Staged dorsolateral decompression and posterior stabilization for severe ventral odontoid compression in basilar invagination: illustrative case

Abstract

BACKGROUND

Basilar invagination (BI) with ventral cervicomedullary compression remains surgically challenging. Although transoral and endoscopic endonasal odontoidectomy are established approaches, some anatomical variations may favor alternative surgical corridors.

OBSERVATIONS

A patient with BI developed progressive quadriparesis after cervical trauma. Imaging demonstrated severe ventral cervicomedullary compression from a retroverted, left-lateralized odontoid process, displacing the cervicomedullary junction contralaterally. CT angiography revealed absence of the left vertebral artery (VA) and medial deviation of the left internal carotid artery (ICA). Because the odontoid was significantly lateralized, causing contralateral displacement of the cervicomedullary junction, and was located behind the ICA, with absence of the ipsilateral VA, ventrolateral decompression was performed through a modified left dorsolateral extradural lateral inferior transcondylar (ELITE) approach. Posterior craniocervical fixation and fusion were subsequently performed. The patient experienced neurological improvement with satisfactory radiographic decompression.

LESSONS

Careful evaluation of the direction of odontoid displacement and surrounding vascular anatomy is critical in selecting the surgical corridor. In selected patients with a significantly lateralized odontoid and off-midline ventral cervicomedullary compression, a modified dorsolateral ELITE approach may provide a safe and direct alternative to conventional midline anterior approaches. Medial ICA displacement and absence of the ipsilateral VA further facilitated the lateral surgical corridor.

https://thejns.org/doi/10.3171/CASE26747

Basilar invagination (BI) with cervicomedullary compression remains surgically challenging, particularly in irreducible cases. Standard management for ventral compression involves anterior odontoidectomy followed by posterior fixation, most commonly via transoral or endoscopic endonasal approaches.^1–7 However, these approaches may be limited by patient-specific anatomy and carry approach-related morbidity.

We present our staged surgical strategy for BI with severe ventral cervicomedullary compression, consisting of initial odontoid decompression through a modified left dorsolateral extradural lateral inferior transcondylar (ELITE) approach, followed by posterior craniocervical fixation and fusion.⁸ This technique was facilitated by a lateralized odontoid process and absence of the ipsilateral vertebral artery (VA).

Illustrative Case

Clinical Presentation

A 46-year-old woman with a long-standing neck tilt since childhood presented with progressive quadriparesis after cervical trauma. Neurological examination demonstrated diffuse motor weakness (Medical Research Council grades III–IV/V) in all extremities. Imaging demonstrated BI with severe cervicomedullary compression. Preoperative reduction with Gardner-Wells tong traction up to 25 pounds was unsuccessful, confirming an irreducible deformity.

Relevant Surgical Anatomy

The patient had BI associated with atlanto-occipital assimilation. The odontoid process was retroverted, causing significant cervicomedullary compression with associated syringomyelia. The odontoid process was lateralized to the left, resulting in rightward and posterior displacement of the thecal sac. Computed tomography angiography demonstrated absence of the left VA extending from the transverse foramen (V2) to the intradural segment (V4). The left internal carotid artery (ICA) deviated close to the midline at the C3 level (Fig. 1).

FIG. 1.

A and B:CT angiograms of the head and neck demonstrating a normal right VA and absence of the left VA from the V2 to V4 segments. C and D:The ICA deviated medially toward the midline at the C3 level. BA = basilar artery; C3 = third cervical vertebra.

These anatomical features favored a lateral surgical corridor for odontoid resection (Fig. 2). An anterior approach was considered technically difficult because of the off-midline position of the odontoid process, its proximity to the left ICA, and the long working distance to its posterior margin, which could limit the extent of decompression and increase the risk of dural, cervicomedullary, and ICA injury. In contrast, the absence of the ipsilateral VA obviated the need for V3 segment mobilization or transposition, allowing a more direct surgical corridor to the odontoid process and avoiding the risks of VA injury and bleeding from the perivertebral venous plexus.⁹

FIG. 2.

