What size is generally considered low risk for a solitary pulmonary nodule (SPN)?

A solitary pulmonary nodule (SPN) that is less than 0.8 cm is generally considered to be low risk for malignancy. This size threshold is based on numerous studies that correlate the size of the nodule with the probability of it being cancerous. Smaller nodules have a significantly lower likelihood of being malignant compared to larger ones.

For nodules that range between 0.8 cm and 2.0 cm, there is an increased risk of malignancy, and those that are 2.0 cm or greater are even more concerning, often requiring further evaluation such as PET scans or biopsy. Nodules that are 3.0 cm or larger are particularly worrisome and usually prompt immediate investigation due to the high probability of cancer. Therefore, nodules under 0.8 cm are generally managed with watchful waiting, while those above this size often necessitate a more aggressive diagnostic approach.