Abstract

In cases of acute unilateral deafness, no consensus exists as to whether tympanotomy and sealing of the round window should be performed routinely. To further address this issue, we conducted a retrospective study of pre-, intra-, and postoperative findings in 97 patients who

had undergone exploratory tympanotomy (EXT) after the onset of sudden and severe unilateral deafness. Our goal was to ascertain, if we could, whether the benefits of EXT outweigh the risks. We also took into account the effects of perilymph fistula (PLF) on the etiology of sudden hearing loss and postoperative outcomes. We found that routine EXT was indeed beneficial for these patients. It was associated with a very low surgical complication rate, and its effects on hearing as assessed by objective measures were beneficial. The greatest benefits were seen in patients who underwent EXT within 7 days after the onset of their hearing loss. With respect to PLF, we found that the presence or absence of the "typical history" of PLF (i.e., a sudden unilateral hearing loss within 48 hours after a precipitating trauma or physical exertion) had no bearing on whether a PLF was actually present in our group; nor was vertigo a reliable predictor of PLF. We recommend that EXT be performed on all patients with new-onset acute unilateral deafness, barring any contraindications, of course. The absence of a typical history of PLF should not dissuade the surgeon from proceeding with EXT.

Introduction

One of the well-documented causes of sudden unilateral hearing loss is the development of a perilymph fistula (PLF). A PLF is an abnormal opening between the inner ear and the external surface of the labyrinth capsule that can allow perilymph to leak (figure). (1-7) In addition to hearing loss, perilymph leaks can lead to disorders of balance. (6,8,9) PLFs can occur spontaneously or as a result of external forces. Most cases are caused by a rupture of the round window membrane (RWM) or the oval window ligament secondary to trauma or stress. (10)

Major advancements in our understanding of PLF as a cause of sudden deafness were made by Lawrence and McCabe, (11) who conducted early animal studies; Simmons, (12) who proposed the theory of membrane breaks in sudden hearing loss; and Stroud and Calcaterra, (13) who were the first to propose the idea of spontaneous oval window PLF.

Goodhill proposed the theory that membrane ruptures could occur as a result of both explosive and implosive mechanisms. (14) During an explosive event, increased intracranial pressure is transmitted to the perilymphatic space, resulting in a rupture of the RWM and a leak of perilymph into the middle ear. During an implosive event, increased pressure is transmitted via the eustachian tube and the middle ear to the round window and the oval window; the resultant membrane rupture drives air into the labyrinth and displaces perilymph into the middle ear.

PLF is difficult to diagnose, and no consensus on treatment has been reached. (15,16) Conservative management of suspected PLF may entail bed rest and antiphlogistic or rheologic therapy. (17) On the other hand, a number of authors recommend rapid exploratory tympanotomy (EXT) and subsequent obliteration of the fistula if present to prevent further loss of perilymph and to effect a complete recovery, (10,15,18-20) However, the benefits of surgery have not been proven beyond doubt, and its indications remain controversial. If the criteria for justifying EXT are too strict, a PLF may go unrecognized and some patients may be sent home without having undergone treatment for a very treatable problem. (20) Conversely, if the indications for EXT are too broad, patients with auditory and vestibular symptoms in the absence of a PLF maybe subjected to middle ear exploration without benefit. (6) Adding to the dilemma is the fact that some PLFs heal spontaneously and some do not. (15)

[FIGURE OMITTED]

In this article, we describe our quality assessment of the value of EXT in treating patients with sudden and severe unilateral hearing loss, primarily by analyzing audiometrically quantified outcomes. Our hope was to accumulate sufficient evidence to be able to recommend for or against performing EXT routinely in these patients.

