Volume measurement of middle ear and mastoid air cell system with impedance audiometry on patients with eardrum perforations

The usefulness of the electroacoustic impedance bridge with a probe tone frequency of 0.22 kHz in the determination of the middle ear and mastoid volumes was evaluated in patients with dry eardrum perforations. The values obtained were compared with the volumes determined by an aspiration technique utilizing the gas laws. Also, a comparison was made between the impedance volumes and the size of the mastoid air cell system as measured on x-ray film in a lateral projection. A significant agreement between the two methods of direct volume determination was found. A good relationship was found between the impedance volume and the mastoid air cell area. The impedance audiometry enables a rapid and valuable estimation of the air reservoir in the middle ear in patients with eardrum perforations.