Congenital atlanto-occipital fusion and its effect on the myodural bridge: a case report utilizing the P45 plastination technique / Fusión atlanto-occipital congénita y su efecto sobre el puente miodural: reporte de un caso utilizando la técnica de plastinación P45

SUMMARY: The atlanto-occipital joint is composed of the superior fossa of the lateral masses of the atlas (C1) and the occipital condyles. Congenital Atlanto-occipital fusion (AOF) involves the osseous union of the base of the occiput (C0) and the atlas (C1). AOF or atlas occipitalization/assimilation represents a craniovertebral junction malformation (CVJM) which can be accompanied by other cranial or spinal malformations. AOF may be asymptomatic or patients may experience symptoms from neural compression as well as limited neck movement. The myodural bridge (MDB) complex is a dense fibrous structure that connects the suboccipital muscular and its related facia to the cervical spinal dura mater, passing through both the posterior atlanto-occipital and atlanto-axial interspaces. It is not known if atlas occipitilization can induce structural changes in the MDB complex and its associated suboccipital musculature. The suboccipital region of a cadaveric head and neck specimen from an 87-year-old Chinese male having a congenital AOF malformation with resultant changes to the MDB complex was observed. After being treated with the P45 plastination method, multiple slices obtained from the cadaveric head and neck specimen were examined with special attention paid to the suboccipital region and the CVJM. Congenital atlanto-occipital fusion malformations are defined as partial or complete fusion of the base of the occiput (C0) with the atlas (C1). In the present case of CVJM, unilateral fusion of the left occipital condyle with the left lateral mass of C1 was observed, as well as posterior central fusion of the posterior margin of the foramen magnum with the posterior arch of C1. Also noted was a unilateral variation of the course of the vertebral artery due to the narrowed posterior atlanto-occipital interspace. Surprisingly, complete agenesis of the rectus capitis posterior minor (RCPmi) and the obliques capitis superior (OCS) muscles was also observed in the plastinated slices. Interestingly, the MDB, which normally originates in part from the RCPmi muscle, was observed to originate from a superior bifurcation within an aspect of the nuchal ligament. Therefore, the observed changes involving the MDB complex appear to be an effective compensation to the suboccipital malformations.

RESUMEN: La articulación atlanto-occipital está compuesta por las caras articulares superiores de las masas laterales del atlas (C1) y los cóndilos occipitales. La fusión atlanto-occipital congénita (FAO) implica la unión ósea de la base del occipucio (C0) y el atlas (C1). La FAO u occipitalización/asimilación del atlas representa una malformación de la unión craneovertebral (MUCV) que puede presentar otras malformaciones craneales o espinales. La FAO puede ser asintomática o los pacientes pueden experimentar síntomas de compresión neural así como movimiento limitado del cuello. El complejo del puente miodural (PMD) es una estructura fibrosa densa que conecta el músculo suboccipital y su fascia relacionada con la duramadre espinal cervical, pasando a través de los espacios intermedios atlanto-occipital posterior y atlanto-axial. No se sabe si la occipitilización del atlas puede inducir cambios estructurales en el complejo PMD y en la musculatura suboccipital. Se observó en la región suboccipital de un espécimen cadavérico, cabeza y cuello de un varón chino de 87 años con una malformación congénita de FAO con los cambios resultantes en el complejo PMD. Se examinaron múltiples cortes obtenidos de la muestra de cabeza y cuello después de ser tratados con el método de plastinación P45, con especial atención a la región suboccipital y la MUCV. Las malformaciones congénitas por fusión atlanto-occipital se definen como la fusión parcial o completa de la base del occipucio (C0) con el atlas (C1). En el presente caso de MUCV se observó la fusión unilateral del cóndilo occipital izquierdo con la masa lateral izquierda de C1, así como fusión posterior central del margen posterior del foramen magnum con el arco posterior de C1. También se observó una variación unilateral del curso de la arteria vertebral por el estrechamiento del espacio interatlanto-occipital posterior. Se observó además agenesia completa de los músculos Rectus capitis posterior minor (RCPmi) y oblicuos capitis superior (OCS) en los cortes plastinados. Curiosamente, se observó que el MDB, que normalmente se origina en parte del músculo RCPmi, se origina en una bifurcación superior dentro de un aspecto del ligamento nucal. Por lo tanto, los cambios observados en el complejo PMD parecen ser una compensación de las malformaciones suboccipitales.

