There is a hole in the middle of the posterior area of the skull base, which is the foramen magnum, and the upper end of the spinal cord is connected to the medulla oblongata
The foramen magnum is the foramen magnum in the middle of the posterior area of the skull base, where the upper end of the spinal cord is connected to the medulla oblongata.The foramen magnum of occipital bone has different shapes, including double semicircular, oval, nearly oval, rhombic, etc. The Chinese people often see oval.
There is gender difference in the size of the foramen magnum, which is larger in men than in women.A projection on the outside of the foramen magnum.Behind it is a shallow condylar fossa, which can pass through the condylar canal, and there are guide veins connecting the blood flow of internal and external cranial veins;And then to the outside is the mastoid process.Generally, the occipital condyle of male is larger than that of female, which has definite significance in gender determination.
pathological changes
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When there are lesions in the foramen magnum, such as hypoplasia of cartilage in the foramen magnum area or hernia of the foramen magnum, it will cause pressure on its traversing structure, which will not only affect the cerebral blood flow and cerebrospinal fluid circulation, but also cause facial and cervical motor sensory dysfunction;Especially when the foramen magnum is damagedCerebellar tonsilThe fourth ventricle and the fourth posterior four pairs of cranial nerves and the initial segment of spinal cord are adjacent, and sometimes it is impossible to operate;If part of the bone is removed, it will lead to bleeding, the stability of the craniocervical junction area decline and other complications.
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The development of the craniocervical junction is very complicated, mainly including the differentiation of neuroectoderm and the induction of paraxial mesoderm by the notochord.The paraxial mesoderm is the precursor of the axial bone and skeletal muscle.When the paraxial mesoderm began to appear, the first two bone nodes gradually formed the base of the occipital bone, and the third bone node formed the jugular tubercle and developed the occipital scale;The fourth bone segment, also called anterior atlas, develops into clivus, neural arch, occipital condyle and the lateral part of the first cervical vertebra.Different from the intramembranous ossification of the occipital squama, most of the sphenoid bone, the petrous part of the temporal bone and the base of the occipital bone belong to endochondral ossification.Around the foramen magnum of occipital bone, the continuous ossification of each part of cartilage and the closure of suture are completed together.The anterior part of the clivus and foramen magnum originates from the combination of sphenoid and occipital cartilage and the growth of the lateral suture of the skull base;With the growth of the petrous part of the temporal bone and the sphenoid temporal junction area, the occipital bone and the posterior cranial fossa gradually declined and were lower than the middle cranial fossa to accommodate the brain stem, cerebellum, and basal cerebral vessels.
For the craniocervical junction area, especially the skull base injury, its mortality and disability rate are high.Common lesions include: intradural/extradural tumors, vertebral artery damage, rheumatic diseases, synovial cysts, demyelinating diseases and medullary cavity.Even surgery is faced with huge risks, and sometimes it is difficult to completely remove the tumor.In order to ensure the safety and effectiveness of the treatment, the surgical methods have been continuously improved.The surgical design should be based on the type and scope of the injury. If the injury is located from the slope to the level of the second cervical vertebra, it is suitable to use the oral pharyngeal approach.With the development of endoscopic technology, nasal endoscopic approach is more suitable for the lesions at the craniocervical junction;The lateral occipital condylar approach can reach the ventral or ventrolateral area of the foramen magnum. Because the above methods will damage some normal tissues, mastering the morphological characteristics of this area can not only reduce the invasion, but also help improve the surgical effect.
Studies have shown that the larger the area of the foramen magnum, the better the anatomical field of vision during surgery.No matter the length or width, the measurement result of the foramen magnum of the male occipital bone is higher than that of the female. Therefore, female patients may need to do more bone resection during surgery.The average length and width of foramen magnum measured in this paper are (34.45 ± 2.95) mm and (29.18 ± 2.15) mm respectively, slightly lower than those of European and American populations, but higher than those of Indian populations, which indicates that there are racial differences in the basic parameters of foramen magnum.
