To investigate the anatomic limitations of the endoscopic transcanal approach to sinus tympani (ST), in particular, how this approach might allow a complete visualization of the ST recesses and to propose a morphologic classification of the ST using computed tomography and to examine if this could be useful for the surgeon in preoperative planning to decide the type of approach to the ST. Case series. Forty patients affected by middle ear disease with ST involvement were included in our study. All patients underwent a preoperative computed tomographic scan of the temporal bone. All patients underwent tympanomastoid surgery with intraoperative use of the endoscope. We assessed the variation in depth of the ST area, analyzing the posterior and medial extension of the medial boundary of the ST, and performing a radiomorphologic classification of the ST. Of the 40 patients, it has been possible to describe the detailed morphology of the shape of the ST in 38. We classified the depth of the ST into 3 types based on radiologic findings: Type A (a limited ST), Type B (a deep ST), and Type C (a deep ST with a posterior extension). Of 35 ST of Types A and B, there was good exposure of the medial boundary of the sinus using a transcanal endoscopic approach in 33 (94.2%), whereas in 3 (60%) of 5 patients of Type C, it was not possible to explore the complete depth of the sinus, especially the ST portion under and posterior to the facial nerve. The transcanal endoscopic approach to the ST is indicated in ST of Types A and B. In ST of Type C, it is not always possible to have good control of the ST; in these cases, a posterior retrofacial approach is suggested.

Conclusion. The endoscopic approach to attic cholesteatoma allows clear observation of the tensor fold area and consequently, excision of the tensor fold, modifying the epitympanic diaphragm. This permits good removal of cholesteatoma and direct ventilation of the upper unit, preventing the development of a retraction pocket or attic cholesteatoma recurrence, with good functional results. Objectives. An isthmus block associated with a complete tensor fold is a necessary condition for creation and development of an attic cholesteatoma. During surgical treatment of attic cholesteatoma, tensor fold removal is required to restore ventilation of the attic region. Use of a microscope does not allow exposure of the tensor fold area and so removal of the tensor fold can be very difficult. In contrast, the endoscope permits better visualization of the tensor fold area, and this aids understanding of the anatomy of the tensor fold and its removal, restoring attic ventilation. Patients and methods. In all, 21 patients with limited attic cholesteatoma underwent an endoscopic approach with complete removal of the disease. Patients with a wide external ear canal were operated through an exclusively endoscopic transcanal approach; patients with a narrow external ear canal or who were affected by external canal exostosis were operated through a traditional retroauricular incision and meatoplasty followed by the endoscopic transcanal approach. Results. In 18/21 patients, the endoscope permitted the discovery of different anatomical morphologies of the tensor fold. Sixteen patients presented a complete tensor fold (one with an anomalous transversal orientation), one patient presented an incomplete tensor fold and one patient presented a bony ridge in the cochleariform region. In all 16 cases of complete tensor tympani fold, the fold was removed and anterior epitympanic ventilation was restored. The ridge bone over the cochleariform process was also removed with a microdrill.