Isolated tuberculosis of the popliteal cyst.

We encountered a case of tuberculosis of a popliteal cyst in a 76-year-old man. He visited our department for treatment of the left knee pain which had not responded to treatment over the previous ten months. At first examination, local rubor, swelling and tenderness on a popliteal cyst were noted. Therefore, curettage of the lesion, including resection of the cyst, was performed. Six weeks later, an abscess had formed in the subcutaneous area over the lateral aspect of the knee, which was cleaned out. The abscess recurred in the same area four months later. At the third operation, curettage of the abscess together with a knee joint synovectomy was performed. Upon pathologic examination, a tuberculous lesion of the popliteal cyst and skin were recognised. However, no tuberculous lesion was detected in the synovia of the knee joint. It is generally agreed that it is possible for a popliteal cyst to be infected from synovial tuberculosis of the knee joint. However, in our case, based on the histopathological and clinical observations, the primary tuberculous lesion appeared to have been in the popliteal cyst, which is very rare indeed. Recent developments in preventative medicine and chemotherapy have markedly reduced the incidence of tuberculous arthritis. However tuberculous arthritis is still an important disease in the differential diagnostic of persistent monoarthritis of the knee. Approximately half of the popliteal cyst communicate with the knee joint. However, it is not frequent for tuberculosis to propagate from the knee joint into the popliteal cyst.(ABSTRACT TRUNCATED AT 250 WORDS)