Preoperative 3D-CT-based planning for complex craniovertebral junction anomalies: Technique and surgical outcome

Abstract

Background:

The craniovertebral junction (CVJ) is surgically challenging due to its complex anatomy and proximity to vital neurovascular structures. This study aims to evaluate the use of 3D multiplanar reconstruction technique and its impact on surgical and radiological outcomes.

Methods:

Thirty patients with CVJ anomalies operated on between July 2022 and December 2024 were included. Of the thirty patients, 15 had basilar invagination, six had atlanto-axial dislocation, five had C2 fractures with instability, and four had Arnold–Chiari malformations with instability. Preoperative 3D-computed tomography (CT) and CT angiography reconstructions were performed to evaluate vertebral artery (VA) anatomy, C2 pedicle, C1 lateral mass, C1–C2 facet joint inclination, pseudo-joints, and craniocervical tilt. All patients underwent C1– C2 fixation or occipito-cervical fixation with joint manipulation using spacers. Pre and postoperative neurological recovery were assessed using Nurick and modified Japanese Orthopedic Association grading. Postoperative CT was done in all cases.

Results:

Twenty-six underwent C1–C2 fixation and four patients underwent occipito-cervical fixation. No VA injuries or screw-related complications occurred. One patient required revision due to implant failure. Neurological improvement occurred in 90% of cases. Radiological indices (Chamberlain line, McRae line, atlanto-dental interval, clivus canal angle) showed significant postoperative improvement.

Conclusion:

Preoperative 3D multiplanar CT reconstruction enables detailed analysis of CVJ anatomy and VA variations, improving safety and surgical outcomes in complex anomalies.

INTRODUCTION

Despite significant advancements in craniovertebral junction (CVJ) stabilization techniques, the surgical management of complex CVJ anomalies remains technically challenging. Large series, such as the American Association of Neurological Surgeons/Congress of Neurological Surgeons survey, have reported a 4.1% risk of VA injury during C1–C2 transarticular screw (TAS) fixation which may occur due to anatomical variations – including high-riding VA, anomalous courses, or narrow C2 isthmuses and can significantly complicate and/or preclude TAS fixation.[2]

Further, sagittally oriented C1–C2 facet joints and atlantoaxial pseudo joints, frequently observed in basilar invagination (BI), further complicate surgical access and screw placement.

There is also a role of high-resolution multi-planar computed tomography (CT) imaging and CT angiography (CTA) in visualizing these complex anatomical relationships and improving surgical safety.[4] Here, we evaluated the surgical and radiological outcomes associated with 30 CVJ surgeries utilizing a 3D multiplanar reconstruction technique to facilitate preoperative planning.

MATERIALS AND METHODS

Study design and patient selection

Thirty patients with CVJ anomalies who underwent surgical intervention between 2022 and 2024, by a single senior neurosurgeon, were included in the study. All patients underwent detailed preoperative imaging, including multi-planar 3D CT and CTA, to assess the anatomy of the vertebral artery (VA), C1 lateral mass, C2 pedicle, C1–C2 facet joint inclination, presence of pseudo joints, and craniocervical tilt. Dynamic CT CVJ in flexion and extension was done in all patients. Volume-rendered reconstructions were generated using freely available open-source medical imaging software to facilitate preoperative planning and screw trajectory mapping.

3D volume rendering technique (VRT) reconstruction procedure and planning

The digital imaging and communications in medicine image file was imported in image viewer and 3D rendering software. After 3D VRT image reconstruction, the bony anatomy of CV junction, c1 –2 joint status, and course of VA were studied. Based on these reconstructions, the optimal screw entry points and trajectories were carefully planned. Furthermore, 3D reconstructed models were used to plan the sequence of surgical steps, including joint manipulation, reduction, screw, and rod fixation [Figure 1].

Figure 1:

3D image reconstruction process. (a) Importing digital imaging and communications in medicine file and creating 3D volume rendering image as shown by yellow arrow. (b) Using crop tool (yellow arrow) to cut the parts of 3D reconstruction not required. (c) Using the scissors tool (yellow arrow) to cut as required for operative planning. (d) Similar cutting process (yellow arrow) with image rotated to lateral view. (e) Posterior view with occipital bone removed to show course of vertebral artery. (f) Add fly through point tool (shown by yellow arrow)- used to make a 3D video of the selected 3D image.

