Atlanto-occipital Assimilation Research Articles

Atlanto-occipital assimilation: A pictorial review of a commonly missed pathology.

Atlanto-occipital assimilation is a congenital craniovertebral junction malformation where the partial or complete fusion of the atlas and occiput occurs. Atlanto-occipital assimilation can be associated with numerous complications, including basilar invagination, atlantoaxial subluxation, Chiari malformation, congenital vertebral bodies fusion, and cord compression. As a result, vigilant identification and accurate reporting of atlanto-occipital assimilation are essential. The purpose of this review article is to discuss the numerous complications and associations of atlanto-occipital assimilation, such that an accurate diagnosis could be made for this commonly missed pathology.

Atlantooccipital assimilation associated with combined atlas arch defect: a radiological case report.

In this report, atlantooccipital assimilation (AS), anterior arch defect (AAD), and posterior arch defect (PAD) of the atlas, and several variations around the craniocervical junction were identified on computed tomography (CT) of a patient of unknown sex and age. Coronal and sagittal CT scans showed AS and bilateral fusion of the atlas and the base of occipital bone. Axial CT scan at the atlas revealed PAD type B on the left side and midline AAD. Morphometric measurements indicated a potential ventral spinal cord compression. In addition, mid-sagittal CT revealed the presence of fossa navicularis magna and incomplete formation of the transverse foramen on the right side. This study reports an extremely rare AS associated with AAD, PAD, and other variations of the clivus and the atlas. To our knowledge, no similar case has been reported in the literature.

Atlanto-occipital Assimilation an Incidental Cephalometric Finding: Diagnosis and Clinical Implications – A Case Report

Occipitalization of atlas is an osseous anomaly of the craniovertebral junction, which occurs at the base of the skull in the region of the foramen magnum. It is the fusion of first cervical vertebra with the occipital bone of the skull. A 16-year-old patient reported with chief complaint of irregularly placed teeth. Routine lateral cephalogram assessment revealed the presence of fusion between first cervical vertebrae (C-1) and base of skull. The radiographic investigation revealed the presence of fusion along with the clinical findings of short neck, short face, cleft palate, missing teeth, and pain during neck extension and flexion. Such cases of craniocervical anomaly can cause orthopedic and neurological problems like abnormal posture of head, restricted neck movements, cervical pain, pain in extremities, wasting of muscles, and convulsions. The comprehensive radiographic assessment of all structures visible in cephalogram of orthodontic patient can help in identification of such anomalies and sensitize the patients about symptomatic or asymptomatic condition.

Klippel Feil Syndrome Type III With Associated Rare Congenital Anomalies (Sprengel Deformity, Scoliosis, and Atlanto-Occipital Assimilation): A Rare Case Report

Klippel Feil Syndrome (KFS) is a congenital anomaly having fusion of 2 or more cervical vertebral bodies characterized by the presence of classic triad of low posterior hairline, short neck, and restricted range of motion. We have reported a rare case of Type III Klippel Feil Syndrome having classical clinical triad with Sprengel deformity and atlantooccipital assimilation. The baby was born at Sanjay Gandhi Memorial Hospital, Mangolpuri, New Delhi, India. The detailed discussion is done in the case report. Prognosis is based on radiological classification by Samartzis et al which classifies KFS under 3 types with type II as the commonest variety. Associated anomalies include scoliosis or kyphosis, renal disease, Sprengel deformity, loss of hearing, synkinesis or mirror movements, congenital heart defects, craniofacial malformations, and skeletal abnormalities of ear, nose, mouth and larynx. Proper management requires multidisciplinary approach including neurologist, orthopedic surgeon, pediatrician, nurse practitioner, physical therapist, and neurosurgeon.

Cervical Sagittal Alignment in Patients With Basilar Invagination.

