Middle Ear Effusion in Otitis Media with Effusion
In a patient with ear pain and no signs of acute infection, the effusion present is middle ear effusion (MEF), which is the defining characteristic of otitis media with effusion (OME)—fluid in the middle ear without signs or symptoms of acute ear infection. 1
Type and Characteristics of the Effusion
The fluid in OME can vary in composition and is classified into distinct types based on clinical and laboratory observations:
- Serous fluid is the most common type, appearing thin and watery 2
- Mucoid fluid (also called "glue ear") is thick and viscous, representing a more chronic inflammatory state 2
- Mixed types can occur, including seromucoid combinations 2
The American Academy of Otolaryngology-Head and Neck Surgery defines OME specifically as the presence of fluid in the middle ear without signs or symptoms of acute ear infection, distinguishing it clearly from acute otitis media (AOM), which involves rapid onset of inflammatory signs and symptoms 1
Clinical Significance of the Effusion
The middle ear effusion in OME typically causes a 20-30 dB conductive hearing loss through two primary mechanisms 3:
- At low frequencies (<1000 Hz): The fluid displaces air from the middle ear space, reducing the admittance (compliance) of the middle ear air cushion 3
- At high frequencies (>1000 Hz): The fluid contacts and loads the tympanic membrane, increasing its effective mass and damping vibration 3
Importantly, the viscosity of the fluid (whether thin serous or thick mucoid) does not significantly affect hearing loss—the volume of fluid and extent of tympanic membrane contact are the critical factors 3
Diagnostic Confirmation
The American Academy of Otolaryngology-Head and Neck Surgery strongly recommends documenting the presence of middle ear effusion with pneumatic otoscopy when diagnosing OME 4:
- Pneumatic otoscopy shows minimal or sluggish tympanic membrane movement when fluid is present, versus brisk movement with a normal air-filled middle ear 1
- Tympanometry should be obtained when pneumatic otoscopy is uncertain, showing a flat or nearly flat tracing when the middle ear is fluid-filled 1, 4
Common Pitfall to Avoid
Do not confuse OME with AOM based solely on the presence of ear pain. While OME is often asymptomatic, ear discomfort can occur with OME due to negative middle ear pressure or fullness sensation 1. The critical distinguishing feature is the absence of acute inflammatory signs (bulging erythematous tympanic membrane, fever, acute onset) that characterize AOM 1.