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Temporal Bone Pathology in Congenital Anomalies of the Oval Window and the Facial Nerve
Auris' Nasus' Larynx (Tokyo) 12, 139-148 (1985).
TEMPORAL BONE PATHOLOGY IN CONGENITAL ANOMALIES OF THE OVAL WINDOW AND THE FACIAL NERVE Ryusuke SAITO, M. D., Shuichi WATANABE, M. D., Akira FUJITA, M. D., Akiko FUJIMOTO, M. D., Ikuo INOKUCHI, M. D., and Yoshio OGURA, M. D. Department of Otolaryngology, Okayama University Medical School, Okayama, Japan
Temporal bones of six infants with congenital ear anomalies were examined for abnormalities of the oval window and facial nerve. These temporal bones were classified into two groups according to the degree of malformation: group A, those with atresia or absence of, the oval window; and, group B, those with hypoplasia of the stapes and annular ligament. Group A, consisting of five ears, were associated with severe middle ear anomalies such as the abnormal course of the facial nerve and absence of the stapes. In group B, consisting of seven ears, the stapes were present and the facial nerve presented minor anomalies such as obtuse angulation at the first genu, central migration of the geniculate ganglion cells, ectopic muscles and a wide bony dehiscence of the facial canal around the oval window. Probable origin of the anomalies in group A could mainly be due to maldevelopment of the facial nerve during an earlier embryonal period while that of group B could have developed after the ninth week of the fetal period and are mostly localized along the second branchial arch. With the recent advances in otomicrosurgery, surgery for hearing improvement can be done for those with anomalies of the sound conducting apparatus. Recently, several investigators have reported temporal bone histopathologic findings on anomalies of the oval window and the facial nerve (HARADA, BLACK, SANDO, and SINGLETON, 1980; KODAMA, SANDO, MYERS, and HASHIDA, 1982). This paper describes the histopathologic findings of congenital anomalies of the oval window and facial nerve in temporal bones of the six patients with multiple malformation. MATERIALS AND METHODS
Twelve ears from six patients, one stillbirth and others from seven days to Received for publication December 24, 1984 139
R. SAITO et at.
140
Table 1. Cases
Diagnosis
Age/Sex
Potter's syndrome
Case 1
Stillbirth/F
Case 2
2m/F
13-15 trisomy
Case 3
7d/F
Case 4 Case 5 Case 6
lylOm/F Im/F ImlOd/M
Chromosomal aberration ofG group 13-15 trisomy 18 trisomy 18 trisomy
Malformation of the external ear Bil. severely low set ear and microtia Rt. aural atresia and bil. microtia Bil. aural atresia and microtia None None Bil. low set ear
one year and ten days, represented two cases of 13-15 trisomy, two cases of 18 trisomy, one case of G group hyperploidy and one case of Potter's syndrome (Table 1). The external ear anomalies included congenital atresia of the external auditory canal in three ears from two cases, bilateral microtia in three cases and lowset ears in two cases. At autopsy, both temporal bones were removed and immediately placed in 10 %formaldehyde solution. After decalcification and dehydration, they were imbedded in celloidin and sectioned horizontally at 20 microns. Every tenth section was stained with hematoxylin and eosin, and mounted for microscopic study. HISTOPATHOLOGICAL FINDINGS
Anomalies of the oval window area examined in this study were morphologically classified into two maior groups. Group A represented those with an atresia or absence of the oval window, absent stapes and a profoundly abnormal course of the facial nerve. Group B represented those with hypoplasia of both the stapes and annular ligament and a mildly abnormal course of the facial nerve. Group A (The group with atresia or absence of the oval window) This group exhibited varying degrees of severe hypoplasia of the oval window as seen in five ears of three cases. The temporal bone findings in these cases were summarized in Table 2. The oval window in three ears was barely identifiable as a rudimentary slit in the lateral bony wall of the vestibule (Fig. 1), whereas two ears were completely obliterated by bony structures. All ears exhibited clearly the fissura ante fenestram which could be a guide to identify the oval window area. The facial nerve, thin and atrophic at the internal auditory canal, took an extremely abnormal course in the absence of the geniculate ganglion, barely reached the first genu from the internal auditory canal and descended along the promontory wall (Fig. 2). The facial nerve in two ears disappeared near the level of the vestigial oval window. The chorda tympani nerve and the greater superficial petrosal nerve were absent in all ears. The stapes was absent in four ears. Both
PATHOLOGY OF OVAL WINDOW ANOMALY Table 2.
