Periodontoid pseudotumor with cranial retroclival extension and brainstem compression in a patient with rheumatoid arthritis: illustrative case

Abstract

BACKGROUND

Periodontoid pseudotumor is a nonneoplastic mass arising around the odontoid process and is most commonly associated with chronic atlantoaxial instability in inflammatory and noninflammatory conditions. Although traditionally managed with direct anterior resection, increasing evidence suggests that posterior stabilization may promote lesion regression by addressing the underlying biomechanical driver.

OBSERVATIONS

A 73-year-old male with a history of rheumatoid arthritis was admitted to the authors’ institution with a history of gait instability and vertigo. Contrast-enhanced MRI of the cervicomedullary junction revealed a retro-odontoid cystic mass with significant cranial extension into the retroclival region and compression on the lateral recess of the fourth ventricle. The patient underwent a C1–2 arthrodesis with the Magerl technique and decompression of the posterior arch of C1. Marked regression of the periodontoid mass was observed on 3-month postoperative MRI, along with significant cervicomedullary junction decompression.

LESSONS

In carefully selected patients with radiological evidence of chronic atlantoaxial instability and favorable C1–2 anatomy, posterior stabilization may represent an effective primary strategy for managing periodontoid pseudotumor, even in cases with cranial extension. This approach may mitigate the morbidity associated with anterior mass resection, although its generalizability is limited by the single-case design and short-term follow-up.

https://thejns.org/doi/10.3171/CASE26169

Periodontoid pannus is a fibrocartilaginous or granulation tissue mass that develops around the dens and can involve the entire craniocervical junction, potentially resulting in compressive myelopathy.¹ It is most frequently associated with inflammatory rheumatic disorders, including rheumatoid or psoriatic arthritis but may also occur in noninflammatory conditions. The underlying pathophysiology is thought to be related to chronic instability of the atlantoaxial junction, leading to reactive soft tissue proliferation. Although the management of periodontoid pannus has traditionally consisted of direct mass removal via transoral or anterolateral approaches, recent surgical reports have demonstrated progressive regression of the pannus following stabilization of the craniocervical junction with or without decompression of the spinal canal. We herein present the clinical case of a patient harboring a retrodontoid pseudotumor demonstrating unusual cranial extension into the paraclival and intracranial compartments, resulting in compressive myelopathy at the level of the bulbomedullary junction and involvement of the lateral recess of the fourth ventricle, treated by CT-guided neuronavigation-assisted C1–2 transarticular fusion with a Magerl technique,² without direct approach of the mass. To the best of our knowledge, this represents the first reported case of a periodontoid pseudotumor with documented intracranial extension.

Illustrative Case

A 73-year-old man with a history of rheumatoid arthritis who was undergoing a 6-month course of methotrexate therapy presented to the emergency department with progressive gait disturbance, loss of appetite, and vertigo. Neurological examination revealed gait instability and mild weakness of the left lower limb. The Babinski sign was negative bilaterally. No clonus was observed.

A contrast-enhanced MR image of the craniocervical junction showed a cystic multilobulated lesion (39 × 26 × 22 mm) with inhomogeneous hyperintensity on T2-weighted scans, centred at the level of a thickened tectorial membrane extending cranially into the right paraclival area. This mass caused complete obliteration of the anterior perimedullary cistern and compression on the medulla and on the right lateral recess of the fourth ventricle. Radiological findings were consistent with a periodontoid rheumatoid pannus or pseudotumor (Fig. 1).

FIG. 1.

Sagittal T2-weighted (A), sagittal T1-contrast-enhanced (B), and coronal T2-weighted (C) MR images showing a dishomogeneous polylobulated, cystic lesion, with a contrast-enhancing capsule, developing from the anterior and posterior portion of the dens and extending cranially towards the bulbomedullary junction, causing compression on the spinal cord and brainstem.

Neurophysiological evaluation with somatosensory and motor evoked potential recordings demonstrated only a mild alteration of the somatosensory pathway of the lower limb, without signs of motor pathway dysfunction. Based on the history of long-standing rheumatoid arthritis and imaging findings consistent with a chronic instability of the craniocervical junction, posterior C1–2 arthrodesis was planned as the primary treatment strategy, avoiding a direct approach to the periodontoid mass.

Preoperative CT angiography was performed to delineate the vertebral artery anatomy and thus optimize the surgical trajectory. Given the favorable morphology of bilateral C1–2 articular complexes and course of the vertebral arteries, a C2-transarticular C1–2 arthrodesis (Magerl construct) was selected.

The patient was placed prone with his head secured in a Mayfield head holder. Intraoperative mobile cone-beam CT scan (CBCT) integrated with neuronavigation (LoopX, Brainlab) was used to guide screw placement. A midline incision was made from the occiput to C4. Subperiosteal dissection of the posterior cervical muscle and exposure of the posterior arch of C1, along with the spinous process and laminae of C2, was achieved. The neuronavigation reference array was fixed to the spinous process of C2. Intraoperative CT was performed, and the images were transferred to the neuronavigation workstation for registration. Following navigated confirmation of the C2 entry points, bilateral paramedian stab incisions were performed to allow transarticular C2 screw insertion under real-time neuronavigation according to the planned trajectories. Intraoperative CT showed the correct placement of the screws, which was also confirmed with postoperative neuroradiological evaluation (Fig. 2). The surgical procedure was completed with decompression of the posterior arch of C1. The patient’s postoperative course was uneventful, and he was mobilized on postoperative day 2. He was referred to the physical therapy unit for gait rehabilitation and for a rheumatological evaluation to restart immunosuppressive therapy. At the 3-month follow-up, the patient demonstrated complete neurological recovery with independent ambulation. Follow-up contrast-enhanced MRI of the craniocervical junction showed a marked regression of the periodontoid pseudotumor (7 × 7 × 6 mm) with complete resolution of the retroclival component and decompression of the cervicomedullary junction (Fig. 3). The patient continued to undergo rheumatological follow-up and remained on a regimen of methotrexate therapy with sustained clinical response.

