Fatal cervical myelopathy in a child with glutaric aciduria type 1.

We report the case of a Syrian female refugee with late diagnosis of glutaric aciduria type 1 characterised by massive axial hypotonia and quadriplegia who only started adequate diet upon arrival in Switzerland at the age of 4 years, after a strenuous migration journey. Soon after arrival, she died from an unexpected severe upper cervical myelopathy, heralded by acute respiratory distress after a viral infection. This was likely due to repeated strains on her hypotonic neck and precipitated by an orthotopic os odontoideum who led to atlanto-axial subluxation. This case reminds us not to omit handling patients with insufficient postural control and hypotonia with great care to avoid progressive cervical myelopathy.

Os odontoideum and craniovertebral junction instability secondary to dystonia: case series and review of the literature.

INTRODUCTION: Os odontoideum refers to a rounded ossicle detached from a hypoplastic odontoid process at the body of the axis. The aetiology has been debated and believed to be either congenital or acquired (resulting from trauma). Os odontoideum results in incompetence of the transverse ligament and thus predisposes to atlantoaxial instability and spinal cord injury. METHODS/RESULTS: Three cases of children with severe dystonic cerebral palsy presenting with myelopathic deterioration secondary to atlantoaxial instability due to os odontoideum are presented. This observation supports the hypothesis of os odontoideum being an acquired phenomenon, secondary to chronic excessive movement with damage to the developing odontoid process. CONCLUSION: In children with cerebral palsy and dystonia, pre-existing motor deficits may conceal an evolving myelopathy and result in delayed diagnosis of clinically significant atlantoaxial subluxation.

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.

Axial superior facet slope may determine anterior or posterior atlantoaxial displacement secondary to os odontoideum and compensatory mechanisms of the atlantooccipital joint and subaxial cervical spine.

OBJECTIVE: To introduce novel parameters in determining directions of os odontoideum (OO) with atlantoaxial displacement (AAD) and compensations of cervical sagittal alignment after displacement. METHODS: Analysis was performed on 96 cases receiving surgeries for upper cervical myelopathy caused by OO with AAD from 2011 to 2021. Twenty-four patients were included in the OO group and divided into the OO-anterior displacement (AD) group and the OO-posterior displacement (PD) group by displacement. Seventy-two patients were included as the control (Ctrl) group and divided into Ctrl-positive (Ctrl-P) group and Ctrl-negative (Ctrl-N) group by axial superior facet slope (ASFS) in a neutral position. ASFS, the sum of C2 slope (C2S) and axial superior facet endplate angle (ASFEA), was measured and calculated by combining cervical supine CT with standing X-ray. Cervical sagittal parameters were measured to analyse the atlantoaxial facet and compensations after AAD. RESULTS: Atlas inferior facet angle (AIFA), ASFS, and ASFEA in Ctrl-P significantly differed from OO-AD.C0-C1, C1-C2, C0-C2, C2-C7, C2-C7 SVA, and C2S in Ctrl-P significant differed from the OO-AD group. C2-C7 SVA and C2S in Ctrl-N significantly were smaller than the OO-PD group. C1-C2 correlated with C0-C1 and C2-C7 negatively in the OO group. Slight kyphosis of C1-C2 in OO-AD was compared with lordosis of C1-C2 in Ctrl-P, inducing increased extension of C0-C1 and C2-C7. Mildly increased lordosis of C1-C2 in OO-PD was compared with C1-C2 in Ctrl-N, triggering augmented flexion of C0-C1 and C2-C7. CONCLUSION: ASFS was vital in determining directions of OO with AAD and explaining compensations. ASFS and ASFEA could provide pre- and intraoperative guidelines. KEY POINTS: • ASFS may determine the directions and compensatory mechanisms of AAD secondary to OO. • ASFS could be achieved by the sum of ASFEA and C2S.

MR documented craniocervical ligamentous injury at age 18 months: delayed formation of OS odontoideum. Complex management issues. Case-based review.

