Fusions at the craniovertebral junction

INTRODUCTION: The surgical management of craniovertebral junction instability in pediatric patients has unique challenges. While the indications for internal fixation in children are similar to those of adults, the data concerning techniques, complications, and outcomes of spinal instrumentation comes from experience with adult patients. Diminutive osseous and ligamentous structures and anatomical variations associated with syndromic craniovertebral abnormalities frequently complicates the approaches and limits the use of internal fixation in children. Cervical arthrodesis in the pediatric age group has the potential for limiting growth potential and causing secondary deformity. Recent advances in image analysis have enabled preoperative planning which is critical to evaluate the size of instrumentation and its relation to the patient's anatomy. Newer techniques have recently evolved and have been incorporated in the management of pediatric patients with requirement for craniocervical stabilization. MATERIALS AND METHODS: Over 750 craniovertebral junction fusions have been reviewed in children. The indications for atlantoaxial arthrodesis were: (a) absent odontoid process, dystopic os odontoideum, absent posterior arch of C1; (b) Morquio's syndrome, Goldenhar's syndrome, Conradi's syndrome, and spondyloepiphyseal dysplasia. The acquired abnormalities of trauma, postinfectious instability, and Down's syndrome completed the indication in children. The indications for occipitocervical fusion were: (a) anterior and posterior bifid C1 arches with instability, absent occipital condyles; b) severe reducible basilar invagination, unstable dystopic os odontoideum, and unilateral atlas assimilation; (c) acquired phenomenon with traumatic occipitocervical dislocation, complex craniovertebral junction fractures of C1 and C2, after transoral craniovertebral junction decompression, cranial settling in Down's syndrome and inflammatory disease such as Grisel's syndrome. Instability was seen in children with clivus chordoma and osteoblastoma. Atlantoaxial fusions were performed mainly with interlaminar rib graft fusion and more recently with the transarticular screw fixation in the older patient. In the teenager, lateral mass screws at C1 and rod fixation were made; C2 pars interarticular screw fixation and C2 pedicle screw fixation. A C2 translaminar screw fixation is described. Occipitocervical fusions were made utilizing rib grafts below the age of 6. A contoured loop fixation was made in children above the age of 7, and recently, rod and screw fixation was also utilized. RESULTS: Abnormal cervical spine growth was not seen in children who underwent craniocervical stabilization below the age of 5. The authors have reserved rigid instrumentation for children above the age of 10 years and dependent on the anatomy.     

Specific entities affecting the craniocervical region: Down’s syndrome

Introduction  The ligamentous laxities and bony abnormalities associated with Down’s syndrome, os odontoideum, achondroplasia, osteogenesis imperfecta, and basilar invagination have been discussed with the imaging of the craniocervical junction. These are significant and require suspicion when dealing with children with the previously mentioned entities. Conclusion  Previous adverse surgical results in managing these patients reflect the lack of understanding of the underlying pathology and the appropriate surgical treatment.     

Surgical approaches: postoperative care and complications “transoral–transpalatopharyngeal approach to the craniocervical junction”

INTRODUCTION: The ventral approach to the craniocervical border has been described for decompression of irreducible extradural pathology. The procedures utilized encompass the transoropharyngeal and median mandibulotomy with glossotomy and the transpalatal procedures. This study was aimed to review the utility of the transoral-transpalatopharyngeal approach. CLINICAL MATERIALS AND METHODS: Seven hundred thirty-three patients underwent transpalatopharyngeal approach for decompression of the brain stem and cervicomedullary junction. Of these, 280 were children below the age of 16 years. The main indication was irreducible ventral pathology compressing the brain stem and cervicomedullary junction. Two hundred two children had irreducible basilar invagination, 28 had proatlas segmentation abnormalities, os odontoideum with a dystopic os odontoideum in 30, and spinal tumors in seven (chordoma, fibrous dysplasia, osteoblastoma). Seven patients with Down's syndrome and irreducible bony compression of the ventral cervicomedullary junction were seen. There were six other miscellaneous diagnoses. All children required craniocervical stabilization which was carried out under the same anesthetic as the transoral procedure. OPERATIVE PROCEDURE: The procedure entailed fiber-optic intubation. The patient was placed in cervical traction prior to the anterior procedure. The soft palate was split only in individuals with a short clivus with a high riding clivus-odontoid articulation. Craniocervical stabilization was performed in the prone position under the same anesthetic. RESULTS: There was one retropharyngeal infection postoperatively. No cesium fluoride leaks were encountered. Velopalatine incompetence was seen in five children who already had preoperative brain stem dysfunction. Neurological recovery was the rule. Patients who had preoperative syringohydromyelia had resolution of the syrinx on postoperative magnetic resonance imaging. DISCUSSION: The author's technique is described. Since 1977, the procedure has been performed in 732 patients (280 children) and has evolved into a safe and direct approach to the ventral cervicomedullary junction with minimal morbidity and mortality.     

