A Morphological Study Of The Suboccipital Cavernous Sinus And Relationship With The Myodural Bridge Complex

Objective: There is a venous compartment that cushions the horizontal part of the suboccipital segment of vertebral artery and the first cervical nerve in the posterior atlantoccipital interspace.Its development,anatomical structure,function and pathological characteristics are similar to those of the cavernous sinus,Arnautovi? hence named it suboccipital cavernous sinus.The suboccipital cavernous sinus communicates with the sigmoid sinus,occipital sinus,marginal sinus,the jugular bulb or internal jugular vein,vertebral venous plexus,vertebral artery venous plexus and suboccipital venous plexus.The vertebral venous plexus plays an important role in venous intracranial outflow.Because it communicates with the vertebral venous plexus,the suboccipital cavernous sinus is considered as functional components of the vertebral venous system and plays a more independent and important role in intracranial venous drainage due to complex vascular communicating relationship.The appearance of SCS varied greatly in MRI images,showing oval or irregular shape.Clinically,suboccipital cavernous sinus is the main source of bleeding during upper cervical surgery.Because it communicates with vertebral venous plexus,suboccipital cavernous sinus may participate in intracranial metastasis of tumor;Dural arteriovenous fistula and other diseases can also occur in the suboccipital cavernous sinus.The myodural bridge is a fibrous connection between the nuchal ligament,rectus capitis posterior minor muscles,the rectus capitis posterior major muscles,the obliqus capitis inferior muscles and the cervical spinal dura mater in the atlanto-occipital space and the atlantoaxial space.In structure,the different origin myodural bridge fibers are linked to each other,and some of the fibers fused together;in function,the contraction of these muscles will create a force that travels to the spinal dura mater through the myodural bridge fibers during head movement.Therefore,these muscles,ligaments and fibers form a structural and functional unit named "myodural bridge complex".The function of the myodural bridge complex is complex.The myodural bridge complex would effectively pull the spinal dura mater and change the negative pressure of the subarachnoid space.Therefore,the myodural bridge complex might affect the cerebrospinal fluid circulation during head movement.The myodural bridge complex also has the functions of preventing in-folding of dura mater,transmitting proprioception,and maintaining the patency of cerebellomedullary cistern.Clinical studies also reported that pathological changes in the myodural bridge complex may cause chronic headache.The suboccipital cavernous sinus and the myodural bridge complex have similar anatomical location,both are located in the atlanto-occipital interspace.On the other hand,the two structures have similar function related to the regulation of intracranial pressure.There are few studies on the detailed anatomical characteristics of suboccipital cavernous sinus,which is prone to injury and bleeding in the upper cervical surgery.Therefore,the present research selected human head and neck specimens study the anatomical relationship between the suboccipital cavernous sinus and the myodural bridge complex and the detailed anatomical characteristics of the suboccipital cavernous sinus.Materials and methods: A total of 19 formalin-fixed head and neck specimens of male with the age range is about 50 to 80 years old were used in this research.Specimens observed including abnormal anatomic variation,trauma,inflammation or mass lesions in the suboccipital region were excluded.Group gross anatomy: six specimens;Group histological study: six specimens;Group P45 sheet plastination: six specimens.One specimen was a horizontal section of the head and neck of a Korean digital human,which was used to reconstruct the suboccipital cavernous sinus and myodural bridge complex.Results: According to the adjacent relationship between the SCS and surrounding anatomical structures,the SCS itself can be divided into three portions in this study by observing the three-dimensional visualization model of the suboccipital cavernous sinus.The lateral portion extends between the foramen of transvers process of atlas and the vertebral artery groove.The middle portion is located in the vertebral artery groove.The medial portion extends between the vertebral artery groove and the dural entry point of the vertebral artery.Moreover,the three-dimensional model showed that the myodural bridge complex covered the middle and medial portion of the suboccipital cavernous sinus.According to the gross dissection,this study found that the suboccipital cavernous sinus communicates with the suboccipital venous plexus and the vertebral venous plexus.There was a fibrous connection between the myodural bridge complex(rectus capitis posterior major muscles)and the wall of suboccipital cavernous sinus.Histological studies showed that the suboccipital cavernous sinus was composed of many small venous sinuses,which were wrapped by fibrous membranes.The fibrous membrane is fused with the thick and dense fibrous arch that closes the vertebral artery groove.The richness of venous sinus inside the SCS is different in its three portions.Compared with the lateral and medial parts,the medial part is less abundant.Moreover,histological staining section and P45 section showed that there were closely arranged and parallel fibers between the suboccipital cavernous sinus and the myodural bridge complex.These fibers were mainly composed of type I collagen fibers.Conclusion: The wall of the suboccipital cavernous sinus is thin,the venous sinuses of the middle portion are less abundant compared to other two portions.The middle portion is protected by a dense fibrous arch that closes the vertebral artery groove.The detailed morphological characteristics of suboccipital cavernous sinus may provide anatomical guidance for avoiding injury to suboccipital cavernous sinus during craniocervical junction surgery.There is a dense fibrous connection between the suboccipital cavernous sinus and the myodural bridge complex.During head movement,the myodural bridge complex may cause changes in intracranial blood volume or intracranial pressure by pulling the suboccipital cavernous sinus.