A Clinical Study On Instabilization Of Craniocervical Malformation

Background and purpose Craniovertebral junction abnormalities are one of the most common diseases in neurosurgery.The abnormalities can be congenital and acquired malformations according to its original formation. The study is mainly based on the congenital malformation. The disease was defined as the congenital malformations of the occipital bone, atlas, axis and pertaining muscles, ligaments, fascias as well as joint capsules around the occipital foramen magnum. It is also called anomalies of atlanto-occipital region or abnormalities at the foramen magnum. The disease consists of basilar invagination, atlantoaxial fusion, segmentation failure of C2-C3, atlantoaxial dislocation, dens dysplasias, the hernia of cerebellum tonsil, torticollis, low hair line and so on. The disease can be seen in different ages, and it usually attacks in young ages. It is a kind of congenital malformation affected the health of people seriously. So far, there has not been an ideal treatment method for thedisease especially in the prevention and treatment of postoperative instabilization although the researches on the disease never stop. We retrospectively viewed the literatures in order to make people know deeply about the instability of the craniocervical junction. The aim of this research is to provide the theory for enhancing the clinical treatment effects of the disease through the retrospectively analysis of the literature of congenital craniocervical malformation.Clinical researches We retrospectively viewed the developmental history of the congenital craniocervical malformations. Subsequent to the first description of the craniocervical malformations in 1815 by Bell, the treat methods evolved from the skeletal traction, the removal of cerebellum tonsil, the decompression of occipital cervical area posteriorly, and the decompression of occipital cervical area with enlarged posterior fossa to the occipitoatlantoaixial posterior fusion with instrumentation, transoral-transphryngeal approach operation, and so on. The operative methods developed rapidly in recent 5 years. More recently, neurosurgeons across the world usually take the transcervical extrapahryngeal and transoral-transphryngeal ventral operations to remove the dens, sometimes by fusing of the spinal column anteriorly or posteriorly to stabilize the congenital craniovertebral abnormalities with atlantoaxial dislocation.Some researches had beem done about clinical practical anatomy about the craniovertebral junction. The occipital bone is formed by fusing of four sclerotomes. The neural arch of the primitive proatlas divides intoanterior and posterior segments. The former gives rise to the occipital condyles, and the latter fuses with atlas to help form its rostral articular facets. The atlas is derived from the first cervical sclerotome. The body of the atlas disappears and forms the original dens. The dens is formed by the Cl sclerotome. The axis is developed from four primary ossification centers. The tip of the dens develops from the proatlas. The occipitoatlantoaxial joints are complex anatomically, and they includes two occipitoatlantal articulations. There are four atlantoaxial joints, with a common synovial lining between the dens and anterior arch of the atlas, the dens and the transverse ligament, and between the lateral masses. The dens is approximated to the anterior arch of atlas by the transverse ligament. The transverse ligament, anterior atlanto-axial ligament, posteror tlanto-axial ligament, posteror longitudinal ligament, cruciate ligament, tectorial membrane, apical dental ligament and anterior atlantoccipital membrane are responsible the stability of atalantoaxial joint. These ligaments restrict the dens to move posteriorly, and avoid atalantoaxial subluxation.There has not disk at the atalantoaxial joint, and the stability of atalantoaxial joint depends on above-mentioned ligaments. In the major people, transverse ligament restrict the excessive movement of dens. The occipitoatlantoaxial provide for ante- and retroflexion, lateral flexion, or tilting and rotation. They function as a ball-and-socket joint. Flexion-extension and axial rotation occur at the atlantoaxial joint, and flexion-extension and lateral bending occur at the occipitoatlantal joint.In the osseoligamentous destruction caused by craniovertebral junction abnormalities, dysgenesis of the odontoid process, failure of atlas segmentation from occiput and so on, can result in loss of stability, and cause subluxiation to produce clinical signs and symptoms. The rupture of cruciate ligament and the fracture of dens can cause instability and subluxiation of atlanto-axial joint as well.The diagnostic studies of the congenital abnormalities of craniovertebral junction are associated with the high cervicomedullary junction abnormalities, brain stem and cerebellum. The clinical features are various. The assisted examinations play vital roles in the diagnosis of the disease. Recently, the assisted examinations such as DR, CR and so on are necessary for the diagnosis of basilar invagination, failure of