Baker's cysts are rare cause of peripheral nerve entrapment and only a few cases of tibial nerve entrapment resulting from the popliteal cyst in the calf muscle have been reported in the literature. We present a case of rheumatoid arthritis complicated by a Baker's cyst with a tibial nerve entrapment. It is important to diagnose a Baker's cyst early and to differentiate it from thrombophlebitis, a popliteal aneurysm, tumor or muscle tear to effect optimal therapy and to obviate a potential neuropathy. Prompt recognition of these cases may save the patients unnecessary procedures and delay in treatment.
Arthritis, Rheumatoid/diagnosis ; Arthritis, Rheumatoid/complications ; Biopsy, Needle ; Case Report ; Electromyography ; Female ; Follow-Up Studies ; Human ; Magnetic Resonance Imaging ; Middle Age ; Popliteal Cyst/surgery ; Popliteal Cyst/diagnosis ; Popliteal Cyst/complications+ACo- ; Tibial Neuropathy/etiology+ACo- ; Tibial Neuropathy/diagnosis ; Treatment Outcome

Here, we describe a popliteal mass that was initially misdiagnosed as a simple popliteal cyst, which finally turned out to be osteochondrolipoma. A 63-year-old housewife presented with sustained knee pain in association with a palpable mass on the popliteal fossa. The mass was in the posteromedial area and soft, non-tender, non-movable in the posteromedial area. Using plain radiography, the mass appeared as a round, soft tissue density lesion containing bony fragments. We performed an ultrasound-guided needle biopsy in conjunction with magnetic resonance imaging, followed by an open excisional biopsy. Microscopically, histological sections showed a lipoma with cartilaginous and osseous differentiation, finally diagnosed as osteochondrolipoma. In conclusion, popliteal masses are not always simple cysts, and the evaluation of masses in the popliteal fossa is always necessary.
Female ; Humans ; Lipoma/complications/*diagnosis ; Middle Aged ; Osteochondroma/complications/*diagnosis ; Popliteal Cyst/etiology ; Soft Tissue Neoplasms/complications/*diagnosis