Disappearance of degenerative, non-inflammatory, retro-odontoid pseudotumor following posterior C1-C2 fixation: case series and review of the literature

Abstract

Purpose: Retro-odontoid pseudotumor, not related to inflammatory or traumatic conditions, is an uncommon pathology. Atlanto-axial instability has been advocated to explain the pathophysiology of retro-odontoid pseudotumor's formation and growth. Despite pseudotumor direct removal through transoral or lateral approach represented the main surgical strategy for a long time, in the last decade several authors highlighted the possibility to treat retro-odontoid pseudotumor by occipito-cervical or C1-C2 fixation without removal of the intracanalar tissue. The goal of this study is to analyze the data collected in a series of patients suffering from cervical myelopathy due to non-inflammatory, degenerative retro-odontoid pannus and treated by posterior C1-C2 fixation. The relevant literature is also reviewed.

Methods: Five patients, not suffering from inflammatory diseases, were treated between 2009 and 2012. Abnormalities of cranio-cervical junction and/or lower cervical spondylotic degeneration were observed in all patients. No evidence of atlanto-axial instability was demonstrated. Clinical and radiological evaluation included pre- and post-operative Nurick score as well as pre- and post-operative X-rays, CT and MRI. In one case, CT scan highlighted an eggshell calcification of the pannus. All patients underwent either a C1-C2 fixation (C1 lateral mass and C2 isthmus-pedicle screws) or occipito-cervical fixation (2 patients) in cases of C0-C1 fusion.

Results: Follow-up ranges from 22 to 45 months (mean 32) in four patients. One patient died of surgery-unrelated disease. Nurick score changes suggest a clinical improvement in four cases. Neuro-radiological evaluation shows a progressive but incomplete reduction of thickness of retro-odontoid pseudotumor in one patient, and its disappearance in the other three cases. A second-stage transoral or posterior lateral approach was not required.

Conclusion: Although the etiopathogenesis of non-inflammatory, i.e., degenerative, retro-odontoid pseudotumor is still controversial, our series (the second largest on degenerative retro-odontoid pannus in the literature) confirms that a posterior approach may be sufficient and transoral surgery is not required.

Fig. 1

Patient 1: lateral radiograph showing extensive degenerative changes involving the cervical spine, with no overt C1–C2 instability (a). Pre-operative sagittal, T1- (b) and T2-weighted (c) MRI scan demonstrating a retro-odontoid pannus severely compressing the spinal cord as well as subaxial degenerative changes. On CT-angiography (d), a non-uniformly enhancing retro-odontoid soft tissue, mostly located on right side, is compressing the spinal cord. Post-operative X-ray showing a C1–C2 fixation (e). At the 8-month follow-up, MRI scan confirms the pannus reabsorption (f)

Fig. 2

Patient 2: a sagittal, T2-weighted MRI showing the severe cord compression due to a large retro-odontoid pseudotumor along with a osteophytosic cord compression at C5–C6 in a patient with DISH; b lateral X-ray showing the C1–C2 fixation and axial CT scan demonstrating the correct device position (c, d). Post-operative, sagittal, T2-weighted MRIs confirming the progressive pannus reabsorption at 5 (e), 8 (f) and 13 (g) months follow-up. The “key-hole” approach to remove the focal compression at C5–C6 is seen on coronal (h) and axial (i) CT scan

Fig. 3

Patient 3: a lateral radiograph and b sagittal, CT scan showing a C0–C2–C3 fixation in a patient with C0–C1 assimilation. Translaminar screws have been used at C2 level (c, d) and lateral mass screws at C3

Fig. 4

Patient 4: a sagittal, T2-weighted MRI demonstrating a retro-odontoid pseudotumor, with patchy signal alteration, compressing the spinal cord. Such appearance is also seen on sagittal CT scan (b), which also shows an eggshell calcification of the pseudotumor. Postoperatively, serial, sagittal follow-up MRIs confirm the progressive pannus reduction in volume (c), respectively, at 4, 10 and 14 months