Surgery is usually performed using a CCD camera and video monitor, but if the endoscopy is expected to be a brief inspection, then viewing through the eyepiece is satisfactory and requires less setup time. Endoscopes with 30- and 70-degree view angles are most commonly used to inspect recesses. It is preferable to use the largest diameter suitable for introduction into the surgical field while allowing sufficient room to pass surgical instruments. Larger-diameter endoscopes yield superior image size and illumination. Endoscopes with 30-degree angulation and 2.7-mm outer diameter are useful for most shallow recesses. For visualizing deep into the facial recess, sinus tympani, or aditus, and looking far into the epitympanum and mastoid antrum, a 70-degree, 2.3-mm-diameter endoscope is used. The 70-degree endoscope lacks any forward view, so it is necessary to insert the endoscope nearly into the final position by looking along its shaft with the naked eye and noting its relationship to the ossicles or other important structures. The endoscope is tilted to bring the ossicles into view and, after noting their location, it is tilted to bring the area of pathology into view. The surgeon should periodically recheck the location of the ossicles, which may be out of the field of view, to avoid disorientation and inadvertent injury.
Large cholesteatomas and retraction pockets that extend deep into the epitympanum or mastoid antrum are beyond the reach of endoscopic resection and should be managed by conventional microsur-gical techniques. Endoscopes may be appropriate to inspect for residual disease in the facial recess, sinus tympani, epitympanum, supratubal recess, and other recesses as needed. in the event that residual matrix is identified, excision may be accomplished using either endoscopic or microscopic dissection.
Small cholesteatomas and shallow retraction pockets may be removed in toto with endoscopic assistance. The atelectatic tympanic membrane or cholesteatoma matrix is initially elevated using conventional microsurgical techniques. The squa-mous epithelium is usually loosely adherent to the neck of the malleus and scutum, allowing for a good starting point for surgical dissection. Elevation of matrix continues until reaching firm adhesions typically encountered deeper in the aditus, facial recess, or sinus tympani. When it is determined that the matrix cannot be further mobilized without significant risk of tearing, the endoscope may be inserted to visualize the adhesions and facilitate their lysis with long angled dissectors.
Because endoscopic dissection is usually done one-handed, it is often helpful to obtain good hemostasis, placing Gelfoam soaked in 1:10,000 epinephrine solution into the middle ear for several minutes prior to the endoscopy. Hemostasis can be improved with frequent irrigation of the field, even with the endoscope remaining in situ. Persistent bleeding necessitates either alternating between suction and dissection or returning to the microscope to evacuate clots and improve hemostasis.
Two-handed dissection under the microscope is always more efficient and should be used whenever possible but discontinued again upon encountering difficult adhesions that disappear from the field of view. Careful elevation of retraction pockets usually results in the intact removal of even very thin squamous epithelium in the majority of cases, and when successfully accomplished a second-stage procedure is unnecessary (Fig. 21-7). Prototypical combined suction-dissectors can improve the efficiency of endoscopic dissection but are not yet commercially available.
After the removal of large epitympanic or antral cholesteatomas, it is often useful to smooth out the adjacent bony surfaces with a diamond drill to reduce the chance of residual disease. Exposure of the medial surface of the scutum, the epitympanic tegmen, and the supratubal recess can be improved with endoscopic assistance (Fig. 21-8).
Canal-wall-down (CWD) mastoidectomy has a significant advantage over intact-canal-wall exposure because of superior visualization into the sinus tympani, elimination of the facial recess, and exte-riorization of the epitympanum, which results in significantly lower risk of residual disease. Thomas-sin et al13 demonstrated that endoscopic-assisted canal-wall-up (CWU) surgery yielded a residual disease rate comparable with CWD surgery. Of 80 patients studied, 44 underwent intact-canal-wall mastoidectomy; 21 of these 44 patients (47.7%) were discovered to have residual disease at a planned second stage. The other 36 patients had endoscopic inspection for cholesteatoma during the
FIGURE 21 —8 Endoscopic view of right mastoid cavity after intact canal mastoidectomy. Diamond drill is passed down bony canal to smooth tegmen bone and ensure cholesteatoma removal.
primary CWU operation and the rate of residual disease dropped to 5.5% as observed at the second-stage procedure. This rate is similar to published series of CWD operations and reflects the improved excision of disease made possible by endoscopic exposure.
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