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The suboccipital cavernous sinus (SCS) and the myodural bridge complex (MDBC) are both located in the suboccipital region. The SCS is regarded as a route for venous intracranial outflow and is often encountered during surgery. The MDBC consists of the suboccipital muscles, nuchal ligament, and myodural bridge and could be a power source for cerebrospinal fluid circulation. Intracranial pressure depends on intracranial blood volume and the cerebrospinal fluid. Since the SCS and MDBC have similar anatomical locations and functions, the aim of the present study was to reveal the relationships between them and the detailed anatomical characteristics of the SCS. The study involved gross dissection, histological staining, P45 plastination, and three-dimensional visualization techniques. The SCS consists of many small venous sinuses enclosed within a thin fibrous membrane that is strengthened by a fibrous arch closing the vertebral artery groove. The venous vessels are more abundant in the lateral and medial portions of the SCS than the middle portion. The middle and medial portions of the SCS are covered by the MDBC. Type I collagen fibers arranged in parallel and originating from the MDBC terminate on the SCS either directly or indirectly via the fibrous arch. The morphological features of SCS revealed in this research could serve as an anatomical basis for upper neck surgical procedures. There are parallel arrangements of type I collagen fibers between the MDBC and the SCS. The MDBC could change the blood volume in the SCS by pulling its wall during the head movement., (© 2023 American Association of Clinical Anatomists and British Association of Clinical Anatomists.)

Recent studies have evidenced that the anatomical structure now known as the myodural bridge (MDB) connects the suboccipital musculature to the cervical spinal dura mater (SDM). In humans, the MDB passes through both the posterior atlanto-occipital and the posterior atlanto-axial interspaces. The existence of the MDB in various mammals, including flying birds (Rock pigeons and Gallus domesticus) has been previously validated. Gentoo penguins are marine birds, able to make 450 dives per day, reaching depths of up to 660 feet. While foraging, this penguin is able to reach speeds of up to 22 miles per hour. Gentoo penguins are also the world's fastest diving birds. The present study was therefore carried out to investigate the existence and characteristics of the MDB in Gentoo penguin (Pygoscelis papua), a non-flying, marine bird that can dive. For this study, six Gentoo penguin specimens were dissected to observe the existence and composition of their MDB. Histological staining was also performed to analyze the anatomic relationships and characteristic of the MDB in the Gentoo penguin. In this study, it was found that the suboccipital musculature in the Gentoo penguin consists of the rectus capitis dorsalis minor (RCDmi) muscle and rectus capitis dorsalis major (RCDma) muscle. Dense connective tissue fibers were observed connecting these two suboccipital muscles to the spinal dura mater (SDM). This dense connective tissue bridge consists of primarily type I collagen fibers. Thus, this penguin's MDB appears to be analogous to the MDB previously observed in humans. The present study evidences that the MDB not only exists in penguins but it also has unique features that distinguishes it from that of flying birds. Thus, this study advances the understanding of the morphological characteristics of the MDB in flightless, marine birds., Competing Interests: Haichang Ocean Park Holding Co., Ltd. is responsible for the breeding of Gentoo Penguin (Pygoscelis Papua) and provides the basic data related to the penguin specimens for this research group. Another part of their work is the study and popularization of science related to penguins. The authors have declared that no competing interests exist. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Background Context: Studies over the past 20 years have revealed that there are fibrous connective tissues between the suboccipital muscles, nuchal ligament, and cervical spinal dura mater (SDM). This fibrous connection with the SDM is through the posterior atlanto-occipital or atlantoaxial interspaces and is called the myodural bridge (MDB). Researchers have inferred that the MDB might have important functions. It was speculated that the function of MDB might be related to proprioception transmission, keeping the subarachnoid space and the cerebellomedullary cistern unobstructed, and affecting the dynamic circulation of the cerebrospinal fluid. In addition, clinicians have found that the pathologic change of the MDB might cause cervicogenic or chronic tension-type headache. Previous gross anatomical and histologic studies only confirmed the existence of the MDB but did not reveal the fiber properties of the MDB. This is important to further mechanical and functional research on the MDB., Purpose: Multiple histologic staining methods were used in the present study to reveal the various origin and fiber properties of the MDB. Muscles and ligaments participating in forming the MDB at the posterior atlanto-occipital or atlantoaxial interspaces were observed, and the fiber properties of the MDB were confirmed. The present study provides a basis for speculating the tensile force values of the MDB on the SDM and a morphologic foundational work for exploring the physiological functions and clinical significances of the MDB., Study Design: Anatomical and histologic analyses of suboccipital structures that communicate with the SDM at the posterior atlanto-occipital or atlantoaxial interspaces were carried out., Methods: Multiple histologic staining methods were used to evaluate the histologic properties and composition of the MDB at the posterior atlanto-occipital or atlantoaxial interspaces in five formalin-fixed head-neck human specimens., Results: The results show that the MDB traversing the atlanto-occipital interspace originated from the rectus capitis posterior minor (RCPmi). The MDB traversing the atlantoaxial interspace originated mainly from the RCPmi, rectus capitis posterior major, and obliquus capitis inferior. These fibers form the vertebral dural ligament in the atlantoaxial interspace and connect with SDM. The MDB is mainly formed by parallel running type I collagen fibers; thus, suboccipital muscle could pull SDM strongly through the effective force propagated by the MDB during head movement., Conclusions: Myodural bridge is mainly formed by parallel running type I collagen fibers; thus, it can transmit the strong pull from the diverse suboccipital muscles or ligaments during head movement. The results of the present study will serve as a basis for further biomechanical and functional MDB research., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The "myodural bridge" was described in literatures as a dense fibrous tissue connecting the sub-occipital musculature with the spinal dura mater in human studies. Now the concept of "myodural bridge" was perceived as an exact anatomical structure presumably essential for critical physiological functions in human body, and might exist in other mammals as well. To determine the existence of the "myodural bridge" in other mammals and to lay a foundation for the functional study, we examined representatives in five different mammalian orders. Based on the anatomical dissections, P45 plastinated sections and histological sections, we found that a dense fibrous tissue connected the rectus capitisdorsalis minor and the spinal dura mater through the dorsal atlanto-occipital interspace with or without the medium of the posterior atlanto-occipital membrane. These observed connective tissues were very similar to the "myodural bridge" previously described in humans. We proposed that the "myodural bridge", as an evolutionally conserved structure, presents in many other mammals. Moreover, we believed that the "myodural bridge" might be a homologous organ in mammals. Thus, this study could provide an insight for our understanding the physiological significance of the "myodural bridge", especially in human.