Os odontoideum as a rare but possible complication in children with dyskinetic cerebral palsy: a clinical and neuroradiologic study

The authors describe a 12-year-old boy with dyskinetic (athetoid-dystonic subtype) cerebral palsy and os odontoideum. Dystonic and choreoathetotic components in cerebral palsy are movement disorders that are difficult to treat and cause major disability. Dystonic posturing causes excessive flexion, extension, and rotation of the neck. Repetitive abnormal movements in patients with this type of cerebral palsy give rise to a higher incidence of pathologic conditions affecting the craniovertebral junction. Os odontoideum is one of these pathologies, and it represents a rare anomaly of the odontoid process. There are only a few reports describing os odontoideum in children with dyskinetic cerebral palsy. This clinical and neuroradiologic study focuses on the problem of atlantoaxial instability and os odontoideum in these forms of cerebral palsy, which is too often underestimated.     

Management of craniocervical junction dislocation

The discovery of a craniocervical junction malformation requires management in three steps: (1) The patterns must be recognized using tomographic measurements (Chamberlain's line, Wackenheim's line). Dynamic flexion-extension studies are necessary to assess stability or instability. Stable patterns range from platybasia to basilar invagination, with gradual deformation, and are frequently associated with Chiari malformation. Unstable patterns characterized by odontoid instability are the equivalent of an odontoid fracture. The origin is malformative (hypoplasia, aplasia of the dens, os odontoidum), but the last may be difficult to distinguish from an old odontoid fracture. They are found in many syndromes (Down, Morquio, etc.). Unstable atlantoaxial patterns with atlas assimilation are hardly reducible; they evolve toward progressive instability. (2) The neurological consequences must be defined from the clinical features of the spinal cord and the cranial nerves. Both static and dynamic MRI scans must be performed; in this way identification of the neural abnormalities (hydromyelia, Chiari, etc.) and of the osseous compression is possible. (3) The most appropriate operative procedure must be selected: stable platybasia with a nervous compression by Chiari is cured only by posterior decompression; odontoid instability is cured by reduction and posterior fixation, using hooks and autologous bone grafts on the posterior arches of C-1 and C-2. Sometimes a transarticular screw fixation of C1-2 is necessary if there is a defect on the C-1 posterior arch. Craniocervical dislocations with assimilation of the atlas require posterior occipito-vertebral bony fixation with grafts and external halo immobilization or internal fixation with hooks or screws, with anterior transoral decompression in a second step.     

Sequential imaging demonstrating os odontoideum formation after a fracture through the apical odontoid epiphysis: case report and review of the literature

Introduction

The mechanism of formation of an os odontoideum is controversial and likely multifactorial. One theory states that the apex of the odontoid separates from the body because of a fracture. The intact alar and apical ligaments pull the fractured segment superiorly. The independent vascular supply of the apex allows the fractured bone to remain viable and remodel into the smooth, corticated bone characteristic of an os odontoideum. However, there are no publications with direct radiographic evidence supporting the theory.

Case report

In this paper, the authors present a 7-year-old child with a fracture through the apical odontoid epiphysis, extending into the body of the dens. Serial imaging studies demonstrate progressive separation of the apex from the body of the odontoid. The fractured segment begins to remodel and assume the classic form of an os.

Conclusion

The authors consider this case to be radiographic evidence supporting an acquired/traumatic origin of os odontoideum. Further, the mechanism of fracture through a cartilaginous epiphysis may explain the formation of an os after “normal” x-ray images or following seemingly minor trauma.     

