[Clinical case of the month. MacLeod syndrome].

MacLeod syndrome is a rare cause of localized hypertransradiancy of the lung. This syndrome is defined by radiological features: localized hypertransradiancy due to oligemia and presence of air-trapping on expiratory chest radiography. Involvement of one entire lung is called "unilateral hyperlucent lung". Whereas the etiology is different, the physiopathology is probably identical to that of the panacinar emphysema of chronic obstructive pulmonary disease. The syndrome is believed to be related to acute bronchiolitis during infancy. Clinical manifestations and prognosis depend mainly on the presence of other lesions due to the same infectious agent like bronchiectasis. Pulmonary function tests, chest CT-scan, ventilation and perfusion scintigraphy and, if necessary, bronchoscopy help the differential diagnosis and detect associated bronchiectasis.