Patients and methods

We retrospectively reviewed the charts of 97 consecutively presenting patients (median age: 49 yr) who had undergone EXT for evaluation of sudden hearing loss in the Department of Otorhinolaryngology--Head and Neck Surgery at Freiburg University Medical School. In our department, EXT and autologous grafting of the round and oval window niches with temporal connective tissue under local anesthesia is recommended for all patients who experience a sudden hearing loss of more than 60 dBnHL in three or more of the octave frequencies from 250 to 8,000 Hz--unless, of course, there is a contraindication by comorbidity or an obvious nonfistula pathogenesis (e.g., acoustic neuroma, multiple sclerosis).

In our study population, 59 patients had lost hearing in the left ear and 38 in the right ear. Preoperatively, all patients had undergone a complete ENT examination, which included pure-tone audiometry, speech audiometry, impedance testing, and caloric examination of the labyrinths with 44[degrees]C and 30[degrees]C water. In addition, 22 patients had undergone preoperative transtympanic electrocochleography according to the method described by Aran. (21) Preoperative brainstem-evoked response audiometry was performed in all patients; if a result was ambiguous (e.g., an absence of recordable waves in a patient with complete deafness) or if it indicated neural inflammation or a cerebellopontine angle tumor (e.g., a prolonged interpeak latency), magnetic resonance imaging (MRI) was obtained. The presence of a neural hearing impairment confirmed by MRI would have rendered a patient ineligible for EXT, hut no such circumstance occurred. Likewise, patients with psychogenic hearing loss were not included in this study because they would not have undergone EXT. Finally, all patients received intravenous infusions pre- and postoperatively to improve microperfusion according to the Stennert infusion schema. (17)

For purposes of comparing results, we placed patients into different groups according to various demographic, clinical, and surgical characteristics:

Sex. Findings in men were compared with those in women.

Age. We classified patients into three groups according to age: 18 to 30 years, 31 to 59 years, and 60 years and older.

History of PLF. Patients were classified according to the presence or absence of a typical history suggestive of PLF. Such a history included a sudden unilateral hearing loss within 48 hours after experiencing an event that is presumed to be a risk factor for PLF--specifically, a precipitating trauma or physical exertion secondary to activities such as heavy lifting, strenuous pushing, severe cough, underwater diving, or barotrauma. (6,8)

Vertigo. Patients were classified according to the presence or absence of vertigo at the onset of their hearing loss.

Duration of symptoms. Patients were classified into three groups according to the length of time that had passed from the onset of their symptoms until they underwent EXT: 1 to 3 days, 4 to 7 days, and 8 days or more. We also combined the audiometric data of patients who underwent surgery 1 to 7 days after the onset of symptoms and compared them with the data of those who underwent surgery after 8 days or more.

Intraoperative findings. When performing EXT, surgeons examined the round and oval window niches at microscopic magnification to look for perforation of any window and for stapedial dislocation. Special attention was paid to a displacement of the RWM during gentle movement of the stapes caused by the transmission of pressure alterations from the oval window to the round window via the perilymph; if the RWM could not be seen, movement was transmitted by the application of a small amount of Ringer solution instilled into the round window niche. In most cases, the increased pressure below the oval window caused by the movement of the stapes resulted in a bulging of the RWM. In the presence of a leak, perilymph cannot transmit pressure alterations to the RWM because the alterations are equalized by the leak. Therefore, patients were classified into three groups--fistula, no fistula, and doubtful--according to the intraoperative findings.

* The fistula designation was applied to cases in which an obvious perforation was visible and no simultaneous pressure transmission from the oval to the round window was noticed.

* The no fistula designation pertained to cases in which no perforation was visible and a simultaneous pressure transmission from the oval to the round window (bulging of the RWM) was noticed.

* The doubtful category covered equivocal findings that neither proved nor ruled out the presence of a fistula--for example, cases in which the round window was hooded.

Electrocochleography. Patients were categorized according to the cochlear microphonics (CM) threshold (<80 or [greater than or equal to]80 dBHL) and according to the compound action potential (CAP) threshold (<70 or [greater than or equal to]70 dBnHL).