Group A.
Case 1
Oval window
141
Case 2
Case 3
Right ear
Left ear
Right ear
Right ear
Left ear
Connective tissue slit
Connective tissue slit
Connective tissue slit
Complete absence
Complete absence
Facial nerve and canal Nerve trunk Extremely underdeveloped Course Descended at the first genu Geni. ganglion Absent GSPNa Absent Chorda tymp. Absent Canal Absent
Stapes
Absent
Stapedius muscle
Absent
Extremely underdeveloped Descended at the first genu Absent Absent Absent Vestigial in the promontory wall
Extremely underdeveloped Diminished after the first genu Absent Absent Absent Absent
Absent
Absent
Absent
Absent
Absent
Absent
Extremely underdeveloped Descended at the first genu Absent Absent Absent Absent at the level of mesotympanum and never is passing out the temporal bone Absent
a Greater superficial petrosal nerve.
Fig. 1. Case 1, right ear, showing slit-like fissure (arrow), suggesting a rudimentary oval window. TC, tympanic cavity; V, vestibule; F AF, fissula antefenestram (hematoxylineosin, x 12).
142
R. SAITO et al.
F ig. 2. Case 2, right ear, showing extremely underdeveloped oval window (arrow) and abnormal course of facial nerve (F). Note facial nerve descending anterior to oval window area. C, cochlea; V, vestibule (hematoxylin-eosin, x 4).
malleus and incus exhibited several anomalies such as fusion of ossicles, absence or deformity of malleus handle, fusion to the promontory and absence of long process of the incus. In all ears studied, the tympanum was small and narrow and divided by an irregular bony crista. The stapedius muscle was absent in all ears. The tensor tympani muscle was present in two ears although abnormalities such as irregular location and course and absence of attachment of its tendon to the malleus neck were observed. The round window niche and its membrane seemed to be small and narrow in size, however, they were morphologically less abnormal when compared with the oval window. The round window niche was obliterated by mesenchymal tissue in four ears. Group B (The group with hypoplasia of the stapes and annular ligament)
Both ears from one case showed a stapedial footplate on a narrow and small oval window. Cartilaginous fixation of the stapedial footplate was seen in two ears (Fig. 3). Immature embryonal forms of stapes were observed in three ears with a thick footplate and crura in which bone marrow spaces remained (Fig. 4). A columella-like stapes was observed in two ears and an anomalous stapes with a bifurcated anterior crus in one ear. The facial nerve in six ears ran the usual course through which the labyrinthine, tympanic and mastoid segments can be identified. The facial nerve in one ear ran anterior to both windows without making the tympanic segment and bifurcated at the mastoid segment. In contrast with its course in the normal temporal bone, the facial nerve in these ears showed several abnormalities such as obtuse angulation at the first genu, hypoplasia of
PATHOLOGY OF OVAL WINDOW ANOMALY
143
Fig. 3. Case 4, right ear, showing cartilaginous fixation (arrow) of anterior margin of footplate. S, stapes; TC, tympanic cavity; V, vestibule; F AF, fissula antefenestram (hematoxylin-eosin, x 20).
Fig. 4. Case 4, left ear, demonstrating immature ring-shaped stapes. Note that fossula postfenestram (arrow) is abnormally wide and communicates with middle ear space. V, vestibule; st, stapedius tendon (hematoxylin-eosin, x 5).
the geniculate ganglion, presence of an ectopic muscle in the tympanic segment (Fig. 5) and extensive dehiscence of the bony wall of the facial canal near the oval window. The chorda tympani and the greater superficial petrosal nerves were
144
R. SAITO et al.
Fig. 5. Case 6, left ear, demonstrating ectopic muscle (arrow) in horizontal segment of facial canal. ttm, tensor tympani muscle (hematoxylin-eosin, x5).
