Diagnosis Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
Anomalies of the Auditory Ossicles Shin-ichi Ishimoto
Microtia/atresia of the external auditory canal (EAC) is a rare disease that occurs in 1 in 10,000–15,000 births. There are thought to be approximately 100 such patients per year in Japan. Nearly 90% of the cases are unilateral and 10% are bilateral. In many microtia patients, an EAC anomaly and middle ear anomaly (including auditory ossicle anomaly) occur in conjunction with an auricular anomaly. Inner ear anomalies rarely occur. Depending on the severity of the EAC anomaly and middle ear anomaly, the selected surgery may be pinnaplasty alone, reconstruction of the EAC, or reconstruction tympanoplasty (tympanic membrane and ossicular chain) aiming for improved auditory acuity. It is therefore essential to understand the severity and condition of the auditory ossicle anomaly to determine the appropriate surgical approach. It would also be very useful if the regularity or severity of the auditory ossicle anomaly could be predicted beforehand based not only on the results of temporal bone high-resolution CT (HRCT), but also on conditions of the anomaly of the auricle and the EAC. Auditory ossicle anomalies in patients with microtia/atresia of the EAC are shown below. The development matrix of the auditory ossicles suggests that the malleus/incus is derived from the first branchial arch cartilage (Meckel’s cartilage) and the stapes from the second branchial arch cartilage (Reichert’s cartilage). An anomaly of the first branchial arch would therefore induce an anomaly of the malleus/incus, whereas disorders of the second branchial arch are considered to cause anomalies in the stapes. Because both the eardrum and the EAC are structures arising from the first branchial arch cartilage, anomalies of the malleus/incus are likely to occur in patients with osseous occlusion in conjunction with microtia/atresia of the EAC. Schuknecht [1] roughly classified microtia/atresia of the EAC into four types in terms of anomalies of the EAC, auricle/auditory osseous anomalies, abnormal migration of the facial nerve, and pneumatization of the mastoid air cells (table 1).
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Department of Otolaryngology, JR Tokyo General Hospital, Tokyo, Japan
Table 1. Descriptions of Schuknecht’s classification of microtia/atresia of the external auditory canal [3]
Type B Type C
Middle ear
meatal stenosis canal cholesteatoma partial meatal stenosis narrow tortuous canal total atresia
normal ossicles
Type D total atresia pneumatization is decreased
malleus and tympanic membrane anomalies tympanic membrane is missing. malleus and incus are fused. tympanic membrane is missing severe ossicular anomalies facial nerve aberrant
In patients with stenosis of the EAC (types A and B), the eardrum is present and an anomaly of the malleus is present, although mild. The handle of malleus is also present and the incus/stapes is almost normal. On the contrary, in patients with osseous occlusion of the EAC (types C and D), the handle of malleus is deficient, and the malleus/incus are often fused in type C patients with anomalies of the auditory ossicles. The auditory ossicle anomaly is more severe in type D patients than type C patients. Abnormal migration of the facial nerve and impaired pneumatization of the mastoid air cells have also been reported (fig. 1). Schuknecht [1] discussed the relationship between the types of EAC anomalies and the handle of malleus in the classification of microtia/atresia of the EAC, and interesting results have been obtained from recent findings. With elucidation of which genes are involved in the development of the middle ear, how the genes are involved in the development of the structures of the middle/external ear was revealed by observation of gene-knockout mice. In knockout mice deficient of Gsc and Prx1 genes, neither the tympanic ring nor the handle of malleus formed, and the EAC also did not form [2]. The relationship between EAC anomalies and formation of the handle of malleus was examined in patients with microtia/atresia of the EAC, and results identical to those of animal experiments were obtained [3]. The above findings suggest that the handle of malleus would exist even when there is no osseous occlusion of the EAC (even if the eardrum cannot be observed due to stenosis of the EAC) (fig. 2). Temporal bone HRCT is indispensable for understanding the severity of the auditory ossicle anomaly before surgery. The grading system of Jahrsdoerfer et al. [4] (see ‘Imaging diagnosis’, this vol., p. 15) is very important for analysis of the temporal bone HRCT, and is useful for predicting the postoperative estate of the EAC and auditory acuity. In particular, emphasis is placed on the anomaly of the auditory ossicles, and 4 points (incudostapedial joint conjugation, presence or absence of malleoincudal bone, presence or absence of stapes) are assigned out of a total of 10 points. The more severe the auricle anomaly was, the more severe was the anomaly of the entire EAC and mid-
Anomalies of the Auditory Ossicles Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
45
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Type A
External auditory canal
Occasional auricular deformity
Normal ossicles Facial nerve
Round window
Mental stenosis
Canal cholesteatoma Normal tympanic membrane
a
Occasional microtia
Frequent malleus and tympanic membrane anomalies
Partial meatal stenosis
Narrow tortuous canal
b
Frequent microtia
Fibrous stenosis
Fused malleus and incus Absent manubrium
Total atresia
46
Bony atresia plate
c
Absent tympanic membrane
Ishimoto Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Fig. 1. Illustrations of types of atresia in Schuknecht’s classification [1].
