What condition of the middle ear is often undetected and characterized by sterile fluid accumulation?

The condition characterized by sterile fluid accumulation in the middle ear that often goes undetected is non-suppurative otitis media. This condition typically occurs when the middle ear becomes filled with fluid without the presence of pus, which is what differentiates it from suppurative otitis media, where there is an infection leading to pus formation. Non-suppurative otitis media can occur due to factors such as allergies, Eustachian tube dysfunction, or viral infections, and because it lacks the obvious signs of infection, it may not be diagnosed until symptoms become more pronounced or it results in hearing loss.

In contrast, suppurative otitis media involves the presence of pus and is usually accompanied by pain, fever, and other more acute symptoms, making it easier to diagnose. Otitis externa, meanwhile, affects the outer ear canal and is not associated with fluid accumulation in the middle ear, and otosclerosis is a bone disorder affecting the stapes bone in the middle ear, leading to conductive hearing loss but not to fluid accumulation. Thus, the characteristics of non-suppurative otitis media make it the correct choice for this question.