In my case I found that the measurements have some variance depending who is reading the scan. My most recent one showed 4.2 (radiologist report) but when reviewed my the senior thoracic specialist at a major university hospital, who I send them to for second opinion, he read 4.5 (does his own measurements). He expects surgery once it reaches 5.0. Before this condition was identified 3 years ago, I did a lot of road cycling. The senior specialist strongly recommended that I do not continue because I live in a mountain region and the rides involve a lot of strain due to elevation changes. I was also told to keep my heart rate under 120 and blood pressure under 120/80. Good to discuss with your cardio on best approach since everyone's specifics are different.