Anatomical determinants of occipitocervical fusion in skull base chordoma resection: a systematic review of the literature with illustrative cases

OBJECTIVE

Skull base chordomas are rare, locally osseo-destructive lesions that present unique surgical challenges due to their involvement of critical neurovascular and bony structures at the craniovertebral junction (CVJ). Radical cytoreductive surgery improves survival but also carries significant morbidity, including the potential for occipitocervical (OC) destabilization requiring instrumented fusion. The published experience on OC fusion after CVJ chordoma resection is limited, and the anatomical predictors of OC instability in this context remain unclear.

METHODS

PubMed and Embase were systematically searched according to the PRISMA guidelines for studies describing skull base chordoma resection and OC fusion. The search strategy was predefined in the authors' PROSPERO protocol (CRD42024496158).

RESULTS

The systematic review identified 11 surgical case series describing 209 skull base chordoma patients and 116 (55.5%) who underwent OC instrumented fusion. Most patients underwent lateral approaches (n = 82) for chordoma resection, followed by midline (n = 48) and combined (n = 6) approaches. OC fusion was most often performed as a second-stage procedure (n = 53), followed by single-stage resection and fusion (n = 38). The degree of occipital condyle resection associated with OC fusion was described in 9 studies: total unilateral condylectomy reliably predicted OC fusion regardless of surgical approach. After lateral transcranial approaches, 4 studies cited at least 50%-70% unilateral condylectomy as necessitating OC fusion. After midline approaches-most frequently the endoscopic endonasal approach (EEA)-at least 75% unilateral condylectomy (or 50% bilateral condylectomy) led to OC fusion. Additionally, resection of the medial atlantoaxial joint elements (the C1 anterior arch and tip of the dens), usually via EEA, reliably necessitated OC fusion. Two illustrative cases are subsequently presented, further exemplifying how the extent of CVJ bony elements removed via EEA to achieve complete chordoma resection predicts the need for OC fusion.

CONCLUSIONS

Unilateral total condylectomy, 50% bilateral condylectomy, and resection of the medial atlantoaxial joint elements were the most frequently described independent predictors of OC fusion in skull base chordoma resection. Additionally, consistent with the occipital condyle harboring a significantly thicker joint capsule at its posterolateral aspect, an anterior midline approach seems to tolerate a greater degree of condylar resection (75%) than a lateral transcranial approach (50%-70%) prior to generating OC instability.

Clinical characteristics of upper cervical spine injuries in children: a retrospective case series

OBJECTIVE

Pediatric cervical spine injuries (CSI) can be devastating, and children < 8 years are particularly at risk for upper CSI given unique anatomical differences. Diagnosis of these injuries can be delayed due to variable clinical presentations and a paucity of existing literature. The authors aimed to characterize the spectrum of pediatric upper CSI.

METHODS

This was a retrospective, single-center case series of trauma patients aged < 16 years who were assessed at a level I pediatric trauma center and diagnosed with upper CSI between 2000 and 2020. Patients were included if they had evidence of bony or ligamentous injury from the occiput to C2 on imaging or autopsy. Data were obtained from manual chart review and analyzed using descriptive statistics.

RESULTS

In total, 502 patients were screened and 202 met inclusion criteria. Of these, 31 (15%) had atlanto-occipital (AO) joint distractions, 10 (5%) had atlanto-axial (AA) joint distractions, 31 (15%) had fractures of C1-2, and 130 (64%) had ligamentous injury without joint distraction. Of the patients with AO injury, 15 patients had complete dislocation. They presented as hemodynamically unstable with signs of herniation and 14 died (93%). In contrast, 16 had incomplete dislocation (subluxation). They usually had stable presentations and survived with good outcomes. Of the patients with AA injury, 2 had complete dislocation, presented with arrest and signs of herniation, and died. In contrast, 8 patients with subluxation mostly presented as clinically stable and all survived with little residual disability. The most common fractures of C1 were linear fractures of the lateral masses and of the anterior and posterior arches. The most common fractures of C2 were synchondrosis, hangman, and odontoid fractures. Overall, these patients had excellent outcomes. Ligamentous injuries frequently accompanied other brain or spine injuries. When these injuries were isolated, patients recovered well.

CONCLUSIONS

Among upper CSI, AO and AA joint injuries emerged as particularly severe with high mortality rates. Both could be divided into complete dislocations or incomplete subluxations, with clear clinical differences and the former presenting with much more severe injuries. Lateral cervical spine radiography should be considered during resuscitation of unstable trauma patients to assess for these CSI subtypes. Fractures and ligamentous injuries were clinically heterogeneous, with presentations and outcomes depending on severity and associated injuries.

[Atlanto-occipital dislocation-A challenge with respect to making the diagnosis and treatment]

BACKGROUND

The correct diagnosis and treatment of the atlanto-occipital dislocation (AOD) remains a major challenge.

OBJECTIVE

To evaluate the different radiological diagnostic criteria for AOD and discuss potential treatment strategies based on a case with AOD and additional fracture of the atlas.

MATERIAL AND METHODS

A 29-year-old male patient is presented who suffered from AOD with concomitant fracture of the anterior and posterior arches of the atlas with rotational atlantoaxial dislocation following an accident in forestry. The following parameters were evaluated for the diagnosis and assessment of postoperative reduction: Powers ratio, the X‑lines-method, Wackenheim line, basion-dens interval (BDI), basion-axial interval (BAI) and occipital condyle-C1 interval (CCI).

RESULTS

Stabilization was performed by occipitocervical spondylodesis from C0 to C2/3. For final reduction it was necessary to reduce the malrotation of the atlas. In the presented case, the revised CCI proved to be a sensitive and valid yet practical parameter. Powers' ratio and the BDI were less suited for assessing the diagnosis. The X‑lines-method, Wackenheim line and the BAI did not adequately detect the pathological situation.

DISCUSSION

The AOD is a severe injury requiring immediate correct diagnosis for later adequate treatment results. Among the published parameters, the revised CCI proved to be a practical and valid parameter to detect AOD. For definitive treatment, the operative occipitocervical stabilization is regarded as the method of choice.

A morphometric study of the atlanto-occipital joint in adult patients with Chiari malformation type I

BACKGROUND

There are many morphometric studies on Chiari malformation type I (CMI) patients, most of which focus on the posterior cranial fossa (PCF). Less attention has been paid to the atlanto-occipital joint. In this study, we aim to evaluate the morphological characteristics of the atlanto-occipital joint in CMI patients.

MATERIALS AND METHODS

The cervical CT imaging data of adult patients diagnosed with CMI but without any bony malformation in craniovertebral junction (CVJ) who were treated by the authors between January 2014 and December 2019 were retrospectively analyzed. The equal number of sex and age-matched healthy individuals were included as the control group. The morphometric analysis was performed by measuring the length and depth of the atlanto-occipital joint, and the depth/length ratio was calculated to evaluate the curvature of the joint.

RESULTS

A total of 47 patients (15 males and 32 females) were included. The mean age of patients was 47.49 ± 9.01 years (range 19-62 years). The mean depth/length ratio of the atlanto-occipital joint in CMI patients was 0.141 ± 0.065 (range 0.027 - 0.274), which was smaller than that of control individuals (0.228 ± 0.057, range 0.069 - 0.379). And the difference was statistically significant (p < .01).

CONCLUSIONS

The atlanto-occipital joints in CMI patients are significantly flatter compared with those in healthy controls. This morphological variation could lead to differences of the atlanto-occipital stability between CMI patients and normal population, which may be related to the pathogenesis of CMI.

Reduction of Atlanto-Occipital Dislocation After Cervical Collar Removal

A 39-year-old male pedestrian-hit-by-car was transferred to our institution with atlantooccipital dislocation (AOD) on outside computed tomography (CT) imaging. On arrival he had a rigid cervical collar in place. Given the reported AOD, we placed the patient flat, removed the cervical collar, and supported the head in neutral alignment with sandbags. Due to a technical issue uploading his prior imaging to our system, the patient underwent repeat CTs at our center. Subsequently, after the outside images were uploaded, we were able to compare his cervical spine CT images before and after removing his cervical collar. On comparison, we noted a substantial reduction in AOD after collar removal. We hope this serves as a reminder of this key step in managing a rare but deadly clinical entity and a small demonstration of the efficacy of this intervention.

Radiologic Features of Atlas Occipitalization and Its Clinical Implications

STUDY DESIGN

Retrospective radiographic analysis.

