This is a constantly evolving topic. The ACR has an Incidental Findings Committee that publishes various guidelines. Some of these guidelines are dated as far back as 2010. In November of 2019, the most recent ACR guideline is dated August 2018. The total numbers of authors on these papers can compete with population numbers of small countries. It is anyone’s guess what statements like: “mediastinal LN of <15mm or benign texture features – no further follow up” and later, in Figure legend: “may consider further action if numerous small lymph nodes are present” actually mean. What is the definition of “numerous”? How about “no further work up” and “consider benign, but may require resection.” In any case, the “bestest” guidelines that humans came up with are linked to here.
Practical points from above references from ACR in the context of incidental findings where ACR says “no further imaging follow up”:
Non-aggressive appearing (fatty hilum present, no fat stranding, not bulky and not “numerous”) lymph nodes in the mediastinum measuring < 15 mm;
Pericardal cyst </= 10 HU, simple, no thickened pericardium or thickened cyst wall, no calcification;
Simple pituitary cyst with no mass effect and no invasion into adjacent structures;
Simple thyroid nodules <1cm (<35yo) and <1.5cm (>/=35yo).
There are papers on pancreatic, adrenal, liver, renal, vascular and other findings. Those are not as easy to summarize.