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Bergman’s Comprehensive Encyclopedia of Human Anatomic Variation, First Edition. Edited by R. Shane Tubbs, Mohammadali M. Shoja and Marios Loukas. © 2016 John Wiley & Sons, Inc. Published 2016 by John Wiley & Sons, Inc.

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EarAman Deep1, Martin M. Mortazavi2 and Nimer Adeeb1

1Children’s of Alabama, Birmingham, Alabama, USA2University of Washington School of Medicine, Seattle, Washington, USA

Anatomical observations are very important for determining the shape, position, and variations of the ear. An anatomical variation can be an isolated anomaly or part of a syndrome and its effect can range from no defect to complex hearing loss. The ear has a very complex structure and careful observations can help in the diagnosis of anomalies and syndromes. The purpose of this chapter is to describe anatomical variations of the ear.

Variations of the external ear

Various classifications are used in the literature to describe anomalies of the external ear. Recently, Hunter and Yotsuyanagi (2005) published a classification modified from the Weerda classification (Table 97.1). They divided the anomalies into three

grades of dysplasia. Grade I anomalies entail minor variations that do not warrant the use of skin and cartilage to repair the structural defect. The category includes macrotia, anomalies of the pinna (protruding ear, cryptotia, Darwin’s tubercle, satyr ear, Stahl ear, shell ear, Mozart ear, and lop ear), absent helical cleft, and anomalies of the lobule and tragus. Grade II dyspla-sia or second‐degree microtia includes anomalies where some normal ear features are detectable and reconstruction requires the use of additional skin and cartilage. This grade covers severely deformed cup ear and mini ear. In Grade III dysplasia, no normal ear features are detectable and complete reconstruc-tion is required. This category includes microtia (unilateral or bilateral) with external acoustic meatus atresia, and anotia or complete absence of the ear.

MicrotiaMicrotia is a congenital anomaly where the pinna is underde-veloped (Luquetti et al. 2012). It ranges from mild structural abnormality to absence of the ear/anotia (Fig. 97.1). Terminol-ogies ranging from “microtia”/“microtia/anotia” to “microtia‐anotia” are used in the literature. It can occur as an isolated anatomical anomaly or as part of a syndrome. Sufferers are pre-dominantly male. Microtia is unilateral in 77–93% of cases with 60% involvement of the right ear. The incidence is 0.8–2.4 per 10,000 live births. Hispanics and Asians have a higher preva-lence than African Americans and Europeans. The highest inci-dence of 8.3 per 10,000 live births has been reported in Navajo Indians (Luquetti et al. 2012).

Various risk factors have been reported including mater-nal diabetes mellitus, low birth weight, advanced maternal age, exposure to thalidomide, retinoic acid derivatives, and mycophenolate mofetil. There is some association of microtia with autosomal trisomies (18, 21, and 22) and trisomy 13 and 18 mosaicism. Single‐gene disorders, for example SIX1 and EYA1 and chromosomal translocation 6p24, are also reported to be associated with microtia.

Herman Marx (1926) proposed the first and most frequently used classification system for the condition. He divided microtia

97

Table 97.1 Classification of anomalies of external ear. Adapted from Hunter and Yotsuyanagi (2005).

Grade of dysplasia Types

Grade I 1. Enlarged ear2. Anomalies of pinna: cryptotia, protruding ear,

satyr ear, Stahl ear, Darwin’s tubercle, Shell ear, Mozart ear, lop ear

Lop ear is divided into mild and moderate malformation:

1. Mild anomalies: helical folding lies above the Darwin tubercle: (a) hiding helix; and (b) constricted helix type IV A

2. Moderate anomalies: helical folding lies above the Darwin tubercle: (a) absence of helix or cleft in helix; (b) anomalies of lobule; and (c) anomalies of tragus

Grade II 1. Cup ear2. Mini ear

Grade III 1. Microtia (unilateral or bilateral) with external canal atresia

2. Anotia

1168 Bergman’s Comprehensive Encyclopedia of Human Anatomic Variation

Table 97.2 Classifications of microtia. Adapted from Luquetti et al. (2012).

Grade/type Description Grade/degree Description

Herman Marx Classification Weerda Classification

Grade I Auricle is abnormal but all landmarks are identifiable

Grade IFirst‐degree Malformations

Macrotia, prominent ear, and cryptotia;

Scaphoid ear, transverse cleft(coloboma), Stahl ear;

Satyr ear;

Darwin tubercle, defromed tragus and antitragus, helix crus absence;

Lobular deformities: aplastic, hypoplastic and hyperplastic lobe, lobular fixation and lobular cleft;

Deformity of cup ear I, IIa, IIb.

