Fleischner Guidelines for Pulmonary Nodules (2017)

Solid Nodule	<6mm	6-8mm	>8mm	Notes
Single
Low risk	No routine f/u	CT @ 6-12 months, then consider CT @ 18-24 months	Consider CT, PET/CT or biopsy @ 3 months	<6mm do not require f/u, but high risk patient or nodule characteristics may warrant 12 month f/u.
High risk	Optional 12 month CT	CT @ 6-12 months, then consider CT @ 18-24 months	Consider CT, PET/CT or biopsy @ 3 months
Multiple
Low risk	No routine f/u	CT @ 3-6 months, then consider CT @ 18-24 months		Use most suspicious nodule to guide management
High risk	Optional 12 month CT	CT @ 3-6 months, then @ 18-24 months		Use most suspicious nodule to guide management

Sub-solid nodule	<6mm	≥6 mm	Notes
Single
Ground glass	No routine f/u	CT @ 6-12 mo to confirm persistence, then q 2 years until 5 years	For suspicious nodules <6mm, consider 2 and 4 year f/u.
Part solid	No routine f/u	CT @ 3-6 months to confirm persistence. If stable and <6mm solid component, then q12 months for 5 years	<6mm part solid nodules too small to be defined. Persistent part-solid nodules with >6mm solid component are highly suspicious.
Multiple	CT @ 3-6 months. If stable, consider CT @ 2 and 4 years	CT @ 3-6 months. Subsequent management based on most suspicious nodule(s)	Multiple <6mm ground-glass nodules usually benign. May consider f/u @ 2 and 4 years in high-risk patients.

References:

MacMahon, H., et al. (2017). “Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017.” Radiology: 161659.