Frequency and localization of congenital anomalies of the middle and inner ears: a human temporal bone histopathological study

International Journal of Pediatric Otorhinolatyngology,16 (1988) l-22 Hsevier

1

POR 00526

Department of OtoIavngologv and PathoIop, Eye and Ear Hospital Pittsburgh, PA 15213 (USA.)

(Received 17 March 1988)

Key words: Congenital anomaly; Middle ear; Inner ear; &man temporal bone;

This study investigated congenital anomalies occu inner ears, with particular attention to their features, localization 0ne hundred human temporal bones obtained from 73 individu tional weeks to 39 years, each of whom had anomalies of the inner ear, were used for this study. The temporal bones ha autopsy, fixed, dehydrated, embedded in cclloi vertically at 20 pm. Every 10th horizontal section or e stained with hematoxylin and eosin, mounted and studied under a In the middle ear the structure most often found to be e implications of the nerve; in the inner ear it was the lateral semicircular canal. anomalies observed are discussed as they relate to fetal development, dysfunction of the ear, zrd clinical interpretation of diagnostic radiological studies.

.* Present address: Department of Otolaryngology, Tohoku University School of Medicine, Send& Japan. ** Present address: Department of Qtolaryngology, Kyoto University Faculty of Medicine, Japan. *+* Present address: Department of Otolaryngology, Kobe University, Kobe City, Japan. Correspondence: I. Sando, Department of Otolaryngology and Pathology, Eye and Ear Nospital of Pittsburgh,230 Lothrop St., Pittsburgh, PA 15213, U.S.A. 0165-5876/88/$03.50 8 1988 ElsevierScience Publishers B.V. (Biomedical Division)

2

Introduction To date, temporal bone studies of congenital anomalies of the middle and inner ear have been liited to reports of the results of histopathological examination of a case or cases of specific anomalous entities. Therefore, we undertook to report quantitatively on anomalies of the middle and inner ears, describing especially the features, localizations, and frequencies with which such anomalies appear, and discussing the relation of these anomalies to structures as they develop normally in the fetus, to middle and inner ear functions, and to the interpretation of the results of diagnostic radiological examinations.

Materials and Methods One hundred human temporal bones obtained from 73 individuals in whom anom&es of the middle ear and/or inner ear had been identified were used. The various pathological conditions present in the study specimens are shown in Table I. The subjects ranged in age from 31 gestation weeks to 39 years, with a mean age of 3.8 years. The distribution of subjects, according to age, is shown in Table II. The temporal bones were removed at autopsy in the routine manner, fixed in 10% formalin solution, decalcified in 5% trichloroacetic acid solution, dehydrated in

TABLE I Pathologic conditions present in 100 temporal bonesfrom 73 individuals Condition

Congenital heart anomalies (CHA) Trisomy 13 syndrome (T13) Multiple congenital anomalies (MCA) Trisomy 21 syndrome (TX) Pierre-Robin syndrome (PRS) Potter syndrome (PS) Trisomy 18 syndrome (T18) Alpon syndrome (AL) Chromosome 16 long arm deletion (C16) Congenital aural at&a (AA) Fanconi syndrome (FS) Treacher-Collins syndrome (TCS) Achondroplasia(ACH) Anencephaly (ANE) Congenital rubella (CR) Goldenhar syndrome (GS) Noonan syndrome (NS) Gculodentodigital syndrome (ODD) Spondyloepiphyseal dysplasia (SE) Total

Number of bones

Number of individuals

19 19 17 12 5 5 5 3 2 2 2 2 1 1 1 1 1 1 1

15 11 15 8 3 3 4 2 1 2 1 1 1 1 1 1 1 1 1

100

73

TABLE II Ages of 73 individuals from whom 100 temporal bones were obtained Age

Premature(31-35 weeks gestation) Premature(36-39 weeks gestation) Newborn (birth-6 days) Neonatal (7 days-30 days) Infant (1 month-23 months) Child (2 years-9 years) Adolescent (10 years-17 years) Adult (18 years-39 years) Total