Surgical technique

All patients underwent surgery in the prone position with skull traction on a horseshoe headrest. A midline posterior incision from the suboccipital region to C4 exposed the C1–2 joint after subperiosteal dissection of muscles and venous plexus. In complex CVJ anomalies, the C2 nerve root ganglia were sacrificed for wider exposure. Joint surfaces were decorticated, and bilateral C1 lateral mass screw trajectories were created under fluoroscopy. Depending on preoperative planning, C2 pedicle or subfacetal screw trajectory was drilled. Interarticular spacers with autologous bone grafts were placed to aid in reduction and fusion. Posterior decompression (C1 arch or foramen magnum) was done when required. Finally, bilateral C1–C2 screws and rods were inserted, and compression was applied sequentially at C2 then C1 screws for fluoroscopy-guided atlantoaxial reduction.

Postoperative analysis

Radiological evaluation included postoperative CT to assess implant positioning and correction of anatomical indices such as the atlantodental interval, Chamberlain line, McRae line, and clivus-canal angle. Neurological status was documented using the modified Japanese Orthopaedic Association (mJOA) scale[5] and Nurick grading[6] (comparing preoperative and at follow-up status).

RESULTS

Demographics and pathologies

Of 30 patients who underwent surgical intervention for various CVJ anomalies 40% (12) were females and mean age of the patients was 34 years. The cohort included 50% (15) patients with (BI; 60% had type 1 and 40% type 2 BI), 20% (6) with atlantoaxial dislocation (AAD), 13.3% (4) with Arnold–Chiari malformation associated with C1– C2 joint instability, and 16.6% (5) with C2 fractures. Of the 15 patients diagnosed with BI, 60% (9) had type I and 40% (6) had type II BI [Table 1].

Table 1:

Diagnosis, radiological features, and surgical management of patients with CVJ anomalies.

Skeletal abnormalities were frequent, with 50% (15) patients exhibiting occipitalization of the atlas combined with C2-C3 fusion, 13.3% (4) patients presenting with os odontoideum and syringomyelia was observed in 36.6% (11) patients with CVJ anomalies.

Course of VA and C1-2 joint analysis

Anomalous VA trajectories crossing the C1–C2 joint were identified in 23.3% (7) patients, while 16.6% (5) showed marked asymmetry in VA caliber. In all cases, the side with normal or hypoplastic VA was approached first during surgery for fixation. CT-based evaluation of C1–C2 joint orientation revealed vertical alignment on one or both sides in 30% (9) patients, all of whom demonstrated a corresponding occipito-C1 pseudojoint on the same side.

Utility of 3D-CTA reconstruction

Based on CTA reconstruction and the delineated course of vertebral artery , the intraoperative dissection and screw insertion trajectory was planned. Micro Doppler probe was used in cases with aberrant VA during dissection, and the artery was carefully mobilized, retracted superiorly to facilitate safe instrumentation. No intraoperative vascular injuries were reported.

Postoperative management

Patients were extubated immediately postsurgery and monitored in the intensive care unit for 24 h. A Philadelphia collar was used by patients postoperatively. A postoperative CT scan was performed on the 1^st day to assess the degree of reduction and implant positioning.

Surgical and radiological outcome

Radiological correction of AAD and BI was achieved in all 30 patients (100%). At follow-up imaging, 86% (26) of patients showed adequate fusion at C1–2 joints. One patient with occipito-cervical fixation required revision surgery at 6 months due to implant failure.

We noticed symptomatic improvement in the form of decreased pain, paresthesia, and reduced spasticity in 90% (27) of patients undergoing surgery. Eighty percent (24/30) showed good neurological recovery in the mJOA scores during the follow-up period. 13.3% (4) patients with Arnold–Chiari malformation and syringomyelia who underwent C1–2 fixation combined with foramen magnum decompression showed a substantial reduction in syrinx at follow-up MRI imaging. All patients had postoperative C2 dermatomal numbness which gradually improved over the period. No major neurological or vascular complications were noticed postoperatively.

Case illustration

Case 1: A 13-year-old female patient presented to us with a history of neck pain with bilateral upper limb tingling sensation following history of fall at school. Her CT imaging showed BI with AAD and occipitalized atlas. Right side c1–2 joint had vertical inclination with c1 lateral mass completely in front of the c2. 3D CT angiogram neck vessel showed abnormal course-persistent intersegmental VA crossing c1–2 joint on the right side [Figure 2]. The patient underwent C1–C2 fixation with mobilization of abnormally coursing VA on the right side as shown in Figure 3.

