CST conducted by Japan Working Group on Endoscopic Ear Surgery

Conventional mastoidectomy requires a large postauricular incision, with elevation of the auricle to widely expose the temporal bone surface. The mastoid air cells are then extensively drilled using several types of burrs, creating a mortar-shaped cavity toward the deep portion. During this process, the surgeon repeatedly adjusts the microscope to maintain a clear view while preserving critical structures: the posterior canal wall is thinned and preserved anteriorly; the dura superiorly, sigmoid sinus posteriorly, and the lateral semicircular canal and facial nerve in the deeper region must all be safely exposed and protected. This traditional and well-established technique represents the foundation of microscopic ear surgery. However, is complete mastoidectomy truly necessary even in cases with well-developed, normal mastoid air cells? The mastoid mucosa possesses gas-exchange functionality. Because ear surgery had long been limited to microscopy, the question of whether it is appropriate to sacrifice normal mastoid air cells has not been sufficiently explored. In contrast, the use of endoscopes in ear surgery has advanced remarkably. Endoscopes provide a very wide field of view due to their wide-angle lenses. Unlike the microscope, whose lens remains outside the temporal bone and therefore distant from the target, the endoscope places the lens inside the temporal bone, enabling bright, magnified, close-up visualization. Endoscopic instrumentation is particularly advantageous for disease involving the mesotympanum, retrotympanum, protympanum, and hypotympanum, where it often outperforms the microscope. Access to the epitympanum can also be achieved through transcanal atticotomy (TCA). We developed percutaneous endoscopic ear surgery (PEES), which involves making a 2 cm incision behind the ear during mastoidectomy and performing a keyhole bone incision of approximately 1 cm toward the mastoid sinus using an electric drill under water irrigation (Otol Neurotol. 2025 Jun 1;46(5):532-538.). Instead of the traditional mortar-shaped drilling, PEES allows a dome-shaped mastoidectomy under endoscopic guidance. A microscope, which only provides a straight-line view, cannot ensure visualization through such a narrow keyhole; however, the endoscope delivers wide, bright visualization within the mastoid cavity. In conventional microscopic mastoidectomy, creating a large surgical field is essential to avoid damage to vital structures in the temporal bone. In PEES, this safety is maintained through the combined use of a navigation system. Cholesteatomas extending from the epitympanum to the antrum—lesions that require TCAA in TEES—represent excellent indications for PEES. After reaching the antrum with PEES, further selective drilling is performed to expand the working space. The cholesteatoma matrix is dissected from the antrum side and pushed toward the epitympanum. If necessary, the contents are reduced through the area of pars flaccida retraction. Subsequently, TCA is performed to remove the cholesteatoma completely, followed by scutum reconstruction using cartilage. As a result, high-level canal wall reconstruction becomes unnecessary, and only scutum reconstruction is required. By incorporating augmented reality guidance within the navigation system, Image-Guided PEES (IGPEES) ensures safety while enabling precise minimally invasive surgery. IGPEES represents a next-generation, innovative extension of TEES. This presentation will outline the principles of otologic navigation systems and provide an overview of PEES and IGPEES techniques.