The Establishment of a Novel Upper Cervical Complex Fracture Classification System.

BACKGROUND CONTEXT: Upper cervical complex fractures are associated with high rates of neurological damage and mortality. The Dickman's classification is widely used in the diagnosis of upper cervical complex fractures. However, it falls short of covering the full spectrum of complex fractures. This limitation hinders effective diagnosis and treatment of these injuries. PURPOSE: To address the diagnostic gap in upper cervical complex fractures, the study introduces a novel classification system for these injuries, assessing its reliability and usability. STUDY DESIGN: Proposal of a new classification system for upper cervical complex fractures. PATIENT SAMPLE: The study comprised the clinical data of 242 patients with upper cervical complex fractures, including 32 patients treated at our hospital, along with an additional 210 cases from the literature. OUTCOME MEASURES: The inter-observer and intra-observer reliability (kappa coefficient, κ) of this classification system were investigated by 3 spine surgeons. The three researchers independently re-evaluated the upper cervical complex fracture classification system 3 months later. METHODS: The proposed classification categorizes upper cervical complex fractures into three main types: Type I combines odontoid and Hangman's fractures into two subtypes; Type II merges C1 with odontoid/Hangman's fractures into three subtypes; and Type III encompasses a combination of C1, odontoid, and Hangman's fractures, divided into two subtypes. Meanwhile, a questionnaire was administered in 15 assessors to evaluate the system's ease of use and clinical applicability. RESULTS: A total of 45 cases (18.6%) unclassifiable by Dickman's classification were successfully categorized using our system. The mean κ value of inter-observer reliability was 0.783, indicating substantial reliability. The mean κ value of intra-observer reliability was 0.862, indicating almost perfect reliability. Meanwhile, thirteen assessors (87.7%) stated that the classification system is easy to remember, easy to apply, and they expressed intentions to apply it in clinical practice in the future. CONCLUSIONS: This system not only offers high confidence and reproducibility but also serves as a precise guide for clinicians in formulating treatment plans. Future prospective applications are warranted to further evaluate this classification system.

Morphometric analysis of atlas lateral mass in Down syndrome cases with relevance to surgical intervention.

PURPOSE: Surgical stabilization of the Atlas vertebrae is indicated for severe atlantoaxial instability (AAI) in patients with Down syndrome (DS). This study aims to evaluate the morphological characteristics of the Atlas lateral mass (ALM) in patients with DS with regard to safe instrumentation for surgical stabilization and to compare them with non-syndromic group. METHODS: This multicenter, retrospective, case-control study included age- and sex-matched patients with and without DS aged > 7 years with a cervical computed tomography (CT) scan. After three-dimensional CT reconstruction, nine parameters were evaluated for both groups. All included measurements were performed by a neuroradiologist who was blinded to clinical data. RESULTS: Forty-three of 3,275 patients with DS were included in this study. Matching number of consecutive patients without DS were identified (mean age: 16 years). Patients with DS were significantly shorter than those without DS. Seven of nine parameters related to ALM were significantly lower in patients with DS than in those in the control group, including anterior wall height (AH), posterior wall height (PH), their ratio, and arch-ALM angle. On adjusting data for patient height, patients with DS had a smaller PH, lower PH/AH ratio, and steeper arch-ALM angle than the control group. CONCLUSIONS: Patients with DS had a smaller posterior ALM wall and a steeper arch-ALM angle than the control group without DS. This information is important for surgical planning of safe posterior ALM exposure and safe instrumentation for surgical stabilization in patients with DS.

Atlantoaxial Instability in the Course of Rheumatoid Arthritis in Relation to Selected Parameters of Sagittal Balance.

Background: Atlantoaxial instability is the most common cervical instability in patients with rheumatoid arthritis (RA). Its course may differ in different patients and may have different degrees of severity and symptoms. Methods: There are a number of studies on systemic factors associated with the development of this instability, but there are few publications in the scientific literature on the influence of biomechanical factors on the development of cervical instability. One of the areas that allows the study of biomechanical factors influencing spine pathologies is the analysis of sagittal balance using radiological parameters. The study of radiological parameters of sagittal balance has contributed to understanding the pathology of selected spine diseases and is currently an indispensable tool in planning surgical treatment. Results: The presented study, conducted on a group of RA patients with cervical instability, was performed to look for a relationship between C1-C2 instability and sagittal balance parameters. Conclusions: Among the examined selected parameters, a statistically relationship between C1-C2 instability and the Cobb angle C1-C7 and OD-HA parameters has been found. This confirms the need for further in-depth research on this areas.

