A 23-year-old man referred by his primary care physician presented with a 1.5-year history of progressive left ankle pain and swelling. He recalled no history of trauma other than stepping on a horseshoe crab when he was 8 years old and having the tail removed in a local emergency department. He denied recent fevers, chills, night sweats, weight loss, or weight gain. Physical examination revealed substantial nonpitting edema around the hindfoot region extending up the distal 1 .3 of his leg. There was no skin discoloration. He had mild tenderness to palpation along the peroneal and posterior tibial tendons. There was normal strength and sensation in the foot and leg. No lymphadenopathy was noted. His laboratory values, including complete blood count, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), uric acid, rheumatoid factor, and Lyme titer were all within normal limits. Imaging studies, including MRI (Fig. 1), CT scan (Fig. 2), and bone scan (Fig. 3), were performed. Based on the history, physical examination, laboratory tests, and imaging studies, what is the differential diagnosis?
Imaging InterpretationSagittal T1-weighted (Fig. 1A), sagittal T2-weighted fat-suppressed (Fig. 1B), and axial T1-weighted fatsuppressed contrast enhanced (Fig. 1C) MR images of the ankle showed a T1 hypointense and T2 hyperintense soft tissue mass remodeling the undersurface of the sustentaculum tali. There was a small irregular central area of low signal consistent with calcification.Coronal ( Fig. 2A) and sagittal (Fig. 2B) reformatted CT images of the ankle showed an area of smooth osseous remodeling at the inferior aspect of the sustentaculum tali. There was a 7-9 4-mm triangular calcification adjacent to the area of remodeling.Radionuclide bone scan (Fig. 3) of the bilateral feet and ankles showed radiotracer uptake in the left posterior calcaneus.Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.