OBJECTIVES

Evaluation of the anatomic features of the craniovertebral junction in patients with occipitalization with and without atlantoaxial dislocation (AAD).

SUMMARY OF BACKGROUND DATA

Atlas occipitalization is a common feature of congenital AAD and usually requires surgical intervention. However, not all instances of occipitalization necessarily lead to AAD. No study has specifically examined and compared the craniovertebral bony morphology in occipitalization with, and without, AAD.

MATERIALS AND METHOD

We reviewed computed tomography (CT) scans of 2500 adult outpatients. Occipitalization cases without AAD (ON) were selected. Meanwhile, a series of 20 inpatient occipitalization cases with AAD (OD) were obtained in parallel. Another 20 control cases without occipitalization were also included. Multi-directional reconstructed CT images of all cases were analyzed.

RESULTS

A total of 18 adults with ON were found in all 2500 outpatients (0.7%). Both anterior height and posterior height of C1 lateral mass in the control group were significantly larger than those in both the ON and OD groups, whereas posterior height in the OD group was significantly less than that in the ON group. Three morphologic types of the occipitalized atlas posterior arch were identified: Type I, bilateral sides were unfused with opisthion; Type II, unilateral side was unfused with opisthion, whereas the other side was fused; and Type III, bilateral sides were fused with opisthion. In the ON group, three cases were type I (17%), six cases were type II (33%), and nine cases were type III (50%). In the OD group, all 20 cases were type III (100%).

CONCLUSIONS

Atlas occipitalization with, and without, AAD results from a distinctly different bony morphology at the craniovertebral junction. The novel classification system based on reconstructed CT images may be useful in prognosticating AAD in the setting of atlas occipitalization.

Exploring the Pathogenesis of Atlanto-Occipital Instability in Chiari Malformation With Type II Basilar Invagination: A Systematic Morphological Study

BACKGROUND

Our previous study suggested that atlanto-occipital instability (AOI) is common in patients with type II basilar invagination (II-BI).

OBJECTIVE

To further understand the pathogenesis of AOI in Chiari malformations (CM) and CM + II-BI through systematic measurements of the bone structure surrounding the craniocervical junction.

METHODS

Computed tomography data from 185 adults (80 controls, 63 CM, and 42 CM + II-BI) were collected, and geometric models were established for parameter measurement. Canonical correlation analysis was used to evaluate the morphological and positional relationships of the atlanto-occipital joint (AOJ).

RESULTS

Among the 3 groups, the length and height of the condyle and superior portion of the lateral masses of the atlas (C1-LM) were smallest in CM + II-BI cases; the AOJ had the shallowest depth and the lowest curvature in the same group. AOJs were divided into 3 morphological types: type I, the typical ball-and-socket joint, mainly in the control group (100%); type II, the shallower joint, mainly in the CM group (92.9%); and type III, the abnormal flat-tilt joint, mainly in the CM + II-BI group (89.3%). Kinematic computed tomography revealed AOI in all III-AOJs (100%) and some II-AOJs (1.5%) but not in type I-AOJs (0%). Morphological parameters of the superior portion of C1-LM positively correlated with those of C0 and the clivus and significantly correlated with AOI.

CONCLUSION

Dysplasia of the condyle and superior portion of C1-LM exists in both CM and II-BI cases yet is more obvious in type II-BI. Unstable movement caused by AOJ deformation is another pathogenic factor in patients with CM + II-BI.

Atlanto-occipital dislocation with concomitant severe traumatic brain injury: A retrospective study at a level 1 trauma center

BACKGROUND

Traumatic atlanto-occipital dislocation (AOD) is a life-threatening injury. Although traumatic brain injury (TBI) is associated with increased mortality in AOD patients, a detailed individual analysis of these patients is lacking in the literature.

METHODS

Patients ≥16 years old who were diagnosed of AOD with concomitant severe TBI from 2010 to 2020 were included in this retrospective study. We examined the epidemiology, injury mechanisms, associated injuries, and outcomes of these patients.

RESULTS

Eight patients were included. Six patients died before any intervention could be performed, and two patients underwent an occipito-cervical fixation, showing a notorious neurologic improvement on follow-up. Cardiorespiratory arrest (CRA) was a strong predictor of subsequent death. CT signs of diffuse axonal injury (DAI) were present in most patients and were confirmed by magnetic resonance imaging (MRI) in survivors. Although TBI was not the main cause of death, it was responsible for the delayed neurological improvement and deferred stabilization. The average sensitivity of the different used methodologies for AOD diagnosis ranged from 0.50 to 1.00, being the Basion Dens Interval (BDI) and the Condyle-C1 interval (CCI) sum the most reliable criteria. Non-survivors tended to show greater distraction measurements. The high incidence of condylar avulsion fractures suggests that their visualization on the initial CT study should heighten the suspicion for AOD.

CONCLUSIONS

Our data suggest that patients with AOD and concomitant severe TBI might be salvageable patients. In those who survive beyond the first hospital days and show neurological improvement, surgical treatment should be performed as they can achieve an important neurologic recovery.

An osteometric and 3D analysis of the atlanto-occipital joint: An initial screening method to exclude crania and atlases in commingled remains

OBJECTIVES

The anatomical features of the atlanto-occipital joint can be potentially useful in re-associating or excluding crania to atlases in commingled remains. This study investigated whether linear measurements and the 3-dimensional (3D) surface of occipital condyles and articular facets of atlases can represent valid insights for this purpose.

METHODS

The variations among eight corresponding linear distances were analyzed in a sample of 150 individuals through six supervised machine learning techniques attempting to develop classifiers able to identify elements belonging to the same individual. Furthermore, a 3D analysis was conducted on the articular surfaces through superimpositions of 3D models of corresponding and non-corresponding crania and atlases obtained by using respectively stereophotogrammetry and laser scanning. This analysis investigated differences in terms of point-to-point distances (Root Mean Square, RMS) of superimposed 3D surfaces.

RESULTS

None of the six machine learning techniques were able to correctly detect a satisfying percentage of correspondent pairs in the overall sample by using the linear variables. The 3D analysis of the articular surfaces found RMS values over 0.53 mm only for superimposed non-corresponding surfaces, which sets a threshold value to identify 32% of incorrect pairs.

DISCUSSION

The re-association of cranium to atlas proved to be challenging and hardly possible when considering only metric variables. However, the 3D geometry of the articular surfaces represents a valid variable for this purpose and 3D analyses pave the way for an initial exclusion of incorrect re-associations, thus should not be considered as a re-association method per se, but as an exclusionary screening technique.

The relationship between radiologic parameters and transverse atlantal ligament injury obtained from MRI scans in patients with an isolated atlas burst fracture: A retrospective observational study

The treatment of an atlas burst fracture depends on whether transverse atlantal ligament (TAL) injury is present. We compared the radiologic parameters associated with the presence of a TAL injury as detected using magnetic resonance imaging (MRI), and verified whether the lateral mass displacement (LMD) criteria currently used to diagnose TAL injuries in atlas burst fractures are reliable or need revision.Thirty patients who presented with isolated atlas burst fractures were included in this retrospective observational study. We measured radiologic parameters, including LMD, atlanto-dental interval, basion-dens interval, internal lateral mass displacement, and external lateral mass displacement, in each patient at the time of initial presentation. The presence of TAL injury was evaluated using MRI. We compared the radiologic parameters and characteristics of patients who presented with TAL injury. We also determined the sensitivity and specificity of an LMD test to accurately diagnose TAL injury based on MRI. Finally, we compared the radiologic parameters according to the presence of surgical treatment and patient union status.Twenty patients presented with an intact TAL, while 10 patients had a TAL injury on MRI. LMD was significantly higher in patients with TAL injury (9.61 vs 3.73 mm, P < .001). In multivariable logistic regression analysis, LMD was also significantly higher in patients with TAL injury. The sensitivity and specificity of LMD for diagnosing TAL injury based on MRI in patients with isolated C1 fractures were 90% and 100%, respectively. The incidence of an LMD greater than 8.1 mm was statistically higher in patients than in those without TAL injury (90% vs 0%, P < .001).Nine patients underwent surgery for isolated atlas burst fractures, and 21 did not. LMD (9.56 vs 4.03 mm, P < .001) and fracture gap (7.96 vs 4.01 mm, P < .001) were significantly higher in patients who underwent surgery.Among the various radiologic parameters, LMD closely correlated with the presence of TAL injury, as patients with an LMD greater than 8.1 mm were more likely to have a TAL injury in the case of atlas burst fractures. LMD is a good method for predicting the presence of TAL injury if MRI is not available.