Number of bones

5

Numberof individuals 4

7

5

15 23 31 8 2 9

11 16 23 6 2 6

100

73

graded solutions of alcohol, and embedded in cell sectioned horizontally and 12 vertic vertkal section was stain glass slide for light microscopic study.

the 100 bones, gg were tal section or ev

ddle ear anomalies Middle ear in genera!. A total of 292 middle ear anomalies were seen in 90 of alie nd their the 100 temporal bones from 73 individuals ove average location in the middle ear are listed in Table I number of anomalies per bone in this study was 2.92, while the average number of anomalies per bone with one or more middle ear anomaly was 3.24. Ninety-two anomalies were observed in the ossicles, 81 in the nerves, 59 in the tymp 19 in the muscles, 13 in the mastoid cavity, 12 in the vessels, and the in the other structures. Qssicles. Ninety-two ossicular anomalies were noted in 49 of the 100 bones studied (average number of anomalies per bone = 0.92; average number of anomalies per bone with ossicular anomalies = 1.88). The ossicular anomalies observed were of 26 different types. Of the 92 ossicular anomalies, anomalies in the stapes were most frequently observed (43,46.7%), being followed by those in the incus (26,28.3%), and those in the malleus (23, 25%). The most frequently observed anomalies were a bulky stapes (19, 20.7%) (Fig. 1), malformed malleus (8, 8.7%), and bulky incus (7, 7.6%). me was studied, Although only one bone with Goldenhar was the one most anomalies were noted in this bone and this co ther conditions in association wit seen to accompany ossicular anomalies.
4 TABLE III

Middle ear anomalies noted in 100 temporal bones from 73 individuals Anomalies nmpanic membrane Replacement by fibrous tissue Replacement by bony plate Thick Dislocated Ossicles Malleus Malformed Dislocated Bulky Absent

Absence of manubrium Bony fixation to the wall Flattened manubrium widely attached to tympanic membrane Incus Bulky Malformed Absent Absence of lenticular process Dislocated Cartilaginous fixation Incudomellear joint poorly developed Bony fusion to malleus Rudimental short process Stapes Bulky Crura attached to more medial portion of footplate fncudostapedial joint absent Absent Columella type Malformed Incudostapedial joint poorly developed Absence of head Absence of anterior crus Crus widely attached to footplate

Number of anomalies 4 3 1 1

8 7 3 2 1 1 1 7 4 3 3 3 2 2 1 1 19 4 4 3 3 3 3 2 1 1

Nerve Facial nerve 33 Wide angle of first genu 14 Hypoplastic 7 Laterally dislocated tympanic and mastoid portions Absence of second genu 3 Anteriorly dislocated tympanic and mastoid portions 3 Displacement of geniculate ganglion cells into internal auditory meatus 2 Absent 1 Bifurcated 1 Hypoplastic and triplicated 1

5

TABLE III (continued) .4zumalies

Chorda tympani nerve Running into connective tissue replacing tympanic membranes Absent Positioned below tendon of tensor tympani muscle Running vertically in center of middle ear Bifurcated Huge Hypoplastic Greatersuperficialpetrosal nerve Absent Muscle Tensor tympani muscle and tendon Located lateral to Eustachian tube Absent Attached to anterior aspect of the Bifurcated& a branch ended the facial nerve sheatb in the Fallopian canal Running straight at the cochleariformprocess Stapedius muscle and tendon Absence of stapedius tendon Absence of stapedius muscle and tendon Huge and widely exposed stapediusmuscle Hypoplastic stapedius muscle

Number of avtomaiies

4 3 2 2 1 1 1 2

2 1 1 1 1 5 4 2 2

Vessels

Stapedial artery Persistenceof stapedial artery Jugularbulb High jugular bulb

5 7

Tympanic caui@

In general Hypoplastic Mesotympaniccavity Bony mass protruding from promonitory Absence of semicanal of tensor tympanic muscle Bony fusion between otic capsule *Id tympanic bone in hypotympani Facial canal Wide dehiscence Large Pyramidaleminence Absent Cochleariformprocess Absent

34 4 8 4

Mastoid caviry

Absent antrum Eustachian tube

Wide bony dehiscence of bony portion Dislocated levator veli palatini muscle Carotid canal

Wide bony dehiscence

13 3 2 2

See Table I hx abbreviations.