Fig. 6. Case 4, left ear, showing abnormal approximation of long process of incus (I) to horizontal segment of facial canal. M, malleus; F, facial nerve (hematoxylin-eosin, x 5).
present in six ears except for one ear. Both malleus and incus, although they contained rudimentary bone marrow spaces, seemed to be normal. In both ears of one case, the long process of the incus was abnormally close to the tympanic
a Greater superficial petrosal nerve.
Normal
Normal
Monopodal stapes Immature embryonal form
Stapes
Absent
Immature embryonal form
Normal Normal Absent at the level Extensive of mesotympanum dehiscence of the bony wall and never is passing out the temporal bone
Stapedius muscle
Normal Normal Extensive dehiscence of the bony wall
Normal
GSPNa Chorda tymp. Canal
No stapedial tendon
Normal
Normal
Normal Normal Extensive dehiscence of the bony wall
Normal Normal Extensive dehiscence of the bony wall
Normal
Normal
Obtuse angle at the first genu Decreased ggl. cell population
Obtuse angle at the first genu Decreased ggl. cell population
Slightly small
Left ear
Normal
Case 6
Normal
Slightly small
Right ear
Immature embryonal form
Central divergence of ggl. cell Normal Normal Moderate dehiscence of the bony wall
Normal
Normal
Normal
Left ear
Columella-like Bifurcated form anterior crus
Obtuse angle at the first genu Central divergence of ggl. cell Normal Normal Moderate dehiscence of the bony wall
Normal
Normal
Normal
Normal
Right ear
Case 5
Normal
Normal
Normal
Underdeveloped Normal and bifurcated at the mastoid segment Descended anterior Normal to both windows
Left ear
Group B.
Cartilaginous fixation of footplate
Geni. ganglion
Course
Facial nerve and canal Nerve trunk
Oval window
Right ear Cartilaginous fixation of footplate
Left ear
Case 4
Cartilaginous fixation of footplate
Case 2
Table 3.
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R. SAITO et al.
segment of the facial nerve (Fig. 6). The tympanic cavity was normal in size in six ears with a small amount of rudimentary mesenchymal tissue in the upper part of the typanum. The stapedial muscle was absent in one ear and only the stapedial tendon was absent:in one ear. The tensor tympanic muscle made an abnormal course in two ears; with one ear presenting an ectopic muscle into the tympanic segment of the facial canal. The round window was rather small and narrow in two ears and was obliterated by mesenchymal tissue in one ear. COMMENT
Congenital anomalies of the oval window have been described as atresia or absence of the oval window or as a fixation of the stapedial footplate (LINDSAY, SAUNDERS, and NAGER, 1960; STEELE, 1969). It has been widely recognized that anomalies of the oval window are frequently associated with facial nerve anomalies. SANDO and WOOD (1971) have reported on temporal bone histopathologic studies of middle ears anomalies with an extensive review of the literature. They indicated that middle ear anomalies were frequently associated with branchial arch anomalies and that the facial nerve and ossicular chain anomalies were the most common in the middle ear. As shown in the Tables 2 and 3, the ears of this study were classified into two major groups by the degree of anomaly of the oval window: Group A, those with atresia or absence of the oval window; and group B, those with hypoplasia of the stapes and annular ligament. Group A represents severe developmental abnormalities of the oval window and group B represents those with less severe abnormalities of the oval window and stapes. In group A, three ears in two cases exhibited the oval window as a barely identifiable connective tissue slit while both ears in one case showed complete absence of the oval window. The facial nerve, in its abnormal course in the temporal bone, was abnormally thin with severe hypoplasia of the nerve trunk. Group B includes seven ears from four cases. The stapes was deformed or immature and embryonal in form in most ears. Two ears showed cartilaginous fixation of the stapes. The oval window was almost normal in size and the facial nerve passed along its usual course in most ears. The facial nerve