Surgical approaches: postoperative care and complications “posterolateral–far lateral transcondylar approach to the ventral foramen magnum and upper cervical spinal canal”

Background  Lesions that affect the lower clivus, foramen magnum, the craniocervical junction, and the upper cervical spinal canal that are anterolateral and at times intradural require access ventral to the cerebellum and spinal cord. The posterolateral transcondylar approach provides such a route. In addition, posterior craniocervical stabilization can be accomplished at the same time. The author has reviewed the technique as well as the surgical results here. Materials and methods  The posterolateral transcondylar approach to the craniocervical junction was utilized in children with schwannoma, meningioma, and chordoma affecting the cervicomedullary junction. Other entities such as neurenteric cysts and hemangioblastoma were also seen. Extradural tumors such as aneurysmal bone cysts of the atlas and the axis vertebrae as well as proatlas segmentation abnormalities and bone tumors were seen. The stability of the craniocervical junction was assessed preoperatively so that a fusion procedure could be accomplished at the same operative setting, if necessary. Preoperative evaluation of the lower cranial nerves was vital. The surgical procedure was accomplished in the prone position. The occipital bone removal was carried out up to the sigmoid sinus and toward the jugular bulb. Relocation of the vertebral artery was made at the atlas vertebra and thus provided posterolateral exposure into the posterior fossa and upper cervical spinal canal. Occipital condyle removal was limited to one-third of the medial occipital condyle. Results  Twenty-five children underwent a posterolateral transcondylar approach. New lower cranial nerve dysfunction occurred in two and only one required a tracheostomy. This was seen in a child with clivus chordoma. A complete removal was accomplished in meningioma and schwannoma as well as in neurenteric cyst and hemangioblastoma. Clivus chordomas required more than one surgical procedure. The tumors of the bone were all treated with simultaneous fusion. Conclusions  The posterolateral transcondylar route is a versatile avenue to approach a variety of lesions ventrolateral to the brain stem and upper cervical cord. Exposure is quite satisfactory with minimal or no retraction of important neurovascular structures in the region. Modifications of this theme can be applied as the lesions require.     

内镜经口入路齿状突切除治疗颅底凹陷简

目的探讨不伴颈枕融合的内镜经口入路切除齿状突治疗颅底凹陷的可行性。方法回顾性分析6例具有难以缓解的延颈髓交界区压迫症状病人的临床资料,临床表现为颈痛、肢体感觉异常、脊髓性四肢轻瘫。术前影像学检查显示后半脱位的游离齿状突压迫颈枕交界区。病人均在没有颈枕后固定和骨性融合的情况下实施内镜经口入路齿状突切除术。结果病人经单纯内镜经口齿状突切除术后均成功获得颈枕交界区减压,且术后清醒即拔除麻醉插管,未行气管切开或术后置入胃管。本组病例术后未出现鼻咽反流、脑脊液漏、局部感染或脑膜炎等术后并发症。术后CT和MRI显示齿状突全切除和颈枕交界区充分减压。随访1～5年,未见颈枕交界区不稳定,且病人神经功能均显著恢复。结论内镜经口入路是到达寰椎和齿状突最近、最直接的手术入路。该入路在实现齿状突完全切除、颈枕交界充分减压的同时,不需要行颈枕后固定及融合,不要求气管切开,不会增加发生并发症的风险。     

