A control CT performed 2 years later demonstrated a nodule containing an air bronchogram, therefore suspicious of malignancy, at the site of the initial non-specific band; the mixed nodule had however disappeared (Figures 1).
A PET-scan was performed with negative results; this can be explained by the drop in diagnostic performance of PET for lesions less than 10 mm, which was the case for this patient. A repeat control CT scan following antibiotic treatment seemed to demonstrate an increase in tissular density, but this was impossible to evaluate properly with 2D measurements.

Although the initial non-specific band was not detected by Lung VCAR, retrospective synchronization based on detection of the nodule on the control scan allowed temporal evolution to be analyzed. It is noteworthy that this volume/time comparison could be performed between a « ground glass » (non-solid) density and a tissular density. Note the inclusion of vascular structures within the segmentation of these lesions; this interfered with volume calculations and consequently the calculation of doubling time (Figures 2).

Growth between the two control scans was definitely established by the software and was consistent with the doubling time of a malignant lesion (Figures 3). In fact, the doubling time of most malignant solid nodules is between 30 and 400 days. Surgery confirmed that this was a primary pulmonary adenocarcinoma.

The disappearance of the mixed nodule underlines the possible inflammatory or infectious nature of these abnormalities. This reinforces the necessity of follow-up 1 month after a trial of antibiotic therapy: malignancy should be suspected if the lesion persists.

Figures 3

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