Figure 2:

Computed tomography (CT) craniovertebral junction (CVJ) and 3D reconstruction (a) Flexion view of the CVJ demonstrating basilar invagination (BI) with atlantoaxial dislocation as shown by yellow arrow. (b) Sagittal CT image showing the orientation of the left C1–C2 joint as shown by yellow arrow. (c) Sagittal CT image depicting vertically oriented C1–C2 facet joints marked by yellow arrow. (d) 3D angiographic reconstruction showing the vertebral artery course with abnormal course on the right side as shown by the yellow arrow. (e) Posterior 3D reconstructed view of CVJ showing assimilated c1 posterior arch shown by the black arrow. (f and g) Sagittal view - 3D reconstructions depicting the orientation of the C1–C2 facet joints as shown in yellow arrow. (h) 3D reconstructed posterior view after removing the assimilated c1 arch to show the anomalous course of vertebral after on the right side across the c1-2 joint as depicted by the yellow arrow.

Figure 3:

Intraoperative pictures (a) View after bilateral c1 lateral mass and c2 pedicle screw placement (marked by yellow arrow). (b) Exposed c2 laminate as shown by yellow arrow, spinous process, and occipitalized atlas. (c) Left c1-2 joint exposure shown by dissector and marked by yellow arrow. (d) Spacer with bone grafts placed in the left c1-2 joint shown by yellow arrow. (e) Rt c1-2 joint with a dissector retracting the anomalous vertebral artery (yellow arrow).

Postoperative CT scan confirms the reduction of AAD and BI along with the correct placement of c1–2 screws bilaterally [Figure 4]. The main steps of the surgery are demonstrated in short Supplementary Video 1.

Figure 4:

Postoperative computed tomography images. (a) Preoperative sagittal image showing basilar invagination (BI) (odontoid invaginating above the clivus line marked in yellow). (b) Postoperative mid-sagittal view showing reduction in BI and atlantoaxial dislocation as shown with yellow line. (c) Left side c1-2 screw (yellow arrow) with spacer (red arrow). (d) Right side c1-2 screw as marked by yellow arrow.

DISCUSSION

Our results reinforce the critical role of 3D multi-planar CT and angiographic imaging in facilitating safe and effective management of complex CVJ anomalies. Individualized evaluation of VA anatomy, C1–C2 joint orientation, and congenital deformities enabled optimized surgical planning, contributing to the avoidance of vascular complications in our cohort. These observations are in line with Chaudhary et al.,[1] and Little et al.,[7] who highlighted the importance of detailed multiplanar imaging for accurate preoperative planning.

The systematic use of 3D imaging also allowed anticipation of vertical joint inclinations, pseudo joint formations, and hypoplastic lateral masses – factors often underappreciated in atlantoaxial instability. This resonates with Goel’s concept of central atlantoaxial instability, which emphasizes the role of C1–C2 facet malalignment and vertical instability even without gross dislocation.[4] His subsequent work further demonstrated that C1–C2 fixation with the plate-and-screw method achieves high success, especially in anomalous anatomy.[5]

Preoperative VA mapping was essential in our series, particularly in patients with anomalous or high-riding arteries. Similar emphasis on careful evaluation has been reported by Neo et al.[8] and Jagetia et al.,[6] while Pavlov et al.[9] proposed intraoperative imaging to reduce iatrogenic risk. Our results – no vascular injuries despite seven patients with VA anomalies – support this approach.

Our surgical workflow of bilateral joint manipulation, spacer placement, and targeted screw trajectories yielded favorable outcomes, with neurological improvement in 90% of patients. These results are in agreement with Shetty et al.[10] who reported that joint distraction techniques enhance decompression, reduction, and fusion. Similarly, Gluf et al. documented a 98% fusion rate in a large series of 191 patients, emphasizing the importance of precise imaging and technique.[3]

In summary, individualized anatomical evaluation, careful VA assessment, and joint-based fixation strategies are fundamental to safe and effective management of CVJ anomalies.[3,5,8]

CONCLUSION

Preoperative 3D-CT and angiographic reconstruction improve surgical safety and neurological outcomes by enabling precise, patient-specific fixation in complex CVJ anomalies.

Additional Information

Disclosures

Human subjects: Informed consent for treatment and open access publication was obtained or waived by all participants in this study. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous 3 years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Ethical approval:

Institutional review board approval is not required as its a retrospective study. This is a retrospective observational study evaluating CT scan based 3d reconstruction as a tool and did not involve any direct patient intervention or identifiable patient information.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Supplementary Video available on

https://doi.org/10.25259/SNI_1095_2025

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