Correct!
5. The left upper lobe nodular opacity shows no specific morphological features

The left upper lobe nodular opacity is somewhat poorly defined, but ultimately shows no specific morphological features. In particular, no evidence of calcification or fat is present within the lesion. The “air crescent” sign is a specific form of cavitation within a nodule in which a thin, curvilinear rim of lucency, consistent with gas, partially surrounds a nodular intracavitary opacity, separating the nodule within the cavity from the wall of the cavity. The “air crescent” sign is typically encountered in the setting of angioinvasive fungal infection in immunocompromised patients, or, in the setting of relatively normal immunity, when fungal colonization of a pre-existing cavity occurs [mycetoma]. The presence of fat within a nodule is characteristic of hamartoma, but requires cross sectional imaging [typically thoracic CT] for demonstration; the small amounts of fat occurring with hamartoma would not be detectable with chest radiography.

The patient underwent unenhanced thoracic CT for further evaluation of the chest radiographic abnormality (Figure 2).

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Figure 2. Left panels: Axial unenhanced thoracic CT displayed in lung (A-F) and soft tissue (G) windows. Right panel: video of CT images in lung windows.

Regarding the thoracic CT examination, which of the following is correct? (Click on the correct answer to proceed to the fourth of nine panels)

  1. The thoracic CT shows a non-specific, non-calcified, lobulated left upper lobe nodule corresponding to the chest radiographic finding
  2. The thoracic CT shows fat within the left upper lobe nodule
  3. The thoracic CT shows no abnormality corresponding to the chest radiographic finding, suggesting that the chest radiographic finding is artefactual
  4. The thoracic CT shows numerous small nodules bilaterally consistent with a miliary pattern
  5. The thoracic CT shows that the opacity corresponding to the chest radiographic abnormality has a morphology consistent with an arteriovenous malformation

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