Complications. We also noted any early and late postoperative complications of EXT.

For each of the various groups, comparisons were based on audiometry conducted in accordance with the procedures established by Yamamoto et al. (22) The following evaluations were made for all patients:

* preoperative pure-tone thresholds at 250 Hz and 1, 4, and 8 kHz

* postoperative audiometric thresholds at these frequencies at least 4 weeks following EXT

* absolute hearing gain at these frequencies

* relative hearing gain--that is, the ratio of hearing gain to the initial hearing level, expressed as a percentage

* the recovery rate--that is, the ratio of hearing gain to the difference in the initial hearing level between the affected and unaffected sides, expressed as a percentage

For comparisons of two variables, we performed statistical analyses with the quantitative nonparametric Wilcoxon test for unpaired groups (Mann-Whitney U test). For comparisons of three variables, we used the Kruskal-Wallis test and the analysis of variance (ANOVA) with Bonferroni correction.

Results

EXT with obliteration of the round and oval window niches was successful in all 97 patients. Postoperatively, the average hearing of all patients improved by almost 40 dB in the low frequencies and by approximately 20 dB in the middle and high frequencies (table 1).

Sex. Our study group was made up of 62 men (64%) and 35 women (36%). Preoperative hearing was slightly better in the men, as were postoperative hearing, absolute and relative hearing gains, and recovery rates; the differences were not statistically significant at any frequency.

Age. In our study population, 14 patients (14%) were aged 18 to 30 years, 60 patients (62%) were aged 31 to 60 years, and 23 patients (24%) were aged 60 and older. We did not find any statistically significant differences in preoperative hearing among these groups. Postoperatively, we found the best audiometric thresholds, the best absolute and relative hearing gains, and the best recovery rates in the youngest group and the worst such findings in the oldest group, but again, these differences were not significant.

History of PLF. A total of 21 patients (22%) had a typical history of PLF, and 76 patients (78%) did not. Preoperative hearing was better in the patients who had a typical history, but the difference was statistically significant only at 8 kHz (p < 0.05) (table 2). Intraoperatively, an RWM rupture was found in a higher percentage of patients who had a typical history of PLF (52%) than in those who did not (31%) (table 3). However, the sensitivity of a typical history was only 29%, and its specificity was 86%. Postoperative hearing, hearing gains, and recovery rates were generally better in patients with a typical history, but differences were not statistically significant in the low and middle frequencies (table 2).

Vertigo. A total of 45 patients (46%) experienced vertigo at the onset of their hearing loss, and 52 patients (54%) did not. Preoperative hearing was significantly worse in the vertigo group (p < 0.01) (table 4). Intraoperatively, signs of rupture were more common in the vertigo group (41 vs. 28%), although the sensitivity of this symptom was only 52% and the specificity was only 58% (table 3). Postoperative hearing, absolute and relative hearing gains, and recovery rates were significantly worse at all frequencies in the vertigo group (table 4).

Duration of symptoms. Some 57 patients (59%) underwent surgery within 1 to 3 days of symptom onset, 23 patients (24%) 4 to 7 days later, and 17 patients (18%) 8 or more days later. Preoperatively, there were no significant differences in audiometric variables among the 3 groups (table 5). Postoperatively, absolute and relative hearing gains and recovery rates were best in the group that underwent EXT from day 4 through day 7 and worst for those who underwent EXT after day 7. These differences were statistically significant at 250 Hz and 1 kHz according to the Kruskal-Wallis test and significant at 4 kHz according to ANOVA.

Intraoperative findings. With respect to the three categories of intraoperative findings--fistula, no fistula, and doubtful--EXT revealed a fistula in 34 patients (35%) and no fistula in 36 patients (37%); the presence of a fistula was doubtful in the remaining 27 patients (28%). Preoperative hearing was better in the fistula and doubtful groups than in the no fistula group, but not significantly so (table 6). Likewise, postoperative hearing and absolute and relative hearing gains were better in the fistula and doubtful groups, although the differences were statistically significant only at 250 Hz. Finally, overall hearing and recovery rates postoperatively were better in the fistula and doubtful groups, but not to a statistically significant degree.