OBJECTIVE: There are two separate theories regarding the genesis of os odontoideum: congenital and post-traumatic. Trauma documentation in the past has been the presence of a normal odontoid process at the time of initial childhood injury and subsequent development of the os odontoideum. True MR documentation of craniocervical injury in early childhood and subsequent os odontoideum formation has been very rare. METHODS: An 18-month-old sustained craniocervical ligamentous injury documented on MRI with transient neurological deficit. Chiari I abnormality was also recorded. Subsequent serial imaging of craniocervical region showed the formation of os odontoideum and instability. He became symptomatic from the os odontoideum and the Chiari I abnormality. The patient underwent decompression and intradural procedure for Chiari I abnormality and occipitocervical fusion. Postoperative course was complicated by the failure of fusion and redo. He later required transoral ventral medullary decompression. He recovered. RESULTS: This is an MR documented craniocervical ligamentous injury with sequential formation of os odontoideum with accompanying changes in the atlas. Despite a subsequent successful dorsal occipitocervical fusion, he became symptomatic requiring transoral decompression. CONCLUSIONS: Os odontoideum here is recognized as a traumatic origin with the presence of congenital Chiari I abnormality as a separate entity. The changes of the anterior arch of C1 as well as the os formation were serially documented and give credence to blood supply changes in the os and atlas as a result of the trauma. The recognized treatment of dorsal occipitocervical fusion failed in this case requiring also a ventral decompression of the medulla.

Congenital atlanto-occipital dislocation in a patient with Down syndrome: a case report.

Down syndrome, also known as trisomy 21, is associated with congenital cervical spine abnormalities, including atlantoaxial instability with or without os odontoideum, atlanto-occipital instability, and hypoplasia of the atlas. Herein, we report a case of Down syndrome complicated by congenital atlanto-occipital dislocation. The patient presented with severe cervical myelopathy at 13 years of age after a 10-year follow-up. Radiography and computed tomography revealed os odontoideum protruding into the foramen magnum and congenital anterior atlanto-occipital dislocation. Additionally, a bifurcated internal occipital crest with a thinned central portion of the occipital bone was noted. Magnetic resonance imaging revealed kyphotic alignment of the spinal cord with severe compression at the foramen magnum level. As the neurological impairment was partially improved by halo vest immobilization, we performed in situ O-C2 fusion with an iliac autograft and decompression of the foramen magnum and posterior arch of C1. An improvement was observed immediately after surgery. Two years after surgery, radiography and computed tomography showed solid O-C2 segment fusion. The accumulation of similar cases is essential for determining the prognosis or optimal treatment for this rare congenital condition.

A young man with Guillain-Barré syndrome, with a stroke-like presentation and physical findings suggestive of cervical myelopathy.

We describe the case of a 44-year-old gentleman with hypertension and asthma presenting to the emergency department after noticing right upper-extremity weakness upon awakening. Brain imaging did not reveal a stroke. Initial neurological examination pointed to cervical myelopathy with radiculopathy as well as possible underlying length-dependent peripheral neuropathy as there was right arm strength of 4/5 and there were brisker (3+) reflexes all over except at the right biceps reflex and both ankle reflexes. Cervical spine magnetic resonance imaging (MRI) showed myelomalacia at the C2 level and an os odontoideum (OO). Os odontoideum is a chronic condition that occurs due to the failure of the center of ossification of the dens to fuse with the body of C2. By the next day after a few hours of sustaining a fall, weakness progressed to quadriparesis, without a sensory level on examination, followed by urinary retention. This situation was attributed to a possible cervical cord contusion due to the fall in the presence of OO, with other possibilities being spinal cord hemorrhage, infarct and transverse myelitis. However, repeat scanning of the cervical spine (MRI) did not reveal any acute cord changes. The initial examination for common causes of peripheral neuropathy did not reveal any findings. Finally, the diagnosis of Guillain-Barré syndrome (GBS) was considered, and treatment was initiated with intravenous immunoglobulin. Cerebrospinal fluid analysis was normal. The diagnosis was confirmed using electromyography. Our patient's initial presentation of monoparesis and progression in an asymmetric descending manner was unusual for GBS. His initial presentation mimicked a stroke, and the later progression masqueraded as cervical myelopathy secondary to a chronic cervical cord lesion. The presence of a cervical cord lesion (upper motor neuron) concealed the expected areflexia in GBS. The presence of OO on spine imaging, absence of expected areflexia in GBS, and progression to paraparesis after the fall sidetracked the direction of the initial investigation and led to a relative delay in diagnosis. Nonetheless, appraising the diagnostic data in the clinical context led to an appropriate diagnosis. We emphasize the importance of reconciling the available clinical and diagnostic information to reach the correct diagnosis.

