Factors influencing on retro-odontoid soft-tissue thickness: analysis by magnetic resonance imaging

Clinical and MR Predictors of Retro-Odontoid Pseudotumor Regression Following Posterior Fixation in Patients with Atlantoaxial Instability

Purpose

To identify clinical and MR predictors of retro-odontoid pseudotumor (ROP) regression after posterior fixation in patients with atlantoaxial instability.

Materials and Methods

We included patients who had undergone posterior fixation for atlantoaxial instability and preoperative and postoperative MR imaging. Patients were classified into two groups according to the degree of ROP regression after posterior fixation: regression (≥ 10% reduction) and no regression (< 10% reduction). Mann-Whitney and Fisher's exact tests were performed to identify the clinical (age and sex) and MR predictors (preoperative ROP thickness, ROP type, MR signal homogeneity of the ROP, spinal cord signal change, spinal cord atrophy, ossified posterior longitudinal ligament, os odontoideum, and atlantodental interval) associated with ROP regression.

Results

We retrospectively assessed 11 consecutive patients (7 female; median age, 66 years [range, 31-84 years]). Posterior fixation induced ROP regression in eight (72.7%) patients. Older age and greater preoperative ROP thickness significantly correlated with ROP regression (p = 0.024 and 0.012, respectively). All patients with preoperative ROP thickness > 5 mm exhibited ROP regression. The other variables were not significantly associated with ROP regression.

Conclusion

Older age and thicker preoperative ROP are associated with ROP regression after posterior fixation in patients with atlantoaxial instability.

Prevalence of likely retro-odontoid pseudotumor in patients receiving dental CBCT examinations

OBJECTIVES

We calculated the prevalence of unsuspected retro-odontoid pseudotumor (ROP) as detected in cone beam computed tomography (CBCT) examinations. Additionally, we examined patient age, sex, and presence and severity of cervical osteoarthritis (OA) as potential risk factors for ROP.

STUDY DESIGN

We retrospectively analyzed de-identified CBCT scans of 455 patients from the Division of Oral and Maxillofacial Radiology at the University of Connecticut School of Dental Medicine. Identification of likely ROP was completed through a likelihood scoring scale (1-4) due to the lack of magnetic resonance images. Severity of cervical OA was determined using 5 osteoarthritic features. An ordinal logistic regression model was used to link potential risk factors to ROP.

RESULTS

In total, 18 patients (3.9%) were classified with probable (11 patients [2.4%]) or definite (7 patients [1.5%]) likely ROP. Older age and the presence and severity of OA were significantly associated with higher ROP scores (P < .001). There was no significant association of ROP likelihood and patient sex (P = .637). An increase of 1 year of age increased the chance of a patient having a higher ROP likelihood score (P < .001). The age-adjusted chance of having a more severe ROP increased with moderate to severe OA (P ≤ .017).

CONCLUSIONS

Prevalence of likely ROP increases with age and OA but is not associated with sex. Individuals with moderate or severe OA are more likely to have ROP.

The Impact of Cervical Degeneration and Sagittal Balance on Retro-Odontoid Soft-Tissue Thickness

OBJECTIVE

To investigate whether retro-odontoid soft-tissue thickness (ROSTT) is associated with cervical degeneration, cervical spine mobility, and sagittal balance of cervical spine.

METHODS

The data of 151 patients who presented at our hospital with cervical spondylosis were reviewed. The ROSTT was measured using T1-weighted sagittal cervical magnetic resonance imaging findings. The assessment of the degree of cervical intervertebral disc degeneration (IVDD) was conducted using sagittal T2-weighted imaging. The T1 slope (T1S), C0-C2 angle, C1-C2 angle, C2-C7 angle, C1-C7 sagittal vertical axis and C2-C7 sagittal vertical axis were measured. The range of motion was assessed by measuring the flexion-extension radiographs. According to the ROSTT, those measuring less than 3 mm were classified as normal group and those measuring larger than 3 mm were classified as thickened group.

