Modern surgical treatment of otosclerosis - Helda - Helsinki.fi

Review of the literature
disturb these structures. This might be due to insertion of a prosthesis that is too long or to
adhesions or negative middle ear pressure forcing the prosthesis deeper into the inner ear.
Membranous connections are also found between the stapes footplate and the utricle in a
one-quarter of otherwise normal temporal bones, and breakage of these might be one
cause for vestibular symptoms (Backous et al. 1999). In Wang’s (2005) report of the
microanatomy of the vestibulum, the mean distance between the undersurface of the
footplate and the saccule was 1.1 mm (SD=0.48 mm), and between the footplate and the
utricle 1.67 mm (SD=0.31 mm). Previous studies of Caucasian populations have provided
similar results of the microanatomy of the vestibular area (Pauw et al. 1991, Backous et al.
1999). There is a cleft between the utricle and the saccule located along the vertical plane
of the anterior crura, with a 45-60º angle facing the saccule. A modified piston prosthesis
with a slope of 45º at its tip to adapt to the anatomical configuration of the vestibulum was
compared with the conventional piston by Wang et al. (2005). When the modified
prosthesis was used, the incidence of vertigo was significantly decreased and
postoperative symptoms were milder and alleviated faster. Similarly, the occurrence of
spontaneous nystagmus and its mean slow phase velocity were reduced in the group
receiving the modified piston (Wang et al. 2005). However, these results have not been
confirmed by other authors and are not in concordance with studies on objective
evaluations of the saccule after stapes surgery, in which vestibular evoked myogenic
potentials (VEMP) originating from the saccule did not decrease after surgery (Singbartl et
al. 2006, Stapleton et al. 2008).
Taste disturbance
The chorda tympani nerve (CTN) is within the operative field and it is usually necessary
to manipulate it in order to achieve free access to the oval window. Patients with an injury
to the CTN present with symptoms of a metallic or sweet taste and numbness or tingling
of the tongue (Mahendran et al. 2005). In a study of 55 stapedotomies by Mahendran et al.
(2005), the CTN was transected in 22 cases and preserved in 33 cases. In patients in whom
the CTN was transected, 95% complained of symptoms, and in patients in whom the nerve
was preserved 52% had symptoms. If the CTN was transected, the symptoms were more
severe and long-lasting. Although electrogustometry showed total loss of chorda function
in almost every instance where the nerve was transected after a postoperative mean of 38
months, only half of the patients had mild to moderate symptoms for more than six
months (Mahendran et al. 2005).
Facial paresis
There are two types of facial palsy after stapes surgery: immediate, due to local
anaesthetic or direct trauma to the nerve, and delayed. Local anaesthetic may produce
facial palsy that resolves within hours. The risk of direct trauma increases if there is an
anomalous course of the facial nerve, but normally it should be easy to avoid (Wellin et al.
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