Myodural Bridge Research Articles

Identification of the Myodural Bridge in a Venomous Snake, the Gloydius shedaoensis: What is the Functional Significance?

Myodural bridges (MDB) are anatomical connections between the suboccipital muscles and the cervical dura mater which pass through both the atlanto-occipital and the atlanto-axial interspaces in mammals. In our previous studies, we found that the MDB exists in seven terrestrial mammal species, two marine mammal species, two reptilian species, and one bird species. A recent study suggested that given the “ubiquity” of myodural bridges in terrestrial vertebrates, the MDB may also exist in snakes. Specifically, we focused on the Gloydius shedaoensis, a species of Agkistrodon (pit viper snake) that is only found on Shedao Island, which is in the southeastern sea of Dalian City in China. Six head and neck cadaveric specimens of Gloydius shedaoensis were examined. Three specimens were used for anatomical dissection and the remaining three cadaveric specimens were utilized for histological analysis. The present study confirmed the existence of the MDB in the Gloydius shedaoensis. The snake’s spinalis muscles originated from the posterior edge of the supraoccipital bones and the dorsal facet of the exocciput, and then extended on both sides of the spinous processes of the spine, merging with the semispinalis muscles. On the ventral aspect of this muscular complex, it gave off fibers of the MDB. These MDB fibers twisted around the posterior margin of the exocciput and then passed through the atlanto-occipital interspace, finally terminating on the dura mater. We observed that the MDB also existed in all of the snakes’ intervertebral joints. These same histological findings were also observed in the Gloydius brevicaudus, which was used as a control specimen for the Gloydius shedaoensis. In snakes the spinal canal is longer than that observed in most other animals. Considering the unique locomotive style of snakes, our findings contribute to support the hypothesis that the MDB could modulate cerebrospinal fluid (CSF) pulsations.

A new hypothesis for the pathophysiology of symptomatic adult Chiari malformation Type I

Chiari malformation Type I (CMI) is characterized by herniation of the cerebellar tonsils through the foramen magnum. The pathophysiology of CMI is not well elucidated; however, the prevailing theory focuses on the underdevelopment of the posterior cranial fossa which results in tonsillar herniation. Symptoms are believed to be due to the herniation causing resistance to the natural flow of cerebrospinal fluid (CSF) and exerting a mass effect on nearby neural tissue. However, asymptomatic cases vastly outnumber symptomatic ones and it is not known why some people become symptomatic. Recently, it has been proposed that CMI symptoms are primarily due to instability of either the atlanto-axial (AA) or the atlanto-occipital (AO) joint and the cerebellar tonsils herniate to prevent mechanical pinching. However, only a small percentage of patients exhibit clinical instability and these theories do not account for asymptomatic herniations. We propose that the pathophysiology of adult CMI involves a combination of craniocervical abnormalities which leads to tonsillar herniation and reduced compliance of the cervical spinal canal. Specifically, abnormal AO and/or AA joint morphology leads to chronic cervical instability, often subclinical, in a large portion of CMI patients. This in turn causes overwork of the suboccipital muscles as they try to compensate for the instability. Over time, the repeated, involuntary activation of these muscles leads to mechanical overload of the myodural bridge complex, altering the mechanical properties of the dura it merges with. As a result, the dura becomes stiffer, reducing the overall compliance of the cervical region. This lower compliance, combined with CSF resistance at the same level, leads to intracranial pressure peaks during the cardiac cycle (pulse pressure) that are amplified during activities such as coughing, sneezing, and physical exertion. This increase in pulse pressure reduces the compliance of the cervical subarachnoid space which increases the CSF wave speed in the spinal canal, and further increases pulse pressure in a feedback loop. Finally, the abnormal pressure environment induces greater neural tissue motion and strain, causing microstructural damage to the cerebellum, brainstem, and cervical spinal cord, and leading to symptoms. This hypothesis explains how the combination of craniocervical bony abnormalities, anatomic CSF restriction, and reduced compliance leads to symptoms in adult CMI.

