Ent doctor said hearing loss due to fixed bone behind ear but no scan done only a hearing test. right ear has loss. no scan. is this sinister?

Sounds OK: If you have conductive hearing loss on the right side only and a normal-appearing eardrum, the most likely cause of hearing loss is otosclerosis. This is fixation of the stapes bone in the middle ear. This can't be seen on scans; the most reliable way to confirm in middle ear exploration. Some ear surgeons will perform a CT to assess for other causes, but most do not.