Decision making

INTRODUCTION: The craniocervical junction is affected by numerous pathological processes. This involves congenital, developmental, and acquired abnormalities. It can result in neurological deficit secondary to neurovascular compression, abnormal cerebrospinal fluid dynamics, and craniovertebral instability. A physiological approach based on an understanding of the craniovertebral junction dynamics, the site of encroachment and stability was formulated in 1977 and has stood the test of time. The author has reviewed 5,300 patients with neurological symptoms and signs secondary to an abnormality of the craniocervical junction. This includes 2,100 children. TREATMENT OF CRANIOVERTEBRAL JUNCTION ABNORMALITIES: The factors that influence the specific treatment are: (1) reducibility of the lesion, (2) mechanics of compression and the direction of encroachment, (3) the presence of abnormal ossification centers and epiphyseal growth plates, and (4) the cause of the pathological process. STABILITY AT THE CRANIOCERVICAL JUNCTION: Instability at the craniocervical junction is considered when the predental space is more than 5 mm in children below the age of 8, when the separation of the lateral atlantal masses is more than 6 mm where the cruciate ligament is felt to be disrupted, and if there is vertical translation of more than 2 mm between the clivus and the odontoid process signifying occipital instability. The gap between the occipital condyle and the lateral atlas facet should never be visible on lateral cervical radiographs. Present day magnetic resonance imaging can visualize disrupted transverse cruciate ligament, alar ligaments, tectorial membrane, and bony malalignment. The primary aim of treatment is to relieve compression at the cervicomedullary junction. Hence, stabilization is paramount in reducible lesions to maintain neural decompression. Irreducible lesions require decompression at the site where the compression has occurred; these were divided into ventral and dorsal compression states. In the former compression state, the operative procedure was a ventral decompression through a palatopharyngeal route, LeForte dropdown maxillotomy, or the lateral extrapharyngeal approach. In dorsal or dorsolateral compression states, a posterolateral decompression is required. If instability is present after decompression, posterior fixation is mandated.     

The importance of vertebral artery proximity to the odontoid process during anterior odontoid approaches

The proximity of the vertebral artery (VA) to the odontoid process makes it vulnerable to injury during surgery. Knowledge of the quantitative anatomy of the VA groove is therefore necessary. In this study we assessed the spatial relationship between the VA and the odontoid process on cadavers by direct measurement and in patients by CT angiography. Our goal was to measure the distances from the VA and vertebrobasilar junction to the odontoid tip. The VA and odontoid process of 10 craniocervical cadavers (“cadavers”) and of 20 patients were evaluated and average measurements obtained. The measured parameters were: (i) distance from the right VA to the odontoid tip (right VA–odontoid tip); (ii) distance from the left VA to the odontoid tip (left VA–odontoid tip), and (iii) distance from the vertebrobasilar junction to the odontoid tip (vertebrobasilar–odotoid tip). On the cadavers, the right VA–odontoid tip distance was 11.55 mm, the left VA–odontoid tip was 11.02 mm, and the vertebrobasilar junction–odontoid tip distance was 24.55 mm. In patients, using CT angiography, the right VA–odontoid tip distance was 11.47 mm and the left VA–odontoid tip distance was 11.50 mm. The VA–odontoid tip distance is important in anterior odontoid approaches. Since the odontoid process may be in close contact with the VA, the relationship between them should be evaluated preoperatively in all candidates for odontoid surgery using three-dimensional CT angiography.     

Neuroimaging findings of retroclival hemorrhage in children: a diagnostic conundrum

Background

Retroclival hemorrhage in children may occur in three compartments, namely epidural, subdural, and subarachnoid, frequently secondary to trauma. Retroclival epidural hematoma may be associated with ligamentous injury, which may further result in instability at the craniocervical junction. Retroclival subdural hematoma may indicate a sentinel event for traumatic injury elsewhere within the brain or posterior fossa. Retroclival subarachnoid hemorrhage may have severe clinical consequences related to vasospasm.

Objective

Neuroimaging is essential in the recognition, localization, and characterization of retroclival hemorrhage into various compartments and for evaluating potential severe clinical consequences such as craniocervical junction instability, underlying traumatic brain injury, and ischemia secondary to vasospasm. The goal of this paper is to discuss the anatomy and biomechanics of the craniocervical junction as well as the neuroimaging findings associated with various compartments of retroclival hemorrhage in children.     

Dimensions of the craniocervical junction in longitudinal analysis of normal growth

Introduction  

Abnormal configuration of the craniocervical junction in the form of basilar impression or invagination, with often-associated platybasia, is a clinically significant cause of neurological symptoms particularly in patients with inherited diseases affecting the connective tissue. To better understand the course of development of these basilar abnormalities and further define their diagnostic criteria in children, we analysed longitudinally changes in the vertical dimensions of the craniocervical junction and in the flexion of the anterior skull base in normal growing individuals.     