[Three-Dimensional Nonlinear Finite Element Modeling and Analysis of Concomitant Atlanto-Occipital Fusion and Atlantoaxial Joint Dislocation].

OBJECTIVE: To establish, with finite element technology, a three-dimensional nonlinear finite element model of the normal occipital bone, atlas and axis and a three-dimensional nonlinear finite element model of concomitant atlanto-occipital fusion and atlantoaxial dislocation, providing a biomechanical method for clinical research on the upper cervical spine. METHODS: Finite element analysis was conducted with the CT data of a 27-year-old male volunteer, and a three-dimensional nonlinear finite element model, i.e., the normal model, of the normal occipital bone, atlas and axis was established accordingly. Finite element analysis was conducted with the CT data of a 35-year-old male patient with concomitant atlanto-occipital fusion and atlantoaxial dislocation. Then, the ideal state of a simple ligament rupture under high load was generated by computer simulation, and a three-dimensional nonlinear finite element model of concomitant atlanto-occipital fusion and atlantoaxial dislocation was established, i.e., the atlanto-occipital fusion with atlantoaxial dislocation model. For both models, a vertical upward torque of 1.5 N·m was applied on the upper surface of the occipital bone. Through comparative analysis of the two models under stress, the data of the range of motion (ROM) for flexion, extension, lateral bending, and rotation were examined. In addition, stress and deformation analysis with 1.5 N·m torque load was conducted to validate the effectiveness of the two three-dimensional nonlinear finite element models established in the study. RESULTS: When the normal model established in the study was under 1.5 N·m torque load, it exhibited a maximum ROM for each unit of flexion, extension, and the ROM approximated the experimental measurement results of human mechanics, confirming the validity of the simulation. The stress and deformation results of the model were consistent with the basic principles of mechanics. The moment-angular displacement of the model showed obvious nonlinear characteristics. Compared with the normal model, the atlanto-occipital fusion with atlantoaxial dislocation model showed reduced ROM of the atlanto-occipital joint under a torque of 1.5 N·m, while the ROM of the C1-C2 joint for the four conditions of flexion, posterior extention, lateral bending, and rotation under load, with the exception of rotating motion, was greatly increased compared with that of the normal model, which was in line with the actual clinical performance of the patient. CONCLUSION: The atlanto-occipital fusion with atlantoaxial dislocation model and the three-dimensional nonlinear finite element model of the normal occipital bone, atlas and axis were successfully established by finite element technology. The models had valid simulation and reliable kinematic characteristics, and could be used as a reliable tool to simulate clinical diseases.

A case of atlanto-occipital fusion with other multiple anatomic variations.

In the routine anatomic measurement study on Asian dry skulls, a skull of atlanto-occipital fusion with other multiple anatomic variations was observed. The entire right half of the atlas vertebra, including the anterior arch, anterior tubercle, posterior arch, and lateral masses, was fused entirely with the occipital bone, while the left fused partly. Besides the atlanto-occipital fusion, the target skull specimen also includes posterior arch defects of the atlas, metopic suture, and wormian bones. So many anatomical variations rarely exist in one specimen. This paper aims to present detailed anatomic case reports and discuss related diseases in an anatomic and clinical study.

CT angiographic evaluation of the V3 vertebral artery course in cases of occipitalized atlas, a study of 25 cases.

