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Updated: Jun 13, 2026

Extracting the Cochlea from a Human Temporal Bone: A Cadaveric Protocol
Published on: August 18, 2023
Surface area-volume relationships for the mastoid air cell system and tympanum in adult humans: Implications for
J Douglas Swarts1, Brendan M Cullen Doyle, Cuneyt M Alper
1Department of Otolaryngology, Children's Hospital of Pittsburgh, University of Pittsburgh, PA, USA. dswarts@pitt.edu
Conclusions:
The middle ear (ME) surface area/volume ratio (SA/V) is greater than that of the tympanum. The rate of ME pressure decrease is proportional to the ME SA/V. The mastoid air-cell system (MACS) will not function as an ME gas reserve unless the blood perfusion/surface area is much greater for the tympanum than the MACS and decreases as MACS volume increases.
Objective:
To measure the MACS and tympanum surface areas and volumes and ascertain whether the MACS could function as an ME gas reserve.
Methods:
Twenty adult subjects with a wide range of MACS volumes underwent CT of their MEs. The left and right surface areas and volumes of the tympanum and MACS were reconstructed and entered into a simple perfusion-limited model of transmucosal gas exchange. In this model the MACS would be a gas reserve if ME SA/V was less than the tympanum SA/V or equivalently, if their ratio was less than a critical value of 1.
Results:
Both MACS and tympanum SA were linearly related to their volumes. MACS SA/V and the ME SA/V were significantly greater than those for the tympanum. Inputting the measured values into the model yielded a critical value of 1.4, which was significantly greater than 1.
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