Cavitating lung nodules and pneumothorax in children with metastatic Wilms' tumor.

Lung metastases evolved into large thin-walled cysts in two children with Wilms' tumor. Histologic examination of one lesion suggested that invasion of a small bronchus or bronchiole, leading to ball-valve obstruction, was responsible. One patient also experienced recurrent pneumothorax, probably on the same basis. The formation of thin-walled cysts has not previously been observed with metastatic Wilms' tumor. Pneumothorax is a rare complication of metastatic Wilms' tumor.