Retro-odontoid pseudotumor
Retro-odontoid pseudotumors, also known as periodontoid pseudotumors, are non-neoplastic soft tissue masses adjacent to the odontoid process (dens) of C2, which can cause cervicomedullary compression 1).
Epidemiology
The prevalence of retro-odontoid soft tissue thickening, particularly with mineralization presumed to represent calcium pyrophosphate deposition, increases significantly with age 2).
Classification
Retro-odontoid pseudotumor (ROP) in patients without rheumatoid arthritis 3). Atlanto-axial subluxation may play a role in developing ROP. ROP unassociated with AAS can be seen in patients without RA but is rare. All cases reported were seen in the elderly and most have severe OA changes at the atlanto-axial joint
Clinical features
These are often asymptomatic. Acute inflammation in these masses (as in Crowned dens syndrome) can manifest as neck pain or headache. As a chronic process, mass effect on the cervical spine can manifest as myelopathy including sensory and motor deficits.
Pathology
Pseudotumors can arise by various mechanisms and etiologies 4) 5).
Rheumatoid arthritis (RA): in which case it may be termed pannus
tenosynovial giant cell tumor
atlantoaxial hypermobility compensating for subaxial ankylosis
diffuse idiopathic skeletal hyperostosis
ossification of the posterior longitudinal ligament
cervical spondylosis/osteoarthritis
deposition diseases
calcium pyrophosphate dihydrate deposition disease (CPPD)
hydroxyapatite deposition disease (HADD)
gout
amyloid arthropathy associated with hemodialysis
dens fracture callus
migrated disc herniation
Diagnosis
Differential diagnosis
Consider:
Retro-odontoid synovial cyst
Epidural hematoma
Epidural lipomatosis.
Treatment
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. Fiani et al. examined the role of external orthoses as both a method of conservative treatment as well as a potential adjunct to the aforementioned surgical procedures 6).
Case series
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 7)
Case reports
An atlanto-occipital assimilation altered the biomechanics of the cervical spine, causing chronic mechanical stress on the transverse ligament and subsequently the development of a retro-odontoid pseudotumor. This is in accordance with previous studies that have attributed the development of retro-odontoid pseudotumor to a loss of mobility of the cervical spine, in cases without associated rheumatoid arthritis or atlanto-axial subluxation 8)
A male patient in his late 90's presented with inability to ambulate, global paresis, and long tract signs in the upper extremities. He was found to have a large odontoid mass with compression at the cranio-cervical junction. He underwent cervical fusion with instrumented fixation from C1-6 and decompressive laminectomy from C4-6. Over a follow-up period of two years, there was improvement in the patient's motor weakness and ambulation. Radiographic evaluation at the two-year mark showed marked reduction in pannus size. Indirect approaches to decompression in patients with retro odontoid pseudo tumor using techniques such as cervical fusion may be a safe for effective treatment in patients of advanced age, with multiple co-morbidities, and inability to tolerate lengthy surgical procedures 9).