Hypoglossal canal: an osteological and morphometric study on a collection of dried skulls in an Italian population: clinical implications

BACKGROUND

The hypoglossal canal is a dual bone canal at the cranial base near the occipital condyles. The filaments of the hypoglossal nerve pass through the canal. It also transmits the meningeal branch of the ascending pharyngeal artery, the venous plexus and meningeal branches of the hypoglossal nerve. The hypoglossal nerve innervates all the intrinsic and extrinsic muscles of the tongue except the palatoglossal and is fundamental in physiological functions as phonation and deglutition. A surgical approach to the canal requires knowledge of the main morphometric data by neurosurgeons.

METHODS

The present study was carried out on 50 adult dried skulls: 31 males: age range 18-85 years; 19 females: age range 26-79 years. The skulls came from the ''Leonetto Comparini'' Anatomical Museum. The skulls belonged to people from Siena (Italy) and its surroundings (1882-1932) and, therefore, of European ethnicity. The present study reports (a) the osteological variations in hypoglossal canal (b) the morphometry of hypoglossal canal and its relationship with occipital condyles. One skull had both the right and left hypoglossal canals occluded and, therefore, could not be evaluated. None of the skulls had undergone surgery.

RESULTS

We found a double canal in 16% of cases, unilaterally and bilaterally in 2% of cases. The mean length of the right and left hypoglossal canals was 8.46 mm. The mean diameter of the intracranial orifice and extracranial orifice of the right and left hypoglossal canals was 6.12 ± 1426 mm, and 6.39 ± 1495 mm. The mean distance from the intracranial end of the hypoglossal canal to the anterior and posterior ends of occipital condyles was 10,76 mm and 10,81 mm. The mean distance from the intracranial end of the hypoglossal canal to the inferior end of the occipital condyles was 7,65 mm.

CONCLUSIONS

The study on the hypoglossal canal adds new osteological and morphometric data to the previous literature, mostly based on studies conducted on different ethnic groups.The data presented is compatible with neuroradiological studies and it can be useful for radiologists and neurosurgeons in planning procedures such as transcondilar surgery. The last purpose of the study is to build an Italian anatomical data base of the dimensions of the hypoglossal canal in dried skulls..

Three-Dimensional Anatomy of the Hypoglossal Canal: A Plastinated Histologic Study

OBJECTIVE

To provide a precise description of the morphology and morphometry of the hypoglossal canal (HC) and its relationship with surrounding structures by using the epoxy sheet plastination technique.

METHODS

Thirty human cadaveric heads were plastinated into 5 sets of gross transparent plastination slices and 43 sets of ultrathin plastination sections. The HC were examined at both macro- and micro levels in these plastination sections and the reconstructed 3-dimensional visualization model.

RESULTS

The HC was an upward arched bony canal with a dumbbell-shaped lumen. According to the arched trajectory of its bottom wall, the HC could be divided into a medial ascending segment and a lateral descending segment. The thickness of the compact bone in the middle part of the HC was thinner than that at the intracranial and extracranial orifices. In 14 of 43 sides (32.6%), the posterior wall or the roof of the HC were disturbed by passing venous channels which communicated the posterior condylar emissary vein and the inferior petroclival vein. The trajectory of hypoglossal nerve in HC is mainly from anterosuperior to posteroinferior. The meningeal dura and the arachnoid extended into the HC along the hypoglossal nerve to form the dural and arachnoid sleeves and then fused with the nerve near the extracranial orifice of the HC.

CONCLUSIONS

Knowledge of the detailed anatomy of the HC can be helpful in avoiding surgical complications when performing surgery for lesions and the occipital condylar screw placement in this complex area.

Retrospective evaluation of the morpometric and morphological anatomy of the occipital condyle, hypoglossal canal and foramen magnum in Turkish populaton with CBCT

PURPOSE

The aim of this study is to morphometrically and morphologically examine the occipital condyle, which is an important anatomical region in terms of surgery and forensic medicine, and its surrounding structures, to evaluate the change in mean values according to gender and age, and to evaluate the correlation of the measurements obtained.

METHODS

180 (90 men, 90 women) CBCT images selected from the archive of Ankara University Faculty of Dentistry. Occipital Condyle length and width, Hypoglossal Canal-Basion distance, Hypoglossal Canal-Opistion distance, Hypoglossal Canal-Occipital Condyle anterior and posterior border distance, Occipital Condyle thickness, Hypoglossal Canal length, the widest diameter of Hypoglossal Canal, the narrowest diameter of the Hypoglossal Canal, the length of the Jugular Tubercle, the width of the Jugular Tubercle, the anterior intercondylar distance, the posterior intercondylar distance, and the Foramen Magnum index were measured. At the same time, the presence of septum or spicule in the hypoglossal canal and protrusion of the occipital condyle were evaluated. The relationship of age, gender, anterior and posterior intercondylar distance, and foramen magnum index measurements with all measurements were examined.

RESULTS

In our study, all measurements were repeated 1 month after the first measurements to evaluate the intra-observer agreement, and the agreement between the obtained measurements and the first measurements was evaluated by calculating the intraclass correlation coefficient and 95% confidence intervals. Men's measurements were found to be significantly higher than women's measurements. When the coefficients of concordance in all measurements were examined, it was observed that there was a perfect concordance.

CONCLUSION

When the results of the study are evaluated, it is seen that the values ​​obtained are generally close to the studies related to CT. Considering this, an idea can be gained as to whether CBCT, which has a lower dose and less cost, can be used as an alternative to CT in studies to be conducted with more comprehensive and different methods in skull base surgical planning.

Morphological analysis and morphometry of the occipital condyle and its relationship to the foramen magnum, jugular foramen, and hypoglossal canal: implications for craniovertebral junction surgery

Anatomical knowledge of the occipital condyle (OC) and its relationships to surrounding structures is important for avoiding injury during craniovertebral junction (CVJ) surgeries. This study was conducted to evaluate the morphology and morphometry of OC and its relationship to foramen magnum, jugular foramen (JF), and hypoglossal canal (HC). Morphometric parameters including length, width, height, and distances from the OC to surrounding structures were measured. The oval-like condyle was the most common OC shape, representing for 33.0% of all samples. The mean length, width and height of OC were 21.3±2.4, 10.5±1.4, and 7.4±1.1 mm, respectively. Moreover, OC was classified into three types based on its length. The most common OC length in both sexes was moderate length or type II (62.5%). The mean distance between anterior tips and posterior tips of OC to basion, and opisthion were 11.5±1.4, 39.1±3.3, 25.2±2.2, and 27.4±2.7 mm, respectively. The location of intracranial orifice of HC was commonly found related to middle 1/3 of OC in 45.0%. JF was related to the anterior 2/3 of OC in 81.0%, the anterior 1/3 of OC in 12.5%, and the entire OC length in 6.5%. These morphological analysis and morphometric data should be taken into consideration before performing surgical operation to avoid CVJ instability and neurovascular structure injury.