Atlantoaxial dislocation due to os odontoideum in patients with Down's syndrome: literature review and case reports.

PURPOSE: To clarify etiology, clinical features, and diagnostic and treatment options of atlantoaxial dislocation (AAD) due to os odontoideum (OsO) in patients with Down's syndrome (DS). METHODS: We described and analyzed three clinical cases of AAD due to OsO in DS patients and reviewed descriptions of similar cases in the scientific sources. RESULTS: According to literature review, more than 80% of DS patients with odontoid ossicles had atlantoaxial instability (AAI). AAI in DS patients with OsO is more often manifested in childhood and adolescence, rarely in adults when ligament relaxation is reduced. Some patients had acute clinical manifestation after a minor trauma without any precursors; in some of the cases, neurological deterioration increased during several years. We found that the earlier surgical treatment of AAD due to OsO in DS patients carries the higher recovery potential. CONCLUSIONS: Most patients with DS and OsO had AAI. The method of appropriate treatment in such cases is a posterior screw fixation. Preoperative halo traction and posterior fusion have proved to be a very useful tool in the treatment of AAD due to OsO in DS patients. Even if irreducibility of the AAD established preoperatively, it should not be an absolute indication for anterior decompression. In such cases, an attempt to reduce the AAD should be made under general anesthesia during posterior fixation.

Treatment of pediatric unstable os odontoideum with adjacent degenerative cyst: case presentation and literature review.

Degenerative cysts associated with an unstable os odontoideum in pediatric patients are uncommon lesions. Reported treatments of such lesions have varied and yielded mixed results with the optimal surgical strategy remaining unclear. The authors report the clinical and surgical outcome of a 13-year-old patient presenting with degenerative cyst adjacent to an abnormal os odontoideum motion segment. The patient was asymptomatic from this lesion which was an incidental finding while undergoing workup for atypical headaches. Clinical and radiologic findings, operative details, and postoperative outcome are described. The patient was successfully treated with posterior cervical fusion without direct cyst decompression. Complete resolution of the cyst was demonstrated on magnetic resonance imaging at 6 months. Computed tomography 8 months postoperatively showed solid bony fusion and normal alignment. Regarding treatment goals in pediatric patients with os odontoideum degenerative cysts, the current case and literature review supports posterior instrumented fusion without direct surgical cyst resection.

Proatlas anomalies in craniofacial malformations: 5-year experience in King Chulalongkorn Memorial Hospital.

