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Prediction of stapes footplate thickness based on the level of hearing loss in otosclerosis.

Introduction

Otosclerosis is the most common cause of conductive hearing loss in the presence of an intact tympanic membrane among patients aged 15 to 50 years. (1,2) Otosclerosis can be a factor in the conductive, sensorineural, and mixed types of hearing loss. (2,3) Sensorineural hearing loss is caused by the hyalinization of the spiral ligament adjacent to the otosclerotic focus, which affects the otic capsule in such a way that it interferes with the function of the organ of Corti. (4,5)

According to many authors, the success of surgery for the treatment of otosclerosis depends more on the surgeon's experience than on the actual technique itself, and some have cast doubt on the adequacy of residents' training in stapes surgery. (6-9) Regardless of which technique is used, a good surgical result is achieved with the closure of the air-bone gap to 10 dB or less; the risk of further sensorineural hearing loss in the operated ear as a complication of the surgery is less than 1%. (7,10) The term "very far-advanced otosclerosis" was proposed by Iurato et al to indicate disease severity in patients whose airand bone-conduction thresholds are both undetectable by standard clinical audiometry ("blank audiogram"). (11)

In this article, we describe our study to evaluate the relationship between hearing thresholds and stapes footplate thickness in otosclerotic patients.

Patients and methods

We conducted a cross-sectional study of patients who had undergone unilateral stapes surgery at Amir-Alam academic hospital in Tehran from May 2005 through February 2006. Inclusion criteria were a primary stapedectomy or stapedotomy that was performed by an experienced surgeon and a chart that contained all the clinical, surgical, and audiologic information.

Our study group was made up of 80 patients--42 women and 38 men, aged 16 to 57 years (mean: 34.0); the mean ages of the women and men were 34.7 and 33.1 years, respectively. Surgery was performed in the right ear in 41 patients and in the left ear in 39 patients.

All patients had undergone preoperative audiometry, and air- and bone-conduction thresholds were obtained from 250 to 8,000 Hz. We then calculated the mean thresholds at 500, 1,000, 2,000, and 4,000 Hz. Mean preoperative air-bone gaps were calculated by subtracting bone-conduction thresholds from air-conduction thresholds at 500, 1,000, 2,000, and 4,000 Hz. We also calculated the Carhart notch for each patient; this value represents the increase in the bone-conduction threshold with the largest depression at 2,000 Hz in the audiometric curve. (2)

Footplate thickness was jointly determined by three expert surgeons, who assigned one of four grades to each case (table 1). There were 33 patients classified as grade 1, 33 as grade 2, 10 as grade 3, and 4 as grade 4 (table 2). Once each case was graded, the surgeons agreed on the main principles and steps of surgery in order to match the technique to the surgeon. Later on, after the surgical portion of the study had been completed, the surgeons agreed to further classify footplate thickness into two larger groups in order to minimize inter- and intraobserver biases. Therefore, patients with grade 1 and 2 footplates were designated as group 1 and those with grade 3 and 4 footplates were designated as group 2.

For statistical analysis, the Student t test, the z-test, the Fisher exact test, and the chi-square test were used to evaluate all data.

Results

Age and sex. The mean ages of the patients in group 1 and group 2 were 33.6 and 35.4 years, respectively-not a significant difference (p = 0.58). Nor was there a significant relationship between sex and the grade of footplate thickness (p = 1.00) (table 2).

Hearing thresholds. The mean preoperative air- and bone-conduction thresholds for all patients are shown in table 3, and the breakdown of thresholds for both groups and all four grades is shown in table 4. When analyzed by group, the mean air-conduction threshold was 48.6 dB in group 1 and 53.8 dB in group 2, a statistically significant difference (p = 0.04). The mean bone-conduction thresholds in the two groups were 16.9 and 19.6 dB, respectively, which represents another significant difference (p = 0.006).

Some 70% of our patients who had an air-conduction threshold greater that 52 dB had a grade 3 footplate thickness.

The mean preoperative Carhart notches in group 1 and group 2 were 9.6 [+ or -] 7.9 dB and 10[+ or -]12.7 dB, respectively-not a significant difference (p = 0.9). Most patients in group 1 had a bone-conduction threshold less than 20 dB, while most of those in group 2 had a higher bone-conduction threshold. Table 5 shows the probability of footplate thickness corresponding to bone-conduction threshold in the two groups.

Air-bonegaps. The mean preoperative air-bone gaps were 31.7 [+ or -] 9.2 dB in group 1 and 34.3 [+ or -] 13.1 dB in group 2. The difference was not statistically significant (p = 0.4).

Discussion

Overall, the incidence of otosclerosis is much lower in men than in women. (3,12) The female-to-male ratio in our study was 1.1:1. We found no significant relationship between sex and footplate thickness, or between age and thickness.