A and B:Preoperative sagittal (A) and axial (B) cervical spine MR images demonstrating compression of the cervicomedullary junction by the odontoid process from the anterior and lateral aspects. C and D: Preoperative 3D CT reconstructions demonstrating atlanto-occipital assimilation. C1 = first cervical vertebra; C2 = second cervical vertebra; La = lamina; LM = lateral mass; OB = occipital bone; OC = occipital condyle; Od = odontoid process; SC = spinal cord.

Surgical Technique

Stage 0: Preoperative Evaluation

The patient underwent active neck flexion, extension, and rotation to identify the safest and most mobile neck position for intraoperative positioning.

Stage 1: Modified Dorsolateral ELITE Approach

The patient was placed in the lateral decubitus position with the head secured in a three-pin head clamp. The neck was moderately flexed, with the head elevated from the dependent shoulder and maintained in a horizontal, vertex-down orientation. The upper shoulder was rotated anteriorly, and the arm was positioned anterocaudally (Fig. 3A). Somatosensory evoked potentials and motor evoked potentials were monitored throughout the procedure. Neuronavigation was used to guide complete odontoidectomy.

FIG. 3.

Intraoperative photographs. A: The patient was placed in the lateral decubitus position with the neck flexed, the upper shoulder rotated anteriorly, and the arm positioned anterocaudally. B: A lazy S–shaped incision extending from the asterion to the C2 transverse process. C and D: Initial (C) and final (D) views of the modified dorsolateral ELITE approach. A = anterior; As = asterion; C3 = third cervical vertebra; FM = foramen magnum; I = inferior; INC = inferior nuchal line; MT = mastoid tip; P = posterior; PD = posterior fossa dura; S = superior; SNC = superior nuchal line; Th = thecal sac.

A lazy S–shaped skin incision was made posterior to the mastoid, extending from the asterion to the level of the C2 transverse process (Fig. 3B). The galeocutaneous flap was elevated, and a thin suboccipital fascial graft was harvested. After incision of the pericranium and suboccipital fascia, the superficial and deep muscle layers were dissected sequentially, followed by exposure of the suboccipital triangle. The V3 segment of the VA was not identified within the C1 groove. The levator scapulae muscle was detached from the C1 transverse process, and a small C2 nerve branch at the C1–2 interlaminar space was sacrificed.

Suboccipital craniectomy and foramen magnum decompression were performed, followed by removal of the condylar fossa and the atlanto-occipital joint. The C1 lateral mass and lamina were removed, exposing the odontoid process and the compressed thecal sac (Fig. 3C). The odontoid process and adjacent C2 elements were resected using a high-speed drill. The transverse ligament and tectorial membrane were removed, resulting in full expansion of the thecal sac, with visible CSF pulsation (Fig. 3D). No CSF leakage was observed. Video 1 demonstrates the key steps of the surgical procedure. Postoperatively, skull traction was applied for 48 hours to maintain craniovertebral alignment while awaiting the subsequent stage of surgery.

VIDEO 1. Modified dorsolateral ELITE approach for odontoidectomy in irreducible BI. The video demonstrates the key operative steps, including extradural craniovertebral junction exposure, odontoid resection, and ventrolateral cervicomedullary decompression. A = anterior; C1 = first cervical vertebra; C2 = second cervical vertebra; C3 = third cervical vertebra; FM = foramen magnum; I = inferior; INL = inferior nuchal line; MP = mastoid process; P = posterior; S = superior; SCM = sternocleidomastoid muscle; SNL = superior nuchal line; Th = thecal sac; TP = transverse process. Click here to view.

Stage 2: Posterior Occipitocervical Fixation and Fusion

The patient was placed in the prone position with her head secured in a three-pin head clamp. Neuronavigation was used for screw placement. An occipital plate and pedicle screws were placed at C3, C5, and C6; C4 was omitted due to screw head interference. Three-level fixation was selected to provide a robust construct for craniocervical reconstruction. A cross-link was added to enhance construct rigidity. Posterolateral fusion using a hydroxyapatite bone graft was performed. Postoperatively, the patient wore a Philadelphia collar for 3 months.