Electrocochleography. In the 22 patients who underwent electrocochleography, we did not find any correlation between those findings and the presence or absence of a PLF intraoperatively. Good CM and CAP thresholds were indicative of better postoperative hearing, better relative hearing gains, and better recovery rates over all frequencies. However, the onlystatistically significant differences were seen in postoperative hearing and relative hearing gain at 1 and 4 kHz for the CAP threshold.

Complications. No early complication occurred, and only 1 late complication was noted. One year postoperatively, a patient was diagnosed with an external ear canal cholesteatoma, which had possibly been induced by our surgical intervention. The cholesteatoma was removed without incident.

Discussion

Management of PLF is controversial because the diagnosis is difficult. The diagnostic criteria for PLF have not yet been fully established, and the value of various diagnostic tests is controversial. (3,4,6,8) No noninvasive test has yet been established to document PLF. (3,4) The Hennebert sign (rotatory nystagmus when positive or negative pressure is applied to the tympanic membrane) has been historically well regarded, but it is actually positive in less than 50% of confirmed cases of PLF; furthermore, it is positive in as many as 30% of patients with Meniere disease. (4)

The reliability of electronystagmography in detecting a PLF is doubtful in patients with canal paresis; electronystagmography has been reported as positive for fistula in 39% of patients with PLF and in 33% of those without it. (3,4) Vartiainen et al found that a positive vestibular fistula test was even more often negative than positive in patients with a surgically demonstrated fistula. (23) Studies have shown that electrocochleography is of little diagnostic value because its sensitivity is low and results in patients with PLF may be similar to those of patients with Meniere disease. (20,24) Therefore, when we suspected PLF in our patients, we relied primarily on the history; we did not perform the electronystagmographic fistula test. Moreover, even though only 22 of our 97 patients (23%) underwent electrocochleography, we were able to confirm that it is of no value in predicting the presence or absence of a PLF.

The existence of a PLF is not only difficult to prove preoperatively, but intraoperatively as well, except in cases in which perilymph can be seen leaking from the inner ear around the stapes footplate or round window. (25) But even when clear fluid is visible, a diagnosis of PLF is not necessarily confirmed because the fluid must be distinguished from local injection. (26) Another intraoperative consideration is the round window reflex, which is missing in patients with PLF because there is only insufficient transmission of pressure alteration. (27) However, the absence of a round window reflex is not pathognomonic for PLF. Therefore, patients who had no round window reflex were put in the fistula group if they had a visible perforation and in the doubtful group if they had a hooded RWM.

Other diagnostic methods have been described, including fluorescein staining, protein tests, and the use of special endoscopes to visualize the round and oval window niches. (16,25,26,28-30) Arenberg and Wu used fluorescein in order to identify PLFs, but this test is invasive, it is associated with several potential side effects, and it may yield a false-negative result in cases of impaired communication between the cerebrospinal fluid and the perilymph. (26)

Silverstein (25) proposed a rapid protein test for the identification of PLFs, and Levenson et al (30) attempted to identify PLFs by isolating [beta]2-transferrin. However, neither test appeared to be reliable. In fact, the [beta]2-transferrin test yielded false negatives in a high percentage of patients with intraoperatively proven PLF. (30) Furthermore, in order to perform these tests, the middle ear must be opened. If the middle ear is being explored, the surgeon may as well perform obliteration and grafting regardless of the test result. In short, these two tests are irrelevant.