On histologic analysis of stapes footplate fragments, the pathologic process in otosclerosis can be classified into three stages: spongiotic, fibrotic, and sclerotic. There is a direct correlation between the stage of otosclerosis and the age of patients. (2)

In our study, we classified footplate thickness into four grades and then, for more reliability, into two groups. It appears that there was a direct relationship between higher bone-conduction thresholds and greater footplate thickness. We also expected to find a relationship between air-bone gaps and footplate thickness, but our findings in this regard were not statistically significant. Instead, we noticed that when bone-conduction thresholds were less than 20 dB, the likelihood of having a thick footplate decreased. Also, we did not find any association between the thickness of the footplate and the histologic stage of the otosclerotic lesion.

In a study by Gros et al, histologic examination of the stapes footplate fragments revealed that most otosclerotic lesions were fibrotic; among the remainder, sclerotic lesions were more common than spongiotic lesions. (2) This is probably an indication that otosclerosis is a dynamic disease, and after the early spongiotic type progresses toward the fibrotic phase, the disease then enters what is variously called a mature, inactive, or sclerotic phase.

Although Gros et al found no significant associations among (1) the phase of the otosclerotic lesion, (2) the level of preoperative conductive hearing loss, and (3) the degree of sensorineural hearing loss, they did find that mean preoperative air- and bone-conduction thresholds and air-bone gaps were worse in patients with the fibrotic type ofotosclerotic lesion than the spongiotic type, and that they were the worst in those with the sclerotic type. (2) Recently, histologic studies have demonstrated that the production of tumor necrosis factor alpha in active otosclerosis might be responsible for sensorineural hearing loss in this disease. (13)

Cherukupally et al showed that bony ankylosis of the footplate was associated with an air-bone gap of greater than 30 dB. (14) However, they reported that the air-bone gap could not reliably predict the degree and extent of bony footplate ankylosis.

Our study protocol would have been better if we had been able to use a measurement technique to assess footplate thickness more precisely and if we could have eliminated all bias. Because three different surgeons were involved, we were concerned about interobserver bias, as mentioned previously. We tried to minimize it by consolidating our data from four small sets and placing it into two larger groups with a more discrete definition of the criteria.

Stapes surgery requires complex surgical skills and experience to achieve good results, is In order to make an estimation of the thickness of the footplate and the amount of drilling required to create a fenestra, several studies have tried to establish the value of multislice computed tomography (CT) in otosclerosis. (16) It seems that using audiometry as an indicator is easier and more acceptable than using CT to predict such data. However, Genc and Sennaroglu showed that there was no difference between bone-conduction thresholds in obliterative otosclerosis and those of the annular form. (17)

Our study showed that when operating on otosclerotic patients who have high hearing thresholds, surgeons may encounter higher grades of footplate thickness intraoperatively. Greater footplate thickness in stapedectomy requires greater surgical skills. Therefore, measuring the thickness of the footplate prior to surgery may help us to be more vigilant and prepared for the difficulties that we might face during the operation.

Malafronte et al have proposed a new classification system for otosclerosis: blue otosclerosis (blue footplate), white otosclerosis (white footplate), and obliterative otosclerosis (footplate not visible).18 They recommend using this classification before performing any manipulation of the stapes, in order to identify the different degrees of difficulty of surgery. However, the ability to predict the difficulty of surgery before going to the operating room with an objective measurement like pure-tone audiometry would be more helpful in teaching hospital settings, where residents are being trained for these operations and are allowed to operate on some patients.

More studies that measure footplate thickness as a quantitative parameter and the relationship between footplate thickness and the histologic pattern of otosclerotic lesions are needed.

References

(1.) Goycoolea MV. Otosclerosis. In: Paparella MM, Shumrick DA, Gluckman JL, Meyeroff WM, eds. Otolaryngology. 3rd ed. Philadelphia: W.B. Saunders; 1991:1489-1512.

(2.) Gros A, Vatovec J, Sereg-Bahar M. Histologic changes on stapedial footplate in otosclerosis. Correlations between histologic activity and clinical findings._Otol Neurotol2003;24(1):43-7.

(3.) House JW, Cunningham CD III. Otosclerosis. In: Cummings CW, Flint PW, Haughey BH, Niparko JK, et al, eds. Cummings Otolaryngology-Head and Neck Surgery. 5th ed. Philadelphia: Elsevier Mosby; 2010:2028-35.

(4.) Antoli-Candela F Jr., McGill T, Peron D. Histopathological observations on the cochlear changes in otosclerosis. Ann Otol Rhinol Laryngol 1977;86(6 Pt 1):813-20.

(5.) Abd el-Rahman AG. Cochlear otosclerosis: Statistical analysis of relationship of spiral ligament hyalinization to hearing loss. J Laryngol Otol 1990;104(12):952-5.

(6.) Coker NJ, Duncan NO III, Wright GI., et al. Stapedectomy trends for the resident. Ann Otol Rhinol Laryngol1988;97(2 Pt 1): 109-13.

(7.) House HP, Hansen MR, A1-Dakhail AA, House JW. Stapedectomy versus stapedotomy: Comparison of results with long-term followup. Laryngoscope 2002; 112 (11):2046- 50.

(8.) Sargent EW. The learning curve revisited: Stapedotomy. Otolaryngol Head Neck Surg 2002; 126(1):20-5.

(9.) Hughes GB. The learning curve in stapes surgery. Laryngoscope 1991;101(12 Pt 1):1280-4.