OBJECTIVES: To study the relationship of the 3rd segment of the vertebral artery to the posterior arch of the atlas in patients with occipitalized atlas, using CT angiography. METHODS: A retrospective study of 25 cases with complete or partially occipitalized atlas who underwent CT angiography evaluation. Fifty vertebral arteries were analyzed in relation to the respective/related half of the posterior arch of the atlas. RESULTS: Out of 50 vertebral arteries, 35 (70%) were anomalous; 31 (62%) traversed though bony canal between the fused occiput and atlas, and 4 (8%) coursed between C1 and C2 (C2 segmental type of vertebral artery). Except one, all anomalous vertebral arteries were associated with a fused corresponding side of posterior arch of atlas. CONCLUSION: The V3 portion of the vertebral artery assumes an anomalous course at the craniovertebral junction in most cases of occipitalized atlas, and this is strongly determined by the fusion status of the posterior arch of the atlas. Aberrations in its course are still seen despite expectations based on this fusion status. Preprocedural CT Angiography provides accurate information of its course to prevent iatrogenic VA injuries. ADVANCES IN KNOWLEDGE: CT Angiography should be performed before any procedures at the craniovertebral junction in cases of occipitalized atlas to prevent iatrogenic, potentially catastrophic injuries to vertebral artery due to its anomalous course in most of these cases. There are very few such studies in the literature, none in radiology literature. We also describe some rare cases, including a case never described in any literature.

Quantitative Measurements of the Skull Base and Craniovertebral Junction in Congenital Occipitalization of the Atlas: A Computed Tomography-Based Anatomic Study.

OBJECTIVE: To study the craniovertebral junction and determine the anatomic characteristics of occipitalization of the atlas (OC) by computed tomography (CT) imaging. METHODS: We retrospectively reviewed 80 cases of patients with OC who underwent cervical CT scanning between March 2012 and March 2014. Forty healthy subjects were recruited as a control cohort. Fusion pattern and associated osseous anomalies were recorded. Fifteen linear quantitative parameters were measured to study the outlet of the foramen magnum, angular dimension of the skull base, posterior cranial fossa, and height of the odontoid process. RESULTS: The most common fusion pattern was the complete osseous fusion (83.75%). Fifty-four patients (67.5%) presented with other osseous anomalies. Measurements of the OC group, such as the length of the clivus, cranial canal angle, and height of the odontoid process, were significantly different than those of the control group. The correlation analysis showed that the C1 lateral facet inclination was significantly correlated with the age of onset. CONCLUSIONS: The outlet of the foramen magnum is severely impaired in patients with OC, and the presence of other osseous anomalies is common. Deformity is not confined to the region of the assimilated atlas; the clivus and odontoid process are also shorter than normal. The lateral facet inclination likely influences disease progression.

Cranio-vertebral junction anomaly: atlanto-occipital assimilation.

Cranio-vertebral junction is a pivot which holds the globe of the head. Bony anomalies at this point are particularly significant because they lodge the spinal cord and lower part of the brain stem. Clinically fusion of the atlas with the lower part of the occiput is known as Atlanto-occipital assimilation or atlas occipitalization, which can be either partial or complete depending upon the extent of fusion. It can present as totally asymptomatic accidental finding or can be a cause behind major neuro-vascular compression. The present case study is an endeavor to explain occipitalization of atlas bone on the basis of embryology and explain its clinical relevance.

Atlanto-occipital fusion and its neurological complications: a case report

During routine activities in the Laboratory of Human Anatomy at the University of Santa Cruz do Sul – Brazil, an atlanto-occipital fusion was observed in a Caucasian cadaver skull. The skull used in our study had complete fusion of the occipital bone with the atlas vertebra, except in traffic areas of the vertebral arteries. Some important neurological disorders seem to be related with atlanto-occipital fusion. The presence of other anatomical variations was not verified. Thus, the present study shall be important for health sciences and those who keep some interest in pathologies associated with brain.