RESULTS

The thickened group had larger cervical IVDD grade, age, C2-C7 angle, and T1S compared to the normal group (all P < 0.05). Additionally, the C0-C2 angle was significantly smaller in the thickened group than in the normal group (P < 0.05). ROSTT showed a negative correlation with C0-C2 angle (r = -0.181, P < 0.05), but positive correlations with both C2-C7 angle (r = 0.255, P < 0.05) and T1S (r = 0.240, P < 0.05). Furthermore, ROSTT was positively correlated with age (r = 0277, P < 0.05) and cervical IVDD grade (Spearman, r = 0.299, P < 0.05).

CONCLUSIONS

Cervical sagittal balance and cervical degeneration have a significant impact on ROSTT. Patients with a higher T1S and severe cervical degeneration are more likely to result in greater ROSTT.

Changes in retro-odontoid mass after upper cervical spine surgery

A non-neoplastic mass posterior to the dens is termed a retro-odontoid mass (R-OM). This retrospective study evaluated radiographic and clinical outcomes and R-OM changes after upper cervical spine surgery. This study included 69 patients who underwent upper cervical spine surgery, including atlantoaxial fusion, occipitocervical fusion, or decompression. All patients underwent preoperative magnetic resonance imaging (MRI). Six-month follow-up MRI examinations were performed in 30 patients who had preoperative R-OMs. Radiographic outcomes of the anterior and posterior atlantodental intervals were measured using X-rays and computed tomography. The R-OM and space available for the cord (SAC) were measured using MRI. Clinical outcomes were evaluated using neck and arm pain visual analog scales, the Japanese Orthopedic Association score, the neck disability index, and the patient-reported subjective improvement rate. The anterior atlantodental interval decreased, while the posterior atlantodental interval and SAC increased postoperatively. Among the clinical outcomes, the neck and arm pain and the neck disability index decreased postoperatively, while the Japanese Orthopedic Association score increased. All clinical and radiographic outcomes improved postoperatively. The R-OM either decreased in size or disappeared after fusion surgery in all cases, except in one patient who underwent decompression surgery. In conclusion, stabilization through fusion surgery is essential for treating R-OM.

Factors Associated with Retro-Odontoid Pseudotumor in Long-Term Hemodialysis Patients

OBJECTIVE

Hemodialysis has been reported to be associated with retro-odontoid pseudotumor (ROP), but its clinical characteristics have not been well described. The purpose of the present study was to investigate the factors associated with ROP in hemodialysis patients.

METHODS

A retrospective clinical study of hemodialysis patients was conducted with the evaluation of computed tomography and magnetic resonance imaging of cervical spinal lesions at a single institution from 2012 to 2020. The patients' characteristics and radiographic findings were assessed. A case-control analysis was performed between patients with ROP (ROP group) and patients without ROP (control group).

RESULTS

We analyzed 46 patients. The mean duration of hemodialysis (± standard deviation) was 21.5 ± 11.8 years. The mean retro-odontoid soft tissue thickness was 4.3 ± 0.3 mm and was correlated with the duration of hemodialysis (r = 0.46, P < 0.01). Thirty patients (65.2%) were included in the ROP group. The ROP group showed a significantly longer duration of hemodialysis (24.9 ± 11.2 years vs. 15.2 ± 10.3 years, P < 0.01) and a higher incidence of osteolytic lesions in the atlantoaxial joint compared with the control group (60.0% vs. 18.8%, P < 0.01). Logistic regression analysis revealed the atlantoaxial osteolytic lesions are associated with retro-odontoid pseudotumor in hemodialysis patients (odds ratio, 5.1; 95% confidence interval, 1.1-24.2; P = 0.04).

CONCLUSIONS

The existence of ROP in hemodialysis patients was associated with osteolytic lesions in the atlantoaxial joint. The finding of atlantoaxial erosive lesions in long-term hemodialysis patients requires spine surgeons to carefully evaluate the presence of ROP.