Retrospective study. To present a morphological map of cervical sagittal alignment in basilar invagination (BI), a congenital anomaly of the craniovertebral junction, and contribute to a comprehensive understanding of cervical sagittal alignment in congenital cervical deformities. Ideal cervical sagittal alignment and surgical targets are debated by scholars. However, most of the literature focuses on the description of cervical sagittal alignment in acquired cervical diseases and normal subjects and few on congenital cervical spine deformities. This study analyzed cervical spine lateral radiographs of 87 BI patients and 98 asymptomatic subjects. They were analyzed for cranial, cervical spine, and thoracic inlet parameters. Patients with BI manifested significantly larger values for the following parameters than asymptomatic subjects: cranial tilt, cranial incidence angle, sagittal vertical axis (SVA) CGH-C7, C2-C7 angle, cervical tilt, and significantly smaller values for the following parameters: cranial slope, C0-C2 angle, C0-C7 angle, SVA C2-C7, spine tilt, thoracic inlet angle, and neck tilt. In the BI group, SVA C2-C7 was the cervical parameter most strongly correlated with the cranial, cervical spine, and thoracic inlet parameters, and was smaller in BI patients with fusion (atlanto-occipital assimilation) than in those without. A significant difference was observed between BI patients and asymptomatic subjects. BI patients have craniums tilted forward and downward, smaller upper cervical lordosis, larger lower cervical lordosis, and smaller thoracic inlet angle. In BI patients, the SVA C2-C7 is an important parameter in cervical sagittal alignment. In both individuals with congenital anomalies of the craniovertebral junction and the asymptomatic population, cervical spine alignment is significantly associated with cranial alignment, particularly thoracic inlet alignment.

Radiologic evaluation of congenital anomalies of anterior and posterior arch of atlas in Omani subjects

The atlas (C1) is known to present congenital anomalies in its anterior and posterior arches. The reported incidence of C1 anomalies is varied among the ethnic groups. We sought to determine the prevalence and various existing variations of C1 arch congenital anomalies in Omani subjects. This study was carried out by reviewing the cervical spine computed tomography scans of all the patients who had been referred to the Radiology Department, Sultan Qaboos University Hospital. Descriptive statistics and chi-square test were employed to analyse the data. A total of 663 subjects aged ≥18 years were included in the present study. Overall prevalence of C1 arch anomalies was 4.37% with 4.07% of isolated posterior arch anomalies, 0.3% of combined anterior and posterior arch anomalies. Among isolated posterior arch anomalies, type A and type B posterior arch defects were found in 3.77% and 0.3% of cases, respectively. Atlanto-occipital assimilation was noted in one case of total study subjects. The prevalence rate of C1 arch anomalies is relatively high in Omani subjects. The baseline data of C1 arch anomalies reported in the present study has a great impact on clinical practice, due to the fact that studying and evaluating the types of congenital anomalies helps in their accurate diagnosis and early intervention.

Embryological considerations and evaluation of congenital anomalies of craniovertebral junction: A single-center experience

Objectives:Craniovertebral junction (CVJ) abnormalities constitute a group of treatable neurological disorders, especially in the Indian subcontinent. Thus, it is essential that clinicians should be able to make a precise diagnosis of abnormalities and rule out important mimickers on multidetector computed tomography (MDCT) as this information ultimately helps determine the management, prognosis, and quality of life of patients. CVJ is the most complex part of the cervical region. Congenital malformations of this region can cause serious neurological deficit and require a surgical intervention. The present study was undertaken to know the embryological basis of the CVJ and to identify commonly observed congenital CVJ abnormalities, their frequency, and mode of presentation.Materials and Methods:Diagnosed cases of CVJ anomalies on dynamic MDCT head were reviewed at a tertiary care center between January 2014 to December 2019. Type of anomaly, clinical presentation, and associated malformations were recorded. Different types of variations were expressed in terms of percentage.Results:Congenital anomalies were seen in 42 cases. Fifteen types of anomalies were detected. Anomalies were either singly or in combination. The CVJ anomalies were more common in young adults (28%), almost equal in both sexes. The most common anomaly was basilar invagination (52.3%), followed by atlanto-occipital assimilation (33.3%), and Arnold–Chiari malformation is the most common soft tissue anomaly. In fourteen cases, additional anomalies of other vertebrae were present. The most common symptoms were weakness of extremities, neck pain, paresthesia, torticollis, and gait disturbances. About 28 patients got improved, 8 patients had residual deficit as that of preoperative status, and 4 patients got deteriorated after surgery, at 1-month follow-up. About 34 patients had improved, 5 remained static, and 3 patients got worsened at the end of 3-month follow-up. About 37 patients had improved, 4 patients remained static, and 2 patients got deteriorated at 6 months of follow-up. The patients with increased atlantodens interval 3–5 mm showed 77% improvement after surgery.Conclusion:Congenital CVJ anomalies, though rare, are fatal. CVJ abnormalities constitute an important group of treatable neurological disorders with diagnostic dilemma. The atlantodental interval is the most important preoperative prognostic marker. Dynamic CT imaging can provide additional useful information to the diagnosis of CVJ instability. To prevent long-term neurological problems, early diagnosis and treatment of congenital bony CVJ anomalies is important.