Unique presentation of occipital condyle giant cell tumor as occipital condyle syndrome - A review

Giant cell tumors (GCTs) of the skull are rare and only a few case series with limited number of cases have been reported till date. In the cranium, GCT usually occurs in the sphenoid and temporal bone, occipital condyle GCTs are very rare. We report a rare presentation of GCT of the occipital condyle manifested as occipital condyle syndrome. Despite gross total resection, they can recur aggressively; the presence of cortical breach might be an indicator of aggressiveness prompting early post-operative imaging and adjuvant therapy.

AO Spine upper cervical injury classification system: a description and reliability study

BACKGROUND CONTEXT

Prior upper cervical spine injury classification systems have focused on injuries to the craniocervical junction (CCJ), atlas, and dens independently. However, no previous system has classified upper cervical spine injuries using a comprehensive system incorporating all injuries from the occiput to the C2-3 joint.

PURPOSE

To (1) determine the accuracy of experts at correctly classifying upper cervical spine injuries based on the recently proposed AO Spine Upper Cervical Injury Classification System (2) to determine their interobserver reliability and (3) identify the intraobserver reproducibility of the experts.

STUDY DESIGN/SETTING

International Multi-Center Survey.

PATIENT SAMPLE

A survey of international spine surgeons on 29 unique upper cervical spine injuries.

OUTCOME MEASURES

Classification accuracy, interobserver reliability, intraobserver reproducibility.

METHODS

Thirteen international AO Spine Knowledge Forum Trauma members participated in two live webinar-based classifications of 29 upper cervical spine injuries presented in random order, four weeks apart. Percent agreement with the gold-standard and kappa coefficients (ƙ) were calculated to determine the interobserver reliability and intraobserver reproducibility.

RESULTS

Raters demonstrated 80.8% and 82.7% accuracy with identification of the injury classification (combined location and type) on the first and second assessment, respectively. Injury classification intraobserver reproducibility was excellent (mean, [range] ƙ=0.82 [0.58-1.00]). Excellent interobserver reliability was found for injury location (ƙ = 0.922 and ƙ=0.912) on both assessments, while injury type was substantial (ƙ=0.689 and 0.699) on both assessments. This correlated to a substantial overall interobserver reliability (ƙ=0.729 and 0.732).

CONCLUSIONS

Early phase validation demonstrated classification of upper cervical spine injuries using the AO Spine Upper Cervical Injury Classification System to be accurate, reliable, and reproducible. Greater than 80% accuracy was detected for injury classification. The intraobserver reproducibility was excellent, while the interobserver reliability was substantial.

Safety analysis and complications of condylar screws in a single-surgeon series of 250 occipitocervical fusions

Objective

Condylar screw fixation is a rescue technique and an alternative to the conventional configuration of occipitocervical fusion. Condylar screws are utilized when previous surgical bone removal along the supraocciput has occurred which makes anchoring of a traditional barplate technically difficult or impossible. However, the challenging dissection of C0-1 necessary for condylar screw fixation and the concerns about possible complications have, thus far, prevented the acquisition of large surgical series utilizing occipital condylar screws. In the largest case series to date, this paper aims to evaluate the safety profile and complications of condylar screw fixation for occipitocervical fusion.

Methods

A retrospective safety and complication-based analysis of occipitocervical fusion via condylar screws fixation was performed.

Results

A total of 250 patients underwent occipitocervical fusions using 500 condylar screws between September 2012 and September 2018. No condylar screw pullouts, or vertebral artery impingements were observed in this series. The sacrifice of condylar veins during the dissection at C0-1 did not cause any venous stroke. Hypotrophic condyles were found in 36.4% (91 of the 250) cases and did not prevent the insertion of condylar screws. Two transient hypoglossal deficits occurred at the beginning of this surgical series and were followed by recovery a few months later. Corrective strategies were effective in preventing further hypoglossal injuries.

Conclusions

This surgical series suggests that the use of condylar screws fixation is a relatively safe and reliable option for OC fusion in both adult and pediatric patients. Methodical dissection of anatomical landmarks, intraoperative imaging, and neurophysiologic monitoring allowed the safe execution of the largest series of condylar screws reported to date. Separate contributions will follow in the future to provide details about the long-term clinical outcome of this series.

Isolated traumatic occipital condyle fractures: Is external cervical orthosis even necessary?

Background:

Occipital condyle fractures (OCFs) have been reported in up to 4–16% of individuals suffering cervical spine trauma. The current management of OCF fractures relies on a rigid cervical collar for 6 weeks or longer. Here, we calculated the rate of acute and delayed surgical intervention (occipitocervical fusion) for patients with isolated OCF who were managed with a cervical collar over a 10-year period at a single institution.

Methods:

This was a retrospective analysis performed on all patients admitted to a Level 1 Trauma Center between 2008 and 2018 who suffered traumatic isolated OCF managed with an external rigid cervical orthosis. Radiographic imaging was reviewed by several board-certified neuroradiologists. Demographic and clinical data were collected including need for occipitocervical fusion within 12 months after trauma.

Results:

The incidence of isolated OCF was 4% (60/1536) for those patients admitted with cervical spine fractures. They averaged 49 years of age, and 58% were male falls accounted for the mechanism of injury in 47% of patients. Classification of OCF was most commonly classified in 47% as type I Anderson and Montesano fractures. Of the 60 patients who suffered isolated OCF that was managed with external cervical orthosis, 0% required occipitocervical fusion within 12 months posttrauma. About 90% were discharged, while the remaining 10% sustained traumatic brain/orthopedic injury that limited an accurate neurological assessment.

Conclusion:

Here, we documented a 4% incidence of isolated OCF in our cervical trauma population, a rate which is comparable to that found in the literature year. Most notably, we documented a 0% incidence for requiring delayed occipital-cervical fusions.

