Evidence for chronic headaches induced by pathological changes of myodural bridge complex

Clinical studies have shown that there may be a certain relationship between pathological changes of the myodural bridge complex (MDBC) and chronic headaches of unknown cause. But there is still a lack of experimental evidence to explain the possible mechanism. This study aims to further confirm this relationship between MDBC and chronic headaches and explore its potential occurrence mechanism in rats. Bleomycin (BLM) or phosphate-buffered saline (PBS) was injected into the myodural bridge fibers of rats to establish the hyperplastic model of MDBC. After 4 weeks, the occurrence of headaches in rats was evaluated through behavioral scores. The immunohistochemistry staining method was applied to observe the expression levels of headache-related neurotransmitters in the brain. Masson trichrome staining results showed that the number of collagen fibers of MDBC was increased in the BLM group compared to those of the other two groups. It revealed hyperplastic changes of MDBC. The behavioral scores of the BLM group were significantly higher than those of the PBS group and the blank control group. Meanwhile, expression levels of CGRP and 5-HT in the headache-related nuclei of the brain were increased in the BLM group. The current study further confirms the view that there is a relationship between pathological changes of MDBC and chronic headaches of unknown cause. This study may provide anatomical and physiological explanations for the pathogenesis of some chronic headaches of unknown cause.

Dynamic asymmetry in cerebrospinal fluid pressure: An indicator of regional differences in compliance

Background

Dural compliance influences the shape and magnitude of the cerebrospinal fluid (CSF) pulsations. In humans, cranial compliance is approximately 2× greater than spinal compliance; the differential has been attributed to the associated vasculature. In alligators, the spinal cord is surrounded by a large venous sinus, which suggests that the spinal compartment may have higher compliance than is found in mammals.

Methods

Pressure catheters were surgically implanted into the cranial and spinal subdural spaces of eight subadult American alligators (Alligator mississippiensis). The CSF was propelled through the subdural space by orthostatic gradients and rapid changes in linear acceleration.

Results

CSF pressure recordings taken from the cranial compartment were consistently, and significantly, larger than those taken from the spinal compartment. After the myodural bridge of Alligator was surgically released, the asymmetry in CSF pressure was decreased.

Conclusion

Unlike the situation in humans, the spinal compartment of Alligator has greater compliance than the cranial compartment, presumably due to the presence of the large spinal venous sinus surrounding the dura. The change in CSF pressures after myodural surgical release supports the hypothesis that the myodural bridge functions, at least in part, to modulate dural compliance and the exchange of CSF between the cranial and spinal compartments.

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

Background

The 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.

Methods

A 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.

Outcomes

In 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.

Discussion

The 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.

Relationship between the sectional area of the rectus capitis posterior minor and the to be named ligament from 3D MR imaging

Background

To evaluate the maximal sectional area (SA) of the rectus capitis posterior minor (RCPmi) muscle and its potential correlation with to be named ligament (TBNL) in the suboccipital area using 3D MR imaging.

Methods

A total of 365 subjects underwent sagittal 3D T₂WI MR imaging of the RCPmi and TBNL. Among them, 45 subjects were excluded due to a particular clinical history or poor image quality. Finally, 320 subjects met the inclusion criteria, including 138 men and 182 women. The 624 RCPmi muscles were classified into positive and negative groups according to their attachment to the TBNL. Two experienced radiologists manually measured the maximum SA of the RCPmi muscle on the parasagittal image with a 30° deviation from the median sagittal plane. The correlations between the SA and the subject’s age, height, BMI, gender, handedness, and age-related disc degeneration were tested by Spearman analysis. The SA differences between different groups were compared using independent samples t-test.

Results

A total of 123 RCPmi-TBNL attachments were identified in the positive group, while 501 RCPmi muscles were identified in the negative group. The SA of the 624 RCPmi muscles was 62.71 ± 28.72 mm² and was poorly correlated with the subject’s age, BMI, or handedness, with no correlation with age-related disc degeneration. A fair correlation was found between the SA and the body height in the whole group, and poor correlation in each male/female group. The SA of the RCPmi muscle in males was significantly bigger than that in women ([75.54 ± 29.17] vs. [52.74 ± 24.07] mm²). The SA of RCPmi muscle in the positive group was significantly smaller than that in the negative group ([55.95 ± 26.76] mm² vs. [64.37 ± 28.97] mm²).

Conclusions

Our results revealed a significantly smaller SA of the RCPmi in subjects with RCPmi-TBNL attachment. Besides, a larger SA of the RCPmi was correlated with the male gender. These findings suggest that the SA of the RCPmi ought to be interpreted with care for each patient since there could be considerable variations.

