Pulmonary cavitations in Mycobacterium kansasii: distinctions from M. tuberculosis

The initial radiographs of 263 patients with pulmonary Mycobacterium kansasii infections were reviewed. Forty-nine untreated patients with active disease had unilateral lesions containing cavities less than 2 cm in diameter. The radiographs of these 49 patients were studied further and were found to have four distinct patterns: pattern 1, a circumscribed opacity containing a single cavity (39%); pattern 2, a circumscribed opacity with multiple lucencies (39%); pattern 3, multiple round or oval opacities containing lucencies (8%); and pattern 4, complex uncircumscribed opacity with lucencies (14%). Adjacent pleural thickening, "drainage area disease," and a "tail" sign were common. The initial radiographs of 27 untreated patients with solitary cavitary lesions less than 2 cm in diameter due to M. tuberculosis were studied for comparison. Only 22% had patterns 1-3 and generally showed more extensive adjacent parenchymal disease than cases with M. kansasii. A single circumscribed opacity containing one or more small cavities together with a "tail" sign, "drainage area disease," and little adjacent parenchymal disease is highly suggestive of M. kansasii infection. Since this infection usually requires more vigorous chemotherapy than tuberculosis, awareness of these findings has a practical implication.