Morphometric analysis of foramen magnum and occipital condyle using CT images for sex determination in a Saudi Arabian population

OBJECTIVE OF THE STUDY

The objective of this study was to evaluate FM and occipital condyles measurements morphometrically for sex determination by using discriminant function analysis and to note visually the variation in the shape of the foramen magnum in a Saudi Arabian population by using CT scan images.

MATERIAL AND METHODS

This study included 472 CT scans (236 males and 236 females; age range, 18-72 years). The foramen magnum shapes were classified into 8 types: oval, egg, round, hexagonal, pentagonal, tetragonal, irregular (A) and irregular (B). The intraobserver and interobserver test was done to calculate the reliability of the measurement. Eight dimensions of the FM and occipital condyle were evaluated to determine the sexual dimorphism using an independent t-test. Sex determination was estimated using discriminate function analysis.

RESULTS

The commonest shape of FM was hexagonal and the tetragonal shape was the least common type. Coefficient of reliability (R) was high, ranging between 0.89 and 0.99, which indicates the measurements are reliable and sufficiently precise. All the eight measurements, the FM length and width, FM index, FM area, the width and length of right and left occipital condyles were significantly greater in males than the female. Univariate discriminant function showed an accuracy rate varying from 61% to 66.6% based on FM or occipital condyles measurements. The multivariate analysis of FM and occipital condyle measurements increased the overall accuracy rate of sex determination to 71.6%.

CONCLUSION

The univariate analysis of FM and occipital condyle measurements indicates, that the FM area (66.1%), FML (62.5%), FMW (62.5%) and ROCL (62.1%) could be reliable individual variables in sex determination. The multivariate analysis including all the eight variables of FM and occipital condyle increased the accuracy rate of sex determination to 71.6% in determining the sex as male (73.3%) or female (69.9%). The shape of the FM is not useful in sex estimation. The results obtained showed a low degree of sexual dimorphism in the basicranium, the use of this method in forensic anthropology could be helpful for assessment on highly fragmented skull bases.

Transcondylar Fossa Approach for Resection of Anterolateral Foramen Magnum Meningioma: 2-Dimensional Operative Video

Among the posterolateral corridors to the ventral foramen magnum (FM), the transcondylar fossa (supracondylar transjugular tubercle) approach (TCFA) is indicated for lesions lying anteriorly to the dentate ligament and above the jugular foramen and hypoglossal canal.^1-13 It involves the drilling of the condylar fossa, namely the exocranial surface of the jugular tubercle. Despite the anatomic variability of the condyle and posterior condylar emissary vein,^14,15 they are important landmarks for the TCFA. The extradural jugular tuberculectomy has no risk of iatrogenic mechanical instability compared with the transcondylar approach. This 2-dimensional operative video (Video 1) aims to show the key technical aspects of the TCFA through the case description of an anterolateral FM meningioma. A 35-year-old male patient with a left anterolateral FM meningioma underwent TCFA in a semisitting position. Drilling of the condylar fossa led to an extradural resection of the jugular tubercle. Posterior condylar emissary veins connecting the sigmoid sinus/jugular bulb with the vertebral venous plexus marked the lateral limit of the approach. Through a suprahypoglossal working corridor, the meningioma was debulked and dissected. Postoperative magnetic resonance imaging confirmed complete resection of the tumor, and the patient was discharged neurologically intact on the third postoperative day. TCFA is a valuable technical option for selected anterolateral FM meningiomas. The perfect knowledge and intraoperative use of specific anatomic landmarks are critical to safely perform the TCFA while maximizing the exposure of the surgical target and decreasing the risk of postoperative mechanical instability of the craniovertebral junction.

Feasibility of occipital condyle screw placement in patients with Chiari malformation type I: a computed tomography-based morphometric study

BACKGROUND

The occipital condyle (OC) screw is an alternative technique for occipitocervical fixation that is especially suitable for revision surgery in patients with Chiari malformation type I (CMI). This study aimed to investigate the feasibility and safety of this technique in patients with CMI.

METHODS

The CT data of 73 CMI patients and 73 healthy controls were retrospectively analyzed. The dimensions of OCs, including length, width, height, sagittal angle, and screw length, were measured in the axial, sagittal, and coronal planes using CT images. The OC available height was measured in the reconstructed oblique parasagittal plane of the trajectory.

RESULTS

The mean length, width, and height of OCs in CMI patients were 17.79 ± 2.31 mm, 11.20 ± 1.28 mm, and 5.87 ± 1.29 mm, respectively. All OC dimensions were significantly smaller in CMI patients compared with healthy controls. The mean screw length and sagittal angle were 19.13 ± 1.97 mm and 33.94° ± 5.43°, respectively. The mean OC available height was 6.36 ± 1.59 mm. According to criteria based on OC available height and width, 52.1% (76/146) of OCs in CMI patients could safely accommodate a 3.5-mm-diameter screw.

CONCLUSIONS

The OC screw is feasible in approximately half of OCs in CMI patients. Careful morphometric analyses and personalized surgical plans are necessary for the success of this operation in CMI patients.

A 360° Approach to the Craniovertebral Junction in a Cadaveric Laboratory Setting: Historical Insights, Current, and Future Perspectives in a Comparative Study

BACKGROUND

We herein outline the experience matured in our equipped Cranio-Vertebral Junction Laboratory for anatomic dissection.

METHODS

An extreme lateral approach (ELA) was performed on 4 fresh cadavers and submandibular approach was performed on 5. An endoscope and navigation-assisted far lateral approach (FLA) was performed in 5 injected specimens. In these specimens, a transoral approach was also performed, as well as a neuronavigation-assisted comparison between transoral and transnasal explorable distances.

RESULTS

As calculated with neuronavigation, statistically significant differences both in the explored craniocaudal (P = 0.003) and lateral (P = 0.008) distances were observed between the transoral approach and endoscopic endonasal approach. In FLA, neuronavigation facilitated identification and partial removal of the occipital condyle; in one case, during endoscopic intradural exploration, tearing of the emerging roots of the 11th cranial nerve occurred. In ELA, the site where the accessory nerve pierces into the sternocleidomastoid muscle was found at a distance from the tip of the mastoid between 3 and 4 cm.

CONCLUSIONS

During dissections, as in the clinical setting, endoscope and image guidance give the surgeon a constant orientation, increasing the accuracy and the safety of the approach. Nonetheless, the encumbrance of the endoscope could represent a limit in deep and narrow corridors as those running across the craniovertebral junction, especially in "oblique" FLA and ELA, in which the surgical target is often hidden by a delicate tangle of nerves and vessels. Its use appears more suitable and safer in "straight" approaches as transoral and transnasal in which there are no neurovascular structures interposed.