Frequent microtia Hypopneumatization
Major ossicular anomalies
Bony atresia plate
Total atresia
Fibrous stenosis
Fig. 1. Continued.
Frequent facial nerve anomaly Absent tympanic membrane
d
a
b
c
d
Anomalies of the Auditory Ossicles Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
47
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Fig. 2. Coronal CT images and surgical view of the temporal bone in a patient with EAC atresia (a, b) and stenosis (c, d). a Surgical view of the right ear with EAC atresia. b Axial CT image of the ear shown in a. c Surgical view of the right ear with EAC stenosis. d Coronal CT image of the ear shown in c. M = Malleus; I = incus; H = manubrium; C = chorda tympani; S = stapes.
dle ear, but such a correlation with auricle anomaly was not observed for an auditory ossicle anomaly alone [5]. This suggests that the more severe the auricular anomaly is, the more severe the entire middle ear anomaly will be, but the severity of an auditory ossicle anomaly cannot be predicted from the severity of the auricular anomaly. In a report that examined the relationship between the severity of the auditory ossicle anomaly and auditory acuity threshold, auditory acuity was approximately 63 dB in patients with osseous occlusion and no difference was observed for auditory acuity threshold [6]. In patients with stenosis, a difference in auditory acuity threshold was observed depending on the severity of the auditory ossicle anomaly, and it was reported to be approximately 64 dB in patients with a severe auditory ossicle anomaly and approximately 54 dB in patients with a mild-to-moderate auditory ossicle anomaly [6]. Thus, auditory acuity threshold rises when the auditory ossicle anomaly is severe in patients with EAC stenosis, but auditory acuity threshold remains almost unchanged irrespective of the severity of the auditory ossicle anomaly in patients with osseous occlusion. As shown above, auditory ossicle anomalies tend to be severe in patients with microtia/atresia of the EAC when the EAC anomaly is more severe, as shown by Schuknecht [3] (table 1). Concerning regularity of auditory ossicle anomaly, accurate analysis of a temporal bone HRCT would be important in addition to prior understanding of the presence of the handle of malleus with or without osseous occlusion by meatoplasty. With respect to the auditory acuity threshold, auditory acuity ranges between 60 and 65 dB in patients with EAC stenosis as in patients with osseous occlusion, except for a slight reduction in auditory acuity threshold when an auditory ossicle anomaly is mild or moderate. A more drastic increase in threshold would suggest the presence of a complication of an inner ear anomaly.
References 5 Ishimoto S, Ito K, Yamasoba T, Kondo K, Karino S, Takegoshi H, Kaga K: Correlation between microtia and temporal bone malformation evaluated using grading systems. Arch Otolaryngol Head Neck Surg 2005;131:326–329. 6 Ishimoto S, Ito K, Karino S, Takegoshi H, Kaga K, Yamasoba T: Hearing levels in patients with microtia: correlation with temporal bone malformation. Laryngoscope 2007;117:461–465.
Shin-ichi Ishimoto Department of Otolaryngology, JR Tokyo General Hospital 2-1-3 Yoyogi, Shibuya-Ku Tokyo 169-0073 (Japan) E-Mail [email protected]
48
Ishimoto Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
1 Schuknecht HF: Congenital aural atresia. Laryngoscope 1989;99:908–917. 2 Mallo M: Formation of the middle ear. Recent progress on the developmental and molecular mechanisms. Dev Biol 2001;231:410–419. 3 Ishimoto S, Ito K, Kondo K, Yamasoba T, Kaga K: The role of the external auditory canal in the development of the malleal manubrium in humans. Arch Otolaryngol Head Neck Surg 2004;130:913–916. 4 Jahrsdoerfer RA, Yeakley JW, Aguilar EA, Cole RR, Gray LC: Grading system of the selection of patients with congenital aural atresia. Am J Otol 1992;13:6–12.