The myodural bridge complex defined as a new functional structure

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Existence and features of the myodural bridge in Gallus domesticus: indication of its important physiological function

The myodural bridge (MDB) is a dense connective tissue that connects muscles with the cervical spinal dura mater via the posterior atlanto-occipital and atlato-axial interspaces. To date, the physiological function of the MDB has not been fully elucidated. Recent studies have identified the presence of the MDB in mammals, but very little information is available on the existence of the MDB in avifauna. We selected Gallus domesticus to explore the existence and the fiber property of the MDB in avifauna. We found that in this species, fibers originating from the ventral aspect of the rectus capitis dorsal minor are fused with the dorsal atlanto-occipital membrane and that numerous trabeculae connect the dorsal atlanto-occipital membrane with the cervical spinal dura mater. Furthermore, the occipital venous sinus is located between the trabeculae. The MDB is mainly composed of collagen type I fibers. Our results show that the MDB is present in G. domesticus and lead us to infer that the MDB is a highly conservative evolutionary structure which may play essential physiological roles.

Orientation and property of fibers of the myodural bridge in humans

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.

Investigation of meningomyovertebral structures within the upper cervical epidural space: a sheet plastination study with clinical implications

BACKGROUND CONTEXT

Over the past two decades, soft-tissue structures communicating with the dura mater within the epidural space have become the focus of many anatomical and histopathologic studies. The relationship between these bridging structures has yet to be evaluated in situ.

PURPOSE

This is the first study that used E12 sheet plastination to investigate the epidural space of the upper cervical spine in situ and its associated bridging structures. Given the complexity of this space, this study may prove useful to clinical anatomists and surgeons who operate within this region.

STUDY DESIGN

Anatomical and microscopic analyses of structures that communicate with the dura mater within the upper cervical region were carried out.

METHODS

Gross dissection in conjunction with microscopy was used to evaluate bridging communications of the upper cervical spine in 10 cadavers. To evaluate the in situ arrangement of these structures, E12 sheet plastination was used on 13 cadavers.

RESULTS

In all 23 specimens, suboccipital fascia coalesced with the dorsal meningovertebral ligament of the atlas, and inserted directly into the posterior surface of the dura as a single but separable laminar layer. At the level of the atlantoaxial interspace, suboccipital fasciae combined and coalesced with the dorsal meningovertebral ligament of the atlas and the axis. These structures inserted into the posterior surface of the dura mater as a single but separable layer. Microscopy validated these findings and E12 sheet plastination revealed the in situ organization of these soft-tissue structures. E12 sheet plastination also provided new information on dural arrangement at the craniocervical junction, which was observed to be composed of periosteum from the occiput but consisted mainly of deep fascia from the rectus capitis posterior minor.

CONCLUSIONS

E12 sheet plastination has provided in situ visualization of bridging structures within the cervical epidural space and offers new insight into these structures, as well as the composition and arrangement of the posterior atlantooccipital membrane and cerebrospinal dura at the craniocervical junction. This study aims to expand on the anatomical understanding of the upper cervical region while defining structures that may reduce neurosurgical complications, and aid in the understanding of the pathophysiology of certain neurogenic disorders.

Histological examination of the human obliquus capitis inferior myodural bridge

This study was designed to examine the anatomical relationship between the obliquus capitis inferior (OCI) muscle and the cervical dura mater at the histological level. Eight human cadavers, with an average age of 65 ± 7.9 years were selected from a convenience sample for suboccipital dissection. Twelve OCI muscle specimens were excised, 100% of which emitted grossly visible soft tissue tracts that inserted into the posterolateral aspect of the cervical dura. These 12 myodural specimens were excised as single, continuous structures and sent for H&E staining. One sample also underwent immuno-peroxidase staining. Microscopic evaluation confirmed a connective tissue bridge emanating from the OCI muscular body and attaching to the posterolateral aspect of the cervical dura mater in 75% of the specimens. Microtome slices of the remaining 25% were not able to capture muscle, connective tissue and dura within the same plane and were therefore unable to be properly analyzed. The sample sent for neuro-analysis stained positively for several neuronal fascicles traveling within, and passing through the OCI myodural bridge. This study histologically confirms the presence of a connective tissue bridge that links the OCI muscle to the dura mater and the presence of neuronal tissue within this connection warrants further examination. This structure may represent a component of normal human anatomy. In addition to its hypothetical role in human homeostasis, it may contribute to certain neuropathological conditions, as well.