Cover Image

The myodural bridge is represented by skeletal muscle fibers attaching to the cervical dura mater. It has been described from a variety of mammals and other amniotes. In this issue of the Journal of Morphology (pp. 123‐133), Grondel and coauthors test an earlier assumption about the presence of the myodural bridge in snakes using histology, computed tomography, and micro‐CT imaging. They find no evidence for a myodural ridge in snakes and discuss the functional implications. The cover image shows a transverse histological section through atlas and axis from Dasypeltis scabra.

The morphology of the suboccipital region in snakes, and the anatomical and functional diversity of the myodural bridge.

The myodural bridge, that is, skeletal muscle fibers attaching to the cervical dura mater, has been described from a variety of mammals and other amniotes. To test an earlier assumption about the presence of the myodural bridge in snakes, a comparative study was designed using a group of Colubrine snakes. Serial histological sections revealed no evidence of the myodural bridge in any of the snakes examined. Further analyses, including histology, computed tomography (CT), and micro-CT imaging of other distantly related snakes, also turned up no evidence of a myodural bridge. The close apposition of adjacent neural arches in snakes may preclude muscle tendons from passing through the intervertebral joint to reach the spinal dura. It is hypothesized that the myodural bridge functions in the clearance of the cerebrospinal fluid (CSF) by creating episodic CSF pressure pulsations, and that snakes are capable of creating equivalent CSF pressure pulsations through vertebral displacement.

A specialized myodural bridge named occipital-dural muscle in the narrow-ridged finless porpoise (Neophocaena asiaeorientalis)

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.

Head-nodding: a driving force for the circulation of cerebrospinal fluid

The myodural bridge (MDB) is a dense connective tissue bridge connecting the suboccipital muscles to the spinal dura mater, and it has been proven to be a normal common existing structure in humans and mammals. Some scholars believe that the suboccipital muscles can serve as a dynamic cerebrospinal fluid (CSF) pump via the MDB, and they found head rotations promote the CSF flow in human body, which provided evidence for this hypothesis. Head movement is a complex motion, but the effects of other forms of head movement on CSF circulation are less known. The present study explored the effects of head-nodding on CSF circulation. The CSF flow of 60 healthy volunteers was analyzed via cine phase-contrast magnetic resonance imaging at the level of the occipitocervical junction before and after one-minute-head-nodding period. Furthermore, the CSF pressures of 100 volunteers were measured via lumbar puncture before and after 5 times head-nodding during their anesthetizing for surgical preparation. As a result, it was found that the maximum and average CSF flow rates at the level of the upper border of atlas during ventricular diastole were significantly decreased from 1.965 ± 0.531 to 1.839 ± 0.460 ml/s and from 0.702 ± 0.253 to 0.606 ± 0.228 ml/s respectively. In the meantime, the changes in the ratio of cranial and caudal orientation of the net flow volume were found differed significantly after the one-minute-head-nodding period (p = 0.017). And on the other hand, the CSF pressures at the L3–L4 level were markedly increased 116.03 ± 26.13 to 124.64 ± 26.18 mmH2O. In conclusion, the head-nodding has obvious effects on CSF circulation and head movement is one of the important drivers of cerebrospinal fluid circulation. We propose that the suboccipital muscles, participating in various head movements, might pull the dura sac via the myodural bridge, and thus, head movement provides power for the CSF circulation.

Abnormal spinal cord motion at the craniocervical junction in hypermobile Ehlers-Danlos patients.