Anomalies of the Auditory Ossicles Shin-ichi Ishimoto
Microtia/atresia of the external auditory canal (EAC) is a rare disease that occurs in 1 in 10,000–15,000 births. There are thought to be approximately 100 such patients per year in Japan. Nearly 90% of the cases are unilateral and 10% are bilateral. In many microtia patients, an EAC anomaly and middle ear anomaly (including auditory ossicle anomaly) occur in conjunction with an auricular anomaly. Inner ear anomalies rarely occur. Depending on the severity of the EAC anomaly and middle ear anomaly, the selected surgery may be pinnaplasty alone, reconstruction of the EAC, or reconstruction tympanoplasty (tympanic membrane and ossicular chain) aiming for improved auditory acuity. It is therefore essential to understand the severity and condition of the auditory ossicle anomaly to determine the appropriate surgical approach. It would also be very useful if the regularity or severity of the auditory ossicle anomaly could be predicted beforehand based not only on the results of temporal bone high-resolution CT (HRCT), but also on conditions of the anomaly of the auricle and the EAC. Auditory ossicle anomalies in patients with microtia/atresia of the EAC are shown below. The development matrix of the auditory ossicles suggests that the malleus/incus is derived from the first branchial arch cartilage (Meckel’s cartilage) and the stapes from the second branchial arch cartilage (Reichert’s cartilage). An anomaly of the first branchial arch would therefore induce an anomaly of the malleus/incus, whereas disorders of the second branchial arch are considered to cause anomalies in the stapes. Because both the eardrum and the EAC are structures arising from the first branchial arch cartilage, anomalies of the malleus/incus are likely to occur in patients with osseous occlusion in conjunction with microtia/atresia of the EAC. Schuknecht [1] roughly classified microtia/atresia of the EAC into four types in terms of anomalies of the EAC, auricle/auditory osseous anomalies, abnormal migration of the facial nerve, and pneumatization of the mastoid air cells (table 1).
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Department of Otolaryngology, JR Tokyo General Hospital, Tokyo, Japan
Table 1. Descriptions of Schuknecht’s classification of microtia/atresia of the external auditory canal [3]
Type B Type C
Middle ear
meatal stenosis canal cholesteatoma partial meatal stenosis narrow tortuous canal total atresia
normal ossicles
Type D total atresia pneumatization is decreased
malleus and tympanic membrane anomalies tympanic membrane is missing. malleus and incus are fused. tympanic membrane is missing severe ossicular anomalies facial nerve aberrant
In patients with stenosis of the EAC (types A and B), the eardrum is present and an anomaly of the malleus is present, although mild. The handle of malleus is also present and the incus/stapes is almost normal. On the contrary, in patients with osseous occlusion of the EAC (types C and D), the handle of malleus is deficient, and the malleus/incus are often fused in type C patients with anomalies of the auditory ossicles. The auditory ossicle anomaly is more severe in type D patients than type C patients. Abnormal migration of the facial nerve and impaired pneumatization of the mastoid air cells have also been reported (fig. 1). Schuknecht [1] discussed the relationship between the types of EAC anomalies and the handle of malleus in the classification of microtia/atresia of the EAC, and interesting results have been obtained from recent findings. With elucidation of which genes are involved in the development of the middle ear, how the genes are involved in the development of the structures of the middle/external ear was revealed by observation of gene-knockout mice. In knockout mice deficient of Gsc and Prx1 genes, neither the tympanic ring nor the handle of malleus formed, and the EAC also did not form [2]. The relationship between EAC anomalies and formation of the handle of malleus was examined in patients with microtia/atresia of the EAC, and results identical to those of animal experiments were obtained [3]. The above findings suggest that the handle of malleus would exist even when there is no osseous occlusion of the EAC (even if the eardrum cannot be observed due to stenosis of the EAC) (fig. 2). Temporal bone HRCT is indispensable for understanding the severity of the auditory ossicle anomaly before surgery. The grading system of Jahrsdoerfer et al. [4] (see ‘Imaging diagnosis’, this vol., p. 15) is very important for analysis of the temporal bone HRCT, and is useful for predicting the postoperative estate of the EAC and auditory acuity. In particular, emphasis is placed on the anomaly of the auditory ossicles, and 4 points (incudostapedial joint conjugation, presence or absence of malleoincudal bone, presence or absence of stapes) are assigned out of a total of 10 points. The more severe the auricle anomaly was, the more severe was the anomaly of the entire EAC and mid-
Anomalies of the Auditory Ossicles Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
45
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Type A
External auditory canal
Occasional auricular deformity
Normal ossicles Facial nerve
Round window
Mental stenosis
Canal cholesteatoma Normal tympanic membrane
a
Occasional microtia
Frequent malleus and tympanic membrane anomalies
Partial meatal stenosis
Narrow tortuous canal
b
Frequent microtia
Fibrous stenosis
Fused malleus and incus Absent manubrium
Total atresia
46
Bony atresia plate
c
Absent tympanic membrane
Ishimoto Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Fig. 1. Illustrations of types of atresia in Schuknecht’s classification [1].
