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.
Retro-odontoid pseudotumor, or odontoid pannus, refers to a disease process characterized by non-neoplastic soft tissue proliferation that is adjacent to the odontoid process of cervical 2 (C2) vertebra, and can lead to compression of the vital neuronal structures of the cervicomedullary region [
Pseudotumor formation can be secondary to a variety of etiologies. The most common causes include rheumatoid arthritis (RA), acute trauma, and congenital abnormalities such as Down syndrome, Morquoi Syndrome, and neurofibromatosis. In the setting of RA, inflammatory infiltrate of synovial joints leads to buckling of the posterior longitudinal ligament (PLL), causing pannus formation [
Correct diagnosis of a retro-odontoid pseudotumor or pannus is crucial to avoiding further disease progression. If left untreated, growing pseudotumor/pannus can induce further spinal cord compression, exacerbating neurological symptoms. Early recognition of cervical myelopathy along with swift surgical evaluation can lower morbidity and improve symptomatic outcomes [
Soft tissue proliferation in the region of the transverse ligament of the atlantoaxial (AA) junction, or pseudotumor, is associated with a diverse list of congenital and acquired conditions (
Three subtypes of RA-associated pannus are known, classified based upon histopathology as hypervascular, hypovascular and fibrous pannus, also known as inflammatory, combined, and fibrous pannus, respectively [
Retro-odontoid pseudotumor is also associated with AAI of various causes, and trauma. As with instability, any alteration in biomechanics of the cervical spine may result in pseudotumor formation by way of repeated injury with inflammation, resulting ligamentous injury and subsequent repair. Pseudotumor-associated with diffuse idiopathic skeletal hyperostosis (DISH), ossification of the posterior longitudinal ligament (OPLL), and cervical spondylosis are thought to occur by the same mechanism. DISH and OPLL result in a decreased range of motion (ROM) of the subaxial cervical spine with resulting compensatory hypermobility of the craniocervical junction. Trauma may result in nonunion and pseudoarthrosis of an odontoid fracture [
In addition, deposition diseases, such as calcium pyrophosphate dihydrate deposition disease (CPPD), gout, and amyloid arthropathy may cause pseudotumor. The underlying disease process of CPPD, referred to as chondrocalcinosis, involves the deposition of calcium pyrophosphate dihydrate crystals in ligaments, synovium, and capsule structures [
Additionally, hemodialysis-associated amyloidosis may cause pseudotumor. For patients on long-term dialysis, accumulation of β-2 microglobulin in the form of amyloid fibrils in joints and surrounding structures can occur. These fibrils can accumulate in the cervical spine, and deposit in the craniocervical junction [
Retro-odontoid pseudotumor formation results in structural and functional concerns that coincide with AAI, which can be assessed clinically and radiographically. AA subluxation, one of the most common causes of pseudotumor formation, can manifest as minor axial neck pain with progressive sequelae occurring as the degree of instability worsens, and eventually may result in death [
AAI associated with retro-odontoid pseudotumor formation displays radiographic features that allow the physician to improve preparedness for intervention and patient outcomes. Acquisition of dynamic conventional radiographs in flexion, neutral, and extension are used for the evaluation of the atlantodental interval (ADI), which is defined as the distance between the anterior tubercle of C1 and the anterior aspect of the odontoid process [
MRI can be used to visualize the pseudotumor, typically ranging from isointense to hypointense relative to the spinal cord on T1-weighted images and hypointense in T2-weighted images [
There are a variety of pathologies resulting in the compression of the anterior upper cervical spinal cord. The most common condition necessitating surgical intervention for ventral cord compression is development of an inflammatory pseudotumor [
Cervical pseudotumor formation most often occurs adjacent to the dens. Common locations include between the anterior arch of C1 and the dens, and between the transverse ligament and the dens [
Historically, the transoral approach to the CVJ has been the gold standard to achieve anterior decompression in this region [
Partial odontoidectomy with preservation of the anterior arch of C1 aims to limit if not elude iatrogenic instability, sometimes allowing avoidance of posterior fixation and its associated risks. Notably, disruption of bony mechanics as well as soft tissue articulations may lead to clinically significant instability [
Duntze et al. [
Nevertheless, Edwards [
The range of access provided by TO and EE approaches differs significantly. The nasopalatine line (NPL) is the inferior boundary for EE procedures. While the NPL may vary with respect to spinal level from patient to patient, the TO approach provides greater caudal access than EE surgery. The TO approach is limited relative to EEA superiorly; this boundary may be extended by splitting the hard and soft palate. However, this may result in velopharyngeal insufficiency (VPI) [
In addition to a plane more favorable for C1 arch preservation, the EEA has the added benefit of mucosal incisions in the nasopharynx (versus TO which incises the oropharynx) [
Both approaches are limited by a steep learning curve and potential for severe neurological morbidity and mortality, with a particularly intimate relationship between the surgical corridor and the brainstem in an EEA. A 2016 meta-analysis and systematic review found that tracheostomy was the most common surgically-related complication associated with transoral odontoidectomy (TOO), occurring in 10.8% of patients [
AAI may both contribute to and result from pseudotumor formation. In cases with AAI, posterior fixation to address the instability is indicated. Reports of pseudotumor regression following surgical fixation alone without direct resection of the lesion are widespread in the literature; techniques for posterior instrumentation as treatment of pseudotumor are discussed below.