Clinical and MR Predictors of Retro-Odontoid Pseudotumor Regression Following Posterior Fixation in Patients with Atlantoaxial Instability.

Purpose: To identify clinical and MR predictors of retro-odontoid pseudotumor (ROP) regression after posterior fixation in patients with atlantoaxial instability. Materials and Methods: We included patients who had undergone posterior fixation for atlantoaxial instability and preoperative and postoperative MR imaging. Patients were classified into two groups according to the degree of ROP regression after posterior fixation: regression (≥ 10% reduction) and no regression (< 10% reduction). Mann-Whitney and Fisher's exact tests were performed to identify the clinical (age and sex) and MR predictors (preoperative ROP thickness, ROP type, MR signal homogeneity of the ROP, spinal cord signal change, spinal cord atrophy, ossified posterior longitudinal ligament, os odontoideum, and atlantodental interval) associated with ROP regression. Results: We retrospectively assessed 11 consecutive patients (7 female; median age, 66 years [range, 31-84 years]). Posterior fixation induced ROP regression in eight (72.7%) patients. Older age and greater preoperative ROP thickness significantly correlated with ROP regression (p = 0.024 and 0.012, respectively). All patients with preoperative ROP thickness > 5 mm exhibited ROP regression. The other variables were not significantly associated with ROP regression. Conclusion: Older age and thicker preoperative ROP are associated with ROP regression after posterior fixation in patients with atlantoaxial instability.

Modified Atlantoaxial Arthrodesis Technique for Atlantoaxial Instability via Intraarticular Autografting Using Structural Iliac Bone: Technical Nuances and Case Series.

OBJECTIVE: The present study described a modified technique of atlantoaxial arthrodesis in patients with atlantoaxial instability (AAI) along with the postoperative clinical and radiological results. METHODS: Five patients underwent this method for their AAI concurrent with C1 arch hypoplasia and/or the development of odontoid pannus causing myelopathy. After thorough exposure of the posterior surface of the C1-2 complex, the bilateral C2 nerve roots were sectioned to allow for easier access to the C1/2 facet joints. To prepare a suitable grafting bed, the C1/2 facet capsule was opened, and then the articular cartilaginous and synovial tissues were thoroughly removed. After being properly fashioned to match the gap between the C1/2 facet joint spaces, the structural bone grafts from the iliac crest were directly inserted into the facet joint spaces. To alleviate cord compression caused by concomitant odontoid pannus and/or hypoplastic C1 arch, C1 laminectomy was necessitated in all cases. Subsequently, posterior screw-rod instrumental fixation was conducted. RESULTS: All 5 patients underwent this procedure successfully. Clinical and radiological follow-up data of all patients indicated favorable relief of clinical symptoms and early rigid C1-2 stability. The sequelae of C2 nerve resection were not remarkable. No other neural or vascular damage associated with this technique was observed. CONCLUSIONS: Modified atlantoaxial arthrodesis via intraarticular autografting using the structural iliac bone combined with posterior instrumentation appears to be an efficient alternative treatment method for AAI patients with concurrent pathologies, even when the C1-2 posterior arches are unavailable for the grafting bed.

C1 Facetectomy and Ventral Fixation of Occipitoatlantoaxial Complex for Concurrent Congenital Atlanto-Occipital Dislocation and Atlantoaxial Instability in a Toy Poodle.

An 8-month-old, 3.4 kg, castrated male Toy Poodle was referred for progressive tetraparesis and respiratory disorder without a history of trauma. Repeated computed tomography (CT) and magnetic resonance imaging (MRI) with different positions of the neck revealed concurrent atlanto-occipital dislocation (AOD) and atlantoaxial instability (AAI) with spinal cord compression. This case was unique due to its congenital nature and the absence of trauma. The surgical treatment involved precise removal of the C1 vertebra's ventral articular facet, which was compressing on the spinal cord, attributed to its fixed and malaligned position within the atlantooccipital joint. Following facetectomy, the stabilization of the occipital bone to the C2 vertebra was achieved by screws, wire, and polymethyl methacrylate. Two days after surgery, the dog recovered ambulation and showed gradual improvement in gait, despite mild residual ataxia. Postoperative CT and radiographs showed successful decompression of the spinal cord. The screw loosening was confirmed at 114 days, which was managed successfully by extracting the affected screws. Through the 21-month monitoring period, the dog showed a normal gait with a wide-based stance of the pelvic limbs when standing and experienced no pain. This case represents the first report of concurrent congenital AOD and AAI treated with a ventral surgical approach, contributing new insights to the understanding and management of such complex cranio-cervical junction disorders in veterinary neurosurgery.