in the temporal bone is primarily composed of three different nerve fiber bundles, namely, the motor fiber, the sensory fiber and the autonomic fiber bundles. The sensory fibers originate from the seventh and the eighth cranial nerve crest cells which develop at the beginning of the fourth week of the embryonal period, and the motor and autonomic fibers begin to extend from the neuroblasts of the pons at about the same time (GASSER, 1975). These fibers coalesce to form nerve trunks which extend peripherally into the first and second branchial arch tissues. The primordium of auditory ossicles appears during the sixth to seventh week of the embryonal period (BAST and ANSON, 1949). According to the appearance of the primordial stapes, the facial nerve curves posteriorly
PATHOLOGY OF OVAL WINDOW ANOMALY
147
to differentiate into the tympanic and mastoid segment in the temporal bone (SAITO, MATSUMURA, TAKATA, OGURA, IWAHORI, and HOSHlNO, 1981). The otic capsule becomes precartilaginous and the oval window begins to form with the impingement of the primordial stapes to the developing otic capsule in the eighth week of the embryonal period. The annulus stapedialis, a derivative of the second branchial arch, fuses with the lamina stapedialis of the otic capsule to form the future stapedial footplate. As the base of the stapes increases in diameter, the lamina stapedialis undergoes a process of dedifferentiation from precartilaginous tissue to connective tissue to form the annular ligament after the ninth week of the fetal stage (BAST and ANSON, 1949). HARADA et al. (1980) reviewed the temporal bone histopathologic findings in five cases with congenital anomalies of the oval window and reported various degrees of anomalies ranging from cartilaginous fixation to complete absence of the oval window. They also stated that these anomalies are due to developmental arrest of the oval window at different stages and can be monistic ally explained by the same embryological basis. KODAMA et al. (1982) reported on temporal bone findings in severe middle ear anomalies with an extremely underdeveloped facial nerve and classified the facial nerve anomalies into two groups, that is, the severely and the moderately anomalous group. They indicated that the abnormalities found in the severely anomalous groups were morphologically similar to those of an early stage of the embryonal period, in which the development of the facial nerve was arrested. Taking these previous reports in the literature into consideration, it is suggested that an early development of the facial nerve has been primarily arrested in the group with absence or atresia of the oval window. On the other hand, in the group with hypoplasia of the stapes and the annular ligament, abnormalities are thought to develop at a later stage of the fetal period and may be localized mainly in the second branchial arch without any developmental anomalies of the facial nerve itself. REFERENCES BAST, T. H., and ANSON, B. J.: The Temporal Bone and the Ear. Springfield Illinois, Charles C. Thomas, 1949. GASSER, R. F.: Atlas of Human Embryos, Hagerstown, Harper and Row, Inc., 1975. HARADA, T., BLACK, F. 0., SANDO, I., and SINGLETON, G. T.: Temporal bone histopathologic findings in congenital anomalies of the oval window. Otolaryngol. Head Neck Surg. 88: 275-287, 1980. KODAMA, A., SANDO, I., MYERS, E. N., and HASHIDA, Y.: Severe middle ear anomaly with underdeveloped facial nerve. Arch. Otolaryngol. 108: 93-98, 1982. LINDSAY, J. R., SAUNDERS, S. H., and NAGER, G. T.: Histopathologic observations in so-called congenital fixation of the stapedial footplate. Laryngoscope 70: 1587-1602, 1960. SAITO, R., MATSUMURA, M., TAKATA, N., OGURA, Y., IWAHORI, N., and HOSHINO, K.: Histopathologic study of congenital aural atresia in human embryo. Arch. Otolaryngol. 107: 215220, 1981.
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148
SANDO, I., and WOOD, R. P., II.: Congenital middle ear anomalies. Otolaryngol. Clin. North Am. 4: 291-318, 1971. STEELE, B. c.: Congenital fixation of the stapes footplate. Acta Otolaryngol. Supp!. 245: 1969.
