| Objective:Through observing posterior tympanum (PT)of cadaver and its surrounding area under endoscopy and microsopy respectively and combining the requirement of all sorts of operations refered to retrotympanum, measured the correlative data at specimen, introduced a new method of studying posterior tympanum and provided suitable anatomical datas. Methods:Thirty temporal bones (left 16, right 14) harvested from cadavers were dissected using an operating microscope and ragid endoscope with 30° or 70° and 2.7-and 4-mm diameters respectively. The view of posterior tympanum were observed and compared under endoscope with different angles through external auditory canal.The cast was made under the guiding of endoscope, and measured by sliding caliper. After removing anterior wall of auditory canal and tympanum through using electric drill under micro--scope, observed posterior tympanum directively from anterior and measured data of recess with caliper and right-angle hooks. After open-mastoidectomy and exposed the ledge of bone anterior to the facial nerve, measured at its upper and its middle and its lower extremities. Results:1. The observation of posterior tympanum under endoscope. Whether 30° or 70° endoscope can look into posterior tympanum roundly, 70° endoscope provide wider lateral visual field, furthermore, 30° endoscope can be grasped the sense of direction and the degree of depth. 4-mm diameters endoscope can provide wider visual field than 2.7-mm endoscope, but the space of operating is much narrower. If the posterior wall of auditory canal is removed, 4-mm diameters endoscope will be easier.Through observation to posterior tympanum, the pyramidal eminence is the most prominent process and can be seen at all specimens.It can beserved as the marker of guiding endoscope. There are 4 specimens (13.3%) that their basements of sinus tympani exceed the vertical portion of facial nerve and the duct of facial nerve process into the lateral wall of sinus tympani. Ponticulus promontori can be seen at 18 specimens(60%) and there are 10 specimens their ponticulus promontories is perforated. Subiculum promontori can be seen at 5 specimens (16. 7%). Chordal eminence also can be served as the marker of guiding endoscope and can be seen at all specimens. Chordal ridge can be seen at 15 specimens(53. 3%).2. The result of sinus tympani:the cast of ST-depth 1.06 —5. 80mm, average 2. 65 + 1. 23mm, widthO. 78 —3. 64mm, average2. 45 + 0. 67mm; directive measurement-depth 1.10 —5.92mm, average 2. 70 + 1.25mm, width 0.84 — 3.42mm, average 2. 52 + 0. 63mm.3. The result of facial nerve recess:the cast of FR-depth 1. 18 — 2.94mm, average 2. 11 ±0. 42mm, width 1. 58—3. 46mm, average 2. 47 + 0. 48mm; directive measurement-depth 1.26 —3.02mm, average 2.14 + 0. 44mm, width 1.64 —3. 46mm, average 2. 50 + 0. 45mm.4. The results of sinus tympani and facial nerve recess were analysed respectively using paired t-test through SPSS statistic software(P> 0.05),the deference of two methods had not obvious statistical significance.5. The bone anterior to vertical portion of facial nerve was crescentic in shape, being narrow at its upper and lower extremities and widest at its middle near pyramidal eminence. Average measurements were 1. 75±0. 29mm at the upper extremity, 2. 80 + 0.72mm at the middle, andl. 73 + 0. 33mm at the lower extremity.Conclusion:We studied posterior tympanum through two methods, measured sinus tympani, facial nerve recess and the bone ledge anterior to facial nerve and observed retrotympanum through 30° and 70° endoscope respectively.1. For the portion of posterior tympanum medial to facial nerve canal, a better view was obtained by using either 30° or 70° endoscope. However, for the portion lateral to facial nerve canal, especially facial recess,70° endoscope was better than 30° endoscope, just because the 70° endoscope provided a wider view of lateral surface. 30° endoscope can control orientation and depth more easily when it was guided into middle ear through external auditory meatus, and 2.7mm endoscope can reach a better balance between convenience of operation and size of view.2. There is no significant difference between the data of making pattern and the data of measurement directly through statistical comparision. The data of former can instruct clinical application. The method is safe, simple and can be served as a new method of measuring posterior tympani.3. For avoiding damaging important structure, improving the safety of operationand reserving function, afforded referential opion to improve successsive rate of operation, short operation-time and avoid complication. |
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