The craniocervical junction (CCJ) is anatomically complex and comprises multiple joints that allow for wide head and neck movements. The thecal sac must adjust to such movements. Accordingly, the thecal sac is not rigidly attached to the bony spinal canal but instead tethered by fibrous suspension ligaments, including myodural bridges (MDBs). The authors hypothesized that pathological spinal cord motion is due to the laxity of such suspension bands in patients with connective tissue disorders, e.g., hypermobile Ehlers-Danlos syndrome (EDS). The ultrastructure of MDBs that were intraoperatively harvested from patients with Chiari malformation was investigated with transmission electron microscopy, and 8 patients with EDS were compared with 8 patients without EDS. MRI was used to exclude patients with EDS and craniocervical instability (CCI). Real-time ultrasound was used to compare the spinal cord at C1-2 of 20 patients with EDS with those of 18 healthy control participants. The ultrastructural damage of the collagen fibrils of the MDBs was distinct in patients with EDS, indicating a pathological mechanical laxity. In patients with EDS, ultrasound revealed increased cardiac pulsatory motion and irregular displacement of the spinal cord during head movements. Laxity of spinal cord suspension ligaments and the associated spinal cord motion disorder are possible pathogenic factors for chronic neck pain and headache in patients with EDS but without radiologically proven CCI.

Investigation of a Novel Cranial Ligament Between the Occiput and Cervical Spinal Dura

Introduction The brain and spinal cord are covered by dura mater which attaches to bones and muscles in the cervical region. Dural connective structures have been described as the Ligamentum Craniale Durae Matrice Spinalis (LCDMS) (Von Lanz, 1929). The myodural bridge complex (MBC) is a component of the LCDMS linking suboccipital musculature to the cervical spinal dura. While performing en bloc dissections of the central nervous system, we found a novel connection between the occiput and the cervical spinal dura that has not been previously described that we have termed, the ligamentum kryptos craniale (LKC). In this study, we provide evidence that the LKC is a previously unrecognized component of the LCDMS. Methods A total of 13 cadavers were dissected. Total spinal laminectomy and en bloc dissection was performed on two cadavers, and the occiput was removed via a coronal cut with inferior borders meeting the lateral most aspect of the foramen magnum. Eleven different cadaver skulls were cut at the euryon in transverse section. Five of the 11 cadavers were hemisected to the level of C5. LKC Length from origin to opisthion, thicknesses at opisthion, length from opisthion to cervical dura, and width at opisthion were measured. All measurements were taken with Mitutoyo Absolute IP-67 digital calipers except for LKC width, in which a flexible ruler was used. Photograph evidence was also obtained, and statistical analysis was conducted using Microsoft Excel. Results The LKC was found in all bodies (13 specimens). Its shape was triangular as it exited the foramen magnum and inserted onto the cervical spinal dura (Fig. 1). Its origin spanned across the internal occipital crest, the inferior ridge of the cerebellar fossa, and the opisthion (Fig. 2). Various measurements of the LKCs were made (expressed as means + SD) including the length from origin to opisthion (1.94 ± 0.3 cm, N = 10), thickness at opisthion (0.58 ± 0.05 mm, N = 6), length from opisthion to cervical dura (10.51 ± 2.59 mm, N = 5) and width at opisthion (5.05 ± 0.44 cm, N = 10). Conclusion Based on the findings of this study, we believe the LKC is a novel component of the LCDMS. Data suggests the MBC attaches to the LKC rather than directly to the cervical spinal dura mater. In the clinical setting, the LKC may be relevant to unknown causes of head and neck pain. Future histological studies and microscopic analysis will be necessary to further categorize this structure. References von Lanz, T. (Jun 1929). Über die Rückenmarkshäute : I. Die Konstruktive Form der harten Haut des menschlichen Rückenmarkes und ihrer Bänder. 118, 252-307.