Atlantoaxial dislocation due to Os odontoideum in down syndrome: Literature review and case reports.

INTRODUCTION AND IMPORTANCE: Os odontoideum is a rare condition commonly associated with atlantoaxial instability (AAI) and leading to atlantoaxial dislocation. The incidence of Os odontoideum is higher in patients with Down syndrome. Similar to odontoid fractures, atlantoaxial dislocation in patients with Os odontoideum can result in neurological deficits, disability, and even mortality. CASE PRESENTATION: We present two cases of Os odontoideum accompanied by Down syndrome. Both patients were hospitalized due to progressive tetraparesis after falls several months prior. Upon examination, the patients exhibited myelopathy and were unable to walk or stand. MRI revealed spinal stenosis at the C1-C2 level due to atlantoaxial dislocation. C1-C2 fixation using Harms' technique was performed in both cases. One case experienced a complication involving instrument failure, necessitating revision surgery. CLINICAL DISCUSSION: Due to the characteristics of transverse ligament laxity, low muscle tone, excessive joint flexibility, and cognitive impairment, children with both Down syndrome and Os odontoideum are at a high risk of disability and even mortality from spinal cord injury. Most authors recommend surgical management when patients exhibit atlantoaxial instability. Additional factors such as low bone density, cognitive impairment, and a high head-to-body ratio may increase the risk of surgical instrument failure and nonunion postoperatively in patients with Down syndrome. CONCLUSION: Os odontoideum is a cause of AAI in patients with DS. Indication of surgery in the presence of AAI helps to resolve neurological injury and prevent further deterioration. The use of a cervical collar is considered to prevent instrument failure postoperatively.

Augmented Reality in Spine Surgery: A Case Study of Atlantoaxial Instrumentation in Os Odontoideum.

Despite advancement in surgical innovation, C1-C2 fixation remains challenging due to risks of screw malposition and vertebral artery (VA) injuries. Traditional image-based navigation, while useful, often demands that surgeons frequently shift their attention to external monitors, potentially causing distractions. In this article, we introduce a microscope-based augmented reality (AR) navigation system that projects both anatomical information and real-time navigation images directly onto the surgical field. In the present case report, we discuss a 37-year-old female who suffered from os odontoideum with C1-C2 subluxation. Employing AR-assisted navigation, the patient underwent the successful posterior instrumentation of C1-C2. The integrated AR system offers direct visualization, potentially minimizing surgical distractions. In our opinion, as AR technology advances, its adoption in surgical practices and education is anticipated to expand.

Subluxación atlantoaxial en artritis reumatoidea. Resolución por odontoidectomía endonasal endoscópica y fusión e instrumentación por abordaje posterior. Reporte de caso

La subluxación atlantoaxial es la lesión más frecuente en la columna cervical causada por la artritis reumatoidea. Se manifiesta por rigidez de nuca, dolor cervical y déficit neurológico. El diagnóstico se realiza con tomografía computarizada e imágenes de resonancia magnética. El intervalo atlanto dental anterior mayor a 5mm indica inestabilidad atlantoaxial, el intervalo atlanto dental posterior menor a 14mm advierte riesgo neurológico. Las indicaciones más frecuentes de cirugía son: dolor cervical severo, inestabilidad y síntomas de mielopatía. Cuando existe compresión medular es necesaria la descompresión cervical alta sea por vía posterior o por vía anterior (odontoidectomía endonasal versus transoral). La línea rinopalatina nos indicará la factibilidad de una odontoidectomía endonasal endoscópica (OEE). El objetivo de la presentación del presente caso es compartir nuestra experiencia con la primera odontoidectomía endonasal endoscópica realizada en nuestro país y fomentar la utilización de la técnica. La cirugía fue realizada en un paciente con cuadriparesia espástica por subluxación atlantoaxial por artritis reumatoidea y que presentó excelente evolución pos operatoria, con recuperación casi completa. La OEE es una técnica operatoria mínimamente invasiva, ideal para pacientes con múltiples comorbilidades y que ofrece de buenos a excelentes resultados.