Quantitative Analysis of the Far-Lateral, Supra-Articular Transcondylar Transtubercular Approach Using Cadaveric Computed Tomography and Magnetic Resonance Imaging

BACKGROUND

Removing the jugular tubercle (JT) is regarded as an important step in the far-lateral approach; however, few cadaveric studies have objectively evaluated it.

OBJECTIVE

To quantitatively analyze the effect of JT removal in the far-lateral approach, using cadaveric computed tomography (CT) and magnetic resonance (MR) imaging.

METHODS

The far-lateral, supra-articular transcondylar transtubercular approach was employed on 23 sides of 13 formalin-fixed cadaveric heads. CT bone images were obtained before and after JT removal, and MR images were obtained before dissection and were merged with the CT bone images. The angles of attack used to approach the ventral region of the medulla, the distances between the medulla and the bony structure, and the volume of the paramedullary space were measured at the level of the JT on axial CT-MR fusion images. The values obtained after JT removal were compared with those obtained before JT removal.

RESULTS

All evaluated values were significantly increased after JT removal, including the angle of attack at the level of the JT (29.8 ± 7.4° vs 58.2 ± 15.5°, P < .001), the distance between the olive and the JT (6.4 ± 2.0 mm vs 9.5 ± 5.0 mm, P = .01), and the volume of the space around the medulla (0.28 ± 0.04 cm3 vs 0.47 ± 0.09 cm3, P < .001).

CONCLUSION

The paramedullary surgical working space widened by JT removal was quantitatively demonstrated in the cadaveric CT and MR imaging study. The measurement methods in this study can be applied to clinical cases and other skull base cadaveric studies.

Restabilization of the Occipitocervical Junction After a Complete Unilateral Condylectomy: A Biomechanical Comparison of Unilateral and Bilateral Fixation Techniques

BACKGROUND

Occipitocervical instability may result from transcondylar resection of the occipital condyle. Initially, patients may be able to maintain a neutral alignment but severe occipitoatlantal subluxation may subsequently occur, with cranial settling, spinal cord kinking, and neurological injury.

OBJECTIVE

To evaluate the ability of posterior fixation constructs to prevent progression to severe deformity after radical unilateral condylectomy.

METHODS

Eight human cadaveric specimens (Oc-C2) underwent biomechanical testing to compare stiffness under physiological loads (1.5 N m). A complete unilateral condylectomy was performed to destabilize one Oc-C1 joint, and the contralateral joint was left intact. Unilateral Oc-C1 or Oc-C2 constructs on the resected side and bilateral Oc-C1 or Oc-C2 constructs were tested.

RESULTS

The bilateral Oc-C2 construct provided the greatest stiffness, but the difference was only statistically significant in certain planes of motion. The unilateral constructs had similar stiffness in lateral bending, but the unilateral Oc-C1 construct was less stiff in axial rotation and flexion-extension than the unilateral Oc-C2 construct. The bilateral Oc-C2 construct was stiffer than the unilateral Oc-C2 construct in axial rotation and lateral bending, but there was no difference between these constructs in flexion-extension.

CONCLUSION

Patients who undergo a complete unilateral condylectomy require close surveillance for occipitocervical instability. A bilateral Oc-C2 construct provides suitable biomechanical strength, which is superior to other constructs. A unilateral construct decreases abnormal motion but lacks the stiffness of a bilateral construct. However, given that most patients undergo a partial condylectomy and only a small proportion of patients develop instability, there may be scenarios in which a unilateral construct may be appropriate, such as for temporary internal stabilization.

The Inferior Nuchal Line as a Simple Landmark for Identifying the Vertebral Artery During the Retrosigmoid Approach

BACKGROUND

The V3 segment of the vertebral artery (V3-VA) is at risk during various approaches to the craniovertebral junction. Several landmarks have been defined to identify V3-VA, but these landmarks are not routinely exposed during a retrosigmoid (RS) approach, where musculocutaneous dissection inferiorly towards the foramen magnum can threaten this arterial segment.

OBJECTIVE

To find a landmark that will identify the V3-VA during the RS approach, and analyze the inferior nuchal line (INL) as this novel landmark.

METHODS

The anatomic relationships between the INL and the V3-VA were assessed in 7 cadaveric heads through RS exposure in the lateral position.

RESULTS

The INL is an L-shaped bony ridge with horizontal (medial) and vertical (lateral) arms, with the vertical arm being more conspicuous in all specimens (INLV). The mean depths of the V3-VA relative to the medial and lateral ends of the INLV were (mean ± standard deviation) 24.9 ± 7.1 mm, and 8.3 ± 3.2 mm, respectively. In all specimens, the V3-VA was located inferior and anterior to the INLV.

CONCLUSION

The INL provides an important landmark during RS approach that can protect the V3-VA from inadvertent injury or identify it for use in an interpositional bypass. The INLV identifies the region of the suboccipital triangle where the V3-VA is embedded. INLV is routinely seen during the RS approach, making it more relevant than other classic landmarks such as the transverse process of C1, C1 posterior arch, and the atlantomastoid line that are not exposed during the RS approach.

Minimally Invasive Tubular Approach for Occipital Condylar Biopsy and Resection: Case Report and Review of Literature

BACKGROUND

Patients with isolated occipital condyle lesions concerning for metastases rarely undergo surgical biopsies and are more commonly treated with empirical radiation with or without chemotherapy. This is likely related to the morbidity associated with open condylar approaches and the importance of surrounding structures. We present a minimally invasive technique to approach the occipital condyle using a tubular dilating retractor system.

CASE DESCRIPTION

A 38-year-old woman with medical history of breast cancer presented with a 2-month history of headache localizing to the right occipital area and right tongue deviation. Magnetic resonance imaging revealed a heterogeneously enhancing mass within the right occipital condyle. The patient was brought into the operating room and placed in prone position. A 2-cm paramedian incision was made on the right approximately 2.5 cm off midline at the level of C1. Sequential dilation using a tubular retractor system was performed under fluoroscopic guidance. Once the condylar cortex was identified and entered, the tumor was immediately visualized and resected. Operative time was 65 minutes and estimated blood loss was 5 mL. The patient was discharged to home on postoperative day 1.