Request reprints from:
Dr. R. Saito, Department of Otolaryngology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama, Japan
TEMPORAL BONE PATHOLOGY IN CONGENITAL ANOMALIES OF THE OVAL WINDOW AND THE FACIAL NERVE Ryusuke SAITO, M. D., Shuichi WATANABE, M. D., Akira FUJITA, M. D., Akiko FUJIMOTO, M. D., Ikuo INOKUCHI, M. D., and Yoshio OGURA, M. D. Department of Otolaryngology, Okayama University Medical School, Okayama, Japan
Temporal bones of six infants with congenital ear anomalies were examined for abnormalities of the oval window and facial nerve. These temporal bones were classified into two groups according to the degree of malformation: group A, those with atresia or absence of, the oval window; and, group B, those with hypoplasia of the stapes and annular ligament. Group A, consisting of five ears, were associated with severe middle ear anomalies such as the abnormal course of the facial nerve and absence of the stapes. In group B, consisting of seven ears, the stapes were present and the facial nerve presented minor anomalies such as obtuse angulation at the first genu, central migration of the geniculate ganglion cells, ectopic muscles and a wide bony dehiscence of the facial canal around the oval window. Probable origin of the anomalies in group A could mainly be due to maldevelopment of the facial nerve during an earlier embryonal period while that of group B could have developed after the ninth week of the fetal period and are mostly localized along the second branchial arch. With the recent advances in otomicrosurgery, surgery for hearing improvement can be done for those with anomalies of the sound conducting apparatus. Recently, several investigators have reported temporal bone histopathologic findings on anomalies of the oval window and the facial nerve (HARADA, BLACK, SANDO, and SINGLETON, 1980; KODAMA, SANDO, MYERS, and HASHIDA, 1982). This paper describes the histopathologic findings of congenital anomalies of the oval window and facial nerve in temporal bones of the six patients with multiple malformation. MATERIALS AND METHODS
Twelve ears from six patients, one stillbirth and others from seven days to Received for publication December 24, 1984 139
R. SAITO et at.
140
Table 1. Cases
Diagnosis
Age/Sex
Potter's syndrome
Case 1
Stillbirth/F
Case 2
2m/F
13-15 trisomy
Case 3
7d/F
Case 4 Case 5 Case 6
lylOm/F Im/F ImlOd/M
Chromosomal aberration ofG group 13-15 trisomy 18 trisomy 18 trisomy
Malformation of the external ear Bil. severely low set ear and microtia Rt. aural atresia and bil. microtia Bil. aural atresia and microtia None None Bil. low set ear
one year and ten days, represented two cases of 13-15 trisomy, two cases of 18 trisomy, one case of G group hyperploidy and one case of Potter's syndrome (Table 1). The external ear anomalies included congenital atresia of the external auditory canal in three ears from two cases, bilateral microtia in three cases and lowset ears in two cases. At autopsy, both temporal bones were removed and immediately placed in 10 %formaldehyde solution. After decalcification and dehydration, they were imbedded in celloidin and sectioned horizontally at 20 microns. Every tenth section was stained with hematoxylin and eosin, and mounted for microscopic study. HISTOPATHOLOGICAL FINDINGS
Anomalies of the oval window area examined in this study were morphologically classified into two maior groups. Group A represented those with an atresia or absence of the oval window, absent stapes and a profoundly abnormal course of the facial nerve. Group B represented those with hypoplasia of both the stapes and annular ligament and a mildly abnormal course of the facial nerve. Group A (The group with atresia or absence of the oval window) This group exhibited varying degrees of severe hypoplasia of the oval window as seen in five ears of three cases. The temporal bone findings in these cases were summarized in Table 2. The oval window in three ears was barely identifiable as a rudimentary slit in the lateral bony wall of the vestibule (Fig. 1), whereas two ears were completely obliterated by bony structures. All ears exhibited clearly the fissura ante fenestram which could be a guide to identify the oval window area. The facial nerve, thin and atrophic at the internal auditory canal, took an extremely abnormal course in the absence of the geniculate ganglion, barely reached the first genu from the internal auditory canal and descended along the promontory wall (Fig. 2). The facial nerve in two ears disappeared near the level of the vestigial oval window. The chorda tympani nerve and the greater superficial petrosal nerve were absent in all ears. The stapes was absent in four ears. Both
PATHOLOGY OF OVAL WINDOW ANOMALY Table 2.