Problems in the selection of surgical approach for the treatment of non-traumatic deformities of the craniocervical junction

Developmental abnormalities or inflammatory disorders provoke deformations and instability of the craniocervical junction. The most dangerous results of these lesions are: sudden brainstem compression or cervical myelopathy. The authors propose the guidelines for surgical management of non-traumatic deformities caused by: a) rheumatoid arthritis of the spine, b) congenital anatomic changes of the occipit and odontoid. Main goals of surgical treatment are decompression and stabilization. The choice of surgical approach and method depends on pathology. It is very important to estimate individual anatomic changes and mobility--possibility of reduction. The authors discuss surgical methods actually used for fusion and decompression of the occipitocervical junction.     

Acute traumatic cervical cord injury in patients with os odontoideum

We retrospectively reviewed acute cervical cord injury after minor trauma in 10 patients with os odontoideum. Their clinical history, neurological symptoms, radiological investigations, follow-up period, American Spinal Injury Association impairment classification and motor score were reviewed. Before their traumatic injury, three patients were asymptomatic and seven reported myelopathic symptoms, including four patients with neck pain, two patients with unsteadiness and one patient with dizziness. Falls were the most common cause of injury (n = 6), followed by minor motor vehicle accidents (n = 3) and assault (n = 1). MRI and dynamic cervical lateral radiographs showed that all patients had atlantoaxial instability and cord compression. Most patients had spinal cord thinning and hyperintensity on T2-weighted MRI. Spinal cord compression was posterior (n = 5), or both anterior and posterior (n = 5). All patients underwent posterior rigid screw fixation and fusion, including atlantoaxial fusion (n = 8) and occipitocervical fusion (n = 2). We conclude that patients with asymptomatic or myelopathic atlantoaxial instability secondary to os odontoideum are at risk for acute spinal cord injury after minor traumatic injury. Fixation and fusion should be undertaken as prophylactic treatment for patients at risk of developing myelopathy and to avoid the neurological deterioration associated with acute traumatic cervical cord injury.     

The use of CT angiography in the preoperative planning of cervical spine surgery in children

Object  The vertebral artery is potentially vulnerable during cervical spine surgery. The aim of this study was to evaluate the initial application and validate the clinical utility of multidetector computed tomography angiography (CTA) in demonstrating the vertebral arteries in relation to the cervical spine and associated pathology prior to surgical intervention in children. Materials and methods  CTA images were obtained in ten children prior to surgery. We retrospectively gathered cases of cervical spine pathology that underwent CT angiography prior to surgery over the course of 2 years. The images were reviewed by two neuroradiologists and discussed with the neurosurgeon. Results  Ten children were imaged; three children had bone tumours, four had segmentation anomalies, one had achondroplasia, one had heterotopic calcification and one had cord compression post-surgical craniocervical fixation. The vertebral arteries were identified in all children, and the course was visualised in relation to normal and pathological bony anatomy on axial 2D and volume-rendered 3D volume. There were no complications of the procedure and no need for magnetic resonance angiography or catheter angiography in any cases. Conclusions  The combination of congenital deformity, small size and a recent trend toward instrumentation of the craniocervical junction in the paediatric population mandates accurate knowledge of the vertebral artery relationships to the local neural and bony structures prior to complex surgical interventions. Whilst we do not advocate imaging of the vertebral arteries in all patients requiring cervical spine surgery, this technique has been shown to be a very useful investigation in selected cases.     

齿状突切除术后颅颈连接不稳定的处理

目的探讨术前未能明确诊断，而齿状突切除术后颅颈连接不稳定的诊断和治疗方法。方法回顾性分析术后8例不稳定病例的诊断治疗经过。结果7例经枕下减压，枕颈融合固定取得了满意效果。无并发症及死亡病例。结论齿状突切除术后颅颈连接不稳定可以通过枕下减压，枕颈融合治疗。     

Surgical treatment of os odontoideum

Os odontoideum is a rare disease. There have been few reports of os odontoideum in the literature. In this study we retrospectively reviewed eight surgically treated patients. One patient underwent C1-2 transarticular screw fixation, five patients underwent C1-2 polyaxial screw and rod fixation and two patients with dystopic os odontoideum underwent occipito-cervical (O-C) fusion. Of the eight patients, neck pain was alleviated in seven (87.5%). Of the six patients who had neurological signs and symptoms, five (83.3%) exhibited neurological improvement. Radiologically, solid fusion was observed in seven patients (87.5%). Active surgical treatment should be considered even in patients with os odontoideum who exhibit mild symptoms. In most patients with os odontoideum, use of the C1-2 polyaxial screw and rod technique may be the most appropriate treatment. In patients with dystopic os odontoideum, O-C fusion should be considered.     

