Keywords
benign paroxysmal positional vertigo - vertigo/surgery - semicircular canals - otologic
surgical procedures
Introduction
Benign paroxysmal positional vertigo (BPPV) is a very common vestibular disorder,
characterized by episodic vertigo following certain provocative head movements. It
is considered to be the most frequent type of peripheral vertigo, although estimates
regarding its frequency among patients with this type of symptoms vary between 5 and
40%.[1]
[2] Since the histopathologic studies of Schuknecht and Ruby,[3] in the early 70's, it has been regarded as a disease that originates in the posterior
semicircular canal, yet many aspects of its pathophysiology remain uncertain.[4]
The vast majority of all BPPV cases are of the posterior canal variant. The pathophysiology
that causes most of these cases is thought to be canalithiasis. This is probably because
most of the free-floating endolymph debris tends to gravitate to the posterior canal,
being the most gravity-dependent part of the vestibular labyrinth in both the upright
and supine positions. Once the debris enters the posterior canal, the cupular barrier
at the shorter, more dependent end of the canal blocks the exit of the debris. Therefore,
the debris becomes "trapped" and can only exit at the end that has no ampulla (the
common crus).[5] The prevalence of horizontal canal BPPV, although lower than that of the posterior
canal type, is significant, accounting for up to 20% of the cases of paroxysmal vertigo[6]; the lower incidence is attributed to its spatial orientation, since the lateral
canal slopes up and has its cupular barrier at the upper end. Therefore, free-floating
debris in the lateral canal would tend to float back out into the utricle as a result
of natural head movements. Superior canal involvement is exceedingly rare.
Current treatment of all forms of BPPV is mostly through canal repositioning maneuvers,
developed to free the canal from lithiasis. Such maneuvers were described by Epley[7] and Semont,[8] and are very effective, with a success rate of up to 98% after three sessions. Furthermore,
spontaneous resolution is frequent, usually occurring after 6 to 8 weeks of the initial
symptoms; thus, BPPV is generally considered a benign disease.
However, positional vertigo is a potentially disabling condition, and a small fraction
of the patients present symptoms and refractory vertigo after repeated canal repositioning
maneuvers and physical therapy. For these patients, surgery may be considered- and
various techniques have been proposed, including utricular ablation, microvascular
decompression, singular nerve section (SNS), and two procedures that are considered
as functionally equivalent, posterior semicircular canal occlusion (PSCO) and laser
assisted “partitioning.”[9]
[10]
[11]
[12]
[13]
[14] The only techniques that have been widely adopted, or that have been studied by
more than one author, are posterior ampullary nerve (“singular nerve”) section and
semicircular canal occlusion (SCO). It is important to note that singular neurectomy
is performed through an external ear canal approach, which can be done under local
anesthesia, while SCO requires a retroauricular incision and simple mastoidectomy.
The objective of this study is to review the current status of these two procedures
and to determine if published data exist to favor one over the other.
Review of the Literature
Search Strategy and Study Selection
Most publications regarding BPPV are not classified by its Medical Subject Heading
(MESH) term. In fact, a search using that term only produces 193 publications. We,
therefore, conducted a search through PaperChase, a service which provides Telnet
access to all references found in the MEDLINE and OLDMEDLINE databases of the National
Library of Medicine, and which can provide great granularity in its search terms.
We then searched for publications containing any of the following words and/or MESH
terms: “Benign Paroxysmal Positional Vertigo”, “Positional”, “Vertigo”, “Postural”,
“Cupulolithiasis” and “Semicircular canals”, which we then cross referenced with “Vertigo/Surgery”,
which unites the term “Vertigo” with surgical treatment. In this way, we obtained
a manageable amount of studies to analyze. The studies that met our inclusion criteria
are summarized in [Table 1]. This cannot be considered as an exhaustive review, but considering the homogeneity
of the results reported, it can be considered a representative analysis of the published
data.