Atlanto-occipital Dissociation in the Setting of Relatively Normal Radiologic Findings

BACKGROUND

Craniocervical junction (CCJ) dislocations are often fatal. Atlanto-occipital dissociation can be challenging to diagnose, especially in patients who present with absent or subtle radiologic signs.

CASE DESCRIPTION

A neurologically intact 37-year-old patient presented to the hospital following a high-speed motor vehicle accident. Initial computed tomography scans showed normal CCJ anatomy, but magnetic resonance imaging (MRI) of the CCJ was performed to further evaluate perimesencephalic subarachnoid hemorrhage. MRI revealed partial disruption of the anterior atlantoaxial membrane and tectorial membrane as well as complete disruption of the posterior atlanto-occipital membrane, ligamentum flavum, and apical ligament, signifying atlanto-occipital dissociation. Halo spinal immobilization was performed in preparation for stabilization with posterior occipitocervical fusion; however, the CCJ distracted widely during surgery owing to the accident-related dislocation, signifying an unstable fracture. Posterolateral fusion was performed, and the distraction injury was corrected via posterior surgical instrumentation.

CONCLUSIONS

Normal occiput-C1 craniometric parameters in the setting of unexplained perimesencephalic subarachnoid hemorrhage does not eliminate the possibility of missed or delayed diagnosis of traumatic atlanto-occipital dissociation injuries. Cervical MRI without contrast should be considered in patients with vertebral artery dissection or perimesencephalic subarachnoid hemorrhage after a blunt injury with neck pain. When MRI shows evidence of disruption of ≥2 atlanto-occipital ligaments, surgical stabilization should be considered, as these are clinically very unstable injuries.

Posterior atlantoaxial facet joint reduction, fixation and fusion as revision surgery for failed suboccipital decompression in patients with basilar invagination and atlantoaxial dislocation: Operative nuances, challenges and outcomes

OBJECTIVE

To report the technical nuances and clinical outcomes of posterior atlantoaxial facet joint reduction, fixation and fusion (AFRF) technique as a revision procedure for BI and AAD patients with failed suboccipital decompression and large occipital bone defect.

PATIENTS AND METHODS

We reviewed 32 patients with BI and AAD who were misdiagnosed as a simple Chiari malformation and received a suboccipital decompression surgery before admission. All patients underwent AFRF as a revision surgery. The separating, fusing, opacifying and false-coloring-volume rendering (SFOF-VR) technique was used to identify the course of the VA. Clinical and radiological outcomes were assessed after revision surgeries.

RESULTS

Clinical symptoms improved in all patients. The postoperative atlantodens interval, Wackenheim line and clivus-canal angle significantly improved (all P < 0.01). Intraoperative dural tear and cerebrospinal fluid leakage occurred in 3 patients and were managed by suture repair and lumbar drain. Abnormal VA was identified in 7 patients and no VA injury occurred with the aid of SFOF-VR technique. The average follow-up was 19.1 months and atlantoaxial bone fusion was confirmed in 31 patients.

CONCLUSION

For BI and AAD patients with failed suboccipital decompression, revision surgery is challenging. Occipitocervical fixation and posterior midline bone grafting are rather difficult due to the large occipital bone defect. The current study demonstrated that the posterior AFRF is a simple, safe and highly effective technique in revision surgery for such cases. For VA variations, the SFOF-VR technique is an effective tool to delineate the course VA.

Glass Fragment Injury to the Craniocervical Junction with Interatlantooccipital Penetration to the Subarachnoid Space: Not-To-Be-Missed Important Aspects of Craniocervical Trauma Even in the Middle of the COVID-19 Pandemic: Case Report and Review of Literature

BACKGROUND

Nonmissile penetrating injuries to the craniocervical junction caused by a glass fragment are rare, and a standard management strategy has not been established.

CASE DESCRIPTION

A 75-year-old Japanese man was brought into our emergency department after receiving a left retroauricular stab wound by broken glass fragments. After spinal immobilization, a computed tomography (CT) scan revealed glass fragments penetrating at the right craniocervical junction to the interatlantooccipital subarachnoid space. CT angiography showed that both vertebral arteries were not injured. Magnetic resonance imaging demonstrated that the glass fragments did not penetrate the cervical cord or medulla oblongata. These glass fragments were removed via a midline incision from the external occipital protuberance to the C7 and with laminectomy without suboccipital craniectomy. Five of the glass fragments were found and removed in total. The dural defect was patched with a free fascia autograft. His postoperative course was uneventful. Postoperative CT angiography showed that both vertebral arteries were intact and the glass fragments had been removed completely.

CONCLUSIONS

CT graphical diagnosis is useful for the management of penetrating craniocervical junction trauma, and it should be considered in the evaluation of patients who have suffered craniocervical penetrating injury even in the absence of major wounds or bleeding. Spinal immobilization of patients with craniocervical penetrating injuries is crucial to avoid not only secondary neurologic damage but also secondary critical vascular damage. Incomplete or inadequate assessment of craniocervical stab wounds results in unexpected hazards that are preventable.

A Novel Instrumentation Approach in a Pediatric Patient with Atlanto-Occipital Dislocation and Cervical Fracture: Case Report

BACKGROUND

Although instrumented stabilization of pediatric atlanto-occipital dislocation (AOD) has been described in the literature, there is little evidence regarding instrumentation techniques in pediatric patients presenting with both AOD and a cervical fracture. We present a case of a 2-year-old male involved in a motor vehicle collision with an unstable C2 fracture and AOD, treated with an occiput-C4 posterior arthrodesis using a rod, crosslink, and cable construct.

CASE DESCRIPTION

This patient suffered a type III C2 fracture and AOD with 4 mm craniocaudal and 3 mm anterior displacement. In the operating room, 2 cobalt chrome connecting rods (3.5 mm) were connected to 1 another with crosslinks at C2 and C4. These were affixed with suboccipital and sublaminar cables at C1, C2, and C4. At 14 months postoperatively, his spine is clinically and radiographically stable. He has spontaneous movement in all 4 extremities, and remains in a persistent vegetative state because of his underlying central nervous system injury.

CONCLUSIONS

Although there is a breadth of literature investigating instrumentation approaches to pediatric AOD, there is minimal evidence on outcomes of patients presenting with both AOD and cervical fracture. The technique we describe has proven safe and effective for this patient.

The myodural bridge complex defined as a new functional structure

PURPOSE

The connective tissue between suboccipital muscles and the cervical spinal dura mater (SDM) is known as the myodural bridge (MDB). However, the adjacent relationship of the different connective tissue fibers that form the MDB remains unclear. This information will be highly useful in exploring the function of the MDB.

METHODS

The adjacent relationship of different connective tissue fibers of MDB was demonstrated based upon three-dimensional visualization model, P45 plastinated slices and histological sections of human MDB.

RESULTS

We found that the MDB originating from the rectus capitis posterior minor muscle (RCPmi), rectus capitis posterior major muscle (RCPma) and obliquus capitis inferior muscle (OCI) in the suboccipital region coexists. Part of the MDB fibers originate from the ventral aspect of the RCPmi and, together with that from the cranial segment of the RCPma, pass through the posterior atlanto-occipital interspace (PAOiS) and enter into the posterior aspect of the upper cervical SDM. Also, part of the MDB fibers originate from the dorsal aspect of the RCPmi, the ventral aspect of the caudal segment of the RCPma, and the ventral aspect of the medial segment of the OCI, enter the central part of the posterior atlanto-axial interspace (PAAiS) and fuse with the vertebral dura ligament (VDL), which connects with the cervical SDM.

CONCLUSIONS

Our findings prove that the MDB exists as a complex structure which we termed the 'myodural bridge complex' (MDBC). In the process of head movement, tensile forces could be transferred possibly and effectively by means of the MDBC. The concept of MDBC will be beneficial in the overall exploration of the function of the MDB.

The Alar Ligaments: A Cadaveric and Radiologic Comparison Study

OBJECTIVE

A precise anatomical description of the alar ligaments is important to better understand their biomechanical and pathologic implications. Although there are several studies regarding their anatomy, the literature is inconsistent. To our knowledge, there are no reports that compare cadaveric morphologic findings with computed tomography (CT) images of the alar ligaments.