Computed tomography (CT) of the petrous bone may demonstrate air in the vestibule in a patient with PLF, but the absence of air does not rule out a PLF. (31)

In our study, we found that neither a typical history of PLF nor the presence of vertigo as a presenting symptom was a reliable indicator of the presence of a PLF. Intraoperatively proven PLFs were found in 52% of patients with a typical history and in 31% of patients without a typical history. Likewise, EXT revealed a PLF in 41% of patients with vertigo and 28% of patients without it. Moreover, equivocal findings were seen in many other patients with and without a typical history and vertigo. Therefore, we conclude that the presence or absence of a typical PLF history or vertigo is of no value in determining whether to perform EXT. On the other hand, a typical history and vertigo both had some prognostic value; postoperative outcomes in our study were better in patients with a typical history and worse in patients with preoperative vertigo. The latter finding is consistent with earlier reports that vertigo is associated with a negative prognosis in patients with hydropic hearing impairment (32) and sudden deafness.(33) The reason that vertigo is associated with the poor prognosis in all three conditions might be attributable to some broader underlying etiology, one that possibly involves the microvascularization of large parts of the labyrinth. (34) Attempts to identify positive prognostic criteria have not lived up to their promise. (16)

Regarding the treatment approach to patients with sudden and severe hearing loss, otologists have a choice: (1) to explore the middle ear of every patient in whom a diagnosis of PLF is possible or (2) to reserve middle ear exploration for those patients in whom PLF is likely based on the so-called typical history. Both options have their drawbacks. If one chooses the first approach, a number of patients without PLF will undergo unnecessary surgery? If one chooses the second approach, a number of patients with PLF who could have been helped will leave without a correct diagnosis and without curative therapy. (20)

In our study, we found that EXT is a very safe procedure. Only 1 of 97 patients (1%) experienced a complication--a cholesteatoma in the ear canal that arose 1 year postoperatively--that might have been caused by EXT. The lesion was removed without incident and did not recur. No other complications of this simple, non-life-threatening procedure occurred. Therefore, based on our risk/benefit assessment, we conclude that the better strategy is to be liberal in recommending EXT. The risk that one will operate on a patient needlessly (but safely) is less serious than the risk that one will miss the diagnosis and leave the patient untreated. Untreated patients with a PLF who do not undergo spontaneous healing and recovery have an unfavorable prognosis, and there is no clinical test that can predict spontaneous healing. (15) Therefore, we cannot support the conservative strategy favored by most clinicians. (35) Instead, we recommend EXT for all patients in whom PLF is being considered, barring contraindications, of course. The absence of a typical history of PLF is no contraindication to EXT. In view of the safety of the procedure and the lack of diagnostic alternatives, we find no compelling reason not to perform EXT. In our opinion, the only real argument against surgery would be a determination of a more likely pathology (e.g., retrocochlear damage) or the presence of a severe concomitant disease that would make surgery unacceptably risky.

Our data did show that conservative management for a few days following the onset of deafness did not diminish the chance of recovery, so we recommend rheologic and antiphlogistic therapy for 3 or 4 days after the onset of symptoms. (17) During this time, spontaneous recovery may occur, thus resolving the problem. Also during this time, diagnostic steps can be taken to detect retrocochlear damage--for example, brainstem-evoked response audiometry or MRI. Barring any relevant improvement in hearing status, EXT should be performed on day 4 to 7.

In our department, we usually perform EXT within 1 week after the onset of sudden and severe hearing impairment. The exceptions noted in our study were attributable to either a patient's initial refusal to undergo surgery quickly or to a trial of conservative management elsewhere prior to referral to our department.

Acknowledgement

The authors gratefully acknowledge Prof. Nicolaos Marangos, now of Athens, Greece, for his contribution to the electrocochleographic examinations.

References

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Wolfgang Maier, MD; Milo Fradis, MD; Susanne Kimpel, MD; Jorg Schipper, MD; Roland Laszig, MD

From the Department of Otorhinolaryngology--Head and Neck Surgery, Albert-Ludwigs University Medical School, Freiburg, Germany (Prof. Maier, Dr. Kimpel, Dr. Schipper, and Dr. Laszig), and the Department of Otolaryngology-Head and Neck Surgery, Bnai-Zion Medical Center, Haifa, Israel (Dr. Fradis).