Table 1
Success rate and incidence of postoperative hearing loss reported by different authors
after singular nerve section or semicircular canal occlusion
|
Author
|
Year
|
Procedure
|
Number of procedures
|
Number of successful procedures (%)
|
Number of cases with postoperative hearing loss (%)
|
|
Gacek[20]
|
1978
|
SNS
|
12
|
10 (83.33%)
|
1 (8.33%)
|
|
Silverstein[18]
|
1990
|
SNS
|
49
|
39 (79.59%)
|
3 (6.12%)
|
|
Gacek[19]
|
1995
|
SNS
|
146
|
138 (94.52%)
|
4 (2.74%)
|
|
Pournaras[22]
|
2008
|
SNS
|
8
|
8 (100.00%)
|
2 (25.00%)
|
|
Parnes[13]
|
1990
|
SCO
|
2
|
2 (100.00%)
|
0 (0.00%)
|
|
Pace-Balzan[23]
|
1991
|
SCO
|
5
|
5 (100.00%)
|
0 (0.00%)
|
|
Anthony[14]
|
1991
|
SCO
|
2
|
2 (100.00%)
|
0 (0.00%)
|
|
Hawthorne[24]
|
1994
|
SCO
|
15
|
15 (100.00%)
|
0 (0.00%)
|
|
Zappia[25]
|
1996
|
SCO
|
8
|
8 (100.00%)
|
0 (0.00%)
|
|
Pulec[26]
|
1997
|
SCO
|
17
|
17 (100.00%)
|
0 (0.00%)
|
|
Walsh[27]
|
1999
|
SCO
|
13
|
13 (100.00%)
|
0 (0.00%)
|
|
Nomura[28]
|
2002
|
SCO
|
2
|
2 (100.00%)
|
0 (0.00%)
|
|
Shaia[21]
|
2006
|
SCO
|
28
|
28 (100.00%)
|
1 (3.57%)
|
|
Kisilevsky[29]*
|
2009
|
SCO
|
32
|
32 (100.00%)
|
0 (0.00%)
|
|
Ahmed[30]
|
2012
|
SCO
|
55
|
55 (100.00%)
|
9 (16.36%)
|
|
Beyea[31]
|
2012
|
SCO
|
77
|
77 (100.00%)
|
3 (3.90%)
|
|
Ramakrishna[32]
|
2012
|
SCO
|
12
|
12 (100.00%)
|
2 (16.67%)
|
|
Zhu[33]
|
2015
|
SCO
|
3
|
3 (100.00%)
|
0 (0.00%)
|
Abbreviations: SNS, singular nerve section; SCO, semicircular canal occlusion.
* Kisilevsky et al report less than 10dB average loss by frequency.
Results
After reviewing the literature, it became evident that BPPV-related surgical cases
have been decreasing since the early 1990s, presumably because of the emergence and
high success rate of the repositioning maneuvers. It is also evident that singular
nerve section (SNS), which was never widely adopted, seems to have been largely abandoned.
Anatomical studies report a wide variation in the possibility of locating the singular
nerve, ranging from 98%, in Kos et al,[15] to 20%, reported by Lewer et al.[16] Both authors agree, however, on the difficulty of correctly identifying the nerve
through a surgical approach via the external ear canal. In 2008, Feigl et al[17] reported an interesting anatomical study in which they documented that a significant
learning curve is needed to obtain adequate results. The largest series published
are those of Silverstein and White,[18] in 1990, and Gacek,[19] in 1995; the latter reported, in an earlier study, an inability to locate the singular
nerve in two of his first 12 patients (16%).[20]
In contrast with SNS, SCO is a much more straightforward technique, and thus, still
a subject of study. Regarding published results and complications, by aggregating
all the patients reported in the studies shown in [Table 1], we can observe that SCO is reported to be successful in eliminating positional
vertigo in 100% of the patients, which is somewhat difficult to believe, although
some papers mention recurrence of vertigo through another canal, and Shaia et al[21] mention an 85% patient satisfaction rate, even though all patients had normalization
of the Hallpike test. On the other hand, SNS is reported to be successful in 79 to
94% of cases, probably due to the anatomical difficulties mentioned above. Both techniques
report a similar incidence of postoperative hearing loss, around 5%.
It is important to note that, although there would seem to be a slightly better success
rate with SCO as compared to SNS, the majority of the studies analyzed do not evaluate
postoperative vertigo using objective and quantifiable instruments, and those that
do, differ between them. It is difficult to assure that the differences between the
procedures regarding results are truly significant. Hearing loss is also loosely reported,
with differing definitions of what constitutes hearing loss and whether or not it
can be attributed to the procedures. Still, both techniques seem to provide important
benefits, with an acceptable risk of hearing and balance loss in selected patients.
Discussion
The choice between SNS and. SCO for the few patients with intractable BPPV is based
on the success rate and risk for hearing loss. This review would seem to indicate
a slightly lower success rate for SNS, perhaps due to the difficulty in locating the
singular nerve near the base of the round window. When performing a SCO, there are
no troubles in locating the semicircular canals for any otologic surgeon, and the
result in hearing preservation depends mostly on how carefully the canal is opened
and manipulated. It is worth mentioning that we have also been using SCO as a conservative
surgical procedure for patients with intractable Ménière's disease and serviceable
hearing, and that our experience in avoiding hearing loss and controlling vertigo
agrees with that of the studies we have reviewed. In our experience, SCO is a very
straightforward technique and it avoids the anatomical difficulty of locating the
singular nerve. Thus, we consider SCO as the technique of choice for those rare patients
who require surgery for intractable positional vertigo.
Final Comments
Both SCO and SNS are effective surgical options for patients with difficult to control,
incapacitating, BPPV. Although SCO requires a retroauricular, transmastoid approach,
it is an easier and safer procedure, thus it should be considered the best alternative.
