Tympanogram Types: Characteristics and Clinical Interpretation
Tympanograms are classified into three main types (A, B, and C) based on the shape of the curve, middle ear pressure, and presence or absence of a discernible peak, which directly correlates with the probability of middle ear effusion. 1
Type A Tympanogram (Normal)
- Characterized by a sharp, high peak at or near 0 daPa pressure, indicating normal middle ear pressure and normal tympanic membrane mobility 1
- Significantly decreases the probability of middle ear effusion, making it the most reassuring finding on tympanometry 1, 2
- Indicates normal middle ear function with intact ossicular chain and patent Eustachian tube 3, 4
Type B Tympanogram (Flat)
- Displays a flattened shape with no discernible peak at any pressure level, representing the most abnormal pattern 1
- Has the highest probability of middle ear effusion or tympanic membrane perforation, both causing conductive hearing loss 1, 2
- Clinical interpretation requires correlation with equivalent ear canal volume (ECV): 1
- Normal ECV (0.3-0.9 ml in children) with flat tracing = middle ear effusion
- Low ECV with flat tracing = probe obstruction by cerumen or contact with ear canal wall
- High ECV with flat tracing = patent ventilation tube or tympanic membrane perforation
- Positive predictive value for middle ear effusion ranges from 49-99% depending on clinical context 4
- Cannot distinguish between acute otitis media and otitis media with effusion—requires clinical correlation with history and otoscopic findings 2, 5
Type C Tympanogram (Negative Pressure)
- Shows a peak shifted toward negative pressure (typically beyond -100 daPa), indicating Eustachian tube dysfunction 1
- Subdivided into C1 (sharp peak) and C2 (rounded peak), with C2 having higher probability of effusion than C1 1
- Has intermediate probability of middle ear effusion and associated hearing loss 1
- Type C alone is an imprecise estimate of middle ear pathology—requires correlation with other clinical findings as it has limited sensitivity and specificity by itself 4
- At symptomatic visits, Type C1 is associated with healthy middle ear in 62% of cases, Type C2 in 54%, while any peaked tympanogram (including Type C) suggests healthy middle ear in 67% of examinations 5
Critical Technical Considerations
- Standard 226 Hz probe tone is used for children ≥6 months and adults, while 1,000 Hz probe tone is required for infants <6 months due to their naturally stiffer, more compliant ear canals that make low-frequency tones insensitive to middle ear effusion 1, 2, 6, 4
- Tympanometry is not reliable in infants younger than 7 months when using standard 226 Hz frequency due to highly compliant ear canals 4
- Testing should be conducted in a quiet area with minimal visual and auditory distractions 1
Clinical Integration and Pitfalls
- Pneumatic otoscopy remains the primary diagnostic method, with tympanometry serving as an objective adjunctive tool when diagnosis is uncertain 2, 5
- Dense cerumen impactions must be removed before diagnostic testing to prevent false Type B readings from probe obstruction 1
- Tympanometry cannot replace careful pneumatic otoscopy for accurate diagnosis—it provides quantitative data but lacks specificity for distinguishing between different middle ear pathologies 5
- In outpatient settings, any peaked tympanogram (Types A, C1, C2) suggests healthy middle ear in 87% of asymptomatic examinations, while flat tympanogram indicates middle ear effusion in 87% of cases 5