There are many etiologies causing symptomatic retro-odontoid pseudotumor without inherent instability of the CVJ or cervical spine. In these instances, posterior approach options include reduction of the lesion via posterior decompression without fixation or direct resection of the lesion. The former has been demonstrated with both C1 laminoplasty or laminectomy without use of any instrumentation or fusion [
Another option for cases not requiring fusion is the high cervical lateral approach as first described by Henry in 1973 for C1–2 vertebral artery access. Naito et al. [
A posterior transdural approach for resection of a ventrally located lesion was described in the literature as early as 1910 by Taylor [
The techniques utilized for treating pseudotumor formations using posterior instrumentation includes O-C fusion as well as C1–2 fusion. The goal with posterior instrumentation is to achieve a similar level of success in pseudotumor regression compared anterior and circumferential approaches, along with comparable clinical improvements in Nurick scoring, while minimizing postoperative complications and recovery times [
The goal in occipital surgical fusion is to prevent further progression of the pseudotumor and improve neurological outcomes; this is achieved by use of intraoperative monitoring as the surgeon slowly decompresses the medulla to prevent tissue damage [
The C1–2 synovial lining around the odontoid is one of the most common regions for pseudotumor formation [
External orthoses have been used independently as a conservative measure and in conjunction with surgery as a routine postoperative treatment. Although there are different types, collars are used to limit motion, to reduce graft loading and migration, and to encourage fusion [
In a survey of North American spine surgeons, 63% stated they routinely use orthoses after cervical spine operations, the primary purpose of which is to limit cervical spinal motion in order to allow for proper union and healing [
Retro-odontoid pseudotumor is an uncommon entity with a diverse set of underlying etiologies, including inflammatory conditions such as RA, as well as nonrheumatological causes such as odontoid fracture, OPLL, DISH, CPPD, and PVNS. A key feature of retro-odontoid pseudotumor pathogenesis is the repeated cycle of ligamentous injury and repair, thought to be initiated most commonly by damage to the transverse ligament as a result of inflammation, trauma, degeneration, and/or an alteration in biomechanics. Clinical manifestations can be broad depending on the severity and specific etiology of the underlying cause and local disease. Regardless, accurate and timely diagnosis is essential to initiate prompt treatment, with the primary objective being to lower morbidity and improve symptomatic outcomes. Despite this being a rare entity, the most common reason for surgical intervention in the case of spinal cord compression is presence of an inflammatory pseudotumor. Irrespective of etiology, a phenomenon that has been observed is the regression of pannus postoperatively after fusion, indicating that excess motion at the craniocervical junction may be a driving factor in retro-odontoid pseudotumor development and progression.
A retro-odontoid pseudotumor or pannus may be treated via various approaches to access the pannus to achieve either ventral or dorsal decompression (
The authors have nothing to disclose.
Supplementary Table 1 can be found via
Pathogenesis of retro-odontoid pseudotumor as a result of rheumatoid and nonrheumatoid etiologies. VEGF, vascular endothelial growth factor. *Includes chronic mechanical stress as induced by acute trauma, diffuse idiopathic skeletal hyperostosis, ossification of the posterior longitudinal ligament, and cervical spondylosis.
Algorithm of surgical approaches.
Illustrative case of a patient with past medical history of rheumatoid arthritis presenting with severe posterior neck pain and bilateral hand weakness. (A) Preoperative midsagittal T2-weighted magnetic resonance imaging (MRI) shows retro-odontoid pannus with compressive upper cervical spinal cord stenosis, along with subaxial cervical stenosis. (B) Postoperative midsagittal T2-weighted MRI shows resultant transnasal resection of pannus. Additional C1–6 decompressive laminectomy and occipital-T2 instrumentation and fusion were performed due to subaxial cervical stenosis.