Isolated tuberculosis of popliteal cyst. Apropos of a case

INTRODUCTION: Isolated localization of tuberculosis in the popliteal cyst is an exceptional affection. CASE REPORT: Mr. M.L., 18-year-old black moroccan, was admitted for a painful swelling of the left popliteal cyst, general state alteration and left thoracic pain. Clinical examination found a 5 cm on 3 cm oval tumefaction at the supero-medial part of the left popliteal hollow. No articular effusion was noted. Left knee X ray was normal, while ultrasound examination showed a modified popliteal cyst. Chest X ray showed a pleural effusion. Tuberculine skin test was positive (18 mm). A subtotal resection of the cyst was performed, evacuating 10 ml of thick pus. The histologic examination of the cyst confirmed its tuberculosis origin. In addition the left pleural biopsy confirmed the diagnosis of tuberculosis as well. The antibacillar treatment based on rifampicine, INH and pyrazinamide was given during 6 months. The evolution was favorable at 2 years of follow-up. DISCUSSION: Knee popliteal cyst is frequently an expression of an inflammatory or traumatic affection. The communication between the articular synovium and the serosa bursa of the lateral gastrocnemius is found in 50 per cent of cases, allowing an association of both localizations of tuberculosis. Hamabuchi described for the first time an isolated popliteal cyst tuberculosis in 1990. This case is similar to Hamabuchi's observation. Clinical and radiographical examinations were normal thus excluding a possible dissemination from the knee joint.