1 Pulmonary nodules appear in about one of every 200 chest X-rays and most chest CT scans. 2  At least 60% of pulmonary nodules seen on chest X-rays turn out to be benign, and 99% of those on chest CT are benign. 3  Pulmonary nodules are much more commonly found than are lung cancers or benign lung tumors. A way to tell the difference between a benign and malignant lung nodule is to chart the rate of growth of the nodule. 2  Benign nodules will grow very slowly, if at all, while cancerous nodules on average can double in size every four months or less.