Study design: A retrospective investigation of the retrodental mass secondary to rheumatoid arthritis (RA).
Objective: To propose a new classification of the retrodental mass in RA, and to evaluate their resorption processes and surgical procedures.
Summary of background data: The retrodental mass secondary to RA has long been recognized as pannus formation. It is also known that pannus will disappear or radically reduce after stabilization of the atlantoaxial segment. The past reports, however, leave unanswered the following question; are there other types of mass with significantly different degeneration processes from the pannus? The need for anterior transoral decompression is still controversial.
Methods: Eleven patients with retrodental masses in RA were retrospectively analyzed. They underwent posterior fusion without decompression for atlantoaxial subluxation and occipitocervical fusion with decompressive laminectomy of the atlas for vertical subluxation. All patients had neurological, radiologic, and magnetic resonance imaging (MRI) evaluations both before and after surgery. MRI study was performed preoperatively and at 1-month interval after surgery until the mass had disappeared or stopped further reduction.
Results: This study identified 3 distinctive types in the rheumatoid retrodental mass on MRI. Type 1 displayed high intensity on T2 and low intensity on T1-weighted MRI or the pattern specific to pannus. Type 2 was identified with low intensity on T2-weighted MRI or pattern specific to pseudotumor. Type 3 displayed a combination of high and low intensity on T2-weighted images or indication that the mass was the mixture of pannus and pseudotumor. All the masses of types 1 and 3 disappeared within 1 month of surgery. The process in type 2 was found a few months slower. In all 11 cases, myelopathy improved postoperatively to the status before the emergence of the symptom.
Conclusions: This article recognized 3 distinctive types of the retrodental mass in RA; type 1 (pannus), type 2 (pseudotumor), type 3 (mixed). It further concludes in all types of the retrodental mass associated with atlantoaxial subluxation secondary to RA, posterior fusion without decompression can achieve improvement of the myelopathy. In type 2 associated with vertical subluxation, on balance between calculable benefits and high risks of anterior transoral decompression, the authors prefer to opt for occipitocervical fusion with decompressive laminectomy of the atlas.