PURPOSE: To review the prevalences of proatlas anomalies in craniofacial malformations and evaluate the relation between craniofacial malformation and proalast anomalies. METHODS: The 221 patients with craniofacial malformation who underwent CT facial bone and 3D brain in King Chulalongkorn Memorial Hospital (KCMH). Then, the craniofacial malformed patients are classified into six groups composed of craniosynostosis, cephalocele, midface anomaly, facial and branchial arch syndrome, facial cleft face, and others. Reviewing image finding by the researcher and the radiologist advisor was done separately and gave the consensus in the case with disagreement. Qualitative analysis of the prevalence of proatlas anomalies was achieved. In addition, assessment of the relationship between craniofacial malformation and proatlas anomalies was conducted using Pearson's chi-square test to determine statistical significance. RESULT: The proatlas anomalies were presented in 26 patients of 221 craniofacial malformed patients. Details of frequentative proatlas anomalies consist of pre-basioccipital arch in eight patients, os odontoideum in five patients, bony mass along the margin of foramen magnum in three patients, atlas assimilation in two patients, hypertrophic occipital condyle in one patient, third occipital condyle in one patient, and mixed characteristic of proatlas anomalies in six patients. These results represented pre-basioccipital arch and os odontoideum as the two most common presentations among proatlas anomalies and also showed significant existence of proatlas diseases in craniofacial malformation (p value = 0.006). CONCLUSION: Our results emphasize the existence of proatlas anomalies which should be carefully looked for, particularly in craniofacial malformed patients due to significant statistical correlation.

Evaluation of 2011 AAP cervical spine screening guidelines for children with Down Syndrome.

PURPOSE: Atlantoaxial instability (AAI) has a higher incidence rate among individuals with Down syndrome (DS) than the non-DS population. In 2011, the American Academy of Pediatrics (AAP) updated its AAI screening guidelines for children with DS from radiographic screening to radiographs only if there are clinical symptoms suggestive of cervical spine pathology. An assessment of whether this alteration has been associated with an increase in AAI-associated spinal cord injury has not been undertaken. METHODS: We provide the first neurosurgical review of a large experience implementing the 2011 AAP guidelines. We reviewed the courses of patients with DS seen at the Sie Center for Down Syndrome at Children's Hospital Colorado who were evaluated for cervical spine disease and determined whether screening radiographic imaging could have led to earlier diagnosis or prevented development of neurological deficits. We also report an illustrative case of a 5-year-old female with Down syndrome who presented with instability after normal screening radiographs per the pre-2011 guidelines. RESULTS: The clinical experience of the Sie Center demonstrates that even when limiting imaging to patients who show signs or symptoms of spine pathology, the vast majority of x-rays are negative. Our exemplary patient presented to the emergency department for neck pain without a history of significant trauma. She was diagnosed and treated for atlantoaxial subluxation associated with os odontoideum. CONCLUSION: Routine radiographic screening may not be sufficiently predictive of DS individuals at risk to develop AAI. This experience supports the appositeness of the de-escalation of care asserted by the guidelines.

Anatomo-radiological importance and the incidence of os odontoideum in Turkish subjects: a retrospective study.

PURPOSE: Os odontoideum is a rare anatomical and morphological variation of the odontoid process and associated with a range of symptoms such as spinal cord and vertebral artery injuries. This study aimed to evaluate the frequency of os odontoideum in Turkish cases by sagittal/coronal cervical magnetic resonance imaging (MRI) and computed tomography (CT) and analyze the relationship with age, gender and related symptoms. METHODS: The incidence of os odontoideum was retrospectively diagnosed by sagittal/coronal cervical CT and MRI out of 16,122 subjects aged 20-70 years (mean 46) in the period between 2014 and 2018. The relationship of os odontoideum with age, gender, and symptoms was recorded. RESULTS: The statistical analysis of the study was performed by the χ² test and two-way mixed ANOVA. Os odontoideum was detected in 18 (0.11%) (11 males; 7 females) out of 16,122 patients. The mean age was 47.5 ± 1.4 years in the females and 43.5 ± 2.5 years in the males (p < 0.05). 6 odontoideum were detected out of 6467 (3756 males, mean 48 ± 0.7, 2711 females, mean 46 ± 1.2) subjects by CT and 12 odontoideum were detected out of 9655 patients (5607 males and 4048 females) by MRI. CONCLUSION: Neck pain was the most frequent symptom. The prevalence of os odontoideum especially round type is more frequent in older male patients over 40 years old with head and neck pain or atlantoaxial instability, and is less common in Turkish subjects when compared to various ethnic groups.