Imaging findings for Atlanto-occipital assimilation with multiple cervical vertebral anomalies in a Beagle dog: A 2 year follow-up

A 3-year-old male Beagle dog was presented for a physical examination, which revealed a mild stiff neck that was affecting movement. The imaging modalities led to our diagnosis of an asymmetric fusion of the occipital condyle and atlas wing consistent with Atlanto-occipital assimilation (AOA). An incomplete ossification of the atlas and axis, dysplastic dens, and a blocked vertebra were also noted. During a two-year follow-up, the dog showed no other clinical signs or disease progression. To our knowledge, this is the first imaging description of AOA in veterinary medicine. We recommend a careful CT (computed tomography) and an MRI (magnetic resonance imaging) evaluation in cases of neck pain and cervical myelopathy, and inclusion of AOA among the differential diagnoses, with the awareness that its clinical signs resemble those of other canine diseases.

Cough Syncope, a Rare Presenting Symptom of Chiari I Malformation and Atlanto-Occipital Assimilation.

Chiari I malformation and atlanto-occipital assimilation are both fairly uncommon conditions. Symptoms usually present during adolescence or adulthood, typically consisting of headache or neck pain. Cough-associated syncope is an unusual presenting symptom. The diagnosis of this condition in a pulmonology department is even rarer.We report the case of a 62-year-old male referred to our pulmonology department due to complaints of cough-associated syncope. After several examinations, a pharyngeal CT scan incidentally showed low positioning of the cerebellar tonsils. Cerebral MRI confirmed the diagnosis of Chiari I malformation and atlanto-occipital assimilation and the patient was effectively treated with surgical decompression.LEARNING POINTSChiari I malformation (CMI) and atlanto-occipital assimilation are both fairly rare conditions. The prevalence of CMI is estimated to range between 1/1,000 to 1/5,000 individuals and the incidence of atlanto-occipital assimilation varies from 0.08 to 3.6%.The most frequent clinical presentation is a paroxysmal headache or neck pain. Cough syncope is an unusual form of presentation, described in few cases.It is important to bear CMI in mind in the differential diagnosis of cough syncope, since there is an effective treatment that improves the patient’s symptoms and quality of life.

Evaluation of congenital anomalies of craniovertebral junction by computed tomography and its embryological basis

Introduction: Craniovertebral junction (CVJ) is the most complex part of the cervical region. Congenital malformations of this region can cause serious neurological deficit and require a surgical intervention. The present study was undertaken to know the embryological basis of the CVJ and to identify commonly observed congenital CVJ abnormalities, their frequency and mode of presentation. Materials and Methods: Diagnosed cases of CVJ anomalies on computed tomography (CT) head were reviewed. Type of anomaly, clinical presentation, other associated malformations were recorded. Different types of variations were expressed in terms of percentage. Result: Congenital anomalies were seen in 26 cases. Fifteen types of anomalies were detected. Anomalies were either singly or in combination. Most common anomaly was basilar invagination (23.8%) followed by atlanto-occipital assimilation (19%). In seven cases additional anomalies of other vertebrae were present. Maximum eight cases were detected in age group of 11-20 years. There was male predominance. Commonest symptoms were weakness of extremities, neck pain, paresthesia, torticollis and gait disturbances. Conclusion: Congenital CVJ anomalies are rare. To prevent long-term neurological problems, early diagnosis and treatment of congenital bony CVJ anomalies is important. Keywords: Craniovertebral junction, Congenital, Anomaly.