Recent studies have identified that the myodural bridge (MDB) between the rectus capitis posterior minor (RCPmi) and the cervical spinal dura mater in the posterior atlanto-occipital interspace in humans. And it was supposed that the MDB may play essential physiological roles. As a result, the MDB is possibly a highly conserved structure in the evolution of mammals. However, there is little confirmative description about the existence of the MDB in marine mammals. The objective of this study was to explore the existence and the fiber property of the MDB in the Neophocaena phocaenoides. Six cadavers of the Neophocaena phocaenoides with formalin fixation were used in this study. One was used for head and neck CT scanning and three-dimensional (3D) reconstruction and suboccipital region dissection, two were for sectional observation by P45 plastinated sheets of head and neck, and three were for histological analysis of suboccipial structures. This is the first study to demonstrate the existence of the MDB in the aquatic mammals. The rectus capitis dorsal minor (RCDmi) originated from the inferior border of the occiput and inserted into the cervical spinal dura mater. At the ventral aspect of the RCDmi, the MDB directly extended through the posterior atlanto-occipital interspace and connected with the cervical spinal dura mater which was consisted of type Ⅰ collagen. In addition, the dorsal atlanto-occipital membrane was not found in the Neophocaena phocaenoides. The tendinous myodural bridge extended from the RCDmi to the spinal dura mater through the posterior atlanto-occipital interspace in the Neophocaena phocaenoides.

