**Core Concept**
Middle ear effusion, also known as serous otitis media, is characterized by the accumulation of fluid in the middle ear space behind the tympanic membrane. This condition can lead to hearing loss and symptoms such as fullness in the ear.

**Why the Correct Answer is Right**
The patient's presentation of persistent fullness, hearing loss, and fluid behind the tympanic membrane is consistent with middle ear effusion. Impedance audiometry showing a type B audiogram further supports this diagnosis, as type B tympanograms are indicative of middle ear fluid. The next step in management is to address the underlying cause of the effusion, which is often related to eustachian tube dysfunction. This can be achieved through tympanocentesis, where the fluid is aspirated from the middle ear.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is not a recognized treatment for middle ear effusion. Myringotomy alone may not address the underlying cause of the effusion.

**Option B:** This option is incorrect as it is not a first-line treatment for middle ear effusion. Antibiotics may be prescribed if there is evidence of bacterial infection, but they do not address the underlying cause of the effusion.

**Option C:** This option is incorrect as it is not a recognized treatment for middle ear effusion. The use of nasal decongestants may help to reduce nasal congestion, but it does not address the underlying cause of the effusion.

**Option D:** This option is incorrect as it is not a recognized treatment for middle ear effusion. The use of antihistamines may help to reduce nasal congestion and alleviate symptoms, but it does not address the underlying cause of the effusion.

**Clinical Pearl / High-Yield Fact**
Middle ear effusion is a common cause of hearing loss in children and adults. It is essential to diagnose and treat the underlying cause of the effusion to prevent long-term hearing loss and other complications.

**Correct Answer: C.**