Os odontoideum: diagnosis and role of imaging.

OBJECTIVE: To elucidate the imaging manifestations of os odontoideum, establish the diagnosis and guide surgical therapy. METHODS: Clinical and imaging data, including X-ray, CT and MR of 24 patients with os odontoideum, were retrieved and reviewed retrospectively. RESULTS: Os odontoideum with intact cortex was divided into round, conical and blunt tooth types. Four cases of orthotopic and 20 cases of dystopic os odontoideum were included. There was anterior displacement of the base of the dens in six cases, posterior displacement in nine cases and no displacement in nine cases. A widening of anterior atlanto-axial space was shown in 14 patients with varying degrees. Thickening of the soft tissue posterior to the dens was observed in 19 patients, spinal canal stenosis in 21 patients, cervical myelopathy in 10 patients and craniocervical junction malformation in 9 patients. Posterior C1-C2 pedicle screw fixation and fusion was performed in 12 patients and 4 patients underwent posterior occipito-cervical fixation and fusion. CONCLUSION: Radiographically, os odontoideum is defined as an independent ossicle of variable size with smooth circumferential cortical margins separated from the axis. Imaging can be used to assess atlanto-axial instability, associated normal or abnormal anatomical structures and guide surgical therapy.

Wiring or Screwing at the Craniovertebral Junction in Childhood: Past and Present Personal Experience.

BACKGROUND: Craniovertebral junction (CVJ) instrumentation and fusion in childhood are frequently performed with either sublaminar wires or screws in lateral masses, and both are considered quite safe procedures. METHODS: Our experience deals with 12 children: six (mean age 9.5 years) harbouring a congenital instability associated with Down's or Morquio's syndromes and primary os odontoideum; and six (mean age 11.5 years) with acquired iatrogenic instability due to transoral anterior decompression for different reasons (inferior clivectomy, anterior arch removal and odontoidectomy). All patients in the 'congenital group', except for one, had preoperative dynamic x-rays and underwent surgical correction by means of posterior wiring, fusion and an external orthosis. All patients in the 'iatrogenic group' had no preoperative dynamic x-rays and underwent a screwing technique with fusion and an external orthosis. RESULTS: The postoperative clinical picture had improved in all patients at the latest follow-up (observation range 63-202 months [mean 118.5 months]), with neuroradiological confirmation of satisfactory bony fusion and with neural decompression in all patients. CONCLUSION: Although it requires a more accurate preoperative neuroradiological setting, the screwing technique takes less time and is characterized by less blood loss and less postoperative discomfort than the wiring technique. The latter features confirm the simplicity, safety (continuous fluoroscopic assistance is not necessary, and there is no risk of neurovascular injuries) and lower expense (neither complex hardware devices nor neuronavigation systems are required) of the screwing technique.

Morphologic Anomalies of Upper Cervical Vertebrae in Swedish Children Born with Nonsyndromic Cleft Lip and/or Palate Compared to Swedish Children without Cleft.

OBJECTIVE: To examine and compare the prevalence of morphologic anomalies of the upper cervical vertebrae in Swedish children with nonsyndromic cleft lip and/or palate to Swedish children without cleft. DESIGN: Retrospective study on lateral cephalograms. SETTING: Division of Orthodontics, Department of Dental Medicine, Karolinska Institutet, Stockholm, Sweden. PATIENTS: The cleft group consisted of 325 children (150 girls and 175 boys) born with nonsyndromic cleft lip and/or palate (mean age: 11.1 years). The control group consisted of 325 children without cleft, matched for age and gender. MAIN OUTCOME MEASURES: Lateral cephalograms exposing upper cervical vertebrae (C1-C3) were examined regarding morphologic anomalies such as posterior arch deficiencies, fusion of vertebrae, odontoid anomalies, and deviations of the vertebral artery canal. RESULTS: The prevalence of children with morphologic anomalies of the upper cervical vertebrae was 24.3% (n = 79) in children with cleft and 12.6% (n = 41) in children without cleft. Posterior arch deficiency and vertebral fusion were significantly more frequent in children with cleft (P < .001). No statistically significant differences were found between the 2 groups regarding odontoid and vertebral artery canal anomalies. CONCLUSIONS: Morphologic anomalies of the upper cervical vertebrae in Swedish children with nonsyndromic cleft lip and/or palate were significantly more frequent compared to similar anomalies in Swedish children without cleft.