METHODS

Eight sides from 4 fresh-frozen cadaveric specimens were used in this study. After routine dissection of the craniocervical junction, the alar ligaments were exposed. We carried out measurements of the alar ligaments, their position within the craniovertebral junction, and their relation to the dens and adjacent structures. Fine-cut CT of the specimens was performed, and the measurements were later compared with the original cadaveric dissections.

RESULTS

Alar ligaments were attached to the upper half of the lateral surface of the dens and ran laterally to its insertion just medial to the occipital condyle. The ligaments were found to have an ovoid cross-sectional area with a nearly horizontal caudocranial trajectory and comparable diameters in both anteroposterior and superoinferior directions between the CT and cadaveric measurements.

CONCLUSIONS

There were small but not statistically significant differences in the measurements between the cadaver specimens and the CT images. There was however, a strong correlation between the proximal and distal insertions, as well as the orientation of the fibers, that suggests CT images can be an appropriate approach to the study of the anatomical and 3-dimensional features of the alar ligaments.

Ankylosing Spondylitis and Neck Pain: MRI Evidence for Joint and Entheses Inflammation at the Craniocervial Junction

BACKGROUND

Magnetic resonance imaging (MRI), which has recently become the leading imaging modality in the study of ankylosing spondylitis (AS), has not been evaluated in the assessment of disease-specific changes at the craniocervical junction (CCJ) in patients with AS.

OBJECTIVES

To describe the spectrum of active inflammatory lesions at the CCJ using MRI in a cohort of patients with AS and neck pain.

METHODS

The study included 18 patients with AS presenting with neck pain and a control group of 9 fibromyalgia patients matched for age and levels of neck pain. All patients underwent a focused rheumatologic examination, X-ray of the cervical spine, and a 3T MRI study, which included STIR, CUBE T2, FSE and FSE FAT SAT sequences before and after administration of gadolinium.

RESULTS

The median age of AS patients was 43 years with a median disease duration of 7 years. Fifteen of 18 patients were under biologic treatment. Seven of 18 AS patients had evidence of cervical syndesmophytes on X-ray films. Active inflammatory lesions of atlanto-occipital joints and apical and alar ligaments were detected in MRIs in 2 out of the 18 patients with AS and in none of the patients with fibromyalgia. Both AS patients with active inflammation of CCJ detected on MRI received treatment with biological agents prior to and during the study.

CONCLUSIONS

Active inflammation of both entheses and joints of the CCJ can be demonstrated by MRI in patients with AS.

Exploration for reliable radiographic assessment method for hinge-like hypermobility at atlanto-occipital joint

PURPOSE

Hinge-like hyper-mobility is occasionally observed at the atlanto-occipital (O-C1) joint. However, it has not been clear if this kind of hinge-like hyper-mobility at the O-C1 joint should be regarded as "pathologic", or referred to as "instability". To solve this issue, we aimed to establish a reliable radiographic assessment method for this specific type of O-C1 instability and figure out the "standard value" for the range of motion (ROM) of the O-C1 joint.

METHODS

To figure out the standard range of the O-C1 angle, we acquired magnetic resonance imaging (MRI) sagittal views of the cervical spine for 157 healthy volunteers [average: 37.4 year-old (yo)] without spine diseases, at neutral, maximum flexion and maximum extension positions.

RESULTS

The average value (AVE) for ROM of O-C1 angle was 9.91°. The standard value for ROM of O-C1 angle was calculated as 0°-21°. There was no statistically significant gender difference. We also found that the older population (≧ 40 yo) significantly had a larger ROM of O-C1 angle (AVE: 11.72°) compared to the younger population (< 40 yo) (AVE: 8.99°).

CONCLUSIONS

We consider that hinge-like instability at O-C1 joint, which cannot be assessed by measuring Powers ratio, can be assessed by measuring the range of O-C1 angles using dynamic-MRI. Evaluation of O-C1 instability is important especially when we perform surgical treatment for diseases with upper cervical instability (such as retro-odontoid pseudotumor). We consider that the current study provides important information in such a case.

Pediatric Craniovertebral Junction Surgery

The craniovertebral junction (CVJ) has attracted more attention in pediatric medicine in recent years due to the progress in surgical technologies allowing a direct approach to the CVJ in children. The CVJ is the site of numerous pathologies, most originating in bone anomalies resulting from abnormal CVJ development. Before discussing the surgical approaches to CVJ, three points should be borne in mind: first, that developmental anatomy demonstrates age-dependent mechanisms and the pathophysiology of pediatric CVJ anomalies; second, that CT-based dynamic simulations have improved our knowledge of functional anatomy, enabling us to locate CVJ lesions with greater certainty; and third, understanding the complex structure of the pediatric CVJ also clarifies the surgical anatomy. This review begins with a description of the embryonic developmental process of the CVJ, comprising ossification and resegmentation of the somite. From the clinical perspective, pediatric CVJ lesions can be divided into three categories: developmental bony anomalies with or without instability, stenotic CVJ lesions, and others. After discussing surgery and management based on this classification, the author describes surgical outcomes on his hands, and finally proceeds to address controversial issues specific for pediatric CVJ surgery. The lessons, which the author has gleaned from his experience in pediatric CVJ surgery, are also presented briefly in this review. Recent technological progress has facilitated pediatric surgery of the CVJ. However, it is important to recognize that we are still far from reliably and consistently obtaining satisfactory results. Further progress in this area awaits contributions of the coming generations of pediatric surgeons.

Diagnostic Utility of Increased STIR Signal in the Posterior Atlanto-Occipital and Atlantoaxial Membrane Complex on MRI in Acute C1-C2 Fracture

BACKGROUND AND PURPOSE

Acute C1-C2 fractures are difficult to detect on MR imaging due to a paucity of associated bone marrow edema. The purpose of this study was to determine the diagnostic utility of increased STIR signal in the posterior atlanto-occipital and atlantoaxial membrane complex (PAOAAM) in the detection of acute C1-C2 fractures on MR imaging.

MATERIALS AND METHODS

Eighty-seven patients with C1-C2 fractures, 87 with no fractures, and 87 with other cervical fractures with acute injury who had both CT and MR imaging within 24 hours were included. All MR images were reviewed by 2 neuroradiologists for the presence of increased STIR signal in the PAOAAM and interspinous ligaments at other cervical levels. Sensitivity and specificity of increased signal within the PAOAAM for the presence of a C1-C2 fracture were assessed.

RESULTS

Increased PAOAAM STIR signal was seen in 81/87 patients with C1-C2 fractures, 6/87 patients with no fractures, and 51/87 patients with other cervical fractures with 93.1% sensitivity versus those with no fractures, other cervical fractures, and all controls. Specificity was 93.1% versus those with no fractures, 41.4% versus those with other cervical fractures, and 67.2% versus all controls for the detection of acute C1-C2 fractures. Isolated increased PAOAAM STIR signal without increased signal in other cervical interspinous ligaments showed 89.7% sensitivity versus all controls. Specificity was 95.3% versus those with no fractures, 83.7% versus those with other cervical fractures, and 91.4% versus all controls.

CONCLUSIONS

Increased PAOAAM signal on STIR is a highly sensitive indicator of an acute C1-C2 fracture on MR imaging. Furthermore, increased PAOAAM STIR signal as an isolated finding is highly specific for the presence of a C1-C2 fracture, making it a useful sign on MR imaging when CT is either unavailable or the findings are equivocal.

Imaging Atlantooccipital and Atlantoaxial Traumatic Injuries

Cervical spine injuries, specifically the atlantooccipital joint and atlantoaxial joint, often involve the spinal canal or large blood vessels that supply blood to the brain. Patient handling, transport, and positioning for imaging plays an important role in diagnosis, treatment, and patient prognosis. This article discusses cervical spine anatomy, specific traumatic spinal injuries, and radiography's role in treating these injuries. Treatment options and imaging before and after treatment also are discussed, and a description of dose reduction techniques is included.

Core curriculum illustration: traumatic atlanto-occipital dislocation

This is the 20th installment of a series that will highlight one case per publication issue from the bank of cases available online as part of the American Society of Emergency Radiology (ASER) educational resources. Our goal is to generate more interest in and use of our online materials. To view more cases online, please visit the ASER Core Curriculum and Recommendations for Study online at: http://www.aseronline.org/curriculum/toc.htm .