Few studies have been conducted specifically on the dense connective tissue located in the posterior medial part of the cervical epidural space. This study was undertaken to examine the presence of this connection between the cervical dura mater and the posterior wall of spinal canal at the level of C1-C2. 30 head-neck specimens of Chinese adults were used. Gross dissection was performed on the suboccipital regions of the 20 specimens. Having been treated with the P45 plastination method, 10 specimens were sliced (9 sagittal and 1 horizontal sections). As a result, a dense fibrous band was identified in the nuchal ligament of 29 specimens (except for one horizontal section case). This fascial structure arose from the tissue of the posterior border of the nuchal ligament and then projected anteriorly and superiorly to enter the atlantoaxial interspace. It was termed as to be named ligament (TBNL). In all 30 specimens the existence of a fibrous connection was found between the posterior aspect of the cervical dura mater and the posterior wall of the spinal canal at the level of the atlas to the axis. This fibrous connection was identified as vertebrodural ligament (VDL). The VDL was mainly subdivided into three parts, and five variations of VDL were identified. These two structures, TBNL and VDL, firmly link the posterior aspect of cervical dura mater to the rear of the atlas-axis and the nuchal region. According to these findings, the authors speculated that the movements of the head and neck are likely to affect the shape of the cervical dural sleeve via the TBNL and VDL. It is hypothesized that the muscles directly associated with the cervical dural sleeve, in the suboccipital region, may work as a pump providing an important force required to move the CSF in the spinal canal.

Purpose: Few reports have been published regarding the microanatomy of the dura mater located at the craniovertebral junction (CVJ). In clinic, the precise microanatomy of the CVJ dura mater would be taken into account, for reducing surgical complications and ineffective surgical outcomes. The main objective of the present investigation was to further elucidate the fiber composition and sources of the cervical spinal dura mater. Methods: The formalin-fixed adult head and neck specimens (n = 21) were obtained and P45 plastinated section method was utilized for the present study. The fibers of the upper cervical spinal dura mater (SDM) were examined in the P45 sagittal sections in the CVJ area. All photographic documentation was performed via a Canon EOS 7D Mark camera. Results: The posterior wall of the SDM sac at CVJ was found to be composed of stratified fibers, which are derived from three sources: the cerebral dura mater, the occipital periosteum, and the myodural bridge (MDB). The proper layer of the cerebral dura mater passes over the brim of the foramen magnum and enters the vertebral canal to form the inner layer of the SDM, and the fibers originating from the periosteum of the brim of the foramen magnum form the middle layer. The fibers of the MDB are inserted into the SDM and form its outer layer. It was found that the total number of fibers from each origin varied in humans. Conclusion: At the CVJ, the posterior wall of the SDM is a multi-layered structure composed of three different originated fibers. The cerebral dura mater, the periosteum located at the brim of the foramen magnum, and MDB contribute to the formation of the SDM. The present study would be beneficial to the choice of surgical approach at the CVJ and the protection of the SDB. [ABSTRACT FROM AUTHOR]

A dense bridge-like tissue named the myodural bridge (MDB) connecting the suboccipital muscles to the spinal dura mater was originally discovered in humans. However, recent animal studies have revealed that the MDB appears to be an evolutionarily conserved anatomic structure which may have significant physiological functions. Our previous investigations have confirmed the existence of the MDB in finless porpoises. The present authors conducted research to expound on the specificity of the MDB in the porpoise Neophocana asiaeorientalis (N.asiaeorientalis). Five carcasses of N.asiaeorientalis, with formalin fixation, were used for the present study. Two of the carcasses were used for head and neck CT scanning, three-dimensional reconstructions, and gross dissection of the suboccipital region. Another carcass was used for a P45 plastination study. Also, a carcass was used for a histological analysis of the suboccipital region and also one was used for a Scanning Electron Microscopy study. The results revealed that the MDB of the N.asiaeorientalis is actually an independent muscle originating from the caudal border of the occiput, passing through the posterior atlanto-occipital interspace, and then attaches to the cervical spinal dura mater. Thus the so called MDB of the N.asiaeorientalis is actually an independent and uniquely specialized muscle. Based on the origin and insertion of this muscle, the present authors name it the 'Occipital-Dural Muscle'. It appears that the direct pull of this muscle on the cervical spinal dura mater may affect the circulation of the cerebrospinal fluid by altering the volume of the subarachnoid space via a pumping action. [ABSTRACT FROM AUTHOR]