CONCLUSIONS

This report, to our knowledge, presents the first case of a minimally invasive tubular retractor system-based approach for biopsy and resection of an occipital condylar metastasis causing occipital condyle syndrome. This approach allows for tissue diagnosis to precisely dictate medical management and minimizes the morbidity associated with traditional open surgical approaches.

Contemporaneous avulsion fractures of the inferior clivus and bilateral occipital condyles with injury of the tectorial membrane

Background:

Craniocervical junction (CCJ) injuries are highly variable, and there are only limited data to suggest their optimal treatment. Here, we present a rare case of concomitant bilateral occipital condyle fractures with an inferior clival avulsion fracture with concomitant focal injury of the tectorial membrane.

Case Description:

Following a motor vehicle accident, a 51-year-old female sustained multiple orthopedic and soft tissue injuries. The cervical computed tomography (CT) showed a bilateral occipital condyle avulsion fractures with an avulsion of the inferior clivus. The cervical magnetic resonance imaging additionally demonstrated focal injury to the tectorial membrane with edema of both atlanto-occipital joints. Although the patient was neurologically intact, the CCJ instability warranted an emergent occiput-C2 (O-C2) posterior instrumented arthrodesis using the modular (multiple piece) occipitocervical (OC) plates/rods. The surgery was uneventful, and the patient remained neurologically intact. The 3-month follow-up cervical X-ray demonstrated continued stability/bony fusion.

Conclusion:

Bilateral condyle fractures with a concomitant inferior clivus fracture are rare, and there is no known optimal strategy. Here, in an intact patient, instability of the CCJ warranted an O-C2 fusion.

Morphometric analysis of occipital condyles using alternative imaging technique

PURPOSE

The occipital condyles (OCs) are crucial anatomical structures in the cranial base. To our knowledge, there is no cone beam computed tomography (CBCT)-based study on the morphometric analysis of OCs. The aim of this study was to evaluate the morphometric analysis of OCs using CBCT.

METHODS

CBCT images of 200 OCs from 100 patients of which 39 males and 61 females in the age group of 18-67 years were included in the study population. Linear and angular measurements of OCs were performed.

RESULTS

The average OC width, length, height, sagittal angle, and effective height were 10.3 ± 1.3 mm, 19.6 ± 2.0 mm, 9.1 ± 1.4 mm, 7.4 ± 1.7 mm, and 35.3 ± 5.2 mm. Condylar width and sagittal angle measurements were found significantly different between the right and left sides; and were not found significant difference between the right and left sides in the measurements of condylar height, length, and effective height. Also the average intercondylar anterior distance (ICAD), intercondylar posterior distance (ICPD), distance between the basion and the anterior apex of the occipital condyle (B-AAOC), distance between the basion and posterior apex of the occipital condyle (B-PAOC), distance between the opisthion and anterior apex of occipital condyle (O-AAOC), and distance between the opisthion and posterior apex of occipital condyle (O-PAOC) were 20.9 ± 1.5 mm, 44.0 ± 2.0 mm, 12.3 ± 1.9 mm, 34.5 ± 4.2 mm, 29.8 ± 1.7 mm, and 27.0 ± 2.1 mm. There was not significant difference in the morphometric measurements among age groups. All morphometric measurements showed a significant difference depending on gender.

CONCLUSIONS

The morphometric evaluation of OCs may be effectively examined using CBCT. Linear and angular measurements data of OCs in the present study may be used as a reference database for future morphometric and surgical investigations.

Anatomical study of the ventral neurovascular structures and hypoglossal canal for the surgery of the upper cervical spine

The aim of this study is to evaluate the anatomical relationship between the bony structures and ventral neurovascular structures around craniovertebral junction (CVJ). Eleven fresh-frozen cadaveric specimens were dissected around CVJ. The anatomical relationships were evaluated between C1 bony structures (midline, lateral margin of the C1 lateral mass (LM) and C1 transverse process (TP)) and ventral neurovascular structure such as ICA and HN. Morphometric evaluation of occipital condyle was also performed. The diameter of the HN and the ICA was 2.4 ± 0.5 mm and 5.1 ± 0.2 mm. The ICA was located lateral to the C1 LM in 44.4% (ICA Group 1) and in front of lateral half of the C1 LM in 55.6% (ICA Group 2). The HN was located lateral to the C1 LM in 85% (HN Group 1) and in front of lateral half of the C1 LM in 15% (HN Group 2). HN Group 2 was significantly more common in ICA Group 2 (p < 0.05, OR = 2.00, 95% CI: 1.07-3.71). There was significant correlation between ICA and HN in terms of the distance from the midline, C1 LM and TP (r = 0.67, 0.87 and 0.76 respectively, P < 0.01). In conclusion, the HN location is related with ICA location and the medially located ICA is a risk factor of the HN located ventral to the C1 LM. These results demonstrate the vulnerability of the neurovascular structures during CVJ surgery and suggest that preoperative 3D-CTA or enhanced CT scan can be useful in guiding surgical technique.

The Far Lateral Approach to the Craniovertebral Junction: An Update

INTRODUCTION

Since 1972, when Hammon first described the far lateral approach (FLA) for treatment of vertebral artery aneurysms, it has undergone numerous modifications, including drilling of the occipital condyle, removal of the laminas of upper cervical vertebrae and so on. Also, the range of indications has increased exponentially.

OBJECTIVE

In this paper we discuss state-of-the-art advances in the FLA, such as promising minimally invasive variants where an endoscope is used, and many others.

METHODS

We reviewed all articles touching upon the FLA in the modern era (from the year 2000 onward) and selected those that presented a significant contribution to the development of the relevant approach. The database used was PubMed.

RESULTS AND CONCLUSION

We found several new caveats not mentioned in other reviews or book chapters. The FLA is an ever-changing field of battle where the common and ultimate goals are to minimize the risk of injuring the major vessel in the region-the vertebral artery-and to provide such an angle of attack upon the tumours in the anterior and anterolateral foramen magnum that it is feasible to ensure gross total resection. This paper is an update on the knowledge about this approach, which we feel is necessary.

A Microanatomical Study of the Far Lateral Approach

OBJECTIVE

The far-lateral approach (FLA) remains a challenge for neurosurgeons due to the complex anatomy of this region, especially in patients with anatomical variations. There is therefore an urgent need for better quantitative knowledge of the microsurgical anatomy of the FLA.