Atlantoaxial dislocation and os odontoideum in two identical twins: perspectives on etiology.

PURPOSE: There are two theories about the origin of os odontoideum: traumatic or congenital. However, most studies favor the hypothesis of traumatic theory. To emphasize the congenital theory, we report a pair of identical twins both with atlantoaxial dislocation and os odontoideum, which is believed to be a congenital defect. METHODS: We present two 14-year-old identical twins with atlantoaxial dislocation and os odontoideum. Neither of the twins had history of trauma in head nor cervical spine. We reviewed and compared the cervical radiographs of the identical twins. Posterior atlantoaxial reduction, pedicle screw fixation and atlantoaxial fusion were performed for the two twins. RESULTS: Radiological examination showed the identical twins had typical atlantoaxial dislocation and os odontoideum. The twins had high similarity in the appearance of atlantoaxial dislocation and os odontoideum. The etiology of the os odontoideum in the twins is believed to be congenital. Both the twins had improvement in neurological function after surgery. CONCLUSION: Although a great number of cases with os odontoideum have been reported to be traumatic, there are some cases believed to be congenital.

Surgical strategies in the management of atlantoaxial dislocation in Down syndrome.

Aims: To study the clinicoradiological features and treatment outcomes of atlantoaxial dislocation (AAD) in Down syndrome. Settings and Design: Retrospective case series. Subjects and Methods: A retrospective chart and radiology review of 9 Down syndrome patients with AAD managed at our center from 2007 to 2018. Statistical Analysis Used: Chi-squared/Fisher's exact test. Results: There were 4 males and 5 females (n = 9). The median age was 14 years (interquartile range [IQR]: 7-15.5). 77.7% (7/9) of patients had severe spasticity (Nurick Grades 4 and 5). The median duration of symptoms was 9 months (IQR: 5-39). The AAD was reducible in all (n = 9) cases. Eight (88.8%) patients had os odontoideum. The mean atlantodental interval (ADI) was 8.5 mm (±2.9). T2W cord hyperintensity was seen in 66.6% (6/9). Posterior C1-2 transarticular fixation was done in 8 and occipitocervical fusion in 1 patient. Follow-up of more than 6 months (7-57 months) was available in 8/9 (88.9%) patients. There was a significant improvement in spasticity (n = 8, mean Nurick Grade 1.7 (±1.1), P = 0.003). Follow-up radiographs (n = 8) showed good reduction and fusion. A preoperative bedbound patient with poor respiratory reserve expired at 10 months following surgery. There were no other complications. Conclusions: Posterior surgical approach for AAD in Down syndrome resulted in good alignment and fusion, with excellent clinical improvement. Patients with elevated PCO2 are poor surgical candidates and require home ventilation facility.

Philosophies And Surgical Techniques on Os Odontoideum Treatment with Literature Review.