Imaging Characterization of Non-Rheumatoid Retro-Odontoid Pseudotumors: Comparison with Atlantoaxial Manifestation of Rheumatoid Arthritis

Backgroundand Objectives: To date, imaging characterization of non-rheumatic retro-odontoid pseudotumors (NRROPs) has been lacking; therefore, NRROPs have been confused with atlantoaxial joint involvement of rheumatoid arthritis (RA). It is important to differentiate these two disease because the treatment strategies may differ. The purpose of this study is to characterize imaging findings of NRROPs and compare them with those of RA. Material and Methods: From January 2015 to December 2019, 27 patients (14 women and 13 men) with NRROPs and 19 patients (15 women and 4 men) with RA were enrolled in this study. We evaluated various imaging findings, including atlantoaxial instability (AAI), and measured the maximum diameter of preodontoid and retro-odontoid spaces with magnetic resonance imaging (MRI) and computed tomography (CT). Results: Statistical significance was considered for p < 0.05. AAI was detected in eight patients with NRROPs and in all patients with RA (p < 0.0001). Seventeen patients with NRROPs and six patients with RA showed spinal cord compression (p = 0.047). Compressive myelopathy was observed in 14 patients with NRROPs and in 4 patients with RA (p = 0.048). Subaxial degeneration was observed in 25 patients with NRROPs and in 9 patients with RA (p = 0.001). Moreover, C2-3 disc abnormalities were observed in 11 patients with NRROPs and in 2 patients with RA (p = 0.02). Axial and longitudinal diameter of retro-odontoid soft tissue and preodontoid and retro-odontoid spaces showed significant differences between NRROP and RA patients (p < 0.0001). Furthermore, CT AAI measurements were differed significantly between NRROP and RA patients (p < 0.05). Conclusions: NRROPs showed prominent retro-odontoid soft tissue thickening, causing compressive myelopathy and a high frequency of subaxial and C2-3 degeneration without AAI.

Cranio-Vertebral Junction Triangular Area: Quantification of Brain Stem Compression by Magnetic Resonance Images

(1) Background: Most of the currently used radiological criteria for craniovertebral junction (CVJ) were developed prior to the popularity of magnetic resonance images (MRIs). This study aimed to evaluate the efficacy of a novel triangular area (TA) calculated on MRIs for pathologies at the CVJ. (2) Methods: A total of 702 consecutive patients were enrolled, grouped into three: (a) Those with pathologies at the CVJ (n = 129); (b) those with underlying rheumatoid arthritis (RA) but no CVJ abnormalities (n = 279); and (3) normal (control; n = 294). TA was defined on T2-weighted MRIs by three points: The lowest point of the clivus, the posterior-inferior point of C2, and the most dorsal indentation point at the ventral brain stem. Receiver operating characteristic (ROC) analysis was used to correlate the prognostic value of the TA with myelopathy. Pre- and post-operative TA values were compared for validation. (c) Results: The CVJ-pathology group had the largest mean TA (1.58 ± 0.47 cm²), compared to the RA and control groups (0.96 ± 0.31 and 1.05 ± 0.26, respectively). The ROC analysis calculated the cutoff-point for myelopathy as 1.36 cm² with the area under the curve at 0.93. Of the 81 surgical patients, the TA was reduced (1.21 ± 0.37 cm²) at two-years post-operation compared to that at pre-operation (1.67 ± 0.51 cm²). Moreover, intra-operative complete reduction of the abnormalities could further decrease the TA to 1.03 ± 0.39 cm². (4) Conclusions: The TA, a valid measurement to quantify compression at the CVJ and evaluate the efficacy of surgery, averaged 1.05 cm² in normal patients, and 1.36 cm² could be a cutoff-point for myelopathy and of clinical significance.

Retro-Odontoid Pseudotumor Formation in the Context of Various Acquired and Congenital Pathologies of the Craniovertebral Junction and Surgical Techniques

Retro-odontoid pseudotumor formation consists of an abnormal growth of granulation tissue typically posterior to the odontoid process, resulting as a manifestation of atlantoaxial instability. This instability can occur as a result of conditions ranging from severe mechanical trauma to metabolic disease or autoimmune conditions such as rheumatoid arthritis. A pseudotumor may impinge on the spinal nerves or even the spinal cord and brainstem, manifesting symptoms from severe neck pain to cervicomedullary compression or myelopathy, and in some cases even sudden death. The objective of this review is to consolidate the findings in published case reports and relevant prior literature reviews regarding the formation of retro-odontoid pseudotumor. We address the pathophysiology involved in acquired and congenital pseudotumor formation, including those associated with rheumatoid arthritis (panni). Additionally, we discuss past and current operative techniques designed to curtail and ultimately regress a retro-odontoid pseudotumor and pannus. Surgical techniques that are addressed include ventral decompression (both transoral and transnasal), dorsal decompression, and indications for posterior instrumentation in pannus formation, particularly in cases that may be sufficiently treated in lieu of an anterior approach. Finally, we will examine the role of external orthoses as both a method of conservative treatment as well as a potential adjunct to the aforementioned surgical procedures.