Grade II Auricle is abnormal and few landmarks are identifiable

Grade IISecond‐degree malformations

Deformity of cup ear III;Microtia: hypopastic upper pinna, hypoplastic middle pinna, and hyoplastic or aplastic lower pinna

Grade III Anotia Grade IIIThird‐degree Malformations

Grade III unilateral or bilateral microtia;Anotia

Tanger Classification Hunter Classification

Type I Complete absence of ear (anotia)

MicrotiaFirst‐degree

All normal ear components are present and the median longitudinal length of ear is greater than two standard deviations below the mean

Type II Complete hypoplasia of ear with and without external acoustic meatus atresia (microtia)

MicrotiaSecond‐degree

Presence of few normal ear components and median longitudinal length of ear is greater than two standard deviations below the mean

Type III Hypoplastic middle third of auricle

MicrotiaSecond‐degree

Some auricular structures are present but these structures do not conform to recognized ear component

Type IV Hypoplastic superior third of auricle, cup and lop ear and cryptotia

Anotia Ear is completely absent

Type V Prominent ear

Figure 97.1 Variations of microtia: (a) typical ear; (b–d) first‐degree dysplasia; (e) second‐degree dysplasia; and (f–i) third‐degree dysplasia.

Source: Luquetti et al. (2012). Reproduced with permission from John Wiley & Sons.

into three grades based on identification of auricular land-marks. Rogers (1968) added grade IV microtia (anotia) to the existing Marx classification. Tanger (1978) published a surgi-cal approach‐based classification system, and Weerda (1988) modified both of these systems and developed a new one. His

classification was based on embryological variations and surgi-cal classification as well as other external ear deformities and minor anomalies. Hunter and Yotsuyanagi (2009) recently pub-lished a classification to standardize the terminologies referring to the external ear (Table 97.2).

Chapter 97: Ear 1169

MacrotiaMacrotia is an abnormal enlargement of the pinna (Fig. 97.2): an ear with length for age measurement above the 97th percen-tile. An adult ear has a width range of 3–4.5 cm and length range of 5.5–7 cm, and the term macrotia is used when the ear meas-ures more than these values. Feingold and Bossert (1974) pro-posed a gold standard measurement. The curves were based on the measurements they made of Caucasian children in Boston. According to Feingold and Bossert, the ear grows about 10% of its length and 40% of its height between the ages of 6 and 14 years. The ear can be divided into three parts:1. Upper third: the part of the ear above inferior crus, which

comprises 33% of the total height of the ear.2. Middle third: inferior crus to incisura, which comprises 43%

of the height of the ear.3. Lower third: incisura to the tip, which comprises 23% of the

total height.In true macrotia, the upper third of the ear is most commonly

enlarged.

Protruding earProtruding ear is one of the most common anatomical varia-tions. It is defined as an ear with a >40 degree angle in relation to the mastoid bone (Fig. 97.3). According to Carey (1993), the gap between the mastoid bone and the helix in protruding ear is greater than 2 cm. Driessen et al. (2011) found a sex difference in protrusion of the ear. In males, for an ear to be prominent, the protrusion should be greater than 21.5 mm for the upper or 20.0 mm for the lower part of the ear. In females, the protru-sion in the upper ear should exceed 17.5 mm and the lower ear 15.5 mm. The auricular length is greater in males and correlates with age in both sexes. The most commonly used method to

assess protrusion is to measure the gap between the rim of the helix and a point on the mastoid perpendicular to the helix rim. Any variation in shape or position of the mastoid can influence the measurement; this is the biggest drawback of the method. Another widely used method is to measure the auriculocephalic angle. If this is greater than 30–40 degrees, various authors regard it as indicating protrusion. In the auriculocephalic angle method any variation of temporal bone convexity or soft tissue above the bone can change the measurement, so it is not fool-proof. Smith (1978) described the protruding ear as a result of a developmental defect in the posterior auricular muscle. One role of the posterior auricular muscle is to draw the pinna towards the skull, and dysfunction of this muscle causes the pinna to protrude. According to the author, the protruding pinna should be considered a part of the neuromuscular defect and not artic-ular cartilage dysmorphogenesis. Association of protruding ears with myotonic dystrophy and congenital muscular dystrophy has been frequently reported in the literature. Anencephaly, tri-somy 8 syndromes, 18p syndrome, 4p syndrome, and Langer‐Giedion syndrome are also associated with protruding ears.

CryptotiaIn cryptotia, the upper pole of helix cartilage is buried under the fold of the skin which results in loss of the auriculoce-phalic sulcus (Fig. 97.4). This is more common in the Japanese than the Caucasian population; its incidence in the former is about 1 in 400 births. The term cryptotia was introduced by Sercer (1934). Altmann (1955) used the phrase “pocket ear” for this anomaly. Gosserez and Piers (1959) called it “congen-ital invagination” of external ear. There is no clear pathology underpinning it, although various hypotheses have been pub-lished. Wreden (1879) reported this anomaly and proposed that abnormal insertion of the superior auricular muscle into

Figure 97.2 Macrotia.