Atlantoaxial subluxation is the most common injury to the cervical spine caused by rheumatoid arthritis. It is manifested by neck stiffness, neck pain and neurological deficit. Diagnosis is made with computed tomography and magnetic resonance imaging. The anterior dental atlanto interval greater than 5mm indicates atlantoaxial instability, the posterior dental atlanto interval less than 14mm warns of neurological risk. The most frequent indications for surgery are: severe neck pain, instability and symptoms of myelopathy. When there is spinal cord compression, upper cervical decompression is necessary, either via a posterior or anterior approach (endonasal versus transoral odontoidectomy). The rhinopalatine line will indicate the feasibility of an endoscopic endonasal odontoidectomy (EEO). The objective of the presentation of this case is to share our experience with the first endoscopic endonasal odontoidectomy performed in our country and to promote the use of the technique. The surgery was performed on a patient with spastic quadriparesis due to atlantoaxial subluxation due to rheumatoid arthritis and who presented excellent postoperative evolution, with almost complete recovery. EEO is a minimally invasive surgical technique, ideal for patients with multiple comorbidities and offering good to excellent results.

Post-Traumatic Central or Axial Atlantoaxial Dislocation Presenting with "Atypical" Symptoms-Analyzing the Role of Dynamic Imaging on the Basis of Experience with 14 Patients Treated by Atlantoaxial Fixation surgery.

BACKGROUND: This is a report of a series of 14 patients who presented with a range of "atypical" cranial, spinal, and systemic symptoms that started after they suffered a relatively severe injury to the head and/or neck several months or years before surgical treatment. The implications of diagnosing and treating central or axial atlantoaxial dislocation (CAAD) is discussed. Also, the role of dynamic rotatory and lateral head tilt imaging in the diagnosis and treatment is analyzed. METHODS: Of the 14 patients, 7 were men and 7 were women, with an age range of 21-64 years (average, 42 years). Due to the severity of the presenting neurological and non-neurological symptoms, all the patients had lost their occupation and were heavily dependent on painkillers and/or antidepressant drugs. In addition to other characteristic clinical and radiological evidence, CAAD was diagnosed made based on the facet alignments on lateral profile imaging in the neutral head position. Dynamic head flexion-extension, lateral head tilt, and neck rotation imaging findings confirmed and subclassified CAAD. All 14 patients underwent atlantoaxial fixation surgery. RESULT: A personalized self-assessment clinical scoring parameter and the World Health Organization Disability Assessment Schedule 2.0 was used to evaluate the outcome. One patient did not follow-up after surgery. At a minimum follow-up of 6 months after atlantoaxial fixation surgery, the remaining 13 patients experienced relief from all major symptoms. CONCLUSIONS: Diagnosing and treating CAAD can have major therapeutic implications for patients presenting with progressively worsening disabling clinical symptoms following relatively severe head and/or neck trauma.

C1-2 hypermobility and its impact on the spinal cord: a finite element analysis.

OBJECTIVE: The authors present a finite element analysis (FEA) evaluating the mechanical impact of C1-2 hypermobility on the spinal cord. METHODS: The Code_Aster program was used to perform an FEA to determine the mechanical impact of C1-2 hypermobility on the spinal cord. Normative values of Young's modulus were applied to the various components of the model, including bone, ligaments, and gray and white matter. Two models were created: 25° and 50° of C1-on-C2 rotation, and 2.5 and 5 mm of C1-on-C2 lateral translation. Maximum von Mises stress (VMS) throughout the cervicomedullary junction was calculated and analyzed. RESULTS: The FEA model of 2.5 mm lateral translation of C1 on C2 revealed maximum VMS for gray and white matter of 0.041 and 0.097 MPa, respectively. In the 5-mm translation model, the maximum VMS for gray and white matter was 0.069 and 0.162 MPa. The FEA model of 25° of C1-on-C2 rotation revealed maximum VMS for gray and white matter of 0.052 and 0.123 MPa. In the 50° rotation model, the maximum VMS for gray and white matter was 0.113 and 0.264 MPa. CONCLUSIONS: This FEA revealed significant spinal cord stress during pathological rotation (50°) and lateral translation (5 mm) consistent with values found during severe spinal cord compression and in patients with myelopathy. While this finite element model requires oversimplification of the atlantoaxial joint, the study provides biomechanical evidence that hypermobility within the C1-2 joint leads to pathological spinal cord stress.

Odontoid Fracture with Accompanying Severe Atlantoaxial Instability in Elderly Patients-Analysis of Treatment, Adverse Events, and Outcome.

