Final answer:
The pediatrician's diagnosis for the girl is mastoiditis, which is an inflammation of the mastoid bone. It is often a complication of acute otitis media (AOM), which is an infection of the middle ear.
Step-by-step explanation:
The pediatrician's diagnosis for the 10-year-old girl is mastoiditis. Mastoiditis is an inflammation of the mastoid bone, which is located behind the ear. It usually occurs as a complication of acute otitis media (AOM), which is an infection of the middle ear. In this case, the girl's ear pain, fever, and discharge from the ear, along with the CT scan showing a swollen mastoid bone, indicate mastoiditis.