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.