Introduction: Os-odontoideum is a rare condition described radiographically and clinically as a congenital anomaly of the second cervical vertebra (axis). It is a smooth, independent ossicle of variable size and shape separated from the base of a shortened odontoid process by an obvious gap, with no osseous connection to the body of C2. Materials and Methods: This study reviewed the literature on OO to evaluate its etiology, clinical presentations, differential diagnosis, imaging modalities, and outcomes in the management of asymptomatic and symptomatic cases of Os Odontoideum. Key articles from PubMed, EMBASE, Google Scholar, and Cochrane were searched. Discussion: Considering etiology, the traumatic hypothesis is favoured over the congenital hypothesis as per recent literature on OO. Clinical presentation varies from asymptomatic to mild neck pain to severe myelopathy and neurodeficit. Various C1-C2 instrumentation and fusion techniques like wiring, trans articular screw and laminar screws have been described with success rates. Conclusion: Os odontoideum is a rare condition with limited existing literature. Considering the significant risks involved if conservative management opts, like severe neuro deficit to sudden death on trivial trauma and the recent improvement of imaging tools helping to understand the pathology of the disease, surgery can be indicated even in an incidentally detected os odontoideum. However, a case-by-case approach can be considered for stable asymptomatic patients depending on factors such as age, activity level, comorbidities, syndromic association, and radiographic findings.

A synovial cyst-induced vertebral artery dissection in bow hunter's stroke: illustrative case.

BACKGROUND: Bow hunter's stroke (BHS) is a rare condition characterized by occlusion of the vertebral artery (VA) due to a head rotation. BHS typically results from neck hyperrotation, often due to anatomical factors. The authors present a case of BHS in a young male patient exacerbated by os odontoideum (OD), resulting in atlantoaxial dislocation, which ultimately led to VA dissection. OBSERVATIONS: A man in his 20s presented with persistent dizziness and nausea and initially received a diagnosis of a brain infarction. However, imaging revealed VA dissection caused by an OD with an associated synovial cyst. Surgical intervention, specifically atlantoaxial posterior fixation, resolved the instability and allowed for natural regression of the synovial cysts, preventing further vascular events. In this case, the OD with atlantoaxial dislocation was identified as the causative factor for BHS. The coexistence of a synovial cyst was a unique finding, likely triggered by chronic irritation caused by the OD. LESSONS: This case emphasizes the importance of thorough cervical spinal evaluation in young patients presenting with posterior circulation stroke. https://thejns.org/doi/10.3171/CASE2487.

Influence of the type of atlantoaxial dislocation secondary to os odontoideum on sagittal alignment and balance of the subaxial cervical spine after posterior atlantoaxial fusion.

OBJECTIVE: This retrospective study aims to investigate the effect of the type of atlantoaxial dislocation due to os odontoideum on the sagittal alignment and balance of the cervical spine after posterior atlantoaxial fusion. METHODS: Data of 48 consecutive patients who underwent posterior C1-C2 fusion to treat atlantoaxial dislocation/instability due to os odontoideum were retrospectively reviewed. Radiographic variables, namely the T1 slope (T1S), C1-C2 angle, C2-C7 angle, C1-C2 sagittal vertical axis (SVA), C2-C7 SVA, and modified atlas-dens interval (MADI), were measured preoperatively, immediate postoperatively, and at final follow-up. Patients were divided into three groups based on the preoperative MADI. Differences within and between groups in radiographic variables and relationships between the investigated variables were analyzed. RESULTS: The MADI was correlated with the preoperative to postoperative changes in the C1-C2 angle (r = 0.776, P < 0.05) and C2-C7 angle (r = - 0.357, P < 0.05). In the group with anterior atlantoaxial dislocation, the C1-C2 angle and C2-C7 SVA were significantly enlarged at final follow-up (P < 0.05), while the C2-C7 angle was significantly reduced (P < 0.05). The changes in C1-C2 angle and C2-C7 angle were opposite between the posterior group and the anterior dislocation group. CONCLUSION: The direction/type of atlantoaxial subluxation correlates with the changes in lower cervical curvature after atlantoaxial fusion. Patients with atlantoaxial posterior dislocation and atlantoaxial instability are less likely than those with atlantoaxial anterior dislocation to develop loss of lordosis after posterior atlantoaxial fusion.