Demonstration of craniocervical junction abnormalities for diagnosis of atlanto-occipital assimilation using MRI

Objectives: Atlanto-occipital assimilation (AOA) is one of the most common skeletal anomalies of the craniovertebral junction (CVJ). Because its clinical symptomatology is non-specific and it has several variations, many cases go unnoticed which may lead to additional and unnecessary radiological examinations. In this study, we aimed to present CVJ abnormalities with MRI to improve diagnostic accuracy of AOA. Methods: Cervical MRIs of the patients registered in PACS between January 2008 and October 2011 were scanned and AOA was detected in 40 cases. Sagittal FSE T1 and T2-weighted cervical MRIs and axial T2*-GRE sequence images were re-evaluated for AOA typing, anterior atlantodental interval (AADI), posterior atlantodental interval (PADI) measurements, spine fusion anomalies, basilar invagination, tonsillar herniation, myelomalacia, suboccipital muscles and vertebral arteries (VAs). Results: CVJ abnormalities were present in all cases and the most frequent association was observed in suboccipital muscles (100%) and VAs (95%). 60% of the cases had decreased PADI, 32% C2–3 vertebrae fusion, 25% increased AADI, 22.5% basilar invagination, 15% myelomalacia and 5% tonsillar herniation. Conclusion: Suboccipital muscle abnormality was found in all AOA cases whatever the severity and type of the bony fusion. VA anomaly was observed as the second most common abnormality and accompanied preferably the cases with lateral body involvement. Being aware of additional CVJ abnormalities in MRI examinations may reduce unnecessary radiological examinations by increasing the AOA diagnosis rate.

Postoperative Regression of Retro-odontoid Pseudotumor After Atlantoaxial Posterior Fixation: 11 Years of Experience in Patients With Atlantoaxial Instability.

Case series study. The aim was to investigate the incidence of retro-odontoid pseudotumor in patients with atlantoaxial instability (AAI) and evaluate pseudotumor regression after posterior fixation. The incidence of retro-odontoid pseudotumor in atlantoaxial instability patients remains uncertain. Moreover, the regression of retro-odontoid pseudotumor after posterior fixation in patients with various underlying diseases needs to be further investigated. From July 2004 to August 2015, 175 patients with AAI underwent posterior fixation operations at our institution. After excluding 11 patients (previous operation, n = 4; history of tumor, n = 7), the final study population comprised 164 patients. The final study population was categorized according to their underlying diseases (rheumatoid arthritis [RA], os odontoideum, atlanto-occipital assimilation, dens fracture, AAI of unknown cause, etc.) and age (adult and pediatric groups). The incidence of retro-odontoid pseudotumor in each group was analyzed. Pre- and postoperative magnetic resonance or computed tomography images were reviewed to assess its regression following surgery. Of the 164 patients included, 38 had retro-odontoid pseudotumor (23.2%). Three were diagnosed with RA and the rest were non-RA patients including os odontoideum (n = 12), dens fracture (n = 6), atlanto-occipital assimilation (n = 4), Morquio syndrome (n = 1), and AAI of unknown cause (n = 12). Pseudotumor size regressed in all 38 patients after atlantoaxial posterior fixation. There was a statistically significant decrease in pseudotumor size (the length between the anterior border of the odontoid process to the posterior border of the pseudotumor) from a mean length of 17.7 to 14.9 mm (P < 0.001). The patients had various underlying diseases and the overall incidence of retro-odontoid pseudotumor in patients with symptomatic AAI was 23.2% at our institution during the past 11 years. All patients who underwent posterior fixation for AAI showed a statistically significant decrease in pseudotumor size. 4.