FIG. 2.

CT scan obtained on the 1st day postoperatively, showing the path of the right (A) and left (B) transarticular screws following the Magerl technique. The asterisk indicates the position of the left vertebral artery. Placement of the screws was done with the guidance of neuronavigation to avoid neurovascular damage.

FIG. 3.

Sagittal (A) and coronal (B) T2-weighted MR images obtained 3 months postoperatively showing significant resorption of the pseudotumor with regression of the bulbomedullary compression. Neuroradiological control shows the regression of the malacic area of the medulla and the decompression of the prepontine cistern.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

The presence of a nonneoplastic mass surrounding the odontoid process has been referred to as retro-odontoid pseudotumor. This entity was classically described as “pannus” reflecting the deposition of inflammatory tissue at the craniocervical junction in rheumatological conditions such as rheumatoid or psoriatic arthritis.^3,4 However, similar lesions have also been reported in posttraumatic conditions,⁵ congenital disorders including Down Syndrome, Morquio syndrome, and neurofibromatosis⁶—and metabolic conditions like amyloidosis, chronic kidney disease, and hypercalcemia.^7–9 Despite this etiological heterogeneity, the pathophysiological mechanism underlying pannus formation relies on a progressive biomechanical alteration of the craniocervical junction, resulting in chronic atlantoaxial instability and repetitive stress on the ligaments and articular structures. Such a mechanism could be responsible for both initiation and propagation of the pseudotumor, as it happens with posttraumatic and inflammatory diseases, respectively.⁶ Once established, the lesion exerts mass effect on the spinal cord and brainstem, leading to clinical manifestations of myelopathy and, in severe cases, life-threatening respiratory distress.¹⁰

Even if conservative management could be considered in patients who are poor surgical candidates,¹¹ surgical management remains the first option to treat this condition. Historically, direct pseudotumor removal by means of anterior approaches (i.e., endoscopic endonasal or transoral approaches) or anterolateral approaches has represented a viable strategy.^12–14 Nevertheless, these approaches are associated with high morbidity and perioperative mortality.

Relying on the pathophysiological mechanism of the chronic atlantoaxial instability, multiple surgical series have reported that posterior stabilization of the craniocervical junction, with or without concomitant spinal cord decompression, can lead to partial or complete regression of the pseudotumor and meaningful clinical improvement.^15–18 Barbagallo et al. reported a surgical series of 5 patients harboring retro-odontoid pseudotumors treated with posterior cervical arthrodesis and spinal canal decompression, with complete or incomplete radiological resorption of the pannus within 4–10 months.¹⁹ In a large surgical series of 38 patients, Park et al. also observed pseudotumor regression after cervical fusion, irrespective of the causative condition.¹⁶

Within this context, our clinical case supports the effectiveness of posterior C1–2 arthrodesis in managing a large retro-odontoid pseudotumor causing compression to not only the spinal cord but also the brainstem, without the need for directly addressing the lesion. Despite the neuroradiological findings, the patient’s clinical presentation was mild, which informed the decision to prioritize posterior stabilization and decompression over anterior mass removal in order to address the presumed biomechanical driver while minimizing surgical risk.

The specific anatomy of the craniocervical junction, along with the course of the vertebral arteries, provided us with the possibility of achieving a C1–2 transarticular Magerl construct, which is considered biomechanically to be the best technique in terms of stability and fusion rate.² Furthermore, we performed surgery with the aid of intraoperative mobile CBCT with neuronavigation, which provided us high accuracy in screw placement, thus avoiding any iatrogenic damage to critical neurovascular structures. The patient’s postoperative course was uneventful, and het was discharged with improvement in his symptoms. At the 3-month follow-up, neuroradiological control showed regression of the pseudotumor and resolution of the brainstem and spinal cord compression.

Lessons

Our clinical case supports existing evidence suggesting that posterior cervical arthrodesis with spinal cord decompression is an effective primary strategy for managing periodontoid pseudotumor. This approach was most notably applied in a patient with marked cranial extension of the lesion toward the brainstem, with subsequent radiological regression and meaningful clinical improvement, without the need for direct anterior mass resection.

This strategy should be considered in carefully selected patients with radiological features of instability, favorable C1–2 osseous and vascular anatomy, and the absence of rapidly progressive neurological deterioration requiring urgent decompression. Comprehensive preoperative assessment of the vertebral artery course is essential, particularly when transarticular fixation is planned, and adjuncts such as intraoperative navigation or CBCT may enhance procedural safety in anatomically constrained surgical corridors.

The interpretation of these findings is limited by the single-patient design and relatively short follow-up. Although this report represents, to our knowledge, the first description of a retro-odontoid pseudotumor with documented intracranial extension treated with C1–2 arthrodesis, larger series and longer-term data are required to establish the durability and generalizability of this stabilization-based approach.

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: Schonauer. Acquisition of data: De Rosa, Palmiero, Oliva, Tafuto. Analysis and interpretation of data: Oliva. Drafting the article: De Rosa, Palmiero, Oliva. Critically revising the article: Parisi. Reviewed submitted version of manuscript: Schonauer. Approved the final version of the manuscript on behalf of all authors: De Rosa. Administrative/technical/material support: Iannuzzo, Tafuto.

Correspondence

Andrea De Rosa: “Antonio Cardarelli” Hospital, Naples, Italy. andrea.derosa@aocardarelli.it.