An anatomical study of the suboccipital cavernous sinus and its relationship with the myodural bridge complex

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.

An anatomical and radiological study of the tectorial membrane and its clinical implications

The radiological image of an intact tectorial membrane (TM) became an important favorable prognostic factor for craniovertebral instability. This study visualized the fascial layers of the TM and adjacent connective tissues with clinical significance by micro-CT and histological analysis. The TM firmly attached to the bony surface of the clivus, traversed the atlantoaxial joint posteriorly, and was inserted to the body of the axis showing wide distribution on the craniovertebral junction. The supradental space between the clivus, dens of the axis, anterior atlantooccipital membrane, and the TM contained profound venous networks within the adipose tissues. At the body of the axis, the compact TM layer is gradually divided into multiple layers and the deeper TM layers reached the axis while the superficial layer continued to the posterior longitudinal ligament of the lower vertebrae. The consistent presence of the fat pad and venous plexus in the supradental space and firm stabilization of the TM on the craniovertebral junction was demonstrated by high-resolution radiologic images and histological analysis. The evaluation of the TM integrity is a promising diagnostic factor for traumatic craniovertebral dislocation.

Atlanto-occipital Dissociation in the Setting of Relatively Normal Radiologic Findings

BACKGROUND

Craniocervical junction (CCJ) dislocations are often fatal. Atlanto-occipital dissociation can be challenging to diagnose, especially in patients who present with absent or subtle radiologic signs.

CASE DESCRIPTION

A neurologically intact 37-year-old patient presented to the hospital following a high-speed motor vehicle accident. Initial computed tomography scans showed normal CCJ anatomy, but magnetic resonance imaging (MRI) of the CCJ was performed to further evaluate perimesencephalic subarachnoid hemorrhage. MRI revealed partial disruption of the anterior atlantoaxial membrane and tectorial membrane as well as complete disruption of the posterior atlanto-occipital membrane, ligamentum flavum, and apical ligament, signifying atlanto-occipital dissociation. Halo spinal immobilization was performed in preparation for stabilization with posterior occipitocervical fusion; however, the CCJ distracted widely during surgery owing to the accident-related dislocation, signifying an unstable fracture. Posterolateral fusion was performed, and the distraction injury was corrected via posterior surgical instrumentation.

CONCLUSIONS

Normal occiput-C1 craniometric parameters in the setting of unexplained perimesencephalic subarachnoid hemorrhage does not eliminate the possibility of missed or delayed diagnosis of traumatic atlanto-occipital dissociation injuries. Cervical MRI without contrast should be considered in patients with vertebral artery dissection or perimesencephalic subarachnoid hemorrhage after a blunt injury with neck pain. When MRI shows evidence of disruption of ≥2 atlanto-occipital ligaments, surgical stabilization should be considered, as these are clinically very unstable injuries.

The craniocervical junction: embryology, anatomy, biomechanics and imaging in blunt trauma

Imaging of the blunt traumatic injuries to the craniocervical junction can be challenging but central to improving morbidity and mortality related to such injury. The radiologist has a significant part to play in the appropriate management of patients who have suffered injury to this vital junction between the cranium and the spine. Knowledge of the embryology and normal anatomy as well as normal variant appearances avoids inappropriate investigations in these trauma patients. Osseous injury can be subtle while representing important radiological red flags for significant underlying ligamentous injury. An understanding of bony and ligamentous injury patterns can also give some idea of the biomechanics and degree of force required to inflict such trauma. This will assist greatly in predicting risk for other critical injuries related to vital neighbouring structures such as vasculature, brain stem, cranial nerves and spinal cord. The embryology and anatomy of the craniocervical junction will be outlined in this review and the relevant osseous and ligamentous injuries which can arise as a result of blunt trauma to this site described together. Appropriate secondary radiological imaging considerations related to potential complications of such trauma will also be discussed.

TEACHING POINTS

• The craniocervical junction is a distinct osseo-ligamentous entity with specific functional demands. • Understanding the embryology of the craniocervical junction may prevent erroneous radiological interpretation. • In blunt trauma, the anatomical biomechanical demands of the ligaments warrant consideration. • Dedicated MRI sequences can provide accurate evaluation of ligamentous integrity and injury. • Injury of the craniocervical junction carries risk of blunt traumatic cerebrovascular injury.

Imaging of Atlanto-Occipital and Atlantoaxial Traumatic Injuries: What the Radiologist Needs to Know

Approximately one-third of all cervical spine injuries involve the craniocervical junction (CCJ). Composed of the occiput and the first two cervical vertebrae, this important anatomic landmark, in conjunction with an intricate ligamentous complex, is essential to maintaining the stability of the cervical spine. The atlantoaxial joint is the most mobile portion of the spine, predominantly relying on the ligamentous framework for stability at that level. As acute onsite management of trauma patients continues to improve, CCJ injuries, which often lead to death onsite where the injury occurred, are increasingly being encountered in the emergency department. Understanding the anatomy of the CCJ is crucial in properly evaluating the cervical spine, allowing the radiologist to assess its stability in the trauma setting. The imaging findings of important CCJ injuries, such as atlanto-occipital dissociation, occipital condyle fractures, atlas fractures with transverse ligament rupture, atlantoaxial distraction, and traumatic rotatory subluxation, are important to recognize in the acute setting, often dictating patient management. Thin-section multidetector computed tomography with sagittal and coronal reformats is the study of choice in evaluating the extent of injury, allowing the radiologist to thoroughly evaluate the stability of the cervical spine. Furthermore, magnetic resonance (MR) imaging is increasingly being used to evaluate the spinal soft tissues and ligaments, and to identify associated spinal cord injury, if present. MR imaging is also indicated in patients whose neurologic status cannot be evaluated within 48 hours of injury. .

Ligaments of the craniocervical junction

The specialized ligaments of the craniocervical junction must allow for stability yet functional movement. Because injury to these important structures usually results in death or morbidity, the neurosurgeon should possess a thorough understanding of the anatomy and function of these ligaments. To the authors' knowledge, a comprehensive review of these structures is not available in the medical literature. The aim of the current study was to distill the available literature on each of these structures into one offering.