Unusual case of enlarging pulmonary mass.

Rounded atelectasis is an uncommon form of pulmonary collapse that presents as an asymptomatic lung mass, and thus, can appear very similar to a pulmonary neoplasm. One feature that has been used to differentiate rounded atelectasis from a pulmonary malignancy is the lack of growth observed in cases of rounded atelectasis. The case presented here demonstrates that it is possible for rounded atelectasis to increase in size. This is the first documented case of enlargement of rounded atelectasis and shows that this disorder should be added to the list of benign causes of an enlarging pulmonary mass.