68 year old woman has an incidentally noted pulmonary nodule on cardiac CT.
Noncontrast Chest CT 3 months later:
A 2 cm ground glass opacity is seen in the right upper lobe, similar in size to the cardiac CT performed 3 months ago.
Close inspection of the opacity on thin-section images demonstrates a solid component 5-6 mm in size at the superior aspect of the lesion.
Because of this solid component, a PET/CT was performed.
Focal moderate FDG uptake (similar to slightly greater than blood pool) is seen in the upper aspect of the opacity, corresponding to the solid component.
Subsequent biopsy and resection of the this lesion demonstrated minimally invasive adenocarcinoma.
Please see topic discussion Pulmonary Nodules: When to Get a PET/CT? This case is an example where focal FDG uptake within a subsolid nodule increased the suspicion for malignancy, despite the small size of the solid component. The Fleischner Society recommends followup chest CT in 3 months for all subsolid nodules > 5 mm. Biopsy or resection is recommended for persistent nodules with solid component >5 mm. PET/CT is recommended only for solid component greater than 8 mm by the Fleischner Society (2017 update). ACR Lung-RADS also suggests PET/CT for nodules with solid component greater than 8 mm. Naidich DP, et al. Radiology 2013;266:304-17. McKee BJ, et al. JACR 2015;12:273-6.
Radiologic correlates of the 2011 classification of pulmonary adenocarcinoma are discussed in a 2013 article in Radiology by Austin et al. Adenocarcinoma in situ appears as a subsolid lesion < 3 cm. Minimally invasive adenocarcinoma appears as a subsolid lesion < 3 cm with solid component up to 5 mm. Invasive adenocarcinoma has solid component greater than 5 mm. Mucinous adenocarcinoma has a variable CT appearance. Austin JHM et al. Radiology 2013;266:62-71.