Biomechanics of the effect of subaxial cervical spine degeneration on atlantoaxial complex in idiopathic retro-odontoid pseudotumor development

OBJECTIVES

Retro-odontoid pseudotumor (ROP), with no rheumatoid arthritis, atlantoaxial instability, or other primary diseases, is defined as idiopathic retro-odontoid pseudotumor (IROP). Cervical spine degeneration is associated with IROP development. This study aims to evaluate the effect of cervical spine degeneration on the atlantoaxial complex and find the possible biomechanical mechanism of IROP development.

METHODS

This study was performed using a three-dimensional (3D) finite element (FE) analysis. A degenerated FE model (FEM) and five operation FEMs (C1-C2 fusion, C0-C2 fusion, C0-C3 fusion, C0-C4 fusion, and C1 posterior arch resection) were established based on a normal 3D FEM of the cervical spine including C0-T1 with the main ligaments and muscles. The parameters, including the C1-C2 range of motions (ROMs) and odontoid-related ligaments' stresses in degenerated and operation FEMs, were obtained and compared with those in normal FEM.

RESULTS

Compared to normal FEM, degenerated FEM had reduced C3-C7 ROMs and increased C1-C2 ROMs and odontoid-related ligaments' stresses. After internal fixation, C1-C2 ROMs and most odontoid-related ligaments' stresses were greatly decreased, but with no significant differences among C0-C2, C0-C3, C0-C4, and C1-C2 fusion models. For the C1 posterior arch resection model, C1-C2 ROMs and most odontoid-related ligaments' stresses increased, compared with normal FEM.

CONCLUSIONS

Cervical spine degeneration plays an important part in IROP development in biomechanics. Atlantoaxial complex compensates for cervical spine degeneration, with increased C1-C2 ROMs and odontoid-related ligaments' stresses. Atlantoaxial fusion or short segmental occipitocervical fusion can effectively reduce the stress and should be considered in IROP treatment.

Thinking beyond pannus: a review of retro-odontoid pseudotumor due to rheumatoid and non-rheumatoid etiologies

Retro-odontoid pseudotumor, or mass-like retro-odontoid soft tissue thickening, is an uncommon but important imaging finding that may be associated with rheumatoid arthritis, crystal deposition diseases, as well as non-inflammatory conditions such as cervical degenerative changes and mechanical alterations. Retro-odontoid pseudotumor is commonly associated with atlantoaxial microinstability or subluxation. MRI and CT have an important role in the detection and diagnosis of retro-odontoid pseudotumor. However, due to a wide range of imaging characteristics and ambiguous etiology, it is a frequently misunderstood entity. The purpose of this article is to review relevant anatomy of the craniocervical junction; describe various imaging appearances, pathophysiology and histology in both rheumatoid and non-rheumatoid etiologies; and discuss differential diagnosis of retro-odontoid pseudotumor in order to help guide clinical management.

Development of a Retro-Odontoid pseudotumor in the absence of atlantoaxial instability or rheumatoid arthritis Post-Laminoplasty: case report

A retro-odontoid pseudotumor (ROP) is commonly associated with atlantoaxial instability (AAI) or rheumatoid arthritis (RA). However, we describe a patient with ROP in the absence of AAI or RA. An 81-year-old man who did not have a history of trauma to the head and neck admitted with neck pain, right upper extremity numbness, lower limb weakness, and walking disturbance. He had a history of C2 dome and C3-7 laminoplasty 10 years ago. Magnetic resonance imaging revealed a retro-odontoid mass with cervical cord compression. Dynamic radiography did not show signs of AAI. He underwent C1 laminectomy without fixation for the ROP. We speculated that the load on C1 and C2 increased because of the progression of kyphosis from C2 to C7 with increases in range of motion, which in turn caused change in the biomechanics of the cervical spine, leading to recurrent partial tear and degradation of the transverse ligament that induced formation of the ROP. Spinal surgeons should keep this complication in mind and inform patients about this potential postoperative complication.

