Posterior atlanto-occipital and atlanto-axial area and its surgical interest

Abstract

Classic anatomical studies describe two membranes -atlanto-occipital and atlanto-axial in the posterior aspect of the craniocervical region. During many surgical procedures in this area, however, we have not found such membranes. Objective: To clarify the anatomical aspects and structures taking part of the posterior atlanto-occipital and atlanto-axial area. Method: Analysis of histological cuts of three human fetuses and anatomical studies of 8 adult human cadavers. Results: In both atlanto-occipital and atlanto-axial areas, we have observed attachment between suboccipital deep muscles and the spinal cervical dura. However, anatomical description of such attachments could not be found in textbooks of anatomy. Conclusion: Our study shows the absence of the classical atlanto-occipital and atlanto-axial membranes; the occipito-C1 and C1-C2 posterior intervals are an open area, allowing aponeurotic attachment among cervical dura mater and posterior cervical muscles.Keywords: posterior atlanto-occipital membrane, atlanto-axial area, neurosurgery. RESUMOEm livros clássicos de anatomia é referida a existência de duas membranas, atlanto-occipital e atlanto-axial, participando do fechamento da região cranio-cervical. Entretanto, em frequentes procedimentos cirúrgicos que envolvem esta região, jamais detectamos a presença de tais membranas. Objetivo: Estudar os aspectos anatômicos e as estruturas que participam do fechamento posterior dos espaços atlanto-occipital e atlanto-axial. Método: Estudo de cortes histológicos de três fetos humanos e estudos anatômicos em 8 cadáveres humanos adultos. Resultados: Em ambos os espaços, atlanto-occipital e atlanto-axial, encontramos uma aderência entre as estruturas musculares profundas e a dura-mater, sem as membranas atlanto-occipital e atlanto-axial descritas nos livros clássicos de anatomia. Conclusão: Não foram encontradas as membranas atlanto-occipital e atlanto-axial no material estudado; os espaços atlanto-occipital e atlanto-axial são abertos permitindo expansões aponeuróticas entre os músculos profundos e a dura-mater.Palavras-chave: membrana atlanto-axial posterior, área atlanto-axial, neurocirurgia.The posterior craniocervical junction is composed of bony and ligamentous structures that together are responsible for biomechanical stability. The atlanto-axial and atlanto-occipital membranes have been described, but their detailed anatomy, histology and biomechanics have not been clarified. This region may be affected by several pathologies, particularly by trauma, tumors and congenital malformations. Thus, a better understanding of its anatomy is essential for surgeons involved in spine care.The atlanto-occipital and atlanto-axial membranes have been described by many authors 1,2 . Pernkopf and Fick initially questioned this anatomical description, in 1952 and 1904, respectively. They noted that the atlanto-occipital membrane differs from the ligamentum flavum, and that it may be absent in some cases in which the dura mater itself constitutes the sole closing of the...

The Posterior Atlantooccipital Membrane: The Anchor for the Myodural Bridge and Meningovertebral Structures

“…Regions of anatomy or spaces that are difficult to visualize will separate and become easily identifiable as a translucent gray-white solid under low magnification. In their anatomical study, Pimenta et al reported the absence of the PAO and atlantoaxial membranes in eight unembalmed adult human cadavers [ 21 ]. The results in Pimeta et al’s study may be due to the inability to identify potential spaces when dissecting formalin-based cadavers.…”

The ratio of the posterior atlanto-occipital interval (PAOI): a novel radiographic ratio method evaluating the risk of cervical spondylotic myelopathy—a case-control study

“…An increased ratio may suggest the existence of stiffness in the lesion of the craniovertebral junction, especially between the atlas and the occipital bone. The posterior interstitial tissue includes many anatomical structures, such as the posterior membrane of the occipital and rectus capitis posterior minor, that are at risk for possible pathological changes including contracture, fibrosis, and stiffness (16)(17)(18)(19). These abnormal changes can induce posterior atlantooccipital stiffness, which results in an increase in the interval ratio.…”

Suboccipital Musculature - Morphology, Functions and Variants - An Update

“…The presence of this connective tissue in between the atlanto-axial and atlanto-occipital interspaces, seems to be of further interest. Membrane-free zones enriched with fatty tissue exist here, which ensures the MDB glides frictionless [29]. This transition zone between the SOM and the spinal canal could be a potential location for dysfunction and lead to various symptoms due to friction, which could be treated by local manual techniques, for example [20].…”