Elevated metabolic activity in L3 L4 without obvious lytic changes

Hi @proteus, welcome to Connect, a community of fellow patients and caregivers who share experiences and give and get support. You'll notice that I moved your message to the Colorectal Cancer group here: https://connect.mayoclinic.org/group/colorectal-cancer/

I did this so that you can connect with other members who have experience with colorectal cancer, like @virgo1952 @wilcy @rexsan20 @amariewilkinson and others.

I'm not a radiologist or a physician and therefore unqualified to interpret the results of your mom's PET scan. But here is some general information about PET scans and metabolic activity.
"A PET scan (positron emission tomography) works to identify areas of hypermetabolic activity anywhere in the body. A radioactive substance is given to the patient and this attaches to glucose, which is attracted to cells that are hypermetabolic. When the scan is done, these areas "light up." Often, but not always, cancer cells fall into this category of being hypermetabolic. In addition, not everything that is hypermetabolic is cancer."

A PET scan is only one step in the diagnostic process. When do you have an appointment with her oncologist to discuss the results of the PET scan and to talk about the next step or test?

We already had an appointment with oncologist and he is suspecting that this could be an inflamation due to the accident she had. But no biopsy performed yet

I hope that is the case. Will she have a biopsy to confirm?

since her mobility is affected and bed ridden for now, doctor has suggested to wait for few more weeks. She is currently going through physio therapy to get her out of numbness and back to mobility. I will start a new thread for this accident to get some neuro suggestion as well.