Atlanto-axial Pannus in Patients with and without Rheumatoid Arthritis

Objective.

Pannus formation in the atlanto-axial joint is a well-recognized complication of rheumatoid arthritis (RA). Occasionally, atlanto-axial pannus is reported when patients without a history of RA undergo magnetic resonance imaging (MRI) of the cervical spine. We sought to further characterize these patients.

Methods.

The Partners HealthCare Research Patient Data Registry was free-text searched for “atlanto-axial” AND “pannus” in cervical spine MRI reports from 2001 to 2015. Cases with MRI reports describing pannus were reviewed. Clinical data were extracted by chart review in cases with confirmed atlanto-axial pannus (n = 105).

Results.

Twenty-nine patients (27.6%) had RA, all of whom except one carried this diagnosis at the time of the MRI scan. Only 1 of 77 patients without a history of RA was subsequently diagnosed with RA (1.3%, 95% CI 0.1–7.0%, median followup 3.6 yrs). Non-RA patients were significantly older (median age 79 vs 63 yrs, p < 0.0001), less frequently female (55% vs 86%, p = 0.0032), and more likely to have undergone prior cervical spine surgery (18% vs 0%, p = 0.016) compared with RA patients. Thirty-four non-RA patients (44.7%) either had a clinical diagnosis of calcium pyrophosphate dihydrate disease (CPPD) or imaging evidence for tissue calcification. There were no significant differences in age or sex between the CPPD subgroup and other non-RA patients. Twenty-eight patients (26.7%) underwent cervical spine surgery.

Conclusion.

Patients without RA diagnosis and incidental atlanto-axial pannus on cervical spine MRI are unlikely to have previously unrecognized RA. Degenerative disease and tissue calcification may contribute to pannus formation in these patients.

Retro-odontoid Degenerative Pseudotumour Causing Spinal Cord Compression and Myelopathy: Current Evidence on the Role of Posterior C1-C2 Fixation in Treatment

BACKGROUND

A retro-odontoid pseudotumour compressing the spinal cord and causing myelopathy is often associated with an inflammatory condition such as rheumatoid arthritis. A degenerative non-inflammatory retro-odontoid pseudotumour responsible for clinically relevant spinal cord compression is a rare condition described in small clinical series and is likely associated with craniovertebral junction hypermobility or instability-like conditions. For several years, direct removal of the lesion through an anterior or lateral approach has been advocated as the best surgical option. However, in the last decade the posterior approach to the craniovertebral junction, to perform C1-C2 fixation and C1 laminectomy without removal of the retro-odontoid tissue, has demonstrated its efficacy in reducing retro-odontoid pannus as well as in obtaining improvement of myelopathy.

METHODS

In this paper we analyse the clinical and radiological outcomes of seven patients (five males and two females) treated with posterior C1-C2 fixation and C1 laminectomy for a degenerative non-inflammatory retro-odontoid pseudotumour responsible for spinal cord compression. C1 laminectomy provided immediate spinal cord decompression. We also review the relevant literature focusing on associated cervical degenerative conditions that may contribute to triggering or acceleration of atlantoaxial hypermobility or 'instability', causing formation of the retro-odontoid tissue.

RESULTS

The mean follow-up period (of six followed-up patients) was 55.8 months (range 10-96 months). In all cases the Nurick score at the latest follow-up visit demonstrated clinical improvement; magnetic resonance imaging during follow-up demonstrated progressive reduction of the retro-odontoid pseudotumour in all but one patient, who died of surgery-unrelated disease in the early postoperative period. No vascular or neural damage secondary to C1-C2 fixation was observed.

