 Figure 14a: (a) Transverse 1-mm CT section through the upper lobes shows multiple variable-sized subsolid nodules bilaterally, including at least one highly suspicious (large size, ground-glass appearance, and solid morphology) part-solid lesion in the left upper lobe (arrow). Initial follow-up would be appropriate in 3–6 months. (b) A more inferior section from the same examination shows another highly suspicious lobulated 10-mm ground-glass nodule in the right upper lobe (arrow), which would also warrant follow up. The findings are most consistent with multifocal primary adenocarcinoma.  Figure 14b: (a) Transverse 1-mm CT section through the upper lobes shows multiple variable-sized subsolid nodules bilaterally, including at least one highly suspicious (large size, ground-glass appearance, and solid morphology) part-solid lesion in the left upper lobe (arrow). Initial follow-up would be appropriate in 3–6 months. (b) A more inferior section from the same examination shows another highly suspicious lobulated 10-mm ground-glass nodule in the right upper lobe (arrow), which would also warrant follow up. The findings are most consistent with multifocal primary adenocarcinoma. Risk Factors for Malignancy: General ConsiderationsNodule Size and MorphologyNodule size has a clear relationship with risk of malignancy, as discussed previously, and it is a dominant factor in management. In these guidelines, nodules are further divided into solid, ground-glass, and part-solid categories. However, the criteria for making these distinctions have not been completely agreed upon and remain controversial. Van Riel et al (59) examined the agreement between experienced thoracic radiologists using traditional subjective criteria to assign nodules to solid, pure ground-glass, and part-solid categories. Both inter- and intraobserver agreement was found to be highly variable in these nodules. Correct classification of nodules as solid or subsolid by all radiologists was achieved in only 58% of cases (59). Nonetheless, it is generally agreed that nodules that are rendered partially invisible when viewed on thin sections with mediastinal (soft-tissue) window settings and a sharp filter can be regarded as subsolid and that any nodule components other than normal vascular or bronchial structures that remain visible on such images are solid. Small solid or semisolid components that represent early signs of invasive adenocarcinoma may be rendered invisible with these settings, and the current consensus is that such nodules are best evaluated subjectively by using a lung window setting and an edge-enhancing (sharp) filter to judge the presence and extent of solid components (52,60 |