Normal Development and Measurements of the Occipital Condyle-C1 Interval in Children and Young Adults

BACKGROUND AND PURPOSE

Widening of the occipital condyle-C1 interval is the most specific and sensitive means of detecting atlanto-occipital dislocation. Recent studies attempting to define normal measurements of the condyle-C1 interval in children have varied substantially. This study was performed to test the null hypothesis that condyle-C1 interval morphology and joint measurements do not change as a function of age.

MATERIALS AND METHODS

Imaging review of subjects undergoing CT of the upper cervical spine for reasons unrelated to trauma or developmental abnormality was performed. Four equidistant measurements were obtained for each bilateral condyle-C1 interval on sagittal and coronal images. The cohort was divided into 7 age groups to calculate the mean, SD, and 95% CIs for the average condyle-C1 interval in both planes. The prevalence of a medial occipital condyle notch was calculated.

RESULTS

Two hundred forty-eight joints were measured in 124 subjects with an age range of 2 days to 22 years. The condyle-C1 interval varies substantially by age. Average coronal measurements are larger and more variable than sagittal measurements. The medial occipital condyle notch is most prevalent from 1 to 12 years and is uncommon in older adolescents and young adults.

CONCLUSIONS

The condyle-C1 interval increases during the first several years of life, is largest in the 2- to 4-year age range, and then decreases through late childhood and adolescence. A single threshold value to detect atlanto-occipital dissociation may not be sensitive and specific for all age groups. Application of this normative data to documented cases of atlanto-occipital injury is needed to determine clinical utility.

Atlanto-occipital dislocation: case report and discussion

Atlanto-occipital dislocation (AOD) is a devastating condition that frequently results in prehospital cardiorespiratory arrest and accounts for 15% of fatal spinal trauma. Atlanto-occipital dislocation occurs 5 times more commonly in children than adults, and is believed to be caused by hyperextension. Because of improvements in prehospital resuscitation, more victims with AOD now survive to reach the emergency department. Neurologic injury is usually severe secondary to ligamentous disruption that allows the cranium to move with respect to the cervical spine, and associated facial and head injuries are common. There are, however, reports of survivors without neurologic deficits. We present the case of a 46-year-old woman who suffered an AOD after a motor vehicle crash and we discuss the diagnosis of this condition. The signs of AOD are often subtle, and the possibility of this diagnosis must be kept in mind in all patients with a neck injury, even in the absence of neurologic signs. A systematic approach to assessing the cranio-cervical relationship on the lateral cervical x-ray and the appropriate use of CT scanning is essential to identifying AOD. Through this case report we hope to familiarize clinicians with mechanisms of injury and appropriate imaging interpretation that will assist in the diagnosis of AOD.

Occipitocervical junction: imaging, pathology, instrumentation

The occipitocervical junction (OCJ) is a highly specialized area of the spine. Understanding the unique anatomy, imaging, and craniometry of this area is paramount in recognizing and managing the potentially devastating effects that pathology has on it. Instrumentation techniques continue to evolve, the goal being to safely obtain durable, rigid constructs that allow immediate stability, anatomical alignment, and osseous fusion. This article reviews the pathologic conditions at the OCJ and the current instrumentation and fusion options available for treatment. The general orthopedist needs to recognize the pathology common in this region and appropriately refer patients for treatment.

Atlanto-occipital ligament calcification: a novel sign in nevoid basal cell carcinoma syndrome

BACKGROUND

The nevoid basal cell carcinoma syndrome (NBCCS), first described by Gorlin and Goltz in 1960, is a hereditary autosomal dominant disease with high penetrance and variable expressivity. Almost 70% of patients with NBCCS have some degree of craniofacial anomaly. Among these, the presence of ectopic calcification have been reported but Atlanto-occipital ligament calcification has never been described. Therefore this investigation was carried out to determine the prevalence of atlanto-occipital ligament calcification on lateral x-ray of NBCCS patients aiming to assess the effectiveness of this sign in NBCCS diagnosis.

PATIENTS AND METHODS

Lateral and frontal cephalometric radiographs of 18 patients (11 males and 7 females), aged 8-61 years, with the diagnosis of NBCCS were evaluated for the presence of intracranial calcifications (diaphragma sellae and falx cerebri) and or calcification of the atlanto-occipital ligament.

RESULTS

A total of 11 patients presented calcification of atlanto-occipital ligament to various degrees and in three cases this represented the only sign of ectopic calcification. When compared to the other two sites of ossification, atlanto-occipital ligament calcification had a similar prevalence.

CONCLUSION

The calcification of the atlanto-occipital ligament should be considered in addition to the other major criteria for NBCCS diagnosis.

Geometry of the articular facets of the lateral atlanto-axial joints in the case of occipitalization

This study investigates if atlanto-occipital fusion affects the size and geometrical configuration of the articular facets of the atlanto-axial joint. Morphometric analysis was performed on the male adult skull, the occipital bone of which is assimilated with the first cervical vertebrae (the atlas). The perimeter, Feret's diameter, surface area, and circularity of the inferior articular fa-cets were measured. However, we did not observe significant bilateral differences in size of the inferior articular facets of the assimilated atlas compared to normal first cervical vertebrae. Geometrical conformation of the articular facets of the atlas and axis was assessed using a coordinate measuring machine (PMM - 12106, Leitz). The results obtained from this machine indicated that the inferior articular facets of the assimilated atlas presented asymmetrical orientation compared to the normal anatomy of the atlas. Hence, in the case of occipitalization, the gap between the articulating facets of the atlas and the axis was measured to be greater than in the normal atlanto-axial joint. Computer assisted tomography was applied to visualise the anatomical relationship between the inferior articular facets of the assimilated atlas and the corresponding facets located on the axis. In this case, radiographic examination revealed that the bilaterally articulating facets (inferior and superior) showed disproportion in their adjustment within the lateral atlanto-axial joints. Thus, we concluded that the fusion of the atlas with the occipital bone altered the geometry of the inferior articular facets of the atlas and influenced the orientation of the superior articular facets of the axis.

A biomechanical rationale for C1-ring osteosynthesis as treatment for displaced Jefferson burst fractures with incompetency of the transverse atlantal ligament

Nonsurgical treatment of Jefferson burst fractures (JBF) confers increased rates of C1-2 malunion with potential for cranial settling and neurologic sequels. Hence, fusion C1-2 was recognized as the superior treatment for displaced JBF, but sacrifies C1-2 motion. Ruf et al. introduced the C1-ring osteosynthesis (C1-RO). First results were favorable, but C1-RO was not without criticism due to the lack of clinical and biomechanical data serving evidence that C1-RO is safe in displaced JBF with proven rupture of the transverse atlantal ligament (TAL). Therefore, our objectives were to perform a biomechanical analysis of C1-RO for the treatment of displaced Jefferson burst fractures (JBF) with incompetency of the TAL. Five specimens C0-2 were subjected to loading with posteroanterior force transmission in an electromechanical testing machine (ETM). With the TAL left intact, loads were applied posteriorly via the C1-RO ramping from 10 to 100 N. Atlantoaxial subluxation was measured radiographically in terms of the anterior antlantodental interval (AADI) with an image intensifier placed surrounding the ETM. Load-displacement data were also recorded by the ETM. After testing the TAL-intact state, the atlas was osteotomized yielding for a JBF, the TAL and left lateral joint capsule were cut and the C1-RO was accomplished. The C1-RO was subjected to cyclic loading, ramping from 20 to 100 N to simulate post-surgery in vivo loading. Afterwards incremental loading (10-100 N) was repeated with subsequent increase in loads until failure occurred. Small differences (1-1.5 mm) existed between the radiographic AADI under incremental loading (10-100 N) with the TAL-intact as compared to the TAL-disrupted state. Significant differences existed for the beginning of loading (10 N, P = 0.02). Under physiological loads, the increase in the AADI within the incremental steps (10-100 N) was not significantly different between TAL-disrupted and TAL-intact state. Analysis of failure load (FL) testing showed no significant differences among the radiologically assessed displacement data (AADI) and that of the ETM (P = 0.5). FL was Ø297.5 +/- 108.5 N (range 158.8-449.0 N). The related displacement assessed by the ETM was Ø5.8 +/- 2.8 mm (range 2.3-7.9). All specimens succeeded a FL >150 N, four of them >250 N and three of them >300 N. In the TAL-disrupted state loads up to 100 N were transferred to C1, but the radiographic AADI did not exceed 5 mm in any specimen. In conclusion, reconstruction after displaced JBF with TAL and one capsule disrupted using a C1-RO involves imparting an axial tensile force to lift C0 into proper alignment to the C1-2 complex. Simultaneous compressive forces on the C1-lateral masses and occipital condyles allow for the recreation of the functional C0-2 ligamentous tension band and height. We demonstrated that under physiological loads, the C1-RO restores sufficient stability at C1-2 preventing significant translation. C1-RO might be a valid alternative for the treatment of displaced JBF in comparison to fusion of C1-2.

