Imaging and characterization of pulmonary nodules in children with solid tumors: what makes a pulmonary nodule a metastasis?

Evaluating pulmonary nodules in children requires balancing reliable detection with minimizing risks, particularly radiation exposure. Chest radiography serves as a useful first-line modality, but computed tomography (CT) remains essential despite concerns about radiation dose and motion artifacts. Pulmonary nodules are frequently identified even in otherwise healthy children, and distinguishing benign lesions from metastatic disease in those with solid tumors continues to be clinically challenging, with no universally accepted diagnostic criteria. This article aims, firstly, to provide clues for defining pulmonary nodules with typically or definitively benign characteristics and, secondly, to underscore an overview of current imaging criteria per tumor group and the clinical implication of the presence of pulmonary nodules on event-free survival and overall survival. Accurate differentiation is crucial because it directly influences staging, management, and prognosis. Several issues like interobserver variability in detection/characterization and the inherent difficulty to finally characterize the nodule's etiology are still to be resolved, but the development of new techniques (magnetic resonance imaging (MRI), etc.) challenges these uncertainties.