) (44). Thus, at least one follow-up scan (3–6 months) is recommended to determine persistence or resolution. For persistent lesions, yearly follow-up for 5 years is recommended to assess stability of the solid component. The recommended end point of 5 years is necessarily somewhat arbitrary, but it is considered reasonable for patients in whom the dimensions and attenuation of a part-solid nodule have remained unequivocally stable over that time period (42).
 Figure 12a: (a) Transverse 1-mm CT section through the right upper lobe shows a 6-mm part-solid nodule with a solid component (arrow) smaller than 4 mm. (b) Follow-up CT section at 6-month follow-up shows complete resolution, consistent with a benign cause.  Figure 12b: (a) Transverse 1-mm CT section through the right upper lobe shows a 6-mm part-solid nodule with a solid component (arrow) smaller than 4 mm. (b) Follow-up CT section at 6-month follow-up shows complete resolution, consistent with a benign cause. For solitary part-solid nodules with a solid component 6 mm or larger, a short-term follow-up CT scan at 3–6 months should be considered to evaluate for persistence of the nodule. For nodules with particularly suspicious morphology (ie, lobulated margins or cystic components), a growing solid component, or a solid component larger than 8 mm, PET/CT, biopsy, or resection are recommended (grade 1B; strong recommendation, moderate-quality evidence.) Abundant evidence enables us to confirm that the larger the solid component, the greater the risk of invasiveness and metastases. A solid component larger than 5 mm correlates with a substantial likelihood of local invasion (7,43,45–54), and this is a threshold criterion in the newly revised T factor staging for adenocarcinoma (Fig 13) (55 |