Corresponding author: Prof. Wolfgang Maier, Department of Otorhinolaryngology--Head and Neck Surgery, Albert-Ludwigs University Medical School, Killianstr. 5, D-79106 Freiburg, Germany. Phone: 49-761-270-4212; fax: 49-761-270-4111; e-mail: maier@hnol.ukl. uni-freiburg.de

Table 1. Pre- and postoperative thresholds and postoperative absolute
and relative hearing gains and recovery rates in the study
group (N = 97)

                                     250 Hz   1 kHz   4 kHz   8 kHz

Preop pure-tone threshold (dB)        82.7    96.4    96.7    97.1
Postop audiometric threshold (dB)     46.7    58.7    72.4    80.3
Postop absolute hearing gain (dB)     36.0    37.7    24.3    16.8
Postop relative hearing gain (%)      48.5    41.5    27.3    20.4
Postop recovery rate (%)              54.8    48.6    45.8    28.7

Table 2. Audiometric findings, hearing gains, and recovery rates
according to the presence or absence of a typical history of perilymph
fistula

                            250 Hz   1 kHz   4 kHz    8 kHz

Preoperative hearing,        81.8    91.3    88.8     83.0 *
  typical history (dB)
Preoperative hearing,        82.9    97.7    98.8    100.9 *
  no typical history (dB)
Postoperative hearing,       41.3    49.5    56.7     59.0 *
  typical history (dB)
Postoperative hearing,       48.1    61.1    76.6     85.9 *
  no typical history (dB)
Absolute hearing gain,       40.5    41.8    32.1     24.0
  typical history (dB)
Absolute hearing gain,       34.8    36.6    22.2     15.0
  no typical history (dB)
Relative hearing gain,       55.3    49.2    39.6     34.4 *
  typical history (%)
Relative hearing gain,       46.7    39.5    24.1     16.7 *
  no typical history (%)
Recovery rate,               68.5    66.1    66.5     40.4
  typical history (%)
Recovery rate,               51.9    44.8    42.3     27.0
  no typical history (%)

* p < 0.05, Wilcoxon test.

Table 3. Intraoperative findings correlated with the
presence or absence of a typical history of perilymph fistula
and the presence or absence of vertigo, expressed as a percentage
of patients (N = 97)

                                Intraoperative finding

                            Fistula   No Fistula   Doubtful

Typical history (%)           52          52          24
No typical history (%         51          51          41
Vertigo (%)                   41          41          39
No vertigo (%)                28          28          34

                           Sensitivity    Specificity

Typical history (%)             29            --
No typical history (%           --            86
Vertigo (%)                     52            --
No vertigo (%)                  --            58

Table 4. Audiometric findings, hearing gains, and recovery rates
according to the presence or absence of vertigo

                           250 Hz    1 kHz     4 kHz     8 kHz

Preoperative hearing,      94.1 *   102.1 *   105.2 *   106.0 *
  vertigo (dB)
Preoperative hearing,      73.4 *    91.7 *    89.7 *    89.9 *
  no vertigo (dB)
Postoperative hearing,     64.1 *    79.3 *    89.5 *    98.0 *
  vertigo (dB)
Postoperative hearing,     32.5 *    42.0 *    58.6 *    65.8 *
  no vertigo (dB)
Absolute hearing gain,     30.0 *    22.8 *    15.7 *     8.0 *
  vertigo (dB)
Absolute hearing gain,     40.8 *    49.7 *    31.1 *    24.1 *
  no vertigo (dB)
Relative hearing gain,     33.6 *    24.7 *    16.9 *    10.3 *
  vertigo (%)
Relative hearing gain,     60.6 *    55.1 *    35.8 *    28.5 *
  no vertigo (%)
Recovery rate,             39.7 *    28.6 *    29.3 *    19.3
  vertigo (%)
Recovery rate,             67.5 *    65.4 *    61.5 *    37.5
  no vertigo (%)

* p < 0.01, Wilcoxon test.

