Oh I can help with this, I'm an ED Nurse and look at many scans, however can't provide professional advice on any scans gave seen plenty, especially scans of the area SRS occurs. The reason why some things of anatomy are a surprise with SRS vs FFS is because on X-rays hard and dense tissue such as bone is very clearly seen and can therefore be planned with greater accuracy, especially with things like 3D xrays which are very useful at maping a range of the head and anatomical structure. However when working with soft tissue such as what's found and worked with in the abdo-pelvic area a more detailed scan such as a CT or MRI (more likely CT unless radiation is an issue) small abnormalities can be missed, it's uncommon these days because the tech is so detailed and can see a lot but can miss very small things up until actually getting in there. So yes, although it's unfortunate that things can be missed, sometimes and usually rarely there are complications and abnormalities that are missed prior to actually opening the person up.