4.2.2 Labyrinthine fistula
The incidence of a labyrinthine fistula during cholesteatoma surgery is approximately 7.5%.9 As osseous tissue mainly originates from or fuses with the lateral semicircular canal, difficulties may arise in the intraoperative identification of the semicircular canal. In such situations, other anatomical landmarks may be used for localizing the semicircular canal: (1) Navigational landmarks for identifying the pyramidal segment of the facial nerve, the stapes and pyramidal eminence also form the anteromedial boundary of the lateral semicircular canal; (2) the horizontal segment of the facial nerve, which passes anteriorly and inferior to the lateral semicircular canal; (3) situated between the sigmoid sinus and the middle cranial fossa dural plate, the sinodural angle also forms the posterior-superior edge of the saucerized mastoid cavity. By proceeding anteriorly from the sinodural angle, the posterior semicircular canal can be localized, enabling the exposure of the lateral semicircular canal. The osseous tissue on the surface of the semicircular canal must be ground layer by layer; (4) the “blue line” of the semicircular canal to confirm the direction of the passage and determine the location of the semicircular canal.
Labyrinthine fistulas can be classified into three types according to the classification system proposed by Dornhoffer and Milewski10: (1) Type I, an erosion of the bony labyrinth with an intact endosteum; (2) Type II, the concomitant involvement of the bony and membranous labyrinths that form a labyrinthine fistula, which features a depth of less than half of the diameter of the semicircular canal and causes lymphatic leakage; (3) Type III: the concomitant damage to the bony and membranous labyrinths that corms a fistula, which features a depth of more than half of the diameter of the semicircular canal and may induce dehiscence. Currently, there is no widely recognized standard for the repair of labyrinthine fistulas, and data do not demonstrate significant differences in postoperative hearing outcomes based on the surgical technique.11 In the present study, patient 1 had a Type I labyrinthine fistula and patient 2 had a Type II labyrinthine fistulas; temporal fascial patching and muscle filling were adopted for the closure of the fistulas, and intravenous dexamethasone was administered for symptomatic treatment. The postoperative vertigo experienced by patients 1 and 2 subsided at 1- and 3-months following surgery, respectively.