Total

Ossic;les Makus Inclus stapes Nerves Facial nerve Chorda tympartiIHSW Greater super&M petrosaInerve Tympanic mwscles Tensar tympani amscle and tendon Stapedius mus& md tendon VesseIs Persik3tent stapedial artery I-Ii&jugular bulb Tympank cavity In general Memyanpanic cavity Facid canaI ~~d~~~~ cO&hlifom process Mastoid cavity Eustahiaa tube Carotid camI

Tympanic inelnbrane

24

1

1

54

6 1 1

8 1

2

%

14 2

4 2 11

1

49

3

1

7 1 1

1

2 1

10 2 1

11

3 2

3

22

%

6

4

7

2 2

12

1

2

2 3 4

12

2

3

1

4%

1

4 2

6

1

2

5

16

1

1 2

2 3 1

1

4

3

1

23

1

2 2

2 2

2

1

1

s

1

1

1 1 1

2

1

1

16

1 %

1

1 1

3% %

2 3 1

%

2

1

1

1

%

1

4 5 38 8 4

5 7

6 %3

65 14 2

23 26 43

292

13 5 2

59

12

19

8%

9 92

Fig. 1. The stapes is abnormal, with rudimentary bulky crura (arrows) in this left ear of a 4monthsld girl with congenital rubella. Hematoxylin and eosin (~39.5). (From Hemenway, .G., Sando, 1. and McChesney, D., Temporal bone pathology following maternal rubella, Arch. Klin. E&p.Qhr-Nas.-Kehkd. 193 (1969) 287-300. Used with permission of the author and publisher).

Nerves. A total of 81 anomalies were identified in 57 of the 100 t (average number of anomalies per bone = 0.81; average n bone with nerve anomaly = 1.42). A total of 17 different types were found: 9 in the facial nerve, 7 in the chorda tympani superficktl petrosal nerve. Of the 81 nerve anomalies, nerve (65, 80.2%); these included a wide (obtuse) angle of the (Fig. 2), plastic facial nerve (14,17.3%), and laterally located tympanic and mastoid portions of the facial nerve (7, 8.6%). Although only one bone with Goldenhar syndrome was studied, there were nerve anomalies in this bone. This was again the accompanying facial nerve anomaly. Another nerve anomalies were frequently noted was Treacher-Collins syndrome (average 2.0 anomalies per bone). Tympanic cavity. A total of 59 tymp per bone = 0.59) we cavity anomalies = quently appearing ones being remark 57.6%) (Fig. 3); absence of the pyr

Fis 2. In this left ear of a 41-day-old girl with trisomy 13 syndrome the angle of facial nerve at its geniculate ganglion area is wide (arrow). In addition, while the posterior semicircularcanal (PSC) is normal, the lateral semicircularcanal (LSC) is poorly developed (fetal form). Hematoxylin and eosin ( x 8.7) (From Sando, I., Leiberman,A., Bergstrom, L., Izumi, S. and Wood, II, RP. Temporal bone histopathological findings in t&my 13 syndrome, Ann. Otol. Rhinol. Laryngol., 84 Suppl. 21, (1975). Used with permission of the author and publisher).