Postoperative Course

The postoperative course was uneventful. The patient remained hospitalized for 2 weeks and was discharged after beginning gait training. Her motor function gradually improved during follow-up. At the 2-year follow-up, the patient was able to use her hands and walk independently, perform daily activities without assistance, and return to work. CT and MRI confirmed stable instrumentation and satisfactory cervicomedullary decompression (Fig. 4).

FIG. 4.

A and B:Two-year postoperative sagittal (A) and axial (B) cervical spine MR images confirming satisfactory cervicomedullary decompression. C: Two-year postoperative cervical radiographs demonstrating appropriate instrumentation. CL = cross-link.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

Although transoral and endoscopic endonasal odontoidectomy remain established treatments for irreducible BI, clinical reports of dorsolateral transcondylar approaches for odontoid decompression are limited.^10–12 The dorsolateral transcondylar approach provides direct access to the ventral cervicomedullary junction through a short, wide surgical corridor parallel to the neuraxis, facilitating anterior decompression with minimal neural retraction. This anatomical trajectory makes it particularly advantageous for off-midline ventral lesions. The approach has been used for both neoplastic lesions, including dumbbell spinal neurinomas, foramen magnum meningiomas, and jugular foramen tumors, and selected nonneoplastic craniovertebral junction disorders, including congenital abnormalities and rheumatoid cranial settling.¹³

In this patient, a lateralized odontoid process, medial deviation of the ipsilateral ICA, and absence of the ipsilateral VA provided a favorable lateral surgical corridor. These anatomical features enabled direct extradural access to the odontoid process through a modified dorsolateral ELITE approach without the need for VA transposition. The procedure remained technically demanding because of the narrow operative corridor adjacent to the lower cranial nerves and the risks of neurological deterioration, VA injury, CSF leakage, and instrumentation-related complications.^9,14,15 Risk mitigation included detailed preoperative vascular imaging, Doppler localization of vascular structures, meticulous layer-by-layer dissection, preservation of a thin bone shell over the thecal sac, intraoperative neuromonitoring, and neuronavigation to facilitate safe odontoid resection and accurate instrumentation. Complete ventrolateral decompression was achieved without vascular injury or CSF leakage, followed by staged posterior fixation and fusion. At the 2-year follow-up, the patient demonstrated sustained neurological improvement with satisfactory radiographic decompression and stable craniocervical alignment. This case adds to the limited clinical experience supporting the feasibility of a dorsolateral approach for selected cases of irreducible BI.

Lessons

This case demonstrates that the direction of odontoid displacement and cervicomedullary compression should be considered when selecting the surgical corridor for irreducible BI. A significantly lateralized odontoid may be more directly accessed through a lateral trajectory rather than a conventional midline anterior approach. Careful evaluation of the surrounding vascular anatomy is essential to determine the feasibility and safety of this approach. In this patient, the absence of the ipsilateral VA eliminated the need for VA transposition. When the VA is present, transposition can be performed safely when required. This approach therefore represents an alternative for selected patients with off-midline ventral craniovertebral junction compression.

Acknowledgments

We acknowledge Dr. Takanori Fukushima for developing the surgical approach. ChatGPT (GPT-5.5, OpenAI) was used for grammar checking and English-language refinement. CapCut was used to generate the video narration.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: all authors. Acquisition of data: Jriyasetapong, Bunyaratavej. Analysis and interpretation of data: Jriyasetapong. Drafting the article: Jriyasetapong, Bunyaratavej. Critically revising the article: all authors. Reviewed submitted version of manuscript: Jriyasetapong, Bawornvaraporn. Approved the final version of the manuscript on behalf of all authors: Jriyasetapong. Administrative/technical/material support: Jriyasetapong, Bunyaratavej. Primary surgeon: Bawornvaraporn.

Supplemental Information

Videos

Video 1. https://vimeo.com/1221509607.

Correspondence

Navabhorn Jriyasetapong: Chulalongkorn University and King Chulalongkorn Memorial Hospital, Bangkok, Thailand. navabhorn.j@chula.ac.th.