Mandibular condylar fractures and acute atlanto-axial subluxation Part 2 A physiopathological factor for the cervical spine sprain

AIM

The aim of this study was to analyze the physiopathology of the acute cervical injure in the event of mandibular condylar fractures.

METHODS

As in the Part 1, 25 non-consecutive cases of condylar mandibular fractures (16 males and 9 females, mean age: 22.96/range 14-36 years) observed and treated in the Maxillofacial Surgery Department of the University of L'Aquila, have been studied. Types of fractures examined included: unilateral: 19 cases (solitary: 12; associated with other mandibular fractures: 7, homolateral: 2); bilateral: 6 cases (equivalent: 2, not equivalent: 4). A control group was constituted of 10 patients, 5 males and 5 females, aged from 19 to 24 years (mean range: 21.6) suffering from acute isolated cervical distorsion (whiplash). The study has been performed by means of the analysis of X-ray and computed tomography (CT)-CT/3D of the mandibular condylar regions, the occipital-atlanto-axial structures and the cervical region.

RESULTS

In all the patients the following constant alterations that link up with these fractures have been observed: the rotation of atlas, the atlanto-axial subluxation and the derangement of the occipital-atlanto-epistropheal joint, homolateral to the side of the mandibular condylar fracture. The cervical spine shows the constant loss of physiological lordosis with hinge between C3 and C4. In the whiplash, as the authors have been able to assess in the control group, there are no alterations of occipital-atlanto-axial joint and the kinetic vector is placed on the longitudinal plane. In the mandibular condylar fractures the kinetic mechanism is completely different regarding the whiplash. The point of entry is the chin and the kinetic vector is oriented down-up, sometimes oblique in the opposite side. Subsequently the kinetic force is transmitted throughout the mandibular structure and causes the condylar or bicondylar fracture. The kinetic vector is placed before on the vertical plane, then on the horizontal plane and later on the vertical plane. Therefore the dynamics of the crash cannot cause the swaying of the head as in the whiplash. Indeed in the mandibular condylar fractures the authors have observed the cervical distortion with the loss of lordosis on the sagittal plane without whiplash and also a constant derangement of the cranio-cervical joint and the atlanto-axial subluxation.

CONCLUSIONS

These results allow to delineate a different physiopathological mechanism: in the event of mandibular condylar fractures, the sprain of the cervical spine seems to be caused by the acute atlanto-axial subluxation.

Mandibular condylar fractures and acute atlanto-axial subluxation. Part 1 - A new clinical and nosographic evidence

AIM

The aim of this study was to analyze the acute repercussions of condylar mandibular fractures on occipital-atlanto-axial joint.

METHODS

Twenty-five non-consecutive cases (16 males and 9 females, mean age: 22.96/range 14-36 years), observed and treated in the Maxillofacial Surgery Department of the University of L'Aquila have been considered. Types of fractures examined included: unilateral: 19 cases (solitary: 12; associated with other mandibular fractures: 7; homolateral: 2); bilateral: 6 cases (equivalent: 2; not equivalent: 4). A control group was constituted of 10 patients, 5 males and 5 females, aged from 19 to 24 years (mean-range: 21.6) suffering from acute isolated cervical distorsion (whiplash). The study has been performed by means of the analysis of X-ray and computed tomography (CT)-CT/3D of the mandibular condylar regions, the occipital-atlanto-axial structures and the cervical region.

RESULTS

In all the cases of fractures of the mandibular condyle an acute alteration of the junctional atlanto-axial structures was present. In case of unilateral solitary condylar fractures the authors have observed an atlas rotation, homolateral to the side of the condylar fracture, independent from the level of the fracture (intra- or extracapsular). The rotation seems to be proportional to the entity of the condylar fragments dislocation on the horizontal plane and it causes a modification of the articular relations between atlas and axis (atlanto-axial subluxation) and between the atlas and the occipital bone. The authors have observed a constant derangement of the cranio-axial joint on the three planes of the space. In particular, on the vertical plane the CT reconstructions show on the right and left side a different height between the atlanto-axial articular spaces. The largest one is homolateral to the side of the condylar fracture. In case of unilateral condylar fractures associated with other mandibular fracture (homolateral or not) the authors have observed the same alterations of the occipital-atlo-epistropheal joint, but while on the horizontal plane the rotation of the atlas is always homolateral to the condylar fracture, on the vertical plane the largest atlanto-axial articular space is homolateral to the mandibular fracture with more dislocation of the fragments of fracture (usually the associated not homolateral mandibular fracture). In case of bilateral condylar fractures the authors have observed no alteration of the cranio-cervical joint. In the non-equivalent fractures, they have observed the atlas rotation on the horizontal plane and the junctional derangement on the vertical plane, homolateral to the condylar fracture with greatest dislocation. In the control group the loss of the physiological cervical lordosis has been observed. Alterations on the horizontal and vertical planes, as the rotation of the atlas, atlanto-axial subluxation or the joint derangement, instead, has never revealed.

CONCLUSIONS

The authors state that these results represent a new nosographic entity associated with the condylar mandibular fractures with important clinical, insurance and legal repercussions.

Craniovertebral junction lesions: our experience with the transoral surgical approach

The aim of this study is to review our experience with the transoral surgical management of anterior craniovertebral junction (CVJ) lesions with particular attention to the decision making and to the indication for a consecutive stabilization. During 10 years (1998-2007), 52 consecutive patients presenting exclusively fixed anterior compression at the cervicomedullary junction underwent transoral surgery. Mean age was 55.85 years (range 17-75 years). Encountered lesions were: malformation (32 cases), rheumatoid arthritis (11 cases), tumor (5 cases) or trauma (4 cases). A total of 79% of patients presented with chronic/recurrent headache (cranial and/or high-cervical pain), 73% with varying degrees of quadrip aresis, and 29% with lower cranial nerve deficits. All of the patients but two, with posterior stabilization performed elsewhere, underwent synchronous anterior decompression and posterior occipitocervical fixation. Adjuncts to the transoral approach (Le Fort I with or without splitting of the palate), tailored to the local anatomy and to the extension of the lesions, were performed in seven cases. Follow-up ranged between 4 and 96 months. Of 35 patients with severe preoperative neurological deficits, 33 improved. The remaining 15 patients who presented with mild symptoms, healed throughout the follow-up. Perioperative mortality occurred in two cases and surgical morbidity in eight cases (dural laceration, cerebrospinal fluid leak with meningitis, malocclusion, oral wound dehiscence and occipital wound infection). Delayed instability occurred in one patient because of cranial settling of C2 vertebral body. A successful surgery achieving a stable decompression at the CVJ is an expertise demanding procedure. It requires accurate preoperative evaluation and, appropriate choice of decompression technique and stabilization instruments. Enlarged transoral approaches (despite higher morbidity) are a supportive means in cases of severe basilar invagination, cranial extension of the lesion or limited jaw mobility.

C1-C2 arthrodesis after transoral odontoidectomy and suboccipital craniectomy for ventral brain stem compression in Chiari I patients

Chiari I malformations are often associated with congenital craniocervical anomalies such as platybasia, basilar invagination, and retroflexion of the odontoid process. Management of ventral brain stem compression associated with Chiari I malformations remains controversial, but several authors report a significant rate of failure with suboccipital decompression alone in the presence of pronounced ventral brain stem compression (VBSC). Treatment options described in the literature for these patients involve anterior, posterior, or combined decompressions with or without concurrent arthrodesis. A combined anterior and posterior approach provides a definitive circumferential decompression but also significantly disrupts the stability of the occipitocervical junction usually necessitating occipitocervical fixation. We describe an alternative surgical treatment for Chiari I patients with significant ventral brain stem compression where a combined anterior and posterior decompression was considered necessary. We report two patients who underwent transoral odontoidectomy with preservation of the anterior arch of the atlas and suboccipital craniectomy with C1 laminectomy followed by C1-C2 arthrodesis. Preservation of the anterior arch of the atlas in conjunction with C1-C2 arthrodesis stabilizes the occipito-atlanto-axial segments while conserving more cervical mobility as compared to an occipitocervical fusion.