Source: Bauer (1997). Reproduced with permission from Elsevier.

Figure 97.3 Protruding ear.

Source: Hunter and Yotsuyanagi (2005). Reproduced with permission from John Wiley & Sons.


the upper part of the helix instead of the eminentia triangularis is the cause. Marx (1926) described this anomaly as a result of pressure from the umbilical cord over the auricle/vascular changes in the auricle. Sercer (1934) attributed it to a cartilage developmental defect. Gosserez and Piers (1959) reported a series of 21 cases. Hirose et al. (1985) conjectured that the cause was a defect in the intrinsic musculature. Hayashi et al. (1993) described familial cases of cryptotia and described its X‐linked inheritance. They also suggested neuromuscular abnormality as a cause of cryptoptia.

Stahl earIn Stahl’s ear, there is an abnormal cartilage fold extension to the helix margin from the crus anthelix through the scaphoid fossa (Fig. 97.5). This abnormality predominantly involves the supe-rior crus of the antihelix. There is also helix narrowing, scaphoid broadening, and superior crus antihelix hypoplasia or absence. In Stahl’s ear, some cases present as an abnormal inferior crus position while in others there is an extra crus, sometimes called a “third crus.” Yamada and Fukuda (1980) published a case series of 38 patients (21 males and 17 females) and classified this anomaly into four subdivisions:1. Posteriosuperior extension of the third crus from the crura

antihelix. The shape of the ridge is sharp.2. Posteriorosuperior extension of the third crus from the crura

antihelix with rounded ridge.3. Posteriorosuperior extension of the third crus, which is wider

and has two ridges.4. Posterioinferior extension of the third crus from the crura

antihelix.In the nineteenth century, Stahl divided auricular variations/

malformations into three subtypes: helix transversus spleni-formis; crus antihelicis trifurcata; and crus superius turgidum. Stahl’s ear comes under the second classification, that is, crus

antihelicis trifurcate. There are various hypotheses regarding the development of this variation but the most widely held is an error in embryonic development during the third month when the helix and scaphoid are formed (Aki et al. 2000).

Shell earIn Shell ear the superior antihelix crus is absent (Fig. 97.6). The inferior crus is horizontal and wider. “Snail ear” and “shell ear” are other names used in the literature (Hunter and Yotsuyanagi 2005).

Question mark earIn cases of question mark ear, the lower third of the ear is affected (Fig. 97.7). It involves the cleft between the helix and

Figure 97.4 Cryptotia.


Figure 97.5 Stahl ear: (a) typical Stahl ear and (b) variant of Stahl ear.


Figure 97.6 Shell ear.



the lobe of the ear. It can also present with a shallow dimple on the skin involving the posterior ear, absence or prominence of the upper helix or ear lobe, and antitragus transposition. It can occur as an isolated anomaly or as part of a syndrome. In this anomaly the scapha is absent and the ear protrudes from the affected site. It is a male‐predominant anomaly with a 2:1 sex ratio and can present as a unilateral or bilateral defect. Its asso-ciation with auriculo‐condylar syndrome (ACS) and its autoso-mal dominant inheritance have been reported. Pan et al. (2010) published a 32‐case series which included 30 sporadic cases and two of familial origin. They divided the ear defect into moderate and severe types depending on the anatomical characteristics. In the moderate type the lobule and inferior part of the helix presented with a cleft, and in the severe type the lobule and infe-rior part of the helix were absent. Question mark ear involves the first and second arches. Auriculo‐condylar syndrome (ACS), Townes‐Brocks syndrome, Treacher‐Collins syndrome, and oculoauriculo‐vertebral spectrum also involve the first and second arches. Question mark ear is closely associated with ACS, which is characterized by the presence of auricular clefts, microstomia, hypoplasia of the mandibular condyle, microg-nathia, temporomandibular joint abnormalities, and round face with prominent cheeks. Masotti et al. (2008) conducted a genome‐wide search and linked ACS to the 1p21.1–q23.3 gene. Due to the occurrence of question mark ear in ACS and its sim-ilar inheritance mode, allelism could be plausible.

Mirror ear/polyotiaPolyotia or mirror ear is characterized by presence of an acces-sory ear (Fig. 97.8). It has a comparable size and can be con-sidered an extra auricle. There is no clear‐cut etiology of this

condition. Abnormal migration of neural crest cells (NCC) has been reported as the potential cause. It can occur as an isolated anomaly or a part of a syndrome complex. Its association with Brachmann‐de Lange syndrome, Treacher‐Collins syndrome and Goldenhar syndrome has been reported in the literature. Lammer (1991) proposed that retinoic acid embryopathy (RAE) is responsible for abnormal migration of NCC. In a retrospec-tive study, he described a case series in which patients exposed to retinoic acid during pregnancy had newborns with external ear defects including partial duplication of the ears.