Group A.
Case 1
Oval window
141
Case 2
Case 3
Right ear
Left ear
Right ear
Right ear
Left ear
Connective tissue slit
Connective tissue slit
Connective tissue slit
Complete absence
Complete absence
Facial nerve and canal Nerve trunk Extremely underdeveloped Course Descended at the first genu Geni. ganglion Absent GSPNa Absent Chorda tymp. Absent Canal Absent
Stapes
Absent
Stapedius muscle
Absent
Extremely underdeveloped Descended at the first genu Absent Absent Absent Vestigial in the promontory wall
Extremely underdeveloped Diminished after the first genu Absent Absent Absent Absent
Absent
Absent
Absent
Absent
Absent
Absent
Extremely underdeveloped Descended at the first genu Absent Absent Absent Absent at the level of mesotympanum and never is passing out the temporal bone Absent
a Greater superficial petrosal nerve.
Fig. 1. Case 1, right ear, showing slit-like fissure (arrow), suggesting a rudimentary oval window. TC, tympanic cavity; V, vestibule; F AF, fissula antefenestram (hematoxylineosin, x 12).
142
R. SAITO et al.
F ig. 2. Case 2, right ear, showing extremely underdeveloped oval window (arrow) and abnormal course of facial nerve (F). Note facial nerve descending anterior to oval window area. C, cochlea; V, vestibule (hematoxylin-eosin, x 4).
malleus and incus exhibited several anomalies such as fusion of ossicles, absence or deformity of malleus handle, fusion to the promontory and absence of long process of the incus. In all ears studied, the tympanum was small and narrow and divided by an irregular bony crista. The stapedius muscle was absent in all ears. The tensor tympani muscle was present in two ears although abnormalities such as irregular location and course and absence of attachment of its tendon to the malleus neck were observed. The round window niche and its membrane seemed to be small and narrow in size, however, they were morphologically less abnormal when compared with the oval window. The round window niche was obliterated by mesenchymal tissue in four ears. Group B (The group with hypoplasia of the stapes and annular ligament)
Both ears from one case showed a stapedial footplate on a narrow and small oval window. Cartilaginous fixation of the stapedial footplate was seen in two ears (Fig. 3). Immature embryonal forms of stapes were observed in three ears with a thick footplate and crura in which bone marrow spaces remained (Fig. 4). A columella-like stapes was observed in two ears and an anomalous stapes with a bifurcated anterior crus in one ear. The facial nerve in six ears ran the usual course through which the labyrinthine, tympanic and mastoid segments can be identified. The facial nerve in one ear ran anterior to both windows without making the tympanic segment and bifurcated at the mastoid segment. In contrast with its course in the normal temporal bone, the facial nerve in these ears showed several abnormalities such as obtuse angulation at the first genu, hypoplasia of
PATHOLOGY OF OVAL WINDOW ANOMALY
143
Fig. 3. Case 4, right ear, showing cartilaginous fixation (arrow) of anterior margin of footplate. S, stapes; TC, tympanic cavity; V, vestibule; F AF, fissula antefenestram (hematoxylin-eosin, x 20).
Fig. 4. Case 4, left ear, demonstrating immature ring-shaped stapes. Note that fossula postfenestram (arrow) is abnormally wide and communicates with middle ear space. V, vestibule; st, stapedius tendon (hematoxylin-eosin, x 5).
the geniculate ganglion, presence of an ectopic muscle in the tympanic segment (Fig. 5) and extensive dehiscence of the bony wall of the facial canal near the oval window. The chorda tympani and the greater superficial petrosal nerves were
144
R. SAITO et al.
Fig. 5. Case 6, left ear, demonstrating ectopic muscle (arrow) in horizontal segment of facial canal. ttm, tensor tympani muscle (hematoxylin-eosin, x5).