tympanic cavity (4, 6.8%). Treacher-Collins syndrome was the condition most frequently accompanying tympanic cavity anomalies (4 per bone). Intnitympanicmuscles. Nineteen muscular anomalies, 13 in the stapedius muscle and 6 in the tensor tympani muscle, were seen (average anomalies per bone = 0.19) in 14 bones (average anomalies per bone with muscular anomaly = 1.36). They were of 9 different types, the most common one being absence of the stapedius muscle tendon, which was noted in 5 bones. Vessels. Twelve vascular anomalies (average anomalies per bone = 0.12) were found in 12 bones (average anomalies per bone with vascular anomaly = 1.0) out of 100 bones. Of those 12 anomalies, 7 were high jugular bulbs and the remaining 5 were persistence of the stapedial artery. Others. Other middle ear anomalies observed were in the mastoid cavity (13, 4.5%), tympanic membrane (9, 3.1%), Eustachian tube (5, 1.7%), and carotid canal (2, 0.7%). In 60 bones (66.6%) of the 90 with middle ear anomalies, inner ear anomalies were also present. Of those 60 bones, 32 (53.3%) had both vestibular and cochlear anomalies, 23 bones (38.3%) had only vestibular anomalies, and 5 bones (8.4%) had only co&ear anomalies. The remaining 30 bones (33.4%) of 90 with middle ear anomalies had no inner ear anomalies.

Fig. 3. This section from the right ear of a 3-3/4-year-old girl with a congenital heart anomaly shows a widely exposLJfacial nerve (arrow).The dehiscence is in the horizontal portion, near the second genu. A remnant of mesenchymal tissue may also be seen in the middle ear space. Hematoxylin and eosin. ( x 8). (From Egami,T., Sando, I. and Myers, E.N., Temporal bone anomalies associated with congenital heart disease, Ann. Otol. Rhinol. Laryngol. 88 (1979) 72-78. Used with permission of the author and publisher).

In addition, no middle ear anomalies were found in 10 of the 100 bones studied art anomalies (5 bones), which had been obtained from patients with congenital multiple congenital anomalies (3 bones), trisomy 13 syndrome (1 bone), or Pierre-Robin syndrome (1 bone). Inner ear anomalies Inner ear in general.

A total of 262 inner ear anomalies were identified in 70 bones. Anomalies and their location in the inner ear are listed in Table V and Table VI. The average number of anomalies per bone was 2.62, while the average number of anomalies per bone with one or more inner ear anomalies was 3.74. One hundred and thirty-seven anomalies were present in the vestibular system, 85 in the cochlea, and 15 in the internal auditory meatus. Vestibular system. There were 137 anomalies in 61 of 100 temporal bones (average per bone = 1.37; average per bone with vestibular anomaly = 2.25). Thirty-three different types of vestibular anomalies were found; 21 in the semicircular canals and 12 in the vestibule.

10 TAE! E V Inner ear

anomalies noted in 100 temporal bones from 73 individuals

Anomalies Cochlea cochlea - in general Poorly developed cochlear turn Anomalously distorted osseous cochlea Osseous cochlea - in general Absence of hook portion Round window Hypoplastic Parallel to tympanic membrane Scala vestibuli Poorly developed in basal turn Modiolus Modiolus - in general Poorly developed Rosenthal’s canal Hypoplastic Absent Spiral lamina Absence of lumen for cochlear nerve Presence of secondary osseous spiral lamina in middle turn Interxalar septum Absent Cochlear aqueduct Anomalously wide Partial absence near labyrinthine orifice Narrow Membranous cochlea Cochlea duct - in general Absence of hook portion Vestibule Vestibule - in general EnWed Osseous vestibule Oval window Poorly developed cartilaginous ligament Bony fusion of footplate to otic capsule Hypoplastic (small) Anteriorly dislocated Membranous vestibule Utricle Macula Angulated macule Rndolympathic duct and sac Utricle-endolymphatic valve Hypoplastic (short) Malformed Absent