Mozart earIn Mozart ear, the anterosuperior auricular margin has a bulg-ing appearance. The cavum conchae protrudes convexly and the external auditory meatus has a slit‐like opening (Fig. 97.9). In other words, the superior pinna margin bulges because of the two‐crura fusion of the antihelix and crus helix. The other char-acteristics of this anomaly are a smaller tragus, absent or poorly developed ear lobe, cavum cochae and crus helicus fusion, non‐prominent antihelix lower half, crus helicus with hori-zontal ridge, and absence of the antitragus. In the literature the terms “lower conchal stria” or “convex conchae” are also used. Paton et al. (1986) published an article on Mozart ears. They carried out surveys among the patients attending ENT clinics in Birmingham (1185 patients) and medical clinics in London (1092 patients) and found only two cases. Yamashita et al. (2011) reported a case of a female patient with Mozart ears.

Lop earsLop ear is an anomaly of the superior one‐third of the pinna (Fig. 97.10). It involves over‐folding of the scapha and helix, absence or smaller size of antihelix superior crus, smaller scapha, and an auricle that is shorter in vertical height. In Cau-casian, African‐descent and Japanese populations the reported incidences are 2–5%, 10–15%, and 38%, respectively. Lop ear can occur as an isolated anomaly or as part of an autosomal dominant inherited disorder such as familial blepharophimo-sis, scalp‐ear‐nipple syndrome, oto‐facio‐cervical, tricho‐rhino phalangeal, brachio‐oto‐renal and lacrimal‐auricular‐dental‐digital syndromes, Kabuki syndrome, and Townes‐Brock syn-drome. It can also occur in association with Fraser and Mengel syndrome which exhibits autosomal recessive inheritance, and also in Trisomy 21 and 4q deletion syndrome (Carey et al. 2006).

Davis (1987) described hillock 3 hypoplasia as a major fac-tor in the pathogenesis of lop ears. According to him, hillock 3 hypoplasia results in forward displacement of the helix to bridge the gap and the resultant pull causes the superior one‐third of the pinna to over‐fold. Karmody and Annino (1995) described lop ear as an anomaly of the cartilage. Manigila and Maniglia (1981) ascribed it to failure of unfolding of the helix during the 12–16th weeks of intrauterine life. Carey et al. (2006) reported the cause of transient lop ear to be pressure on the fetal auricle from the brim of the maternal pelvis. Interestingly, in the Japanese population the incidence of lop ear at birth is 38% and

Figure 97.7 Question mark ear.

Source: Pan et al. (2010). Reproduced with permission from Elsevier.


Figure 97.8 Polyotia.

Source: Gore et al. (2006). Reproduced with permission from Elsevier.

Figure 97.9 Mozart ear.

Source: Paton et al. (1986). Reproduced with permission from BMJ Publishing Group.

Figure 97.10 Lop ear: (a) milder; and (b) severe form.



at 1 year of age has decreased to only 6%. This could indicate correction of a transient lop ear initially caused by intrauterine compression.

Hunter and Yotsuyanagi (2005) subclassified lop ear into a milder form and a moderate form. The milder form includes an anomaly limited to helix folding above Darwin’s tubercle. In the moderate form of lop ear, the folding of the helix extends below Darwin’s tubercle.

Upper auricular detachmentIn upper auricular detachment, there is no attachment between the crus helix and the anterior or ascending helix. The root of the helix and the distant lower end are also detached. The only site of attachment is to the mastoid area. In the literature, congenital amniotic bands and absence of mesenchymal fusion among the mandibular and hyoid arch hillocks are described as a potential cause of this anomaly (Hunter and Yotsuyanagi 2005).

Ear lobe indentations/pitsEar lobe pits occur most commonly in patients with Wiedmann‐Beckwith syndrome (WBS). Various terminologies such as dim-ples, creases, pits, and indentations are used in the literature (Fig. 97.11). Irving (1967) published a series of 11 cases and described the occurrence of semi‐horizontal linear grooves in the ear lobe. Kosseff et al. (1972) described the bilateral focal occurrence of 1–2 mm indented areas that were well demar-cated on the posterior helix rims in a patient with WBS. There is no clearly defined cause of this anomaly. Best (1991) suggested

that an infarction or localized degeneration could cause poste-rior helical bits. Embryonic exposure to retinoic acid has also been suggested as a cause.

Darwin’s tubercleDarwin tubercle is a small blunt projection from the helix. Davis (1987) described it as a site of fusion between hillocks 4 and 5. Carey (1993) suggested that a Kossef tubercle persists in embryos up to seven weeks of age; after that it disappears. No association with any syndrome or other anomalies has been reported in the literature (Fig. 97.12).