Neurological complications Secondary to Atlanto-occipital Assimilation: A Case Report

Neurological complications Secondary to Atlanto-occipital Assimilation: A Case Report

Classification and surgical treatment of basilar invagination

Objective To present a new classification of basilar invagination (BI) and evaluate guiding use and effect of the classification for the treatment of BI. Methods Consecutive 34 patients with BI were surgically treated in our department from July 2000 to June 2013. There were 17 males and 17 females, aged from 7 to 59 years (mean, 34.5 years). The clinical symptoms and signs were recorded, and preoperative imaging examination including anteroposterior, lateral, dynamic X-rays, MRI, CT and 3-dimensional reconstruction views of cervical spine were performed to identify the series. 34 patients with BI were associated with anomalies including atlantooccipital assimilation in 21 cases, C2-3 fusion in 16 cases, and atlantoaxial dislocation in 24 cases. According to with or without atlantoaxial dislocation, BI was classified into Type I with dislocation in 24 cases and Type II without dislocation in 10 cases. Type I was divided into reducible subtype A in 6 cases and irreducible subtype B in 15 cases under the condition of skull traction. Type I was performed with reduction by traction or release between C1-2 through anterior or posterior approach, while Type II with decompression by resection abnormal structures through anterior or anteroposterior approach. All patients were underwent posterior instrumentation and fusion. The postoperative X-rays, MRI or CT was taken to observed the results of decompression, fixation and fusion. Neurological function was assessed by JOA scale and Ranawat's score. Results The average operation time was 210 min, and blood loss was 240 ml. Except for 2 death cases, 32 cases were followed up, and the followed-up was ranged from 11 to 37 months (mean, 17.4 months). JOA scores increased from 8.4 to 14.6 with 71.1% of recovery. The excellent and good rate was 72.4%. According to Ranawat's score, preoperative score was class II in 11 cases,class IIIA in 17 cases and class IIIB in 6 cases, while postoperative score was class I in 20 cases, class II in 11 cases and class IIIA in 1 case. The perioperative complications was present in 9 cases, including infection in 3 cases, cerebrospinal fluid (CSF) leakage in 2 cases, respiratory dysfunction in 2 cases, vertebral artery injury and cleft palate in 1 case. Conclusion The new classification of BI can effectively guide and schedule the treatment. Careful evaluation,operation and prevention of perioperative complications are important to ensure the success of surgery. Key words: Skull base; Atlanto-occipital joint; Atlanto-axial joint; Dislocations; Spinal fusion

Chiari I malformation associated with atlanto-occipital assimilation presenting as orthopnea and cough syncope

Although it is not uncommon for patients with Chiari I malformations to present with respiratory complaints, cough syncope is a rare presenting symptom. We report an adult patient who had both a Chiari I malformation and atlanto–occipital assimilation, and complained of cough syncope, orthopnea, and central sleep apnea. The patient underwent decompressive craniectomy of the posterior fossa and a cervical level 2 laminectomy. However, due to an initial under-appreciation of the profound narrowing of the foramen magnum as a result of these concomitant pathologies, the patient had continued impaired cerebrospinal fluid flow, leading to a symptomatic pseudomeningocele and required a more extensive decompression that included a cervical level 3 laminectomy as well as a temporary lumbar drain. On 2year follow-up, he remained asymptomatic.

Klippel–Feil syndrome with atlanto-axial dislocation, anomalous vertebral artery, dextrocardia and situs inversus

A 26-year-old male presented with progressive compressive yelopathy and left shoulder numbness since last 6 months. e had a short neck with restricted movements since birth, but as otherwise healthy and independent. His X-ray and computed omography (CT) of CVJ revealed central irreducible congenital tlantoaxial dislocation with atlanto-occipital assimilation and 2-3 fusion (Fig. 1A–D). MRI of CVJ showed cervicomedullary ompression with cervical cord syrinx (Fig. 1E). Chest X-ray and ltrasound of abdomen confirmed the clinical findings of dexrocardia and situs inversus (Fig. 1F). 3D CT angiography was erformed to evaluate the VA’s at CVJ. It showed small caliber ight vertebral artery with left persistent first intersegmental artery rossing across the C1-2 facets and joint space. This persistent first ntersegmental artery (left VA) also looped abnormally, initially

Cervical Myelopathy Secondary to Atlanto-occipital Assimilation: The Usefulness of the Simple Decompressive Surgery.