atlas segmentation from occiput, atalanto-axial fusion and subluxiation. For example, if the odontoied process extends more than one third of its length above the Chamberlain's line the diagnosis of atalanto-axial subluxiation exists. The vertebral instability can be judged by the measure of atalantoaixal space of the crainovertebral junction in the flextion-extension position.When the tip of odontoied process extends above the Chamberlain's line the diagnosis of basilar invagination exists. Plain X-ray examination is preferable to others for atlanto-axial fusion and segmentation failure of C2-C3. the technique fo the 3-Demesional reconstruction of CT, especially SCT (spinal computed tomographu) is more clear anatomically, and benefits for diagnosis of the disease accurately. The technique candirectly reflex the moving and subluxational degree of odontoied process. It is important to avoid repeating unnecessary examination. For some patients with serious bony malformation, which X-ray examination is hard for diagnosing, SCT can diagnose accurately. But for abnormalities of brain, spine and soft tissue, such as cerebellum tonsil hernia, the compression of spine and brain stem, myelopathy and hydrocephalus, examination of MRI has especially importance.The neurosurgical managements of craniovertebral junction abnormalities has been varied dramatically since 1830. No single anterior or posterior surgical procedure can be used for all patients with craniovertebral abnormalities. The different operation must be selected on an individual patient. Presently, all abnormalities can be classified into these operative categories for treatment.CD Posterior decompression with or without fusion This operative method can be used for the compression for the dorsal brain stem and spine. The dysfunction of cerebellum, cranial nerves, syringomyelia as well as Arnold-Chiari malformation was often present in patients. For many patients with basilar invagination, the tip of odontoid process above the foramen magnum higher than 20mm, or with basilar fracture of odontoid process and so on, it is irreducible lesions that required posterior occiptocervical and/or atlantoaxial and/or occipitoatlantoaxial fusion. It is required high level operative technique of posterior decompression especially for patients with unstable craniovertebtal junction. Patients must be positioned carefully. When remove parts of Ci,C2, patients must be kept automatic breath during the administration of anesthesia. There have many posterior fusing methods including contoured loop instrumentation, wring and bone grafts, posterior atlantoaxial transarticular screw fixation (magerl), titanium loop and Halifax clamp or Apofix. For patients with unstable craniovertebtal junction, occipitoatlantoaxial bone fusion was usually combined. Bone donor site are either rib or iliac crest. More recently Songar cables have been substituted for twisted wire. Patients are kept in skeletal traction for 6 to 12 months by Halo vest after operation. Titanium loop used for fixation do not affect the MRI examination in recent years. (2) Transoral-transphryngeal approach operation The goal of transoral-transphryngeal operation is to correct ventral irreducible compression of cervicomedullary junction, especially for patients with atlantoaxial subluxation resulted in ventral compression of medulla from dens. The operation must be done under the microscope. The key of the operation is to remove the odontoid process and associated soft tissue radically. After operation dura mater reposition can be seen. Some patients needed to resect lower part of clivus. The breadth of abrasion is about 3cm. the key close of pharyngeal mucus membrane is to use interrupting suture. Patients are also routinely kept in skeletal traction for 6 months by Halo vest after operation. With the operative technique advanced, the complication during perioperation appeared scarcely. The unstable factor still exists and makes the disease deteriorate in the long-term follow-up.(D Transcervical extrapharyngeal approach The approach have merits of both Posterior decompression with or without fusion and transoral-transphryngeal approach operation. Meanwhile, suboccipital decompression and removal of odontoid process or posterior arch of Cl can be resolved, at the same time, the occipitocervical fixed fusion can be done to reconstruct the stabilization of the occipitocervical junction. But the disadvantages of the approach are serious injury, suboccipital decompression incompletely, the increase of hypoglossal nerve injury. This approach has not enough clinical experiences, and it still needs further studies.Conclusions With the studies deeply developed, the treatment level of the disease improved dramatically, but the satisfaction for the treatment and long-term effects of the disease is not ideal. The main question is base on postoperative stabilization of crainocervical junction. How to keep the postoperative stabilization of crainocervical junction is still a big challenge. Presently, the reports about instabilization of crainocervical junction abnormalities are scarce, and it is our study aim.