(10.) Mathews SB, Rasgon BM, Byl FM. Stapes surgery in a residency training program. Laryngoscope 1999;109(1):52-3.

(11.) lurato S, Ettorre GC, Onofri M, Davidson C. Very far-advanced otosclerosis. Am J Otol 1992;13(5):482-7.

(12.) Topsakal V, Fransen E, Schmerber S, et al. Audiometric analyses confirm a cochlear component, disproportional to age, in stapedial otosclerosis. Otol Neurotol 2006;27(6):781-7.

(13.) Sziklai I, Batta TJ, Karosi T. Otosclerosis: An organ-specific inflammatory disease with sensorineural hearing loss. Eur Arch Otorhinolaryngol 2009;266(11): 1711-18.

(14.) Cherukupally SR, Merchant SN, Rosowski JJ. Correlations between pathologic changes in the stapes and conductive hearing loss in otosclerosis. Ann Otol Rhinol Laryngol 1998;107(4):319-26.

(15.) Freitas VA, Becker CG. Guimaraes RE, et aL Surgical treatment of otosclerosis in medical residency training. Braz J Otorhinolaryngol 2006;72(6):727-30.

(16.) Priya SR, Singh PP, Upreti L, Vaid L. High resolution computed tomography in stapedial otosclerosis. Indian J OtolaryngoI Head Neck Surg 2011. http://rd.springer.com/article/10.1007/sl2070011-0412-6#. Accessed June 16, 2012.

(17.) Genc A, Sennaroglu L. Is it possible to predict diffuse obliterative otosclerosis preoperatively by audiologic examination. Int J Audiol 2007;46(5):203-7.

(18.) Malafronte G, Filosa B, Cantone E._New macroscopic classification of stapedio-ovalar otosclerosis: A simplified rating for training in stapedotomy. Otol Neurotol2008;29(7):889-92.

Hadi Samimi-Ardestani, MD; Mohammadtaghi Khorsandi-Ashtiani, MD; Elmira Ghoujeghi, MD; Mohsen Rajati, MD; Mahtab Rabbani-Anari, MD; Aman Ghoujeghi, MD

From the Otorhinolaryngology Research Center, Department of Otolaryngology-Head and Neck Surgery, Amir-Alam Hospital, Tehran University of Medical Sciences School of Medicine, Tehran, Iran (Dr. Samimi-Ardestani, Dr. Khorsandi-Ashtiani, Dr. E. Ghoujeghi, and Dr. Rabbani-Anari); the Ear, Nose & Throat Research Center, Department of Otolaryngology--Head and Neck Surgery, Ghaem Hospital, Mashhad University of Medical Sciences School of Medicine, Mashhad, Iran (Dr. Rajati); and the Department of Otolaryngology-Head and Neck Surgery, Taleghani Medical Center, Shahid Beheshti University of Medical Sciences School of Medicine, Tehran (Dr. A. Ghoujeghi). The study described in this article was conducted at Amir-Alam Hospital.

Corresponding author: Mahtab Rabbani-Anari, MD, Otorhinolaryngology Research Center, Amir-Alam Hospital, South Saadi Ave., PO Box 11457-65111, Tehran, Iran. Email: m_rabani@razi.tums.ac.ir
Table 1. Grades of footplate thickness

Grade   Description of footplate opening

1       Opened with low pressure
2       Opened easily with repeated motion by hand
3       Opened by drilling (difficult task)
4       Not opened because the footplate was obliterated

Table 2. Distribution of footplate thickness according to sex

             Group 1             Group 2

        Grade 1   Grade 2   Grade 3   Grade 4    Total

Men       10        21         5         2        38
Women     23        12         5         2        42
Total     33        33        10         4        80

Table 3. Mean preoperative air- and bone conduction thresholds by
frequency for all patients

                    Frequency (Hz)

            500    1,000   2,000   4,000

Air (dB)    53.0    50.8    45.2    49.1
Bone (dB)   11.6    14.3    23.6    20.1

Table 4. Mean air- and bone-conduction thresholds according to
footolate thickness

                 Group 1              Group 2

            Grade 1   Grade 2    Grade 3   Grade 4    p Value

Air (dB)    48.6 [+ or -] 11.9   53.8 [+ or -] 15.1      0.04
            48.8          48.5   51.0          61.0

Bone (dB)   16.9 [+ or -] 9.8    19.6 [+ or -] 9.2      0.006
            17.0          16.9   19.9          18.7

Table 5. Probability of the degree of footplate thickness
according to bone-conduction threshold

                 Bone-conduction
                 threshold

           <20 dB   >20 dB

Group 1      0.99     0.01

Group 2      0.43     0.57
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Title Annotation:ORIGINAL ARTICLE
Author:Samimi-Ardestani, Hadi; Khorsandi-Ashtiani, Mohammadtaghi; Ghoujeghi, Elmira; Rajati, Mohsen; Rabban
Publication:Ear, Nose and Throat Journal
Article Type:Report
Geographic Code:7IRAN
Date:Aug 1, 2012
Words:2362
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