Atlanto-occipital assimilation is one of the most common osseous anomalies observed at the craniocervical junction. Most patients with atlas assimilation show no symptom, but some have neurological problems such as myelopathy that may require surgical treatment. Occipitocervical fusion may be required if atlato-occipital assimilation is accompanied by occipito-axial instability. However, in cases of symptomatic atlas assimilation with minor cord compression without instability, simple decompressive surgery may be the treatment modality. This report describes a case of successful treatment of a patient with myelopathy secondary to atlanto-occipital assimilation without instability, using posterior simple decompressive surgery.

Acquired Chiari Malformation Secondary to Atlantoaxial Vertical Subluxation in a Patient With Rheumatoid Arthritis Combined With Atlanto-occipital Assimilation

A 65-year-old woman with a history of rheumatoid arthritis presented with a rare case of acquired Chiari malformation secondary to atlantoaxial vertical subluxation, associated with congenital atlanto-occipital assimilation. Syringomyelia and tetraparesis improved immediately after posterior fossa decompression and simultaneous occipito-cervical junction fusion. The progression of acquired Chiari malformation is not well known. We concluded that coexisting assimilation accelerated crowded foramen magnum following atlantoaxial vertical subluxation and induced acquired Chiari malformation over the course of a few years.

Congenital craniocervical anomalies pose a vulnerability to spinal cord injury without radiographic abnormality (SCIWORA)

Though the incidence of cervical spine injuries in the pediatric population is relatively low at 1.2% of trauma patients, these injuries are often associated with severe neurologic deficits [1]. Upper cervical spine injuries are more common in children less than 11 years old [1–3]. This may be explained by the unique biomechanics of the pediatric cervical spine [4] as well as the anatomy [3, 5–8]. Furthermore, the craniocervical junction (CCJ) has a dynamic complex anatomic relationship between the occiput and the atlantoaxial structures. Congenitally anomalous CCJ can lead to an acute or chronic disability related to spinal cord compression [1, 9]. Most anomalies of the CCJ are asymptomatic and occult without the presence of an underlying syndrome that may herald its presence such as Klippel-Feil, Goldenhar syndrome, or numerous additional skeletal dysplasias [10]. We present a case of spinal cord injury without radiographic abnormality (SCIWORA) secondary to minor trauma in a pediatric patient with a congenital left atlanto-occipital assimilation joint.

Endoscopically Assisted Anterior Release and Reduction Through Anterolateral Retropharyngeal Approach for Fixed Atlantoaxial Dislocation

A prospective study. To evaluate a novel technique involving an endoscopically assisted anterior release and reduction through an anterolateral retropharyngeal approach with minimum follow-up interval of 31 months. Irreducible atlantoaxial dislocation is typically a chronic process that requires surgical treatment. However, the current literature does not agree on the single best method of treatment. Previously, the best outcomes have been reported with transoral reduction followed by anterior or posterior fixation. Despite recent innovations, numerous complications remain associated with this approach. About 21 consecutive irreducible atlantoaxial dislocation patients with mean age of 32 years underwent endoscopically assisted anterior release and reduction through the anterolateral retropharyngeal approach followed by posterior fixation. The primary pathologies included 8 late odontoid fractures, 7 cases of os odontoideum, 5 with laxity of the transverse ligament, and 1 with atlanto-occipital assimilation with a hypoplastic odontoid. Neurologic status was evaluated using the Japanese Orthopedic Association scoring system. Radiographic parameters including the atlantodental interval (ADI) and cervicomedullary angle were also measured. Follow-up data were obtained for a minimum of 31 months. Anatomic reduction was achieved in 20 cases and near-anatomic reduction in 1 case. All patients had an uneventful recovery with significant improvement in neurologic function and radiographic parameters. No complications were seen. The atlantodental interval was corrected from an average 6.3 mm before surgery to 2.7 mm after surgery (P < 0.01). The cervicomedullary angle was also corrected from an average 109 degrees before surgery to 152 degrees after surgery (P < 0.01). Preoperative muscle strength was on average 3.5 (on scale from 1 to 5) and improved after surgery to 4.5 (P < 0.01). The average preoperative and postoperative Japanese Orthopedic Association scores were 9.6 and 15.5, respectively, indicating 82.8% improvement. Endoscopically assisted anterior retropharyngeal release combined with posterior fixation is a safe and effective alternative for the treatment of irreducible atlantoaxial dislocation.