Fig. 6. Case 4, left ear, showing abnormal approximation of long process of incus (I) to horizontal segment of facial canal. M, malleus; F, facial nerve (hematoxylin-eosin, x 5).
present in six ears except for one ear. Both malleus and incus, although they contained rudimentary bone marrow spaces, seemed to be normal. In both ears of one case, the long process of the incus was abnormally close to the tympanic
a Greater superficial petrosal nerve.
Normal
Normal
Monopodal stapes Immature embryonal form
Stapes
Absent
Immature embryonal form
Normal Normal Absent at the level Extensive of mesotympanum dehiscence of the bony wall and never is passing out the temporal bone
Stapedius muscle
Normal Normal Extensive dehiscence of the bony wall
Normal
GSPNa Chorda tymp. Canal
No stapedial tendon
Normal
Normal
Normal Normal Extensive dehiscence of the bony wall
Normal Normal Extensive dehiscence of the bony wall
Normal
Normal
Obtuse angle at the first genu Decreased ggl. cell population
Obtuse angle at the first genu Decreased ggl. cell population
Slightly small
Left ear
Normal
Case 6
Normal
Slightly small
Right ear
Immature embryonal form
Central divergence of ggl. cell Normal Normal Moderate dehiscence of the bony wall
Normal
Normal
Normal
Left ear
Columella-like Bifurcated form anterior crus
Obtuse angle at the first genu Central divergence of ggl. cell Normal Normal Moderate dehiscence of the bony wall
Normal
Normal
Normal
Normal
Right ear
Case 5
Normal
Normal
Normal
Underdeveloped Normal and bifurcated at the mastoid segment Descended anterior Normal to both windows
Left ear
Group B.
Cartilaginous fixation of footplate
Geni. ganglion
Course
Facial nerve and canal Nerve trunk
Oval window
Right ear Cartilaginous fixation of footplate
Left ear
Case 4
Cartilaginous fixation of footplate
Case 2
Table 3.
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R. SAITO et al.
segment of the facial nerve (Fig. 6). The tympanic cavity was normal in size in six ears with a small amount of rudimentary mesenchymal tissue in the upper part of the typanum. The stapedial muscle was absent in one ear and only the stapedial tendon was absent:in one ear. The tensor tympanic muscle made an abnormal course in two ears; with one ear presenting an ectopic muscle into the tympanic segment of the facial canal. The round window was rather small and narrow in two ears and was obliterated by mesenchymal tissue in one ear. COMMENT
Congenital anomalies of the oval window have been described as atresia or absence of the oval window or as a fixation of the stapedial footplate (LINDSAY, SAUNDERS, and NAGER, 1960; STEELE, 1969). It has been widely recognized that anomalies of the oval window are frequently associated with facial nerve anomalies. SANDO and WOOD (1971) have reported on temporal bone histopathologic studies of middle ears anomalies with an extensive review of the literature. They indicated that middle ear anomalies were frequently associated with branchial arch anomalies and that the facial nerve and ossicular chain anomalies were the most common in the middle ear. As shown in the Tables 2 and 3, the ears of this study were classified into two major groups by the degree of anomaly of the oval window: Group A, those with atresia or absence of the oval window; and group B, those with hypoplasia of the stapes and annular ligament. Group A represents severe developmental abnormalities of the oval window and group B represents those with less severe abnormalities of the oval window and stapes. In group A, three ears in two cases exhibited the oval window as a barely identifiable connective tissue slit while both ears in one case showed complete absence of the oval window. The facial nerve, in its abnormal course in the temporal bone, was abnormally thin with severe hypoplasia of the nerve trunk. Group B includes seven ears from four cases. The stapes was deformed or immature and embryonal in form in most ears. Two ears showed cartilaginous fixation of the stapes. The oval window was almost normal in size and the facial nerve passed along its usual course in most ears. The facial nerve in the temporal bone is primarily composed of three different nerve fiber