What is the most appropriate next step in the evaluation of a solitary pulmonary nodule found on a chest x-ray in a young nonsmoking male?

The most appropriate next step in the evaluation of a solitary pulmonary nodule found on a chest x-ray in a young nonsmoking male is to perform a CT scan of the chest. A CT scan provides a more detailed evaluation of the nodule's characteristics, including size, shape, and the presence of any calcifications. This detailed imaging helps to assess the likelihood of malignancy and enables clinicians to make more informed decisions about further management.

In the context of a solitary pulmonary nodule, CT scans can help determine if the nodule is stable, growing, or has suspicious features that warrant an intervention, such as a biopsy or further imaging. Given the patient's demographic characteristics—young and a nonsmoker—there could be a lower likelihood of lung cancer, but thorough evaluation is still warranted.

The other options may be considered at later stages depending on the results of the CT scan. Needle biopsy and fiberoptic bronchoscopy are more invasive procedures that come into play if there's high suspicion for malignancy or if the nodule has characteristics highly suggestive of cancer based on CT findings. A positron emission tomography scan might be used later if malignancy is suspected, as it provides metabolic information about the nodule, but the initial evaluation would ideally start