Thanks for the responses.
Many also think this is a pubic cartilaginous cyst.
Dr. Taneja shared the below case of a smaller example.
Dr. Vanhoenacker shared an article he wrote regarding this entity (see attached). I attached another article with retropubic examples.
Some wondered about infection, which is understandable. But there are no clinical signs/sxs of infection, no edema around the mass or symphysis, and no restricted diffusion.
Management decisions are to be determined.
Drew
retropubic.pdf
subpubic cartilaginous cyst.pdf