METHODS

The study was performed using the dried skulls and atlas vertebrae of 50 Chinese adults, in which significant clinical parameters were measured. We further used 12 cadaveric heads to simulate the FLA to explore the step-by-step anatomy entailed by this procedure, enabling us to obtain key images and related information.

RESULTS

Limited to hypoglossal canal, the occipital condyle posterior was abraded by roughly 10 mm, which provided good exposure to the ventral front of the foramen magnum. When occipital artery exits the occipital groove, the mean diameter was 2.20 mm. The average occipital artery suboccipital segment length was 65.26 mm. The posterior spinal artery (PSA) and posterior inferior cerebellar artery (PICA) generally originated from the fourth vertebral artery segment intradurally, and the mean distances from the PSA and PICA to the dural entry point of the vertebral artery were 2.62 mm and 8.71 mm, respectively. The incidence of PSA and PICA arising from the third vertebral artery segment was 16.67% and 4.17%, respectively.

CONCLUSIONS

Understanding the important anatomic structures of the CVJ region and developing improved knowledge of the microsurgical anatomy of the FLA offer an opportunity to ensure safe exposure and treatment of lesions in the ventral and ventrolateral regions of the CVJ.

Spontaneous Fractures in the Setting of Extensive Craniocervical Pneumatization: Case Report and Literature Review

BACKGROUND

Cranial pneumatization in humans is normally confined to the paranasal sinuses and the petrous and mastoid parts of the temporal bones.

CASE DESCRIPTION

We present a case of left-sided fractures of the occipital condyle and lateral mass of the atlas in the setting of extensive craniocervical pneumatization but in the absence of trauma, with a resulting unilateral hypoglossal nerve palsy.

CONCLUSIONS

We discussed the possible etiology of this rare disease, its management, and prognosis.

[Feasibility of screw placement on posterior occipital condyle assisted by occipital tangent angulation]

Objective: To investigate the practicability of occipital tangent angle in assisting posterior occipital condylar screw placement and to verify the safety and accuracy of self-made screw placement device for auxiliary screw. Methods: Occipito-cervical region specimens of 12 adult corpses were selected and scanned by thin-cut CT examination.The three-dimensional reconstruction of occipital and atlas was simulated for each specimen, and 3-matic software was used to measure the setting parameters, including occipital tangent angle, head obliquity, internal inclination angle, length of the screw and the distance from the inferior margin of hypoglossal canal to the screw axis.Using the self-designed occipital condylar screw placement device, combined with occipital tangent angle, internal inclination angle and insertion point, the posterior occipital condylar screw specimen was inserted with nails with assisting tool.The occipito-cervical region was reconstructed and scanned by thin-cut CT examination again after the operation to measuring the parameters of screw placement after actual screwing.The paired t test was used to compare the parameters of screw placement before and after operation. Results: Pre-operative three dimensional reconstruction of occipital condyle screw showed that the head obliquity was 5.3°±0.9°, the tangent angle was 14.9°±3.7°, the internal inclination angle was 28.1°±5.9°, and the length of screw insertion was (21.4±1.7) mm respectively; the distance from the inferior margin of hypoglossal canal to the screw axis was (4.74±0.36) mm.There was no significant difference in the parameters of analogue nailing between the left and right occipital condyles before the operation (t=-1.32, -0.48, 0.10, 0.23, 0.09, all P>0.05). The occipital condylar screw was safely implanted with screw placement device.The screw was located in the ideal nail insertion channel after operation by CT scan evaluation, without any injury to the hypoglossal canal, the atlanto-occipital articular surface and other structure.After the operation, the actual nailing parameters were measured: the head inclination angle was 5.2°±0.7°, the tangent angle was 15.1°±3.2°, the internal inclination angle was 28.2°±4.2°, the length of screw insertion was (21.5±1.7) mm, the distance from the inferior margin of hypoglossal canal to the screw axis was (4.54±0.29) mm.There was no significant difference between the left and right side in the actual screw placement parameters (t=-0.77, 0.82, 0.56, 0.22, 0.21, all P>0.05). It was found that there was no significant differences in the head obliquity, the occipital tangent angle, the internal inclination angle, length of screw entry, and the distance from the inferior margin of hypoglossal canal to the screw axis before and after the operation (t=0.56, -0.47, -0.18, -0.70, 1.89, all P>0.05). Conclusion: The occipital tangent angle can be measured directly in the process of posterior occipital condyle screw insertion to guide occipital condylar screw insertion, and the self-made occipital condylar screw placement device can effectively combine the three parameters: occipital tangent angle, head inclination angle and insertion point, which can improve the safety of posterior occipital condylar screw insertion.

Morphometric Evaluation of Occipital Condyles: Defining Optimal Trajectories and Safe Screw Lengths for Occipital Condyle-Based Occipitocervical Fixation in Indian Population

Study Design

Computed tomographic (CT) morphometric analysis.

Purpose

To assess the feasibility and safety of occipital condyle (OC)-based occipitocervical fixation (OCF) in Indians and to define anatomical zones and screw lengths for safe screw placement.

Overview of Literature

Limitations of occipital squama-based OCF has led to development of two novel OC-based OCF techniques.

Methods

Morphometric analysis was performed on the OCs of 70 Indian adults. The feasibility of placing a 3.5-mm-diameter screw into OCs was investigated. Safe trajectories and screw lengths for OC screws and C0–C1 transarticular screws without hypoglossal canal or atlantooccipital joint compromise were estimated.

Results

The average screw length and safe sagittal and medial angulations for OC screws were 19.9±2.3 mm, ≤6.4°±2.4° cranially, and 31.1°±3° medially, respectively. An OC screw could not be accommodated by 27% of the population. The safe sagittal angles and screw lengths for C0–C1 transarticular screw insertion (48.9°±5.7° cranial, 26.7±2.9 mm for junctional entry technique; 36.7°±4.6° cranial, 31.6±2.7 mm for caudal C1 arch entry technique, respectively) were significantly different than those in other populations. The risk of vertebral artery injury was high for the caudal C1 arch entry technique. Screw placement was uncertain in 48% of Indians due to the presence of aberrant anatomy.

Conclusions

There were significant differences in the metrics of OC-based OCF between Indian and other populations. Because of the smaller occipital squama dimensions in Indians, OC-based OCF techniques may have a higher application rate and could be a viable alternative/salvage option in selected cases. Preoperative CT, including three-dimensional-CT-angiography (to delineate vertebral artery course), is imperative to avoid complications resulting from aberrant bony and vascular anatomy. Our data can serve as a valuable reference guide in placing these screws safely under fluoroscopic guidance.