Cup earsThere is much confusion regarding the difference between cup ears and lop ears. Rogers (1968) described it as a deformity with features of both protruding ears and lop ears. In cup ears the protrusion results from overdevelopment of the concave con-cha. A shorter helix and faulty antihelix are a few of the common features it shares with lop ears. Due to the forward cupping of the lobule, the vertical height of the ear from the superior pole to the lobule bottoms is less than in a normal ear. Peterson and Schminke (1968) published a study of a family with 12 members from five generations with cup‐shaped ears. In addition to cup ears, the proband had Pierre Robin syndrome.

Variations of the auditory meatus

Aural atresiaAural atresia is a congenital anomaly involving failure of devel-opment of the external acoustic meatus. Depending on sever-ity, it can involve the tympanic membranes, middle ear ossicles, mastoid cells, and cochlea. The incidence of this anomaly is

Figure 97.11 (a) Ear pits and (b) indentations. (c) Horizontal lobular grooves in patient with Beckwith‐Weidemann syndrome.


Figure 97.12 Darwin’s tubercle.



1:10,000–20000 live births. It is male‐predominant. The inci-dence of unilateral atresia is 3–5 times higher than bilateral atresia, and in unilateral atresia the right ear is more commonly involved. The anomaly is usually sporadic but an autosomal recessive mode of inheritance is also known. The association of aural atresia with Pierre Robin, CHARGE, Treacher‐Col-lins, Crouzon’s, Goldenhar’s, Mobius, Klippel‐Feil, Fanconi’s, DiGeorge, and VATER syndromes has been reported in the lit-erature. It also coexists with cleft palate, hemifacial microsomia, posterior cranial hypoplasia, hydrocephalus, and genitourinary abnormalities.

There are various classifications of aural atresia (Table 97.3):Altmann (1955) divided atresia into three degrees depending

on severity:1. First‐degree: The external acoustic meatus is mildly deformed,

the tympanic cavity has normal or hypoplastic characteristics, the ossicles are deformed, and the mastoid is well aerated.

2. Second‐degree: This includes intermediate deformities. The external acoustic meatus either ends blindly or is absent, the tympanic cavity is narrow, the ossicles are either deformed or fixed, and the mastoid cells are poorly pneumatized.

3. Third‐degree: This includes severe deformities. The external acoustic meatus is absent, the middle ear is hypoplastic, the ossicles are deformed, and there is no mastoid cell pneumati-zation.De la Cruz and Teufert (2010) modified Altmann’s classifica-

tion into minor and major malformations:• Minor malformations: Mastoid cell pneumatization is nor-

mal, inner ear is normal, oval window footplate, and normal facial nerve course in relationship to it are found.

• Major malformation: Mastoid cell has poor pneumatization, oval window/footplate is either abnormal or absent, facial nerve course in relationship to the footplate and inner ear are abnormal.Schuknecht (1989) introduced another classification based

on surgical techniques and intraoperative findings:• Type A: Atresia involves cartilaginous external acoustic

meatus, corrected with meatoplasty.• Type B: Cartilaginous and bony parts of external acoustic

meatus are narrow, with small tympanic membrane and mildly deformed malleus and incus. Correction involves canalplasty with or without ossicular chain reconstruction.

• Type C: Complete atresia of the external acoustic meatus. Mastoid cell and middle ear have normal pneumatization.

• Type D: Complete atresia of external acoustic meatus with poorly pneumatized middle ear.Jahrsdoerfer et al. (1992) introduced a point‐based classifi-

cation system using radiological findings of the temporal bone obtained from high resolution CT scans. A total of 10 points can be awarded on the basis of anatomical findings. Open oval window, normal middle ear space, normal course of facial nerve, presence of malleus‐incus complex, well‐pneuma-tized mastoid cells, normal incus–stapes connection, normal round window, and normal appearance of external ear are each awarded one point. Presence of stapes scores two points. A score of 10 = excellent, 9 = very good, 8 = good, 7 = fair, 6 = marginal and less than 5 counts as poor post‐surgical prog-nosis. A score of 8 corresponds to an 80% success rate in hear-ing restoration to normal or near normal level. A score of less than 5 is not considered for surgical intervention. Siegert et al.

Table 97.3 Classifications of aural atresia. Data from Altmann (1995) and De la Cruz and Teufert (2010).