bundles, namely, the motor fiber, the sensory fiber and the autonomic fiber bundles. The sensory fibers originate from the seventh and the eighth cranial nerve crest cells which develop at the beginning of the fourth week of the embryonal period, and the motor and autonomic fibers begin to extend from the neuroblasts of the pons at about the same time (GASSER, 1975). These fibers coalesce to form nerve trunks which extend peripherally into the first and second branchial arch tissues. The primordium of auditory ossicles appears during the sixth to seventh week of the embryonal period (BAST and ANSON, 1949). According to the appearance of the primordial stapes, the facial nerve curves posteriorly
PATHOLOGY OF OVAL WINDOW ANOMALY
147
to differentiate into the tympanic and mastoid segment in the temporal bone (SAITO, MATSUMURA, TAKATA, OGURA, IWAHORI, and HOSHlNO, 1981). The otic capsule becomes precartilaginous and the oval window begins to form with the impingement of the primordial stapes to the developing otic capsule in the eighth week of the embryonal period. The annulus stapedialis, a derivative of the second branchial arch, fuses with the lamina stapedialis of the otic capsule to form the future stapedial footplate. As the base of the stapes increases in diameter, the lamina stapedialis undergoes a process of dedifferentiation from precartilaginous tissue to connective tissue to form the annular ligament after the ninth week of the fetal stage (BAST and ANSON, 1949). HARADA et al. (1980) reviewed the temporal bone histopathologic findings in five cases with congenital anomalies of the oval window and reported various degrees of anomalies ranging from cartilaginous fixation to complete absence of the oval window. They also stated that these anomalies are due to developmental arrest of the oval window at different stages and can be monistic ally explained by the same embryological basis. KODAMA et al. (1982) reported on temporal bone findings in severe middle ear anomalies with an extremely underdeveloped facial nerve and classified the facial nerve anomalies into two groups, that is, the severely and the moderately anomalous group. They indicated that the abnormalities found in the severely anomalous groups were morphologically similar to those of an early stage of the embryonal period, in which the development of the facial nerve was arrested. Taking these previous reports in the literature into consideration, it is suggested that an early development of the facial nerve has been primarily arrested in the group with absence or atresia of the oval window. On the other hand, in the group with hypoplasia of the stapes and the annular ligament, abnormalities are thought to develop at a later stage of the fetal period and may be localized mainly in the second branchial arch without any developmental anomalies of the facial nerve itself. REFERENCES BAST, T. H., and ANSON, B. J.: The Temporal Bone and the Ear. Springfield Illinois, Charles C. Thomas, 1949. GASSER, R. F.: Atlas of Human Embryos, Hagerstown, Harper and Row, Inc., 1975. HARADA, T., BLACK, F. 0., SANDO, I., and SINGLETON, G. T.: Temporal bone histopathologic findings in congenital anomalies of the oval window. Otolaryngol. Head Neck Surg. 88: 275-287, 1980. KODAMA, A., SANDO, I., MYERS, E. N., and HASHIDA, Y.: Severe middle ear anomaly with underdeveloped facial nerve. Arch. Otolaryngol. 108: 93-98, 1982. LINDSAY, J. R., SAUNDERS, S. H., and NAGER, G. T.: Histopathologic observations in so-called congenital fixation of the stapedial footplate. Laryngoscope 70: 1587-1602, 1960. SAITO, R., MATSUMURA, M., TAKATA, N., OGURA, Y., IWAHORI, N., and HOSHINO, K.: Histopathologic study of congenital aural atresia in human embryo. Arch. Otolaryngol. 107: 215220, 1981.
R. SAITO et al.
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SANDO, I., and WOOD, R. P., II.: Congenital middle ear anomalies. Otolaryngol. Clin. North Am. 4: 291-318, 1971. STEELE, B. c.: Congenital fixation of the stapes footplate. Acta Otolaryngol. Supp!. 245: 1969.
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Dr. R. Saito, Department of Otolaryngology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama, Japan