3.1 Characteristics of patients
All seven EC-LSC patients were women with a mean age of 45.9 years and a disease duration of 4–25 years. Two of the patients (patients ID5 and ID7) received revision surgery due to postoperative recurrence. All seven patients suffered from middle ear cholesteatoma. Three patients had concomitant tympanosclerosis and one patient had concomitant adhesive otitis media. Canal wall down mastoidectomy was performed in all patients, and concurrent ossicular chain reconstruction was performed in four patients (total ossicular replacement prosthesis [TORP], three; partial ossicular replacement prosthesis [PORP], one) (Table 1).
The most common site of ossification was the tympanic antrum (6/7 patients), followed by the attic. Complete ossicle damage occurred in two patients. The fusion of the osseous tissue and the ossicles was observed in the other five patients, resulting in abnormalities in ossicle morphologies. Fusion also occurred between the osseous tissue and lateral semicircular canal, which obstructed the aditus ad antrum and induced local drainage disorders in severe cases. The bone tissue was visible upon postoperative pathological examination. As the density of osseous tissue formed from ossification is close to or slightly lower than that of the normal bone, it is often difficult to distinguish between osseous tissue and the bone of the semicircular canal during surgery. Cholesteatoma tissue or granulation tissue is usually concealed between the osseous tissue and normal bone, as shown in Figure 1② (patient ID2) and Figure 2. In two of the seven patients, semicircular canal fistulas of differing degrees were found intraoperatively (Patient 1: the “blue line” of the lateral semicircular canal was exposed intraoperatively and the membranous semicircular canal was intact (Figure 1③); Patient 2: a 2-mm semicircular canal fistula occurred intraoperatively during bone grinding). Fascial patching and temporal muscle filling were separately adopted for the closure of the lateral semicircular canal fistulas, and dexamethasone was administered intraoperatively and postoperatively. Both patients with lateral semicircular canal fistula experienced postoperative vertigo, which subsided at 1 month and 3 months postoperatively, respectively, with the administration of symptomatic treatment.