Welcome! I am Dr. Altman, a licensed veterinarian and I am happy to answer your questions.
The good news is if they are bilaterally symmetrical as you say then they are likely a normal variation of anatomy for her
The concern is always going to be if there is an isolated mass that is only on one side or moreso on one versus the other side
If it is a concern then it is always best to have your vet evaluate her to ensure it is nothing to be concerned about but when you mention it is bilaterally symmetrical my first inclination is normal variation
Please let me know if this information makes sense and any additional questions I can assist with but I have never had in 15 years a patient that has bilaterally symmetrical masses that were bad or cancerous
what is the cause,will it need treatment based on your obviously limited ability to examine her
It could be muscling, fat, or even a variation in rib placement that can cause protrusions evenly on both sides
Very likely no treatment will be needed for this situation