1 INTRODUCTION
Lateral semicircular canal prominences, which have relatively fixed positions, are key anatomical landmarks used to locate the facial nerve in middle ear surgery. The color and bone density of these prominences differ distinctly from those of the compact bone around the tympanic antrum, which enables easy identification of them during middle ear surgery. Hence, these prominences often serve as key structural landmarks during temporal bone dissection. Extensive ossification over the lateral semicircular canal (EC-LSC) is a complex condition encountered by surgeons during middle ear surgery that usually occurs in patients with a long history of chronic otitis media or cholesteatoma. Clinical cases of EC-LSC were first reported by Fleury et al. in 1978,1 who categorized EC-LSC into three types: massive, diffuse attico-antral, and localized.2However, the literature has since featured relatively scant reports on EC-LSC. Hoshino et al.3 performed surgeries on 89 patients with attic cholesteatoma over three and a half years. In eight patients, they identified bony tissue proliferation at the tympanic antrum or aditus ad antrum as typical characteristics of EC-LSC. A previous study suggested that infectious stimuli at an early stage of the disease might stimulate such osteoplastic activity,3 while another study indicated that EC-LSC might be induced by trauma.4 Regardless of its etiology, the membranous labyrinth are apparent in such patients. Notably, the bony lateral semicircular canal carina, a key landmark, is often encased in dense bone. Hence, difficulties usually arise upon encountering the facial nerve and membranous labyrinth, and – as the incidence of iatrogenic fistula during surgery is extremely high – inexperienced otologists may be prone to operating errors. In the present study, we retrospectively analyzed all the data of patients who underwent surgery for otitis media or cholesteatoma within the 3 years to elucidate the clinical characteristics of EC-LSC. Findings from this study will help inform preoperative planning, intraoperative procedures, and postoperative management of symptoms.