Altman Classification De la Cruz Classification

Degree Description Malformation Description

First External acoustic meatus has mild deformity, tympanic cavity with normal or hypoplastic characteristics, ossicles deformity and well aerated mastoid

Minor Mastoid cell has normal pneumatization, normal inner ear, oval window footplate and normal facial nerve course in relationship to the footplate

Second Includes intermediate deformities. External acoustic meatus either ends blindly or is absent, tympanic cavity is narrow, ossicles are either deformed or fixed, and poorly pneumatized mastoid cells

Major Mastoid cell has poor pneumatization, oval window/footplate is either abnormal or absent, abnormal facial nerve course in relationship to the footplate and abnormal inner ear

Third Includes severe deformities. External acoustic meatus is absent, hypoplasia of middle ear, deformed ossicles, and absence of mastoid cell pneumatization

– –

Schuknecht Classification

Type Description

A Atresia involves cartilaginous external acoustic meatus, corrected with meatoplasty

B Cartilaginous and bony part of external acoustic meatus is narrow, small tympanic membrane and mildly deformed malleus and incus. Correction involves canalplasty with or without ossicular chain reconstruction procedure

C Complete atresia of external acoustic meatus. Mastoid cell and middle ear has normal pneumatization

D Complete atresia of external acoustic meatus with poorly pneumatized middle ear


(1996) introduced a more extensive 28‐point‐based prognostic rating scale. In a patient with bilateral malformation, a score greater than or equal to 15 is recommended for middle ear reconstruction and in a unilateral malformation the cutoff is 20 points (Table 97.4).

Colman (1974) classified aural atresia patients with conduc-tive hearing loss into three groups:• Group I: Consists of minor anomalies, meatus is narrow but

open, ossicular fixation involves stapes.• Group II: Pinna is deformed, external meatus is completely

closed, and middle ear has complex abnormalities.• Group III: Severe deformity of the pinna and the middle ear.

Mastoid cell pneumatization is absent and there are cochlear deformities.Group I had excellent post‐surgical results and group II had

variable results. Group III had poor outcomes.

Variations of the internal auditory canal

Narrow internal auditory canalNarrowing of the internal auditory canal coexists with anom-alies of the external middle and inner ear. The normal diam-eter of the internal auditory is 4 mm with a range of 2–8 mm. The canal is considered narrow when the diameter is less than 2 mm. It contributes to 12% of temporal bone defects. Vesti-bulocochlear nerve has a trophic influence on the growth of the internal auditory canal and hypoplasia or aplasia of the vestibulocochlear nerve results in abnormal development of the canal and therefore causes narrowing. Another hypothe-sis is that a mechanical obstruction caused by bony stenosis results in aplasia or hypoplasia of the vestibulocochlear nerve. This hypothesis is less likely to be the cause because most cases reported in the literature have normal facial function (Demir et al. 2005).

Duplication of internal auditory canalDuplication of the internal auditory canal is a rare anomaly. It mostly occurs unilaterally, but bilateral occurrences have been reported. According to Weissman et al. (1991), the facioacous-tic primordium separates abnormally in this condition, which causes the fibers of the vestibulocochlear and facial nerves to follow aberrant courses and results in duplication. According to Curtin and May (1986), chondrification of the internal audi-tory canal’s mesenchymal precursor is delayed, which causes the facial nerve to follow a course away from the vestibulocochlear nerve. The wide gap between the two nerves results in abnormal ossification and therefore duplication.

Variations of the facial nerve

The two most common facial nerve anatomical variations encountered in the middle ear are displacement of the facial nerve and absence of the bony sheath due to dehiscence or absence of the fallopian canal. Dehiscence of the fallopian canal exposes the facial nerve due to lack of the bony sheath. The nerve has only a thin layer of fibrous membrane and is vulnerable to herniation into the tympanic cavity. Fallopian canal dehiscence occurs during ontogenetic development. During this period the ossification process closes the facial nerve sulcus. Malformation of Reichert’s cartilage precludes closure of the sulcus and results in dehiscence or complete absence of the bony canal. There are various hypothetical explanations of the facial nerve displace-ment. One is based on the failure of late fusion between the second brachial arch and otic capsule, which prevents anterior migration of the facial nerve (Al‐Mazrou et al. 2003).

Exposure of the facial nerve in the middle ear can be divided into three degrees:• First‐degree: Severe fallopian canal dehiscence without facial

nerve displacement.• Second‐degree: The facial nerve is completely herniated from

the fallopian canal and lies on the oval window with minimal or no attachment to the stapes.

• Third‐degree: The facial nerve lies over the promontory.Rohrt and Lorentzen (1976) divided the facial nerve displace-

ment into four groups (Table 97.5):• Group I: Stapes footplate is partially obliterated by the facial

nerve.• Group II: Facial nerve bifurcation.• Group III: Oval window and stapes are deformed and the

facial nerve lies on the footplate.• Group IV: Facial nerve lies on the promontory.

Jahrsdoerfer (1981) published a case series of facial nerve anomalies and divided them into three categories based on ana-tomical variation and ease of surgical correction (Table 97.5): (1) facial nerve overlies the stapes and oval window; (2) dis-placement of the facial nerve along with presence of the oval window; or (3) displacement of the facial nerve along with absence of the oval window.