The morphology, biomechanics, and physiological function of the suboccipital myodural connections

The myodural bridge (MDB) connects the suboccipital musculature to the spinal dura mater (SDM) as it passed through the posterior atlanto-occipital and the atlanto-axial interspaces. Although the actual function of the MDB is not understood at this time, it has recently been proposed that head movement may assist in powering the movement of cerebrospinal fluid (CSF) via muscular tension transmitted to the SDM via the MDB. But there is little information about it. The present study utilized dogs as the experimental model to explore the MDB’s effects on the CSF pressure (CSFP) during stimulated contractions of the suboccipital muscles as well as during manipulated movements of the atlanto-occiptal and atlanto-axial joints. The morphology of MDB was investigated by gross anatomic dissection and by histological observation utilizing both light microscopy and scanning electron microscopy. Additionally biomechanical tensile strength tests were conducted. Functionally, the CSFP was analyzed during passive head movements and electrical stimulation of the suboccipital muscles, respectively. The MDB was observed passing through both the dorsal atlanto-occipital and the atlanto-axial interspaces of the canine and consisted of collagenous fibers. The tensile strength of the collagenous fibers passing through the dorsal atlanto-occipital and atlanto-axial interspaces were 0.16 ± 0.04 MPa and 0.82 ± 0.57 MPa, respectively. Passive head movement, including lateral flexion, rotation, as well as flexion–extension, all significantly increased CSFP. Furthermore, the CSFP was significantly raised from 12.41 ± 4.58 to 13.45 ± 5.16 mmHg when the obliques capitis inferior (OCI) muscles of the examined specimens were electrically stimulated. This stimulatory effect was completely eliminated by severing the myodural bridge attachments to the OCI muscle. Head movements appeared to be an important factor affecting CSF pressure, with the MDB of the suboccipital muscles playing a key role this process. The present study provides direct evidence to support the hypothesis that the MDB may be a previously unappreciated significant power source (pump) for CSF circulation.

Existence and features of the myodural bridge in Gentoo penguins: A morphological study.

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.

Hirayama Disease can be Caused by Loss of Attachment of the Cervical Posterior Dura to the Pedicle due to Immunological Abnormalities of the Dura and Posterior Ligaments: A New Hypothesis

Hirayama disease is a rare and self-limiting cervical myelopathy related to neck flexion in adolescents, predominantly male, originally described by Hirayama in 1959 and until today reported worldwide. It characteristically presents with asymmetric distal upper extremity muscular weakness and atrophy without objective sensory disturbance or lower extremity involvement, which spontaneously halts within 3-5 years after onset with some sequelae. Neuroradiological and autopsy/neuropathological studies have shown that the condition is caused by chronic ischemic changes to the anterior horn cells of the lower cervical cord due to abnormal forward-shifting of the lower cervical posterior dura on neck flexion. Although the true pathomechanism of the dural changes is still unknown, various hypothetical theories have been formulated: "tight dural canal in flexion", "flexion myelopathy", "engorgement of the posterior venous plexus", and "disproportional growth between the vertebral column and the contents of the spinal canal during puberty" (Hirayama). However, rarity of the condition and asymmetric cord involvement cannot be explained with these theories alone. Combination of a "posterior epidural ligament [sparse at C6-C7] factor" proposed by Shinomiya , "loss of dorsal dural attachment from the pedicle even in neutral position in the MRI" pointed out by some neuroradilogists, and "pathological abnormalities of elastic and collagen fibers in the operatively-resected dura" reported by several spinal surgeons suggest that abnormal changes of the dura and posterior ligaments, as well as the existence of "myodural bridge" at C1-C2 described by some neuroanatomists, can cause the dural forward-shifting of the lower cervical cord. In addition to these mechanical factors, immunological abnormalities such as hyperIgEemia and upreguration of some cytokines and chemokines in serum/CSF of patients with Hirayama disease have been reported. Furthermore, immune cells comprise -17% of all cells in the dura in rats. In conclusion, although further immunological studies of the patient's cervical dura and surrounding structures are required, I propose, in addition to Hirayama's theory, a new hypothesis about the pathomechanism of Hirayama disease, "loss of dorsal dural attachment from the pedicle due to immunological abnormalities of the dura and posterior ligaments", which can resolve the remaining problems of the condition. (Received May 25, 2020; Accepted July 2, 2020; Published December 1, 2020).

Development of myodural bridge located within the atlanto-occipital interspace of rats.