(1) Background: In elderly patients with type II odontoid fractures, accompanying severe atlantoaxial instability (AAI) is discussed as a marker possibly warranting more aggressive surgical therapy. This study aimed to characterize adverse events as well as the radiological and functional outcomes of surgical vs. conservative therapy in patients with odontoid fracture and AAI. (2) Methods: Patients aged 65 years and older with type II odontoid fracture and AAI treated were included. AAI was assumed if the mean subluxation across both atlantoaxial facet joints in the sagittal plane was greater than 50%. Data on demographics, comorbidities, treatment, adverse events, radiological, and functional outcomes were analyzed. (3) Results: Thirty-nine patients were included. Hospitalization time was significantly shorter in conservatively treated patients compared to patients with ventral or dorsal surgery. Adverse events occurred in 11 patients (28.2%), affecting 10 surgically treated patients (35.7%), and 1 conservatively treated patient (9.1%). Moreover, 25 patients were followed-up (64.1%). One secondary dislocation occurred in the conservative group (11.1%) and three in the surgical group (18.8%). (4) Conclusions: Despite the potential for instability in this injury, conservative treatment does not seem to lead to unfavorable short-term results, less adverse events, and a shorter hospital stay and should thus be considered and discussed with patients as a treatment option, even in the presence of severe AAI.

Atlantoaxial joint stabilization using patient-specific 3-D-printed drill guides and 3-D-printed titanium plates or polymethyl methacrylate is effective in toy-breed dogs.

OBJECTIVE: To report the clinical outcomes in toy-breed dogs with atlantoaxial instability (AAI) stabilized with patient-specific 3-D-printed titanium plates or polymethyl methacrylate (PMMA), both with the assistance of 3-D-printed drill guides. ANIMALS: 15 client-owned dogs undergoing surgical treatment for AAI between January 1, 2020, and October 31, 2022. METHODS: The clinical characteristics, diagnostic images, and neurological outcomes of 15 dogs treated for AAI using 3-D-printing technology were reviewed. Postoperative CT images were examined to evaluate the screw placement accuracy in the atlas and axis. Clinical outcomes, including postoperative neurological improvement and screw loosening, were evaluated in dogs treated with a patient-specific titanium plate and those treated with PMMA. RESULTS: Patient-specific titanium plates (7 dogs) and PMMA (8 dogs) were used for AAI stabilization. The mean follow-up period was 15.2 months (range 7 to 22 months). A reduction of the axis without vertebral canal violation was confirmed on postoperative CT in 14 dogs. The mean deviation from the preoperative planning ranged from 0.30 to 1.27 mm at the insertion and exit points of 84 screws using this method. The neurological grade had improved in each dog postoperatively and at the final follow-up. Screw loosening was noted in 4 dogs in the titanium plates groups without neurological deterioration. CLINICAL RELEVANCE: Patient-specific 3-D-printed drill guides and titanium plates or PMMA are effective for AAI stabilization in toy-breed dogs, providing accurate guidance.

Accuracy and risk factors of Magerl screw placement in robot-assisted atlantoaxial surgery: A case series study.

BACKGROUND: To assess the accuracy of robot-assisted Magerl screw placement and explore the factors affecting the accuracy. METHODS: A retrospective analysis of patients who underwent robot-assisted Magerl screw placement was performed. The accuracy of Magerl screw placement was evaluated according to the Gertzbein and Robbins scale. RESULTS: 47 Magerl screws were placed in 24 consecutive patients. 32 Magerl screws were narrower than the C2 isthmus height and 26 of them were grade A. 15 Magerl screws were wider than the C2 isthmus height and all of them were grade B. Temporary fixation after decompression and a smaller difference between the C2 isthmus height and screw diameter were associated with a higher probability of cortical breach. CONCLUSION: The accuracy of robot-assisted Magerl screw placement was excellent. Temporary fixation after decompression and a smaller difference between the C2 isthmus height and screw diameter increased the risk of cortical breach.

Case report: C1/2 rotational instability progressing to extreme subaxial hyperkyphosis in an adolescent with severe catatonia.

