Double Lesion Sign 

If you encounter atelectasis of the RUL and RLL sparing RML, it is difficult to comprehend a single endobronchial lesion to account for both lesions. There has to be two independent endobronchial lesions. Hence, it was proposed that it is unlikely to be due to primary bronchogenic cancer. The concept is based on our knowledge of anatomy. 

Caution: Do not rule out lung cancer when you see this phenomenon. You just have to find an alternate explanation for the second lesion. The second lesion could be due to aspiration of blood from the first lesion.