NARROWEST (ISTHMUS) PORTION OF EUSTACHIAN-TUBE - A COMPUTER-AIDED 3-DIMENSIONAL RECONSTRUCTION AND MEASUREMENT STUDY

Nine normal human temporal bones from persons 16 to 88 years old were studied by computer aided three-dimensional reconstruction and measure ment. The length of the eustachian tube (ET) lumen in three portions ( from pharyngeal orifice to tympanic orifice: cartilaginous, junctional , and bony) averaged 23.6 +/- 4.3 mm, 3.0 +/- 1.9 mm, and 6.4 +/- 2.6 mm. The narrowest portion of the ET lumen was in the cartilaginous por tion in all cases: 20.5 +/- 4.2 mm from the pharyngeal orifice and 3.1 +/- 1.6 mm from the pharyngeal margin of the junctional portion. The cross-sectional area of the narrowest portion was 0.65 +/- 0.2 mm(2). The tendon of the tensor veri palatini muscle (TVPM) inserted into the lateral lamina in the narrowest portion of the ET lumen in five of ni ne cases. These results suggest that contraction of the TVPM opens the narrowest portion of the ET lumen to ventilate the middle ear and tha t this portion also plays a role in protecting the middle ear.