Frequent microtia Hypopneumatization
Major ossicular anomalies
Bony atresia plate
Total atresia
Fibrous stenosis
Fig. 1. Continued.
Frequent facial nerve anomaly Absent tympanic membrane
d
a
b
c
d
Anomalies of the Auditory Ossicles Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
47
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
Fig. 2. Coronal CT images and surgical view of the temporal bone in a patient with EAC atresia (a, b) and stenosis (c, d). a Surgical view of the right ear with EAC atresia. b Axial CT image of the ear shown in a. c Surgical view of the right ear with EAC stenosis. d Coronal CT image of the ear shown in c. M = Malleus; I = incus; H = manubrium; C = chorda tympani; S = stapes.
dle ear, but such a correlation with auricle anomaly was not observed for an auditory ossicle anomaly alone [5]. This suggests that the more severe the auricular anomaly is, the more severe the entire middle ear anomaly will be, but the severity of an auditory ossicle anomaly cannot be predicted from the severity of the auricular anomaly. In a report that examined the relationship between the severity of the auditory ossicle anomaly and auditory acuity threshold, auditory acuity was approximately 63 dB in patients with osseous occlusion and no difference was observed for auditory acuity threshold [6]. In patients with stenosis, a difference in auditory acuity threshold was observed depending on the severity of the auditory ossicle anomaly, and it was reported to be approximately 64 dB in patients with a severe auditory ossicle anomaly and approximately 54 dB in patients with a mild-to-moderate auditory ossicle anomaly [6]. Thus, auditory acuity threshold rises when the auditory ossicle anomaly is severe in patients with EAC stenosis, but auditory acuity threshold remains almost unchanged irrespective of the severity of the auditory ossicle anomaly in patients with osseous occlusion. As shown above, auditory ossicle anomalies tend to be severe in patients with microtia/atresia of the EAC when the EAC anomaly is more severe, as shown by Schuknecht [3] (table 1). Concerning regularity of auditory ossicle anomaly, accurate analysis of a temporal bone HRCT would be important in addition to prior understanding of the presence of the handle of malleus with or without osseous occlusion by meatoplasty. With respect to the auditory acuity threshold, auditory acuity ranges between 60 and 65 dB in patients with EAC stenosis as in patients with osseous occlusion, except for a slight reduction in auditory acuity threshold when an auditory ossicle anomaly is mild or moderate. A more drastic increase in threshold would suggest the presence of a complication of an inner ear anomaly.
References 5 Ishimoto S, Ito K, Yamasoba T, Kondo K, Karino S, Takegoshi H, Kaga K: Correlation between microtia and temporal bone malformation evaluated using grading systems. Arch Otolaryngol Head Neck Surg 2005;131:326–329. 6 Ishimoto S, Ito K, Karino S, Takegoshi H, Kaga K, Yamasoba T: Hearing levels in patients with microtia: correlation with temporal bone malformation. Laryngoscope 2007;117:461–465.
Shin-ichi Ishimoto Department of Otolaryngology, JR Tokyo General Hospital 2-1-3 Yoyogi, Shibuya-Ku Tokyo 169-0073 (Japan) E-Mail [email protected]
48
Ishimoto Kaga K, Asato H (eds): Microtia and Atresia – Combined Approach by Plastic and Otologic Surgery. Adv Otorhinolaryngol. Basel, Karger, 2014, vol 75, pp 44–48 (DOI: 10.1159/000350602)
Downloaded by: Siriraj Medical Library, Mahidol University 198.143.39.97 - 3/25/2016 2:30:30 AM
1 Schuknecht HF: Congenital aural atresia. Laryngoscope 1989;99:908–917. 2 Mallo M: Formation of the middle ear. Recent progress on the developmental and molecular mechanisms. Dev Biol 2001;231:410–419. 3 Ishimoto S, Ito K, Kondo K, Yamasoba T, Kaga K: The role of the external auditory canal in the development of the malleal manubrium in humans. Arch Otolaryngol Head Neck Surg 2004;130:913–916. 4 Jahrsdoerfer RA, Yeakley JW, Aguilar EA, Cole RR, Gray LC: Grading system of the selection of patients with congenital aural atresia. Am J Otol 1992;13:6–12.