Relationship Between the Horizontal Part of the Sigmoid Sinus and the Line Through the Digastric Point and Posterior Edge of the Condyle: An Anatomic and Radiologic Study

OBJECTIVE

This study aims to determine whether the line between the digastric point and posterior edge of the occipital condyle (DC line) could be a new surface landmark for the posterior margin of the horizontal part of the sigmoid sinus.

METHODS

Cadaveric specimens were used to show the relationship between the DC line and retrosigmoid craniotomy. Three-dimensional computed tomography angiography images of adult heads (56 sides) were analyzed to measure the distance between the DC line and the horizontal part of the sigmoid sinus at the digastric point, posterior edge of the condyle, and midpoint of the line.

RESULTS

The DC line was roughly parallel and posterior to the posterior margin of the sigmoid sinus. The distance between the DC line and the posterior edge of the sigmoid sinus at the digastric point, condyle, and midpoint of the line measured 4.7 ± 3.3 mm, 5.9 ± 2.6 mm, and 1.3 ± 2.2 mm, respectively. All sigmoid sinuses coursed anterior to the digastric point and condyle but in 17.9% (10/56 sides) the posterior edge of the sigmoid sinus extended a maximum of 4.1 mm posterior to the midpoint of the DC line.

CONCLUSIONS

The DC line can be used as a new surface landmark for estimating the position of the horizontal part of the sigmoid sinus. The posterior edge of the sinus may extend posterior to the line at the midpoint; thus, care should be taken to prevent sinus injury when drilling around the midpoint of the line.

Occipital Condyle Fracture Extending to the Inferior Part of the Clivus

Although rarely reported in the literature, serious occipital and condylar fractures have been diagnosed more often with the widespread use of computed cranial tomography in traumas. In this paper, a 16-year-old female with a left occipital fracture extending from the left occipital condyle anterior of the hypoglossal canal to the inferior part of the clivus is presented. The fracture which had caused a neurological deficit was cured with conservative treatment. For delayed hypoglossal nerve paralysis due to swelling within the canal, methylprednisolone was started, and a complete cure was attained in about 10 days. Traumatic damage of bony structures of the condyle and clivus at the junction of many vital nerves, vessels, and ligaments may lead to traumatic deficit and death.

Computed Tomography-Based Occipital Condyle Morphometry in an Indian Population to Assess the Feasibility of Condylar Screws for Occipitocervical Fusion

Study Design

A retrospective computed tomography (CT)-based morphometric study of 82 occipital condyles in the Indian population, focusing on critical morphometric dimensions with relation to placing condylar screws.

Purpose

This study focused on determining the feasibility of placing occipital condylar screws in an Indian population using CT anatomical morphometric data.

Overview of Literature

The occipital condylar screw is a novel technique being explored as one of the options in occipitocervical stabilization. Sex and ethnic variations in anatomical structures may restrict the feasibility of this technique in some populations. To the best of our knowledge, there are no CT-based data on an Indian population that assess the feasibility of occipital condylar screws.

Methods

We measured the dimensions of 82 occipital condyles in 41 adults on coronal, sagittal, and axial reconstructed CT images. The differences were noted between the right and left sides and also between males and females. Statistical analysis was performed using the t-test, with a p-value of <0.05 considered significant.

Results

Mean sagittal length and height were 17.2±1.7 mm and 9.1±1.5 mm, respectively. Mean condylar angle/screw angle was 38.0°±5.5° from midline, with mean condylar length and width of 19.6±2.6 mm and 9.5±1.0 mm, respectively. Average coronal height on the anterior and posterior hypoglossal canal was 10.8±1.4 mm and 9.0±1.4 mm, respectively. The values in females were significantly lower than those in males, except for screw angle and condylar width. Based on Lin et al.'s proposed criteria, eight of 82 condyles were not suitable for condylar screws.

Conclusions

Preliminary CT morphometry data of the occipital condyle shows that condylar screws are anatomically feasible in a large portion of the Indian population. However, because a small number of population may not be suitable for this technique, meticulous study of preoperative anatomy using detailed CT data is advised.

Occipitocervical Instability After Far-Lateral Transcondylar Surgery: A Biomechanical Analysis

BACKGROUND

After a far-lateral transcondylar approach, patients may maintain neutral alignment in the immediate postoperative period, but severe occipitoatlantal subluxation may occur gradually with cranial settling and possible neurological injury. Previous research is based on assumptions regarding the extent of condylar resection and the change in biomechanics that produces instability.

OBJECTIVE

To quantify the extent of bone removal during a far-lateral transcondylar approach, determine the changes in range of motion (ROM) and stiffness that occur after condylar resection, and identify the threshold of condylar resection that predicts alterations in occipitocervical biomechanics.

METHODS

Nine human cadaveric specimens were biomechanically tested before and after far-lateral transcondylar resection extending into the hypoglossal canal (HC). The extent of condylar resection was quantified using volumetric comparison between pre- and postresection computed tomography scans. ROM and stiffness testing were performed in intact and resected states. The extent of resection that produced alterations in occipitocervical biomechanics was assessed with sensitivity analysis.

RESULTS

Bone removal during condylar resection into the HC was 15.4%-63.7% (mean 35.7%). Sensitivity analysis demonstrated that changes in biomechanics may occur when just 29% of the occipital condyle was resected (area under the curve 0.80-1.00).

CONCLUSION

Changes in occipitocervical biomechanics may be observed if one-third of the occipital condyle is resected. During surgery, the HC may not be a reliable landmark to guide the extent of resection. Patients who undergo condylar resections extending into or beyond the HC require close surveillance for occipitocervical instability.

Morphological and Morphometric Analysis of Hypoglossal Canal in North Indian Dry Skulls and It's Significance in Cranial Base Surgeries

INTRODUCTION

Hypoglossal Canal (HC) is a paired bony passage which is situated above the Occipital Condyle (OC) and transmits hypoglossal nerve and blood vessels. Studies on the osteotic variations of HC has been a field of considerable interest to research workers especially because of its clinical, radiological and surgical significance.

AIM

The aim of the present study was to analyze the morphological and morphometric features of HC and its topographical relationship with OC.

