We have been taught that the tympanic membrane stretches across the end of the external auditory canal as a thin, taut drumhead passively vibrated by airborne sound. Much evidence supports this conception.
However, I believe the tympanic membrane is a dynamic, complicated organ that is in many situations neither passive, thin, nor flat; a serous fluid accumulates within its middle layers, and often a double-convex shape is assumed.
There are several phenomena that are not adequately explained by our present interpretation of tympanic membrane structure, and these are herein enumerated. I contend that the presence of a highly mobile fluid system within the drumhead resolves these questions.
The search for historic evidence to support this concept involves both Dr. H. Shrapnell and Dr. H. Helmholtz. In 1832, Shrapnell wrote two articles for the London Medical Gazette in which he discredited the theories of Home and Albinus regarding the structure of the tympanic membrane. He described the pars flaccida and speculated on its function. He noted the mucosal layer of the pars flaccida was covered with mucus, while the pars tensa had a “glistening, shiny surface.” The work of Dr. Helmholtz in 1863 and 1869 is perhaps even more pertinent. In 1863 he presented the thickness of the tympanic membrane as 0.1 mm. Yet six years later his calculations projected a double-convex contour of the eardrum. As he could not reconcile these calculations with his original impressions, he deferred“ … special description and discussion … in order that this experiment might be better performed.”
It is the purpose of this article to suggest that the tympanic membrane has a variable thickness related to physiologic need, and photography and scientific works by Nilson, Stenfors, McMinn, Taylor, Lim, Graham, and others are utilized to support this contention.
Reprint requests: Ned I. Chalat, M.D., 929 Fisher Building, Detroit, Michigan 48202
© 1980, The American Journal of Otology, Inc.