LAUSR

AIM The potential significance of relationship of atlantoaxial instability with retroodontoid pseudotumor, pannus and/or a cyst (RPC) is analyzed. METHODS We retrieved the database of craniovertebral junction related instability cases treated by atlantoaxial fixation during the period January 2000 to March 2020. We identified 63 cases where there was a RPC in the region posterior to the odontoid process or posterior to the posterior aspect of the C2 body. RESULTS The RPC was 'solid' in 10 cases, predominantly cystic in 39 cases and had both solid and cystic components in 14 cases. The vertical dimension of the RPC varied from 4.5 mm to 10.5 mm (average 7.9 mm), transverse dimension ranged from 2 mm to 5.2 mm (average 3.4 mm). In 51 cases the RPC was in the midline and in 9 cases it was eccentric in location. In 38 cases there was erosion of C2 body adjoining the RPC. Analysis of investigations revealed that in 100 percent cases the dome of the RPC was in line of the most susceptible point of potential bone compression of neural structures. The RPC was eccentric in location in 9 cases presenting with torticollis. RPC indicated the presence of atlantoaxial instability even when there were no other positive and validated radiological indicators. Following atlantoaxial stabilization, the RPC spontaneously regressed or disappeared. Direct resection of the RPC was neither done nor was necessary in any case. CONCLUSIONS The RPC are secondary consequences of atlantoaxial instability and need not be primarily addressed by surgical resection. Their location suggests that they might have a neural protective function.