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Background
Many important pathologies present as incidental pulmonary nodules on thoracic imaging, but identification and characterization of nodules can often be challenging and subject to a number of pitfalls. The purpose of the exhibit is to demystify key processes and pitfalls of nodule detection and characterization with a case-based review of problematic nodules and ways to avoid misses and misinterpretations.

Educational Goals / Teaching Points
The exhibit discusses key processes and pitfalls of pulmonary nodule detection and characterization on thoracic imaging, with a case-based review of problematic scenarios and ways to avoid misses and misinterpretations.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Search errors, detection errors, and decision-making errors can be causes of nodule misses and misinterpretations. Many factors can impair proper nodule detection such as workstation lighting, visual search pattern, image noise, lesion contrast characteristics, and challenging anatomic locations. Radiologists should be aware of the technical pitfalls that can impair proper nodule detection, such as motion artifact and volume averaging. Once a nodule is detected, characterization and decisions about management are prone to additional errors. Examples of decision-making errors include malignancies impersonating benign patterns of nodules, such as branching/clustered intravascular metastases mistaken for infection or pulmonary embolism, endobronchial tumor mistaken for infections or secretions, or cyst-associated adenocarcinoma mistaken for infection or parenchymal scar. A comprehensive review of benign etiologies that can mimic malignancy will be illustrated, for instance benign para-osteophyte fibrosis mistaken for subsolid adenocarcinoma. Additionally, radiologists should be cognizant of malignant etiologies that masquerade as benign patterns such as metastatic liposarcoma mistakenly interpreted as hamartoma, and metastatic osteosarcoma mistakenly interpreted as calcified nodule. Lastly, key positron-emission tomography (PET) /CT nodule pitfalls will be illustrated with case-examples such as misregistration artifact and low level Fluorodeoxyglucose (FDG) uptake by adenocarcinoma.

Conclusion
Understanding common pitfalls and limitations of nodule interpretation on thoracic imaging is necessary to provide prompt detection, accurate characterization and appropriate diagnosis of pulmonary nodules.