CONCLUSION

C1-C2 fixation associated with C1 laminectomy is an effective surgical option to treat myelopathy secondary to a degenerative retro-odontoid pseudotumour. In these cases, direct removal of intracanalar tissue compressing the spinal cord is not required, as C1-C2 fixation is sufficient to cause its disappearance.

Postoperative Regression of Retro-odontoid Pseudotumor After Atlantoaxial Posterior Fixation: 11 Years of Experience in Patients With Atlantoaxial Instability

STUDY DESIGN

Case series study.

OBJECTIVE

The aim was to investigate the incidence of retro-odontoid pseudotumor in patients with atlantoaxial instability (AAI) and evaluate pseudotumor regression after posterior fixation.

SUMMARY OF BACKGROUND DATA

The incidence of retro-odontoid pseudotumor in atlantoaxial instability patients remains uncertain. Moreover, the regression of retro-odontoid pseudotumor after posterior fixation in patients with various underlying diseases needs to be further investigated.

METHODS

From July 2004 to August 2015, 175 patients with AAI underwent posterior fixation operations at our institution. After excluding 11 patients (previous operation, n = 4; history of tumor, n = 7), the final study population comprised 164 patients. The final study population was categorized according to their underlying diseases (rheumatoid arthritis [RA], os odontoideum, atlanto-occipital assimilation, dens fracture, AAI of unknown cause, etc.) and age (adult and pediatric groups). The incidence of retro-odontoid pseudotumor in each group was analyzed. Pre- and postoperative magnetic resonance or computed tomography images were reviewed to assess its regression following surgery.

RESULTS

Of the 164 patients included, 38 had retro-odontoid pseudotumor (23.2%). Three were diagnosed with RA and the rest were non-RA patients including os odontoideum (n = 12), dens fracture (n = 6), atlanto-occipital assimilation (n = 4), Morquio syndrome (n = 1), and AAI of unknown cause (n = 12). Pseudotumor size regressed in all 38 patients after atlantoaxial posterior fixation. There was a statistically significant decrease in pseudotumor size (the length between the anterior border of the odontoid process to the posterior border of the pseudotumor) from a mean length of 17.7 to 14.9 mm (P < 0.001).

CONCLUSIONS

The patients had various underlying diseases and the overall incidence of retro-odontoid pseudotumor in patients with symptomatic AAI was 23.2% at our institution during the past 11 years. All patients who underwent posterior fixation for AAI showed a statistically significant decrease in pseudotumor size.

LEVEL OF EVIDENCE

4.

Restrictions of cervical flexion after laminoplasty increase in the mechanical stress at the occipitocervical junction in non-rheumatoid arthritis patients

Increased range of motion (ROM) at O-C2 after cervical laminoplasty is thought to be a compensatory change due to loss of cervical ROM after surgery. Retro-odontoid pseudotumor in non-RA patients is also caused by loss of ROM at C2-C7 causing mechanical stress on upper cervical spine. The aim of this study was to measure the occipitocervical alignment before and after cervical laminoplasty, and examine the factors associated with postoperative retro-odontoid soft tissue (ROST) enlargement. The study comprised 72 non-RA patients (51 males and 21 females, mean age 65.2years) who underwent cervical laminoplasty. The cervical angles (O-C1, O-C2, C1-C2, and C2-C7) were measured and ROST thickness was evaluated on mid-sagittal T1-weighted MRI before surgery and 2years after surgery. Correlations between radiographic changes and postoperative ROST enlargement were examined. The results shows that postoperative ROM and kyphotic angle in flexion position at O-C2 significantly increased, and postoperative ROM and kyphotic angle in flexion position at C2-C7 significantly decreased compared with preoperative values. On stepwise multiple regression analysis, age (beta=0.273, p<0.01) and restriction of cervical flexion postoperatively (beta=0.235, p<0.01) were independently associated with ROST enlargement. In conclusion, occipitocervical ROM increased and C2-C7 ROM, especially C2-C7 kyphotic angle in flexion, reduced after cervical laminoplasty. The ROST enlargement was associated with reduction in cervical flexion. These results indicate that preservation of cervical ROM, especially kyphotic angle in flexion, after cervical laminoplasty contribute to reduction of mechanical stress at the occipitocervical junction.