Relationship between the morphology of the atlanto-occipital joint and the radiographic results in patients with atlanto-axial subluxation due to rheumatoid arthritis

The upper cervical spine is a common focus of destruction from rheumatoid arthritis (RA). Atlanto-axial subluxation (AAS) presents with marked frequency among patients with instability. However, there are occasional patients who show no motion between the occipital bone and atlas on a dynamic cervical radiograph in AAS patients. This study investigated the morphology of the atlanto-occipital joint (AOJ) in AAS patients due to RA using computed tomography, and examined the relationship between its morphology and other radiographic results. Twenty-six consecutive patients with AAS due to RA treated by surgery were reviewed. The subjects included 18 females and 8 males. The average patient age was 59.3 years. The mean duration of RA was 14.3 years. In all the patients, the AOJ was morphologically evaluated using sagittal reconstruction view on computed tomography before surgery. Moreover, the ADI value was investigated at the neutral and maximal flexion position, and atlanto-axial angle (AAA) at the neutral position in preoperative lateral cervical radiographs. The morphology of the AOJ on a CT sagittal reconstruction view was classified into three types as follows: a normal type which showed a maintenance of the joint space, a narrow type which showed a disappearance of the joint space and a fused type which showed the fusion of the AOJ. The pre-operative CT sagittal reconstruction image of the AOJ demonstrated a normal type bilaterally in six cases (Group A). In 15 cases (Group B), CT image demonstrated narrowing on at least one side of the AOJ. In five cases (Group C), CT images demonstrated fusion on at least one side of the AOJ. The average ADI value at the flexion position was 10.7 mm in Group A, 11.7 mm in Group B, and 12.6 mm in Group C. There was no significant difference among those groups. The average ADI value at the neutral position before surgery was 2.8 mm in Group A, 5.9 mm in Group B, and 10.4 mm in Group C. There was no significant difference between Group A and B (P > 0.105), and Groups B and C (P > 0.032), however, there was a significant difference between Groups A and C (P < 0.004). The average AAA value was 25.3 degrees in Group A, 19.3 degrees in Group B and 3.4 degrees in Group C. There was no significant difference between Groups A and B (P > 0.230), however, there was a significant difference between Groups A and C (P < 0.002), and Groups B and C (P < 0.007). This study showed that fusion or ankylosis of the AOJ induced an enlargement of the ADI and anterior inclination of the atlas in the neutral position, despite the fact that normal findings of AOJ showed a slight displacement of the atlas to axis in RA patients showing AAS involvement. This morphology may progress to SAS and VS due to AOJ after atlanto-axial arthrodesis.

Reassessment of the craniocervical junction: normal values on CT

BACKGROUND AND PURPOSE

As the standard of care for the evaluation of the cervical spine shifts from plain radiographs to multidetector row CT (MDCT), a re-examination of the normal anatomic relationships of the occipitovertebral articulations is needed. We aimed to define the normal anatomic relationships of craniocervical articulations on MDCT and address any discrepancies with currently accepted ranges of normal on plain radiographs.

MATERIALS AND METHODS

A total of 200 patients underwent an MDCT scan of the cervical spine with multiplanar reconstructions (MPR). We measured the basion-axial interval (BAI), basion-dens interval (BDI), Powers ratio, atlantodental interval (ADI), and atlanto-occipital interval (AOI) in each patient. After statistical analysis, we compared these values to previously accepted data on plain radiographs.

RESULTS

Ninety-five percent of the population was found to have a BDI less than 8.5 mm compared with 12 mm on data from plain radiographs. The Powers ratio demonstrated no significant difference compared with data obtained by plain radiographs. Ninety-five percent of the population was found to have an ADI less than 2 mm, compared with 3 mm previously accepted. The AOI demonstrated 95% of the population ranged between 0.5 mm and 1.4 mm. The BAI was difficult to reproduce on CT images.

CONCLUSION

Normal values for the craniocervical relationships on MDCT are significantly different from the accepted ranges of normal on plain radiographs. We propose these values as normal for the adult population.

ATLANTO-OCCIPITAL DISLOCATION

OBJECTIVE

Although atlanto-occipital dislocation has long been recognized as an extremely unstable and often lethal injury, no single radiodiagnostic criterion published to date has achieved failure-proof status. This is because most existing diagnostic tests exploit bony landmarks remote from the injured condyle–C1 (OC1) joint so that patient positioning could inadvertently line up these landmarks and conceal actual disruption of the joint. Many of the landmarks used are wide apart and/or noncoplanar; their measurements are subject to errors related to x-ray angle, target–film distance, and superimposed bony outlines. We propose using the actual occipital condyle–C1 interval (CCI) obtained from high-resolution reconstructed computed tomographic scans as the indicator for OC1 joint disruption. We hypothesize that the normal CCI is very small and has great left-right symmetry and that atlanto-occipital dislocation is always manifested by an abnormal widening of the CCI and/or by left-right joint asymmetry irrespective of the shifting of other remote bony landmarks. Part I of this study establishes standard normal values for CCI in children.

METHOD

Sagittal and coronal reformatted images were obtained from thin axial computed tomographic scans performed on 89 children, 18 for nontraumatic complaints and 71 as part of a minor head trauma protocol but later exonerated for cervical injury. The interval between condyle and C1 was measured at four equidistant points on the joint surface on the sagittal and coronal images of all 178 joints (left and right) in the group. Sagittal and coronal CCIs are the means of four sagittal and four coronal measurements, respectively. The combined or true CCI for an individual joint was taken as the mean of both the sagittal and coronal (total of eight) measurements.

RESULTS

The mean combined CCI of all 178 joints was 1.28 mm ± 0.26 (standard deviation [SD]). None of the 178 CCIs exceeded 1.95 mm, and none of the individual joint interval measurements exceeded 2.5 mm. Left-right symmetry was tested by computing the mean left-right difference in CCI from all 89 subjects equal to 0.047 mm ± 0.002 (SD); or only 3% of the mean combined CCI. When the mean of all right CCIs (1.333 mm ± 0.31 SD) is contrasted with the mean of all left CCIs (1.327 mm ± 0.30 SD), the difference is 0.006 mm, or 1.09% of the mean total CCI (P = 0.792). Left-right symmetry is also apparent in conformational anatomy in both sagittal and coronal images. Linear regression analysis between CCI and age shows no statistical difference in CCI between age groups from 0.5 to 18 years. Linear regression performed separately on the right and left CCIs suggests that left-right symmetry is also stable through this age range.

CONCLUSION

The normal OC1 joint in children 0 to 18 years is tightly held together by ligaments with a mean CCI of 1.28 mm in the 89 subjects tested. There is great left–right joint symmetry in both CCI and conformational anatomy. CCI and left-right symmetry do not appear to change significantly with age. It is reasonable to set a maximum CCI as a discriminator between normal and disrupted OC1 joints to indicate atlanto-occipital dislocation.

Occipitoatlantoaxial instability and congenital thoracic vertebral deformity in Pierre Robin sequence: a case report

STUDY DESIGN

Case report of a patient with Pierre Robin sequence who presented with occipitoatlantoaxial instability and congenital thoracic deformity.

OBJECTIVE

As there are lack of similar cases in the literature, we would like to introduce a case of a patient with associated malformations, the consultations that we consider that are obligatory, and our decision-making process. We would also like to demonstrate the follow-up plan and the further key points about either the conservative or the surgical solution of the problem.

SUMMARY OF BACKGROUND DATA

The occurrences of 2 malformations (Pierre Robin sequence and occipitoatlantoaxial instability) together are very rare. We have found only 1 publication in the related literature about this topic. We consider that this rare appearance is due to the difficulty in diagnosing this problem. There is no clinical evidence that musculoskeletal examinations are indicated in a patient with Pierre Robin sequence, and it is difficult to check for all the possible deformities.

METHOD

As congenital scoliosis appeared only at 6 years of age in the case of this child with Pierre Robin syndrome, we promptly began to investigate for other musculoskeletal defects. We would like to demonstrate the investigation process and emphasize the necessity of conventional and functional radiographs, computed tomography, and magnetic resonance images.