Number of anomalies

24 1

7 5 4 3 2 5 20 2 1

3

18

6

9 3 1

11 TABLE V (continued) Anomalies Endolymphatic duct Sinus anomalously enlarged Endolymphatic sac Ending in otic capsule Semicircularcanal Superior semicircular canal Semicircular canal - in general Partial absence Osseous semicircular canal Hypoplastic (small) osseous canal Membranous semicircular canal Membranous canal Hypoplastic (small) Partial absent Ampulla Absence of crista Ampulla anomalously enlarged Absence of ampulla Posterior semicircular canal Semicircular canal - in general Total absent Osseous semicircular canal Hypoplastic (small) Anomalously large Membranous semicircular canal Membranous canal Hypoplastic Ampulla Ampulla anomalously enlarged Hypoplastic (flattened) crista Lateral semicircular canal Semicircular canal - in general Total absence Partial absence Osseous semicircular canal Anomalously large Hypoplastic (small) Membranous semicircular canal Membranous canal Hypoplastic (small) Ampulla Hypoplastic (flattened) crista Ampulla anomalously enlarged Crista quarta Otic capsule Absence of periosteal layer in part of otic capsule

Number of anomalies 2 3

2 3

1 1 2 2 1

2 6 1

2 3 1

15 3 13 2

2 9 3 2 5

12 TABLE V (continued) Anomalies

Number of anomalies

Internal auditory meatus Shallow and wide shallow

10 5

Nerve Statoacoustic nerve Cochlearnerve Spiralganglion cells displaced into internal auditory meatus Vestibularnerve Bifurcatednenre to lateral semicircularcanal crista Bifurcatednerve to posteriorsemicircularcanal crista Aberrantcourse of singularnerve from posteriorcranial fossa Aberrantcourse in vestibule to lateral semicircularcanal crista Absence of singular nerve

3 2 2 1 1

Vessel Persistenceof vessels in a p&lymphatic scala

6

5

Of the total number of vestibular anomalies, the most frequently observed were enlargement of the vestibule (l&13%), total absence of the lateral semicircular canal (15, 11%) (Fig. 4), abnormally large osseous lateral semicircular canal (13, 9.5%), hypoplastic (short) endolymphatic sac (9,6.6%), and poorly developed cartilaginous ligament in the oval window (7, 5.1%) (Fig. 5). The condition most frequently associated with vestibular anomalies was trisomy 18 syndrome (average 3.2 per bone), and trisomy 13 syndrome (average 2.9 per bone). Cochlea. Eighty-five cochlear anomalies were noted in 44 of 100 bones studied (average anomalies per bone = 0.85; average anomalies per bone with cochlear anomaly = 1.93). Sixteen different types of cochlear anomalies were observed (Table W. Of the 85 cochlear anomalies, the most frequently seen were: poorly developed cochlear turn (24, 28.2%) (Fig. 6); and abnormally wide cochlear aqueduct (20, 23.5%). The conditions most frequently associated with cochlear anomalies were trisomy 13 syndrome (average 2.6 per bone), Fanconi syndrome (average 2.0 per bone), and congenital rubella (average 2.0 per bone). In 60 bones of the 70 (85.7%) with inner ear anomalies, middle ear anomalies were also present. Of those 60, 32 (53.3%) had both vestibular and cochlear anomalies, 23 bones (38.3%) had only vestibular anomalies, and 5 bones (8.3%) had only cochlear anomalies. The remaining 10 bones (14.3%) of 70 with inner ear anomalies had no middle ear anomalies; 4 bones had only cochlear anomalies, 3 bones had only vestibular anomalies, and 3 bones had both vestibular and cochlear anomalies.

Table VI continued on p, 14.

Vestibule Vestibule (in general) Osseous vestibule Oval window Membranous vestibule Utricle Macula Endolymphatic duct and sac Utricle-endolymphatic valve Endolymphatic duct Endolymphatic sac

Cochlea Cochlea (in general) Osseous cochlea Osseous cochlea (in general) Round window Scala vestibuli Modiolus Modiolus (in general) Rosenthal’s canal Spiral lamina Interscalar septum Cochlear aqueduct Membranous cochlea Cochlear duct (in general)

Lmation

2

1

1

3 1

4

1

5

4

3

2 2

2

2

MCA

11

1

4 4 4 5 13

2

1

16

T13

1

2

5

1 1 1

3

U-IA

Conditions

2

1

1

2

T21 PRS

Location of inner ear anomalies in different pathologic conditions

TABLE VI

2

PS

2 2

2

2

1

Tl8

AL

1

Cl6

1

AA

2

3

1

2

1

FS TCS ACH 1

ANE

2

1

1

1

CR GS NS

ODD

1

SE

13 2 3

6

7 9 5 5

18

6

19

3

23

3 3 2 26

Total

24

19 19

3

25 57

62

85

9

Internal auditory meatus Nerve Statoacoustic nerve Cochlear nerve Vestibular nerve

* See Table I for abbreviations.