Introduction: Autism spectrum disorder (ASD) is characterized by deficits in social communication, repetitive behaviors, and can be accompanied by a spectrum of psychiatric symptoms, such as schizophrenia and catatonia. Rarely, these symptoms, if left untreated, can result in spinal deformities. Research question and case description: This case report details the treatment of a 16-year-old male ASD patient with catatonic schizophrenia and mutism, presenting with neck pain, left-rotated torticollis, and fever. MRI revealed atlantoaxial rotational instability and spinal cord compression from a dislocated dens axis. After inconclusive biopsies, empirical antibiotics, hard collar and halo fixation treatment, persistent instability necessitated C1/2 fusion. The ongoing catatonia was addressed with electroconvulsive therapy. Concurrently, he developed severe subaxial hyperkyphosis. The report examines the decision-making between conservative and surgical management for an adolescent with significant psychiatric comorbidity and progressive spinal symptoms against a backdrop of uncertain etiology. Materials and methods: A case report and review of the literature. Results: Posterior C1-C7 stabilization was successfully executed, effectively restoring cervical sagittal alignment, which was maintained throughout a two-year follow-up. Concurrently, the catatonia resolved. Discussion and conclusion: To our knowledge, this is the third reported case of severe cervical deformity associated with fixed posture in a psychiatric patient. This case report emphasizes the critical importance of multidisciplinary collaboration in managing the interplay between neuropsychiatric disorders and severe spinal deformities. It showcases the practicality and efficacy of surgical intervention for persistent cervical deformity in pediatric schizophrenia patients, highlighting the necessity for a comprehensive risk-benefit analysis.

Posterior intra-articular distraction technique to treat pediatric atlantoaxial instability.

PURPOSE: Surgical treatment for atlantoaxial instability in pediatric patients is challenging. We report our experience with posterior intra-articular distraction technique in treating this disorder. METHODS: This is a retrospective descriptive study which included 15 patients of atlantoaxial instability whose age was less than 16 years at the time of clinical presentation. All patients underwent anterior soft tissue released through a posterior-only approach, followed by intra-facet cage implantation, cantilever correction, and instrumentation. Clinical results were measured using the Japanese Orthopedic Association (JOA) scale and radiographic measurements including the atlantodental interval (ADI), posterior atlantodental interval (pADI), the distance of odontoid tip above Chamberlain's line, clivuscanal angle (CCA), and triangular area (TA) of craniovertebral junction. RESULTS: The follow-up period ranged from 18 to 72 months, with an average of 41.2 ± 15.2 months. The JOA score increased from 13.6 ± 2.3 to 16.6 ± 0.8. ADI decreased from 4.31 ± 2.37 to 1.85 ± 1.09 mm, and TA decreased from 261.96 ± 107.99 to 197.12 ± 72.37 mm2. pADI increased from 12.89 ± 3.52 to 18.25 ± 3.89 mm, and CCA improved from 132.19 ± 16.34 to 144.35 ± 13.91°. All changes in measurements showed statistically significant. There were no evidence of surgery-related complications or iatrogenic secondary cervical deformity during follow-up. Radiological evaluation showed satisfactory corrections and bony fusions of C1-2 facet joint in all cases. CONCLUSION: Posterior intra-articular distraction followed by cage implantation and cantilever correction can be one of the safe and effective ways to solve atlantoaxial instability in pediatric patients.

Dens Growth After Surgical Fixation in Children with Morquio-Brailsford Disease.

Mucopolysaccharidosis type IVA is a lysosomal storage disorder caused by a deficiency of the enzyme N-acetyl-galactosamine-6-sulphate sulphatase. Mucopolysaccharidosis type IVA is multisystemic disease with significant spinal involvement and atlantoaxial instability leading to neural compression and significant morbidity. Dens hypoplasia is a common feature of this condition. In this study we demonstrate that after spinal fixation, there is new growth of dens in significant proportion of patients, suggesting atlantoaxial instability as one of the major driving forces of lack of development of dens in this condition.

Neurovascular considerations in patients with Down syndrome and moyamoya syndrome.

In this article, we describe a rare and complex case of moyamoya syndrome in a 7-year-old boy with Down syndrome and atlantoaxial subluxation. The patient presented with an ischemic stroke in the left hemisphere and cervical cord compression with increased cord edema. Diagnostic digital subtraction angiography revealed unique patterns of vascular involvement, with retrograde flow through the anterior spinal artery, ascending cervical artery, occipital artery, and multiple leptomeningeal arteries compensating for bilateral vertebral artery occlusion. This case underscores the underreported phenomenon of upward retrograde flow through the anterior spinal artery in bilateral vertebral artery occlusion. We address the rare manifestation of posterior circulation involvement in moyamoya syndrome, highlighting the importance of considering atlantoaxial instability as a contributing factor, as the absence of atlantoaxial stability is a risk factor for vertebral artery dissection. This study contributes valuable insights into the intricate relationship of moyamoya syndrome, Down syndrome, and atlantoaxial instability, urging clinicians to consider multifaceted approaches in diagnosis and treatment. It also emphasizes the potential significance of the anterior spinal artery as a compensatory pathway in complex vascular scenarios.