Craniovertebral junction database analysis: incidence,classification, presentation,and treatment algorithms

INTRODUCTION: The initial treatment of bony lesions at the craniocervical junction consisted of posterior decompression with enlargement of the foramen and removal of the posterior arch of the atlas and axis vertebra. This was regardless of the site of compression. Needless to say, the results were poor when an irreducible ventral lesion at the craniocervical junction caused compression of the cervicomedullary area. It was predictable that an adverse outcome would occur in approximately 35-40% of patients treated with dorsal decompression with a fixed anterior abnormality at the craniovertebral junction. Thus, it became essential to identify the causes of failure and recognize the pathology as well as attempt to improve the treatment. The need to identify natural history led to a prospective database. This database now lists 5,300 patients who were analyzed. Of these, 2,000 were children and this has been reviewed here. CRANIOVERTEBRAL ABNORMALITIES IN CHILDREN: Review of symptoms showed that children with craniovertebral abnormalities present with failure to thrive, weakness, basilar migraine, dysphagia, sleep apnea, scoliosis, and the cervical central cord syndrome. Torticollis was seen in the very young. IMAGING TECHNIQUES AND TREATMENT FOR CRANIOVERTEBRAL ABNORMALITIES: New imaging techniques were utilized as they became available. Unexplained neurological symptoms and signs associated with craniovertebral abnormalities in children required angiography which was performed with dynamic motion studies. All children with reducible craniocervical abnormalities underwent stabilization. In irreducible abnormalities, decompression was paramount with a fusion to be done immediately. The decompression was accomplished in the direction in which encroachment occurred. TREATMENT ALGORITHM AND CLASSIFICATION: A treatment algorithm was formulated as a result of this database and a classification of the craniovertebral abnormalities; that holds good for the entire spectrum.     

The complex Chiari: issues and management strategies

“Complex Chiari” malformations may be defined as cerebellar tonsil herniation combined with one or more of the following radiographic findings: brainstem herniation through the foramen magnum (Chiari 1.5 malformation), medullary kink, retroflexed odontoid, abnormal clival-cervical angle, occipitalization of the atlas, basilar invagination, syringomyelia or scoliosis. Patients with “complex Chiari” malformation are different from those with typical Chiari 1 malformation in that their management strategy has a higher chance of including other operative interventions aside from a typical suboccipital decompression. These other operative procedures include odontoid resection and craniocervical fusion. This paper outlines specific scenarios where these other operative procedures must be considered and carried out.     

C1-C2 transarticular screw fixation for treatment of C1-C2 instability

C1-C2 instability has traditionally been treated by C1-C2 posterior wiring and bone grafting. However, this technique has an incidence of non-union which may exceed 10%. Transarticular screw fixation has developed as a technique of providing increased strength of fixation of C1-C2 arthrodesis, while at the same time avoiding the need for postoperative halo bracing and avoiding the risk of neurological injury associated with the passage of sublaminar wires. We present a retrospective review of 12 patients with C1-C2 instability treated by C1-C2 transarticular screw fixation. Eight patients underwent this procedure as primary treatment, and 4 after a failed Gallie fusion. Five patients had a cruciate ligament rupture, 5 had an odontoid process fracture, 1 had os odontoideum, and 1 had rheumatoid instability. There was no surgical morbidity or mortality and, at a mean follow up of 12.1 +/- 3 months (range 8-14 months), all patients had achieved solid fusion, and all neurological symptoms referable to the instability had resolved. C1-C2 transarticular screw fixation has been shown to be safe and effective and has a number of advantages when compared to traditional posterior wiring techniques. We recommend that this technique be considered as a primary treatment of C1-C2 instability.