Table 97.4 Twenty‐eight point‐based prognostic scale for aural atresia surgical outcome. Adapted from Siegert et al. (1996).

Entity Points

External auditory meatus: bone atresia; soft tissue atresia; normal

0; 1; 2

Mastoid cell aeration: absent; fair; excellent 0; 1; 2

Middle ear space: absent; medium; large 0; 1; 2

Middle ear aeration: absent; minor; major 0; 1; 2

Facial nerve: major variation; minor variation; normal 0; 2; 4

Vessels: major variation; minor variation; normal 0; 1; 2

Malleus and incus: absent; deformed; normal 0; 1; 2

Stapes: absent; deformed; normal 0; 2; 4

Oval window: obliterated; open 0; 4

Round window: obliterated; open 0; 4


Vascular variations

Vascular variations of the middle ear are of great surgical impor-tance. The most commonly encountered include an aberrant internal carotid artery, dehiscence of the carotid artery canal, a high jugular bulb, dehiscence of the high jugular bulb, and a persistent stapedial artery. The incidence of aberrant internal carotid artery is less than 1%, dehiscence of high jugular bulb has an incidence of 1%, and the incidence of high jugular bulb ranges over 6–22%.

An aberrant internal carotid artery is a very important vas-cular anomaly in terms of surgical significance as bleeding from it can be life‐threatening. It is caused by agenesis of the first embryonic segment of the internal carotid artery. It can pres-ent as pulsatile tinnitus, hearing loss, or serous otitis media. On a high‐resolution CT scan it presents as a retrotympanic mass with enlarged inferior tympanic canaliculus, absence of bony plate and the vertical segment of the internal carotid artery canal. Various hypotheses regarding the cause of this anomaly have been presented in the literature. A persistent stapedial artery during embryogenesis can cause traction on the internal carotid artery and displace it into the tympanic cavity, and the displacement can also be caused by bony carotid canal agenesis.

A high jugular bulb is the most common anomaly in the mid-dle ear. It is mostly unilateral with a right side to left side ratio of 2:1, but bilateral cases have been reported. High jugular bulbs can be medial or lateral. A lateral high jugular bulb protrudes into the middle ear cavity and a medial jugular bulb lies superior and medial to the cochlea. The condition usually presents as a pulsatile tinnitus.

Dehiscent jugular bulb, as the name suggests, is dehiscence of the sigmoid plate and jugular bulb that extends superolaterally into the middle ear cavity. It has great surgical importance as it has only a thin layer of mucosa and could cause catastrophic bleeding in the event of accidental intraoperative injury. It can present as a bluish discolored mass behind the tympanic cavity.

A persistent stapedial artery (PSA) is a rare vascular anomaly of the middle ear. The incidence of PSA is 0.2–4.8 per thousand adults. It usually presents as pulsatile tinnitus and conductive hearing loss due to ankylosis of the stapes. It can also present as sensorineural hearing loss by eroding

against the otic capsule. It can occur as an isolated anomaly or in combination with an aberrant internal carotid artery and stapes and facial nerve anomalies. Association with Paget’s disease, thalidomide exposure, otosclerosis and trisomy 13 has been reported in the literature. Normally, the stapedial artery originates from the hyoid artery during the fifth week of embryonic life. From its origin it travels intracranially via the stapes obturator foramen. It divides into dorsal and ventral branches. The middle meningeal artery arises from its dorsal branch. The ventral branch gives rise to the infraorbital and inferior alveolar arteries extracranially after its exit via the foramen spinosum. The ventral branches further anastomose with the developing external carotid artery. During the tenth week of gestation, the stapedial artery degenerates through reversal of blood flow at the foramen spinosum and separates the internal from the external carotid artery. The presence of a stapedial artery in postnatal life indicates the absence of its passage through the foramen spinosusm so the anastomosis between the internal carotid and middle meningeal arteries persists and results in PSA (Lau et al. 2004).

Variations of the round and oval windows

Round window atresia mostly occurs as part of a syndrome complex, for example mandibulofacial dysostosis, cretinism, stapes ankylosis, mondini anomaly, and extensive otosclerosis. Its occurrence as an isolated anomaly has also been reported in the literature. It can present both unilaterally and bilaterally. The round window develops during the eleventh week of gestation. It first appears as an embryonic connective tissue condensation between the fossula of the cochlear fenestra and the scala tym-pani. During otic capsule ossification, the presence of a carti-lage ring prevents ossification of the round window opening. In the absence of the cartilaginous ring, ossification obliterates the opening and causes congenital atresia. In congenital absence of the oval window there is no connection between the otic cap-sule bone and the vestibule. There is complete closure of the oval window by a thick bony plate or a concentric narrowing. The foot plate and anular ligament are absent (de Alarcon et al. 2007).

Table 97.5 Classification of facial nerve’s variations in the middle ear. Data from Rohrt and Lorentzen (1976) and Jahrsdoerfer (1981).