Vessel Total

3

Otic capsule

25

1 1

4

9

4 126

1

1 1 35

1

5 6

1

T2I PRS

2 3

9 3

1

2 3

2 2

1 2

T13 MCA

1 7

2 2

3

1

CHA

Conditions

Posterior semicircular canal (PSC) PSC (in general) osseous PSC Membranous PSC Membranous canal Ampulla Lateral semicircular canal (LSC) LSC (in general) osseous LSC Membranous LSC Membranous canal Ampulla

Semicircular canals Superior semicircular canal (SSC) SSC (in general) osseous ssc Membranous SSC Membranous canal Ampulla

Location

TABLE VI (continued)

9

2

2

2

1

PS

21

2

1

1 3

1 1

1

1

1

2

2

Cl6

16149

TI8 AL

2

1

11

AA FS TCS ACh- ANE

1 5210

1

CR GS NS ODD

2

1

2 13

2 4

2 5

5 9

18 15 15

2 7 6

2 3 7

SE Total

14

48

15

12

6 262

15 14

5

75

Fig. 4. In this photomicrograph a section from the left ear of a 36-year-old man with a congenital heart anomaly, the lateral semicircular canal can be seen to be absent. As a result, the utricle (UTR) is enlarged and incorporates the lateral semicircular canal crista (LC). The posterior semicircular canal (PSC) is normal. UM, utricular macula. Hematoxylin and eosin. (x13). (From Egami, T., Sando, I. and Myers, E.N., Temporal bone anomalies associated with congenital heart disease, Ann. Otol. Rhinol. Laryngol., 88 (1979) 72-78. Used with permission of the author and publisher).

In addition, no inner ear anomalies were found in 30 of the 100 bones studied, which were obtained from patients with congenital heart anomalies (9 bones), trisomy 21 syndrome (7 bones), multiple congenital anomalies (4 bones), Alport in syndrome (2 bones), congenital aural atresia (2 syndrome (2 bones), Pierrebones), Potter syndrome (2 bones), oculodentodigital syndrome (1 bone), or Goldenhar syndrome (1 bone).

16

Diiussion

Many clinical reports and literature reviews have discussed middle ear and inner ear anomalies. In addition, many temporal bone histopathologic reports have described the appearance of congenital middle and inner ear anomalies associated with specific entities such as chromosomal aberrations [1,6,8,10,12,15,18,19,22,23,28], Treacher-Collins syndrome [21], Pierre-Robin syndrome [7], congenital heart anomalies [3], anencephaly [4,33], Goldenhar syndrome [24,31], and VATER syndrome [ZO].Many reports and literature reviews have also been published describing the histopathological appearances of classic inner ear dysplasias [2,16,26,27].Kelemen [ll] published an extensive study of anomalies present in 54 patients with congenital conditions; however, further histopathological quantitative analysis of middle and inner ear anomalies accompanying a variety of congenital conditions would be of great benefit to clinical otology. For this reason, we undertook this task. The middle and inner ear anomalies we observed in this study may be classified as absence, hypoplasia, and other abnormalities of middle or inner ear structures. Hypoplasia of middle ear structures was the most common anomaly among the

Fig. 5. In this section through the left ear of an l&day-old boy with Treacher-Collins syndrome, the oval window is small (arrows).The cartilaginous stapes footplate is ankylosed anteriorly.The utricle (UTR) is enlarged. FA, fissula ante fenestram;FP, fissula post fenestram. (X 15.2). (From Sando, I., Hemenway, W.G. and Morgan, W.R., Histopathology of the temporal bone in mandibulo-facial dysostosk (Treacher-Collins syndrome).,Tram-&n. Acad. Ophthalmol. Otolaryngol, 72 (1968) 913-924. Used witih permission of tbe author and publisher).

