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100%, but 74% (3). In one study, which included various
patients with an indication for middle ear surgery, the
prevalence was very low (19).
Diagnostic Test Measures
The sensitivity ranged between 60 and 95% in seven
studies (2,3,6,16–20). The two studies (2,3) that com-
pared CT to histopathology found lower sensitivities of
60 and 66% than the studies comparing CT to middle ear
surgery (6,16–20). Specificity was 100% in two studies
(3,18). In another two studies specificity was lower: 83%
and 75% (16,17,19). Specificity could be calculated for
one of the studies that compared CT to histopathology
and was not different from the specificities found in the
studies that compared CT to middle-ear surgery (100%
(3) compared with 75 to 100% [16–19]).
Post-test Probability of Otosclerosis
In patients with a clinical suspicion of otosclerosis, the
positive post-test probability of otosclerosis with an
abnormal CT was 99% (16,17). The positive post-test
probability was much lower in a study population of
patients with an indication for middle-ear surgery (23%)
(19). The negative post-test probabilities were reported in
three studies: 51%, 53%, and 67% (3,16–18). In patients
with an indication for middle-ear surgery, the negative
post-test probability of otosclerosis with a normal CT
was only 3% (19).
DISCUSSION
Summary of Main Results
The pretest probability or prevalence of otosclerosis
was very high in the majority of the included studies
(2,3,6,16–18,20). In those studies with a high prevalence
of disease (74–97%), both positive and negative post-test
probabilities were (relatively) high (3,16–18). Positive
post-test probability was 99% in one of these studies
(16,17) and negative post-test probabilities ranged
between 51% and 67% (3,16–18). In one study (19)
with a low prevalence of disease (9%), both positive and
negative post-test probabilities were much lower com-
pared with studies with a high prevalence of disease (23%
and 3%, respectively). Overall, reported sensitivities
ranged between 60% and 95% (2,3,6,16–20). The sen-
sitivity and specificity for operatively confirmed otoscle-
rosis were 61 to 95% (6,16–20) and 75 to 100% (16–19),
respectively. The sensitivity and specificity for histopa-
thologically confirmed otosclerosis were 60 to 66% (2,3)
and 100% (3), respectively.
The diagnostic measures and post-test probabilities
were generally higher in newer studies. The advance-
ments in scanners and techniques may have attributed to
higher detection rates in newer studies. Prevalence influ-
ences post-test probabilities; post-test probabilities are
generally higher in studies with a high prevalence of
disease and lower in studies with a low prevalence
of disease. Indeed, the studies with a high prevalence
of otosclerosis reported higher post-test probabilities than
those studies with a low prevalence of otosclerosis.
Prevalence of disease in these studies may have been
influenced by the choice of inclusion and exclusion
criteria (suspected otosclerosis based on clinical history
and physical examination versus intraoperatively con-
firmed otosclerosis) and the choice of reference test
(middle-ear surgery versus histopathology).
Previous studies and reviews highlight the importance
of CT in the diagnostic evaluation of otosclerosis
(2,3,28). However, the prevalence of otosclerosis in
patients with a clinical suspicion of otosclerosis and/or
an indication for surgery is generally high. As a result,
preoperative CT has little to add in establishing otoscle-
rosis and may not be necessary to confirm the diagnosis.
Although its role in diagnosing otosclerosis is limited, CT
imaging may still be useful in establishing the extent of
disease and cochlear involvement, and in detecting
concomitant abnormalities.
CT scans were qualitatively analyzed in the included
studies. Otosclerosis is usually confirmed on CT on the
basis of visual confirmation of double ring signs, hypo-
densities around the otic capsule, and/or thickening of the
footplate. Several authors adopted a more quantitative
approach and measured bone densities in the area
immediately anterior to the oval window: the fissula ante
fenestram (20,21,29,30). These studies did find statisti-
cally significant differences in Hounsfield units measured
over the fissula ante fenestram region between patients
with otosclerosis and control patients, but not in several
other regions surrounding the otic capsule. Tringali et al.
(20) performed analyses in a subgroup of patients with
otosclerosis and normal-appearing CT scan and found no
significant differences for densitometric measurements in
this subgroup compared with control subjects without
otologic disease and control patients with cholesteatoma.
Unfortunately, none of these studies defined a cut-off
value that can be used to create two-by-two contingency
tables and calculate diagnostic test measures.
Quality of Evidence
The majority of the included studies were character-
ized by a moderate relevance and moderate risk of bias.
Most studies only included patients with surgically con-
firmed otosclerosis. As a result, prevalence of otoscle-
rosis is 100% in these studies and only sensitivities can be
calculated. Second, only studies using surgery or
histology as a reference test were included, since this
is the only adequate reference test for confirming oto-
sclerosis. This implies that all included patients had an
indication for surgery. This causes a substantial risk of
selection bias, because the study populations probably
will not include patients with very mild disease or
patients with a severe sensorineural component. There-
fore, these results will not translate into the general group
of patients with otosclerosis.
Potential Biases in Review
To our knowledge, this is the first review to not only
systematically evaluate, but also critically appraise the
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