Isolated middle lobe atelectasis: aetiology, pathogenesis, and treatment of the so-called middle lobe syndrome.

Isolated atelectasis of the middle lobe has been known for many years as the "middle lobe syndrome". Several clinical studies have shown that it may bae caused by malignant tumours. A 10-year study of 135 patients with isolated middle lobe atelectasis is presented. Fifty-eight patients (43%) had malignant tumours. Of 38 who had a thoracotomy, lung resection was possible in 25. In 20 patients regional or systemic dissemination of the tumour had been diagnosed before operation. Seventy-seven patients had benign diseases, of which 74 were non-specific infections. Bronchography was performed in 46 of these cases, and all had abnormal findings in the middle lobe, eight revealing definite bronchiectasis. In three cases tuberculosis was found. In 16 cases the benign diagnosis was established at thoracotomy. Only three patients out of 58 with malignant tumours lived more than five years. Atelectasis of the middle lobe is always a sign of potential malignancy especially in patients with a previously normal chest radiograph.