Fig. 6. The left ear of a 6.5week-old boy with trisomy 13 syndrome shows an incompletely developed cochlea. There is absence of the interscalarseptum (arrow)and a poorly developed modiollls ( utricle; IAM, internal auditory meatus. Hematoxylin and eosin ( X 10.6). (From Sando, I., Leiberman,A., Bergstrom, L., Izumi, S. and Wood, II R.P. Temporal bone histopathological findings in trisomy 13 syndrome, Ann. Otol. Rhinol. Laryngol., 84, Suppl. 21 (1975) l-20. Used ti,th permission of the author and publisher).

middle ear anomalies (134 anomalies, 45.9% of 292). The facial nerve was the most frequently hypoplastic structure, accounting for 51 anomalies (38.1%). oplastic stapes (33 anomalies, 24.6%), a hypoplastic malleus (18 anomalies, 13.4%), and hypoplastic incus (16 anomalies, 11.9%) were also seen frequently. Also, hypoplasia of the inner ear structures was the most common anomaly among the inner ear anomalies observed in our study (16’1of 262 anomalies, 63.7%). 8f those hypoplasfrequently observed tic structures, the poorly developed cochlear turn was the hypoplastic structure, accounting for 24 anomalies (1 . Abnormally wide co&ear aqueduct (20 anomalies, 1.2%),enlargement of the vestibule (18 anomalies, lO.G%),and abnormally large osseous lateral semicircular canal (13 anomalies, 7.8%) were also frequently seen. Because most of the hypoplastic middle and inner ear structures appeared to resemble those structures seen in early stages, we feel that the anomalies may be due to interruption of development early in fetal life. more, a Mondini-type of inner ear dysplasia, as described by Schuknecht identified in 53 of 70 bones (75.7%), which were classified as having structural absence of part of the inner ear such as absence of the lateral semicircular CWd.

18 TABLE VII Relationshipof anomalies of stapes to those of maik~ and incur Mallew and/or incus

Anomalies of stapes Normal stapes

First branchial arch anomalies: anomaliesof ma&us head and incus bo&

Second branchial arch anomalies: anomalies of malleus handle and incus long process

4 9

11 2

The head of the malleus, the neck of the malleus, the body of the incus, and the short process of the incus originate in the first bran&al arch, while the manubrium, the long process of incus, and the stapes originate from the second branchial arch [17]. For this reaso 2, anomalies of the malleus and/or incus may be divided into two different kinds of anomalies, the first being first branchial arch anomalies and the second being second branchial arch anomalies. In this study, the fact that anomalies of the manubrium of the malleus and/or the long process of the incus occurred in temporal bones with a large number of stapes anomalies (Table VII) appears to confirm that these structures are all embryologically derived from the same structure (the second branchial arch). The anomaly most frequently noted in the facial nerve was a wide (obtuse) angle of the first genu. Graphic reconstruction of the facial nerve’s course of development in the human embryo, performed by Gasser [5], shows that at 8.5 gestational weeks the geniculate ganglion subtends a narrower angle than it does in the fetus of 8 weeks, but that it is still much greater than a right angle. At 9 gestational weeks, the angle of the geniculate ganglion approximates a right angle. The angle of the genu varies in different human specimens from 45 O to 105 O [32]. Lang [13] measured the angle between the lateral border of the distal labyrinthine part and the medial border of the proximal tympanic part to be an average of 51.7 O (range from 21.5 O to 91° ). Therefore, we identified an abnormally wide angle of the first genu of more than 110’. Frequent occurrence of this kind of facial nerve anomaly should be noted particularly by surgeons so that damage of an anomalous nerve can be avoided. Remnants of embryological structures such as bone marrow and mesenchymal tissue may be classified separately from the major malformations as anomalies of delayed disappearance. The most frequently observed anomalies of that kind were huge bone marrow cavity in the incus (21 anomalies, 7.2%), largely filled with mesenchymal tissue (20 anomalies, 6.8%), and huge bone marrow cavity in the malleus (19 anomalies, 6.5%) (Table VIII). It is interesting to note that those anomalies of delayed disappearance appeared most often in cases with Treacher-Collins syndrome (average number of anomalies of delayed disappearances per bone= 2.2) and in cases with trisomy 13 syndrome (average per bone = 1.3).