([dagger] p < 0.05.

Table 5. Audiometric findings, hearing gains, and recovery rates
according to the duration of hearing loss prior to tympanotomy

                           250 Hz       1 kHz    4 kHz   8 kHz

Preoperative hearing,      84.0         97.9      97.9    96.6
  1 to 3 days (dB)
Preoperative hearing,      75.7         93.5      90.0    92.8
  4 to 7 days (dB)
Preoperative hearing,      87.6         95.0     101.5   104.7
  [greater than or equal
  to] 8 days (dB)
Postoperative hearing,     46.5 *       59.3 *    72.6    78.9
  1 to 3 days (dB)
Postoperative hearing,     30.9 *       40.4 *    59.6    71.7
  4 to 7 days (dB)
Postoperative hearing,     68.5 *       81.5 *    89.4    96.2
  [greater than or equal
  to] 8 days (dB)
Absolute hearing gain,     37.5         38.7 *    25.4    17.7
  1 to 3 days (dB)         ([dagger])
Absolute hearing gain,     44.8         53.0 *    30.4    21.1
  4 to 7 days (dB)         ([dagger])
Absolute hearing gain,     19.1         13.5 *    12.1     8.5
  [greater than or equal   ([dagger])
  to] 8 days (dB)
Relative hearing gain,     50.1 *       42.5 *    27.3    20.4
  1 to 3 days (%)
Relative hearing gain,     63.9 *       58.4 *    38.1    28.9
  4 to 7 days (%)
Relative hearing gain,     22.3 *       15.1 *    12.8     8.6
  [greater than or equal
  to] 8 days (dB)
Recovery rate,             56.7 *       48.3 *    46.1    24.6
  1 to 3 days (%)
Recovery rate,             73.1 *       75.6 *    69.5    51.0
  4 to 7 days (%)
Recovery rate,             18.6 *        9.0 *    17.3    15.2
  [greater than or equal
  to] 8 days (dB)

* p < 0.01 Kruskal-Wallis test

([dagger]) p < 0.05.

Table 6. Audiometric findings, hearing gains, and recovery rates
according to the presence or absence of a perilymph fistula on
exploratory tympanotomy

                         250 Hz   1 kHz   4 kHz   8 kHz

Preoperative hearing,    82.1      94.1    92.4    91.2
  fistula (dB)
Preoperative hearing,    86.5      99.8   102.2   103.8
  no fistula (dB)
Preoperative hearing,    78.1      94.4    94.6    95.6
  doubtful (dB)
Postoperative hearing,   43.1 *    55.7    67.5    74.1
  fistula (dB)
Postoperative hearing,   58.9 *    68.8    81.5    89.3
  no fistula (dB)
Postoperative hearing,   34.4 *    48.7    66.3    75.8
  doubtful (dB)
Absolute hearing gain,   39.0 *    38.4    24.9    17.1
  fistula (dB)
Absolute hearing gain,   27.6 *    31.1    20.7    14.6
  no fistula (dB)
Absolute hearing gain,   43.7 *    45.8    28.3    19.8
  doubtful (dB)
Relative hearing gain,   53.2 *    43.1    30.1    22.8
  fistula (%)
Relative hearing gain,   36.0 *    33.2    21.2    15.3
  no fistula (%)
Relative hearing gain,   59.6 *    50.8    32.2    24.2
  doubtful (%)
Recovery rate,           56.0      44.4    47.6    35.0
  fistula (%)
Recovery rate,           41.5      40.4    40.3    27.5
  no fistula (%)
Recovery rate,           67.5      61.8    49.5    23.3
  doubtful (%)

* p < 0.05, Kruskal-Wallis test.