Correct!
2. Foregut duplication cyst
The least likely etiology for the observed radiographic findings among those listed is a foregut duplication cyst. While foregut duplication cysts can enlarge, which indicates that the mere lack of visualization of the abnormality on the previous chest radiograph does not absolutely exclude this diagnosis, foregut duplication cysts typically grow slowly; the marked change over a 2-year period would be highly unusual for a foregut duplication cyst. In contrast, such rapid change would not be unusual for the other choices listed. Additionally, a foregut duplication cyst would not expected to be associated with the chest wall abnormalities also seen in this patient, and the margins of the soft tissue / fluid collection in the mediasitnum in this patient are somewhat irregular and associated with visible peripheral wall thickening; both findings atypical for an uncomplicated foregut duplication cyst. In contrast, an abscess, particularly arising from the chest wall or sterno-clavicular joint (septic arthritis) certainly could present with the combination of osseous destruction / fragmentation associated with a low attenuation soft tissue and fluid focus projecting into the mediastinum. Metastatic lymphadenopathy could certainly result in both the chest wall and soft tissue findings, as could a primary neoplasm of the chest wall, such as multiple myeloma. Finally, although exceedingly rare, primary mediastinal sarcomas can present with soft tissue lesions in this location [particularly if the abnormality arose from the adjacent right brachiocephalic vein in this patient], and could cause adjacent chest wall invasion with osseous destruction.
Which of the following would be most useful for further evaluation of this patient? (Click on the correct answer to proceed to the sixth of seven pages. The next page has two embedded videos and may be slow to load.)