The myodural bridge (MDB) is a dense connective tissue structure that connects the subocciptal musculature to the spinal dura mater. The purpose of this study was to clarify morphological evolution characteristics and compositional changes in the fibrous structures of MDB during its growth and development in the atlanto-occipital interspace. For this, histological sections from Sprague-Dawley (SD) rats (age, E17 to adulthood) were stained with Masson's Trichrome and Picrosirius Red. The results demonstrated that at age E18, the posterior arch of the atlas was completely closed and MDB fibers had already begun to form. In rat embryos (E18-E21), only few fibers and muscles were present in the suboccipital region, and these were lightly stained. In postnatal rats, an obvious increase in the amount of fibers and muscle tissues was noted. At age P1, MDB fibers originated from the rectus capitis posterior minor muscle and merged into the atlanto-occipital membrane, which was closely attached to the spinal dura mater. As rats matured, MDB fibers gradually became denser and more organized. This study also showed that in postnatal rats, MDB was mainly composed of type I collagen fibers. By observing the development of MDB in SD rats, the function of MDB can be further understood. This study provides a morphological basis for future functional studies involving the MDB.

Pressure point knockouts and neurodynamics

Without understanding the underlying neurodynamics, for decades, martial artists have safely employed a phenomenon known as pressure point knockouts (PPK). PPK are low-force martial arts techniques that reversibly alter consciousness in the receiver. Beyond altered consciousness, symptoms of the PPK include pupillary dilation, pallor, diaphoresis, loss of motor control, altered respiration, and, reportedly, altered heart rate. PPK are primarily attacks to the head, frequently combined with an extremity manipulation but also include techniques to reverse the effects, known as revivals. PPK practitioners often use a series of theories drawn loosely from Traditional Chinese Medicine to explain both the attacks and revivals. This study examines PPK and then discusses two related categories of information: the trigeminocardiac reflex (TCR) and the study of neurodynamics. The trigeminocardiac reflex is an unusual constellation of autonomic effects encountered in reaction to stimulation of the trigeminal nerve. Neurodynamics recognizes that excessive mechanical tension of nerves can have adverse effects both peripherally and centrally on the nervous system, as seen in the double crush syndrome. By combining these categories, this paper proposes a theory of PPK which uses neurodynamic tension of the upper cervical spine transmitted via the myodural bridges of the suboccipital muscles, enhanced by extremity neurodynamic positioning and the double crush phenomenon, to elicit a version of the trigeminocardiac reflex. Viewed within the context of the TCR and neurodynamics, the practice of PPK presents a novel laboratory to study aspects of the treatment of difficult cranial vault and maxillofacial problems.

Scanning Electron Microscopic Observation of Myodural Bridge in the Human Suboccipital Region

A scanning electron microscopic study performed on three cadaveric specimens focused on the human suboccipital region, specifically, myodural bridge (MDB). This study showed the connection form of the MDB among the suboccipital muscles, the posterior atlanto-occipital membrane (PAOM) and the spinal dura mater (SDM), and provided an ultrastructural morphological basis for the functional studies of the MDB. Since the myodural bridge was first discovered by Hack, researches on its morphology and functions had been progressing continuously. However, at present, research results about MDB were still limited to the gross anatomical and histological level. There was no research report showing the MDB's ultrastructural morphology and its ultrastructural connection forms between PAOM and SDM. A scanning electron microscope (SEM) was used to observe the connection of myodural bridge fibers with PAOM and SDM in atlanto-occipital and atlanto-axial interspaces, and the connection forms were analyzed. Under the SEM, it was observed that there were clear direct connections between the suboccipital muscles and the PAOM and SDM in the atlanto-occipital and atlanto-axial spaces. These connections were myodural bridge. The fibers of the myodural bridge merged into the spinal dura mater and gradually became a superficial layer of the spinal dura mater. MDB fibers merged into the SDM and became part of the SDM in the atlanto-occipital and atlanto-axial space. MDB could transfer tension and pulling force to the SDM effectively, during the contraction or relaxation of the suboccipital muscles. N/A.

