollis and right sided hemiparesis. Plain radiographs revealed an increased atlanto-dental interspace (ADI) with a retroflexed odontoid. Open mouth view showed asymmetry of the articular processes of the atlas with respect to the dens. Computed tomography (CT) of the CVJ delineated the third occipital condyle. Furthermore, on dynamic CT study, a type 3 atlanto-axial rotatory fixation (AARF) was clearly demonstrated. Magnetic resonance imaging (MRI) of the CVJ revealed severe right-sided spinal cord compression by the retroflexed and rightward deviated dens. It also revealed disruption of the left alar and transverse ligaments. The patient was treated with 8 weeks of cranial traction and reasonable alignment was obtained. This was followed by C1-C2 lateral mass screw fixation and C1-C2 interlaminar wiring to maintain the alignment. A review of the literature did not reveal any cases of condylus tertius associated with non-traumatic AARF. An accurate knowledge of the embryology and imaging features of this rare CVJ anomaly is useful in the prompt diagnosis and management of such patients.
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