RESULTS

We have not found similar cases to refer to, so we made our decision about conservative treatment of the craniocervical instability knowing that we will have to follow up the progression of both the congenital thoracic scoliotic deformity and the occipitoatlantoaxial instability later.

CONCLUSION

To recognize a rare case is a big challenge indeed due to the lack of the investigational protocol, the key points of the decision process, the prognostic classification system, and the progression of the disease. We recommend that one should individualize and follow up the patient frequently.

Atlantoaxial subluxation–induced myelopathy in cleidocranial dysplasia

✓The authors describe the clinical course and treatment of a patient with cleidocranial dysplasia in whom spastic myelopathy developed due to atlantoaxial subluxation. This 27-year-old woman with cleidocranial dysplasia and a history of atlantoaxial subluxation presented with spastic myelopathy. Surgery was performed twice for cervical myelopathy and atlantoaxial subluxation, including laminectomy at the atlas and cervicooccipital fusion in which the Luque rod system was used, as well as C1–2 fusion via the transpharyngeal route. Solid bone fusion was achieved by 7 months postsurgery. Postoperative magnetic resonance imaging studies demonstrated that spinal cord compression was relieved, but atrophy persisted. At 2 years postsurgery there was no neurological disease progression, but spasticity persisted. The patient could walk with a cane. Cleidocranial dysplasia is an extremely rare cause of myelopathy in patients with atlantoaxial subluxation; the authors know of only two reports of this condition. When managing cleidocranial dysplasia, the practitioner should always be aware that atlantoaxial subluxation may be the cause of cervical myelopathy.

Craniocervical junction arachnoid cyst causing hydrocephalus: case report and review of the literature

OBJECTIVE

Arachnoid cysts (ACs) of the craniocervical junction are extremely rare entities. This report describes a craniocervical junction AC with unusual clinical course at an unusual anatomical location.

METHODS

A 21-year-old man was admitted to our clinic after a craniospinal trauma. Examination was unremarkable. Computed tomography scans demonstrated mild to moderately enlarged third and the lateral ventricles, but the fourth ventricle was typically normal. Neuroimaging studies obtained after the onset of clinical symptoms revealed marked enlargement of the ventricular system and a new cyst formation at the C1-2 level which was absent before. He underwent suboccipital craniectomy and C1-2 laminectomies. The cyst was fenestrated into subarachnoid space.

RESULTS

He made a good recovery. The histopathological diagnosis was confirmed as AC.

CONCLUSION

Due to rarity of this clinical entity, we urge readers to keep in mind the possibility of the development of this kind of AC with unusual clinical course.

Bone morphogenetic protein for salvage fusion in an infant with Down syndrome and craniovertebral instability. Case report

The authors describe the use of bone morphogenetic protein (BMP) to promote bone fusion in an infant with craniovertebral instability after two attempts at arthrodesis had failed. To their knowledge, this is the first such report. Management of craniovertebral instability remains challenging in infants with Down syndrome. Surgical treatment may result in nonunion in this patient population. The authors report on a 4-month-old boy with Down syndrome who suffered a high cervical spinal cord injury secondary to craniovertebral instability. Two attempts to fuse and stabilize the craniovertebral junction resulted in nonunion. Finally, the use of BMP led to a stable fusion construct within 6 months without encroachment on the spinal canal. At 4 years of follow up, the patient has a solid fusion mass. The case suggests a role for the use of BMP to promote fusion in this patient population.

Diagnosis and treatment of a chronic atlanto-occipital subluxation in a dog

A 6-year-old Labrador retriever-cross was evaluated for an abnormal gait and head carriage 6 weeks after suffering trauma. The dog was presented with an ambulatory tetraparesis and was reluctant to move his head. Myelography and computed tomography demonstrated a subluxation of the atlanto-occipital joint with compression of the spinomedullary junction and the brain stem by the occipital bone. Removal of the compressive part of the occipital bone resulted in improvement of the clinical signs within 6 weeks, and resolution of clinical signs occurred 8 months after surgery.

Occipitalization of the atlas in children. Morphologic classification, associations, and clinical relevance

BACKGROUND

Occipitalization is defined as a congenital fusion of the atlas to the base of the occiput. We are not aware of any previous studies addressing the morphologic patterns of occipitalization or the implications of occipitalization in children. We present data on what we believe is the largest reported series of children with occipitalization studied with computed tomography and/or magnetic resonance imaging, and we provide a description of their clinical characteristics.

METHODS

We retrospectively reviewed all cases of occipitalization in children included in our spine database. Patient charts and imaging studies were reviewed. A new morphologic classification of occipitalization was developed from the two-dimensional sagittal and coronal reformatted computed tomographic reconstructions and/or magnetic resonance images. The classification includes four patterns according to the anatomic site of occipitalization (Zones 1, 2, and 3 and a combination of those zones), and it was applied to this group of patients. Imaging studies were also reviewed for evidence of cervical instability and for other anomalies of the craniovertebral junction.

RESULTS

Thirty patients with occipitalization were identified. There were twenty-four boys and six girls with a mean age of 6.5 years. The morphologic categorization was Zone 1 (a fused anterior arch) in six patients, Zone 2 (fused lateral masses) in five, Zone 3 (a fused posterior arch) in four, and a combination of fused zones in fifteen. Seventeen patients (57%) had atlantoaxial instability, and eight of them had an associated C2-C3 fusion. Eleven patients (37%) had spinal canal encroachment, and five of them had clinical findings of myelopathy. The highest prevalence of spinal canal encroachment (63%) was noted in patients with occipitalization in Zone 2.

CONCLUSIONS

Occipitalization is associated with abnormalities that lead to narrowing of the space available for the spinal cord or brainstem. The risk of atlantoaxial instability developing is particularly high when there is an associated congenital C2-C3 fusion. Two-dimensional sagittal and coronal reformatted computed tomographic reconstructions and/or magnetic resonance images can help to establish the diagnosis and permit categorization of occipitalization in three zones, each of which may have a different prognostic implication.

The sniffing position provides greater occipitoatlanto-axial angulation than simple head extension: A radiological study

PURPOSE

While the anatomic sniffing position has traditionally been considered the standard head and neck position for laryngoscopy, recent evidence suggests that the sniffing position provides no significant advantage over simple head extension. To establish if the sniffing position provides an anatomic advantage, we compared the occipito-atlanto-axial extension angle, a key determinant for obtaining a good laryngeal view during laryngoscopy, in simple head extension and sniffing positions.

METHODS

Thirty volunteers with normal cervical spines were studied. Radiological examinations of the lateral cervical spine were taken and compared in each of the following three positions for each subject: neutral position (flat on the table with no pillow and without head extension or flexion); simple head extension (head maximally extended without a pillow); and the sniffing position (head extension with cervical flexion obtained by 7 cm occipital elevation).

RESULTS

Mean angles of the occipito-atlanto-axial extension in simple head extension and the sniffing position were 20.4 degrees+/-5.1 degrees and 24.2 degrees+/-5.6 degrees, respectively (P<0.01).

CONCLUSION

The anatomic sniffing position provides greater occipito-atlanto-axial extension compared to simple head extension. These findings should be taken into consideration when optimizing patient positioning for laryngoscopy.

Concomitant fracture of bilateral occipital condyle and inferior clivus: what is the mechanism of injury?

With the routine use of multi-slice high resolution computed tomography, increasing number of occipital condyle fractures have been reported in the last decade. The authors report a very rare case of bilateral occipital condyle fracture complicated by the fracture of the inferior clivus and discuss the possible mechanisms of injury.

Basilar impression in osteogenesis imperfecta: can it be treated with halo traction and posterior fusion?

Basilar impression (BI) and hydrocephalus complicating osteogenesis imperfecta (OI) is usually treated by anterior transoral decompression and posterior fixation. Nevertheless, it may be questioned if posterior fusion following axial halo traction is adequate in patients with symptomatic BI complicating OI. We report on a case with progressive symptomatic hydrocephalus and BI complicating OI that was successfully treated by halo traction followed by posterior occipitocervical fusion. However, after a symptom free interval of 2 years the patient suffered from recurrence of symptomatic hydrocephalus needing additional ventriculoperitoneal (VP) shunt placement. In conclusion, posterior fusion without additional VP shunt placement may not be effective in the long term for ameliorating symptoms and signs and halting progressive hydrocephalus in BI complicating OI.