RESUMO
During the last 10 years the pathological substrate of the middle lobe syndrome was analysed in 60 surgically cured cases aged 7-59: there were 36 lung chronic suppurations, 20 neoplasias and 4 tuberculoses. In all these cases it was shown that, together with the specific lesions (infectious, tuberculosis, neoplastic) of bronchial walls and lung parenchyma a more or less obvious and high bronchial obstruction developed leading to obstructive pneumonitis with intralobular lipospongiocytosis. Investigated at different evolutive phases, this pneumonitis led to an extended restructuring of the lung tissue which occupied differently sized areas of the middle lobe. In the neoplastic and tuberculous cases, the restructured lung areas often included neoplastic emboli or infiltrations of neoplastic cells, or, respectively, remnant, reshuffled tuberculous lesions. None of cases presented zones of pure atelectasis.