* See Table I for abbreviations.

Total

Filled with mesenchymal tissue 10

4

3

2

Incus Huge marrow cavity

Tympanic cavity in general Largely filled with mesenchymal tissue Completely filled with mesenchymal tissue

1941

25

5

2

951

1s

3

3

CHA Tl3 MCA

Conditions *

Malleus Huge marrow cavity

Lsxation

Anomalies with dehzyed disappearance of embryonic structures

TABLE VIII

5

1

2

1

1

11 3

5 1

3 1

3 1

1

1

2

2

1

1

1

1

75

13

20 2

21

19

T2I PRS PS Tl8 AL C16 AA FS TCS ACH ANE CR GS NS ODD SE Total

20

All middle and innr, ear anomalies may be classified in another way, in terms of their effects on middle and inner ear function; (1) anomalies that would definitely lead to dysfunction, such as interrupted hearing due to absence of stapes or

~seq~brium due to the absence of the lateral semicircular canal, (2) anomalies that could possibly be associated with dysfunction, such as a hypoplastic facial nerve disturbing facial expression or a shortened cochlea or a hypoplastic lateral semicircular canal crista, and (3) anomalies that probably would not lead to dysfunction, such as high jugular bulb or an abnormal course of the posterior ampullary nerve. Using this c!assification, we found that anomalies of the middle ear that would probably not lead to dysfunction (149 of 292, or 51.0%) were the most common, followed by anomalies that could possibly be associated with dysfunction (78 of 292, or 26.7%), while the anomalies that would definitely lead to dysfunction were the least common (65 of 292, or 22.3%). In the inner ear, however, we found that anomalies that could possibly be associated with dysfunction were the most common (175 of 262, or 66.8%), followed by the anomalies that would definitely lead to dysfunction (45 of 262, or 17.2%) and anomalies that would not

lead to dysfunction (42 of 262, or 16.0%). These findings may be clinically significant because more than 49.0% of middle ear anomalies and the majority of inner ear anomalies (220 of 262, or 84.0%)appear to be associated either possibly or definitely with inner ear dysfunction. The application of polytomographic radiography to the diagnosis of the middle and inner ear problems has been described in recent decades [9,14,30,34,35].Now, high-resolution computed tomography has emerged as the method of choice for evaluation of the temporal bone [29]. It is worthwhile to mention that 52.4% (153 of 292 anomalies) of middle ear anomalies and 43.1% (113 of 262 anomalies) of inner ear anomalies we described in this study can be detected tomographically, because

they represent bony malformations larger than 0.5 mm. The remaining anomalies are either undetectable or difficult to detect by tomography because they occur in a membranous structure or involve minor osseous structures of the middle ear.

This study elucidated the types, locations, and frequencies of occurrence of middle and inner ear anomalies noted in 100 temporal bones from 73 individuals with various pathological conditions. We have shown the associations of some of those anomalies with abnormal fetal development, with dysfunction of the middle and inner ears, with abnormal radiological results, and with delayed disappearances. However, because of the limited number and age of patients used in this study, it is important for further quantitative investigations to take place so that the results of this study may be confirmed and the true incidexxe of specific middle and inner ear anomalies associated with various pathological conditions be established.

21

en

The authors wish to express their deep gratitude to Eugene N. Professor and Chairman, Department of Qtolaryngology, and to M.D., Department of Radiology, University of Pittsburgh School of encouraging them to study this subject and for giving u preparation of this paper. This study was supported by 13787 from the National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health.

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