Anatomy and clinical relevance of sub occipital soft tissue connections with the dura mater in the upper cervical spine.

BackgroundThe upper cervical region is a complex anatomical structure. Myodural bridges between posterior suboccipital muscles and the dura might be important explaining conditions associated with the upper cervical spine dysfunction such as cervicogenic headache. This cadaver study explored the upper cervical spine and evaluated the myodural bridges along with position of spinal cord in response to passive motion of upper cervical spine.MethodsA total of seven adult cadavers were used in this exploratory study. The suboccipital muscles and nuchal ligament were exposed. Connections between the Rectus Capitis Posterior major/minor and the Obliquus Capitis minor, the nuchal ligament, posterior aspect of the cervical spine, flavum ligament and the dura were explored and confirmed with histology. The position of the spinal cord was evaluated with passive motions of the upper cervical spine.OutcomesIn all cadavers connective tissues attaching the Rectus Capitis Posterior Major to the posterior atlanto-occipital membrane were identified. In the sagittal dissection we observed connection between the nuchal ligament and the dura. Histology revealed that the connection is collagenous in nature. The spinal cord moves within the spinal canal during passive movement.DiscussionThe presence of tissue connections between ligament, bone and muscles in the suboccipital region was confirmed. The nuchal ligament was continuous with the menigiovertebral ligament and the dura. Passive upper cervical motion results in spinal cord motion within the canal and possible tensioning of nerve and ligamentous connections.

Microanatomy of the dura mater at the craniovertebral junction and spinal region for safe and effective surgical treatment.

Few reports have been published regarding the detailed microsurgical anatomy of the dura mater at the craniovertebral junction (CVJ), although many neurosurgeons have had the opportunity to conduct surgeries in this region, such as in cases of Chiari malformation. The authors aimed to evaluate the detailed and precise microsurgical anatomy of the dura mater at the CVJ for safe and effective surgical treatment at this area. This study consisted of dissection of 4 formalin-fixed, continuous, human cadaveric dura maters, extending from the posterior fossa to the C2 level. After removing the occipital bone and C1 laminae, a dural incision was made to harvest the specimen. The following structural and topographical aspects of the dura mater in each region were studied: 1) thickness, 2) morphological characteristics, and 3) vascular structures. The average thicknesses of the dura mater were 313.4 ± 137.0 μm, 3051.5 ± 798.8 μm, and 866.5 ± 359.0 μm in the posterior cranial fossa, CVJ, and spinal region, respectively. The outer layer of the posterior cranial dura mater and the tendon of the rectus capitis posterior minor muscle were connected, forming the "myodural bridge." The dura mater at the CVJ had a well-developed vascular network. These vascular structures were determined to be veins or the venous sinus, and were mainly located around the interface between the inner layer of the cranial dura mater and the rectus capitis posterior minor muscle layer. Regarding the morphological features, the bulging located in the inner layer of the dura mater at the CVJ was determined to be the marginal sinus, and contained a pacchionian granulation that allowed for CSF circulation. In the spinal region, the dura mater was characterized by a single, thick layer enclosing the collagen fibers with almost the same orientation. The dura mater at the CVJ displayed dynamic morphological changes within an extremely short segment. Its characteristic anatomical features were not similar to those in the cranial regions. The dural bulging at the CVJ was determined to be the venous sinus. During surgery in the posterior fossa, CVJ, and spinal cord, different procedures should be used because of the specific microsurgical anatomy of each region.

The myodural bridge of the American alligator (Alligator mississippiensis) alters CSF flow.