MATERIALS AND METHODS

The present study was done on 50 human dry skulls. The HC was looked for presence of spur and septa along with its location in the canal and were classified into different types accordingly. The distance of extracranial and intracranial openings of HC from the posterior end of OC was measured by Sliding Vernier caliper. Angle of inclination of HC with the midsagittal plane was measured with the help of goniometer.

RESULTS

In the present study, we observed osteotic variations in the HC in 52% skulls. The spur (Type 2) was seen in 28% and incomplete septa (Type 3) was noted in 26% skulls. In some cases, spur and septa were seen in different locations of same HC. However, complete septa (Type 4) were not observed in our study. Spur and septa, both were present more frequently on the left side. The external and internal distance of HC from posterior end of OC was more on the left side in comparison to the right side. The anterior angle of HC to the midsagittal plane is less in comparison to posterior angle in case of double internal opening of HC.

CONCLUSION

The present study regarding morphologic and morphometric analysis of HC and its relation to the OC will provide important information in North Indian population. It will enable effective and reliable surgical intervention in the area of HC and craniovertebral junction leading to better postoperative outcome.

[Occipitocervical junction: Aanatomy, craniometry and pathology]

The occipitocervical junction comprises of the occiput condyles, the atlas, and the axis. The radiological evaluation of this region is supported by craniometric measurement methods which are based on predefined anatomical landmarks. The main pathologies of the occipitocervical junction are traumatic injuries, congenital anomalies or normal variants, infections, arthropathies, and tumors. In this article, the anatomy of the occipitocervical junction as well as the most important craniometric measurement methods are explained. Moreover various pathologies and similar appearing normal variants are presented.

Solitary Langerhans cell histiocytosis of the occipital condyle: a case report and review of the literature

BACKGROUND

Despite the recent advent of various radiographic imaging techniques, it is still very difficult to correctly distinguish a pediatric osteolytic lesion in the occipital condyle, which makes it further complicated to decide on the necessity of and the adequate timing for radical resection and craniocervical fusions. To establish a legitimate therapeutic strategy for this deep-seated lesion, surgical biopsy is a reasonable choice for first-line intervention. The choice of surgical approach becomes very important because a sufficient amount of histological specimen must be obtained to confirm the diagnosis but, ideally, the residual bony structures and the muscular structures should be preserved so as not to increase craniocervical instability. In this report, we present our experience with a case of solitary Langerhans cell histiocytosis (LCH) involving the occipital condyle that was successfully treated with minimally invasive surgical biopsy with a far lateral condylar approach supported by preoperative 3D computer graphic simulation.

CASE REPORT

An 8-year-old girl presented with neck pain. Magnetic resonance imaging and computed tomography (CT) revealed an osteolytic lesion of the left occipital condyle. At surgery, the patient was placed in the prone position. A 3-cm skin incision was made in the posterior auricular region, and the sternocleidomastoid and splenius capitis muscles were dissected in the middle of the muscle bundle along the direction of the muscle fiber. Under a navigation system, we approached the occipital condyle through the space between the longissimus capitis muscle and the posterior belly of the digastric muscle and lateral to the superior oblique muscle, verifying each muscle at each depth of the surgical field and, finally, obtained sufficient surgical specimen. After the biopsy, her craniocervical instability had not worsened, and chemotherapy was performed. Twelve weeks after chemotherapy, her neck pain had gradually disappeared along with her torticollis, and CT showed remission of the lesion and marked regeneration of the left occipital condyle. Within our knowledge, this is the first reported case of LCH involving the occipital condyle. Although very rare, our case indicated that LCH can be an alternative in the differential diagnosis of osteolytic lesions in the craniocervical junction, in which early bone regeneration with sufficient cervical stability is expected after chemotherapy.

CONCLUSIONS

In cases of pediatric osteolytic lesions, when they initially presented with apparent cervical instability, craniocervical fusion may possibly become unnecessary after a series of treatments. Thus, the effort to maximally preserve the musculoskeletal structure should be made until its histological diagnosis is finally confirmed.

Pediatric giant cell tumor of the tendon sheath of the craniocervical junction involving the occipital condyle

INTRODUCTION

Giant cell tumor of the tendon sheath (GCTTS), also called pigmented villonodular synovitis, is a common lesion of the synovial membrane of the hand joint, but it uncommonly involves the axial skeleton, especially in pediatric populations. Furthermore, GCTTS originating from the occipital condyle has not been reported previously.

CASE REPORT

A 15-year-old girl presented with a palpable neck mass for 1 year, and imaging studies revealed a less demarcated and heterogeneously enhanced mass in the suboccipital region. The tumor was originating from the occipital condyle that eroded the skull and atlas, and it was completely resected via a far lateral transcondylar approach followed by transarticular screw fixation. After the resection, we performed occipitocervical fusion to prevent spinal instability. The patient made an uneventful recovery after surgery. Recurrence has not been observed after 5 years of follow-up.

DISCUSSION

We report this rare case and briefly review the general features and unusual locations of GCTTS with recommendations for treatment modalities.

Traumatic Atlanto-occipital Dislocation (AOD)

OBJECTIVE

Traumatic atlanto-occipital dislocation (AOD) results from high energy trauma and is an uncommon and usually fatal injury due to an injury to the cervicomedullary junction. Recently, improved prehospital management, early diagnosis and effective treatment led to increasing reports of survival. This study of patients with AOD initial imaging modalities recognizes the clinical features and diagnostic considerations for a quick diagnosis.

METHODS

In this article, five survived adult patients with traumatic AOD are presented and retrospectively reviewed. Diagnosis was made by lateral cervical spine x-ray, cervical computed tomography (CT), or magnetic resonance imaging(MRI). Treatment consisted of early immobilization, respiratory support, and subsequent occipitocervical fusion.

RESULTS

Four patients were male and the other one was female. Three were diagnosed early and the others were delayed in confirmations. One was type I AOD and four were type II AOD. All patients were applied occipitocervical fusion. Two cases were worse; neurological states and the other three that showed no change. Lateral X-ray film of all patients in the prevertebral soft tissue swelling at the C2 level was noted. The mean thickness of prevertebral soft tissue C2 level was 17.88 mm(15.18 to 20.17mm). Two were in the normal range of dens-basion index(DBI), three showed abnormalities, and Power's ratio was abnormal in 3 patients.

CONCLUSION

As for damages caused by a strong external force in patients with severe prevertebral soft tissue swelling at C2 level abnormaly, the doctor determines whether more should be carefully AOD and considers 3D CT or MRI to confirm AOD in these patients.