MRI appearance of retrocalcaneal bursitis and rheumatoid nodule in a patient with rheumatoid arthritis.

Rheumatoid arthritis is an autoimmune disorder of unknown etiology characterized by symmetric, erosive synovitis and sometimes multisystem involvement. Rheumatoid nodules have been reported in as many as 20-30% of patients with rheumatoid arthritis; however, they are not commonly seen in the feet. We present magnetic resonance (MR) findings of a rarely seen case of rheumatoid bursitis in the retrocalcaneal bursa associated with a subcutaneous rheumatoid nodule inferior to the calcaneus which histologically confirmed the rheumatoid arthritis. To the best of our knowledge, this is the first case that rheumatoid bursitis in the retrocalcaneal bursa associated with the rheumatoid nodule in the foot was revealed by MR imaging.