Disorders of the volume, pressure or circulation of the cerebrospinal fluid (CSF) lead to disease states in both newborns and adults; despite this significance, there is uncertainty regarding the basic mechanics of the CSF. The suboccipital muscles connect to the dura surrounding the spinal cord, forming a complex termed the 'myodural bridge'. This study tests the hypothesis that the myodural bridge functions to alter the CSF circulation. The suboccipital muscles of American alligators were surgically exposed and electrically stimulated simultaneously with direct recordings of CSF pressure and flow. Contraction of the suboccipital muscles significantly changed both CSF flow and pressure. By demonstrating another influence on CSF circulation and pulsatility, the present study increases our understanding of the mechanics underlying the movement of the CSF.

Existence of Myodural Bridge in the Trachemys scripta elegans: Indication of its Important Physiological Function

Existence of Myodural Bridge in the Trachemys scripta elegans: Indication of its Important Physiological Function

Equine myodural bridges - An Anatomical and integrative/functional description of myodural bridges along the spine of horses: Special focus on the atlanto-occipital and atlanto-axial regions.

Introduction: Socalled myodural bridges (MDB) linking the suboccipital muscles to the dura mater have been described in the human, canine, small ruminants, monkeys, rodents, porpoises, crocodiles, sperm whales, chickens and lately in equines. They are believed to have biomechanical functions and might also play a role in head/neck pathology and the pumping function of the cerebrospinal fluid. Up to now these bridges have only been described briefly in the horse in terms of their anatomy, and then only in relation to Ehlers-Danlos syndrome. The aim of this study was therefore to investigate and thoroughly describe the anatomy, biomechanics and integration of this complex throughout the equine spine, with special focus on the upper neck, the cervicothoracic- and the lumbosacral transitions. Pathology in these regions is well recognized in horses. Material and methods: Horses were dissected, the heads and spine prepared in several anatomical planes, the heads MR-scanned and histology performed on the AO and AA MDBs. Results: Gross anatomical observations showed that muscle-membrane-spinal dura mater connections (MDB) were evident in the full equine columna vertebralis, and were specifically developed in the upper cervical, the cervicothoracic and the lumbosacral transitions. In the upper cervical region, the m. rectus capitis minor and major and the m. obl. cap caudalis attached tightly to the dorsal intervertebral AO and AA membranes. On the ventral membrane surface there was a trabecular connection to dura mater. The two membranes differed markedly in the amount of elastic fibers giving them different biomechanical function. The structures of the AO MDB were evident on the MRI scans. Conclusions: Horses, like humans, other mammals, a reptile and a bird to date, have myodural bridges, which are tightly integrated with surrounding structures as well as the biomechanics of the upper neck. In addition, similar structures are present throughout the whole spine.

The myodural bridge complex defined as a new functional structure.

The connective tissue between suboccipital muscles and the cervical spinal dura mater (SDM) is known as the myodural bridge (MDB). However, the adjacent relationship of the different connective tissue fibers that form the MDB remains unclear. This information will be highly useful in exploring the function of the MDB. The adjacent relationship of different connective tissue fibers of MDB was demonstrated based upon three-dimensional visualization model, P45 plastinated slices and histological sections of human MDB. We found that the MDB originating from the rectus capitis posterior minor muscle (RCPmi), rectus capitis posterior major muscle (RCPma) and obliquus capitis inferior muscle (OCI) in the suboccipital region coexists. Part of the MDB fibers originate from the ventral aspect of the RCPmi and, together with that from the cranial segment of the RCPma, pass through the posterior atlanto-occipital interspace (PAOiS) and enter into the posterior aspect of the upper cervical SDM. Also, part of the MDB fibers originate from the dorsal aspect of the RCPmi, the ventral aspect of the caudal segment of the RCPma, and the ventral aspect of the medial segment of the OCI, enter the central part of the posterior atlanto-axial interspace (PAAiS) and fuse with the vertebral dura ligament (VDL), which connects with the cervical SDM. Our findings prove that the MDB exists as a complex structure which we termed the 'myodural bridge complex' (MDBC). In the process of head movement, tensile forces could be transferred possibly and effectively by means of the MDBC. The concept of MDBC will be beneficial in the overall exploration of the function of the MDB.