The Effects of Clinical Factors and Retro-Odontoid Soft Tissue Thickness on Atlantoaxial Instability in Patients with Rheumatoid Arthritis

BACKGROUND

Rheumatoid arthritis (RA) is an autoimmune disease that often occurs in the atlantoaxial segment of the cervical spine and results in instability that can cause severe pain and neurologic symptoms. Thickening of soft tissue posterior to the odontoid process of the atlantoaxial segment is referred to as retro-odontoid soft tissue (ROST) thickness or pseudotumor. The mechanism of ROST thickness is still unknown.

METHODS

Among patients diagnosed with RA, those with cervical radiographs and magnetic resonance imaging records were selected for investigation of their clinical symptoms, laboratory findings, radiologic evaluation, and RA medication history.

RESULTS

A total of 199 patients were selected and divided into lower and upper median groups according to the ROST thickness value. In patients with RA, the median ROST thickness value was 2.3 mm (interquartile range, 1.4-3.4). The median value of the anterior atlanto-dens interval (ADI) was 2.4 mm, with a significant difference being observed between the lower and upper median ROST thickness groups (P = 0.001). Multivariable linear regression analysis revealed a correlation between Steinbrocker stage and the positivity of rheumatoid factor. For each unit increase in the Steinbrocker stage, the ROST thickness increased by 0.35 mm (β, -0.349; 95% confidence interval -0.643 to -0.055; P = 0.020). For every 1-mm increase in the ADI, ROST thickness decreased by 0.16 mm (β, -0.163; 95% confidence interval -0.264 to -0.062; P = 0.002).

CONCLUSIONS

This study showed a statistical correlation between ROST thickness and ADI related to biomechanical changes in the dynamic atlantoaxial segment, thereby suggesting the value of a prospective study.

Factors associated with retro-odontoid soft-tissue thickness in rheumatoid arthritis

OBJECTIVE Increasing soft-tissue mass posterior to the odontoid process causes spinal cord compression. Retro-odontoid pseudotumors are considered to be associated with atlantoaxial instability in patients with rheumatoid arthritis (RA), but the exact mechanism by which these lesions develop has not been elucidated. The purpose of this study was to identify the relationships between retro-odontoid soft-tissue (ROST) thickness and radiological findings or clinical data in patients with RA. METHODS A total of 201 patients with RA who had been followed up at the outpatient clinic of the authors' institution were enrolled in this study. ROST thickness was evaluated on midsagittal T1-weighted MRI. The correlations between ROST thickness and radiographic findings or clinical data on RA were examined. The independent factors related to ROST thickness were analyzed using stepwise multiple regression analysis. RESULTS The average thickness of ROST was 3.0 ± 1.4 mm. ROST thickness showed an inverse correlation with disease duration (r = -0.329, p < 0.01), Steinbrocker stage (r = -0.284, p < 0.01), the atlantodental interval (ADI) in the neutral position (r = -0.326, p < 0.01), the ADI in the flexion position (r = -0.383, p < 0.01), and the ADI in the extension position (r = -0.240, p < 0.01). On stepwise multiple regression analysis, ADI in the flexion position and Steinbrocker stage were independent factors associated with ROST thickness. CONCLUSIONS Although the correlations were not strong, ROST thickness in patients with RA was inversely correlated with ADI and Steinbrocker stage. In other words, ROST thickness tends to be smaller as atlantoaxial instability and peripheral joint destruction worsen. Clinical trial registration no.: UMIN000000980 (UMIN Clinical Trials Registry).

Odontoid pseudotumor and serial postfusion radiographic evaluation in a patient with a C1–2 mass

Odontoid pseudotumor is a mass occurring around the odontoid process in the cervical spine and can cause significant neurological symptoms at the craniocervical junction due to compression of the spinal cord and cervicomedullary junction at this level. A literature review was performed to provide input on options for treatment and prognosis for this lesion. The literature search found 12 papers in which pseudotumor was treated with posterior decompression and fixation. Posterior decompression and fixation with serial imaging to monitor the size of the pseudotumor postsurgery is a safe and effective treatment option for odontoid pseudotumors.

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

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.