Rohrt Classification Jahrsdoerfer Classification

Group Description Category Description

I Stapes footplate is partially obliterated by the facial nerve I Facial nerve overlies on the stapes and oval window

II Facial nerve bifurcation II Displacement of facial nerve along with presence of oval window

III Oval window and Stapes are deformed and facial nerve lies on the footplate

III Displacement of facial nerve along with absence of oval window

IV Facial nerve lies on the promontory – –


Variations of the Eustachian tube

Anomalies of the Eustachian tube (ET) are not common and mostly occur as part of a syndrome complex. Anatomical var-iations can involve the bony or more commonly the cartilagi-nous part. ET anomalies are reported to be associated with cleft palate deformities, Down syndrome, the oculoauriculoverte-bral spectrum, and Klippel‐Feil syndrome. The normal width of the ET is 1.5 mm; enlargement of its bony portion is rare. The oculoauriculovertebral spectrum is characterized by man-dibular hypoplasia, vertebral anomalies, microtia and epibulbar dermoids and lipodermoids. Haginomori et al. (2003) reported a case of enlargement of the bony part of the Eustachian tube in a patient with oculoauriculovertebra spectrum; the diameter of the ET was 7 mm. Jovankovičová et al. (2012) described a case of Klippel‐Feil syndrome with an enlarged right‐sided ET with a width of 5.5 mm.

Variations of the inner ear

There are various classifications to describe inner ear malforma-tions. The most commonly used classification was introduced by Jackler et al. (1987) and was based on radiographic appearances. This was further modified by Marangos (2002) and Sennaroglu and Saatci (2002). Jackler et al. divided the malformations into two categories, A and B. Category A entailed congenital anom-alies with an absent or malformed cochlea, and category B entailed congenital malformations with a normal cochlea.

The radiological classification was based on radiographic appearances with the following size reference ranges: the coch-lea was considered small if it was less than 7 mm measured vertically (normal size 8–10 mm); and a vestibule greater than 5 mm in vertical measurement was considered enlarged. The intraosseous portion of the vestibular aqueduct with diameter greater than 2 mm was categorized as enlarged. Internal audi-tory canals with greater than 10 mm vertical diameter and less than 3 mm vertical diameter were considered enlarged and nar-rowed, respectively (Table 97.6).

Marangos (2002) modified Jackler’s classification and divided inner ear variations into four categories. Category A entailed malformations with deficient embryonic development, cate-gory B included aberrant embryonic development, category C included isolated malformations, and category D included syn-dromic malformations (Table 97.7).

Sennaroglu and Saatci (2002) further categorized cochle-ovestibular malformations into five subdivisions based on cochlear, vestibular, semicircular canal, internal auditory canal, and vestibular cochlear aqueduct defects. They also pro-posed a categorization of cochlear malformations based on embryonic developmental arrest: Michel deformity caused by developmental arrest at the third week, aplasia of the cochlea by late third week arrest, common cavity malformation dur-ing fourth week arrest, cystic cochleovestibular malformation/

Table 97.6 Classification of inner ear anomalies. Adapted from Jackler et al. (1987).

Category A (aplasia or cochlear malformations)

Complete aplasia of labyrinth Absence of inner ear development

Aplasia of cochlea Deveopmental absence of cochlea, vestibule and semicircular canals are normal or malformed

Hypoplastic cochlea Small cochlea, vestibule and semicircular canal are normal or malformed

Incoplete partition of cochlea Cochlea small and incomplete, vestibule and semicircular canals are normal or malformed

Common cavity Common cavity formation between cochlea and vestibule with absence of internal architecture, semicircular canal is either normal or deformed.

Category B (normal cochlea)

Vestibule and lateral semicircular canal dysplasia

Vestibule is enlarged and lateral. Semicircular canal is short and dilated.

Enlarged vestibular aqueduct Vestibular aqueduct is enlarged with normal semicircular canal.

Table 97.7 Classification of inner ear anomalies. Adapted from Marangos (2002).

Category Types

A: incomplete embryonic development

Michel deformity/completely aplastic inner ear; common cavity; cochlear aplasia or hypoplasia with normal development of posterior layrinth; posterior labyrinth aplasia or hypoplasia with normal development of cochlea; completely hypoplastic labyrinth; dysplasia mondini type

B: aberrant embryonic development

Vestibular aqueduct enlargement; internal auditory canal narrowing; longer lengthed crista transeversa; tripartitus of internal auditory canal; cochlea and meatus incompletely separated

C: hereditary malformations of isolated origin

Hearing loss of X‐linked origin

Category D Malformations with syndromic association

incomplete partition type I by fifth week arrest, hypoplasia of the cochlea during sixth week arrest, Mondini deformity/ incomplete partition type II by seventh week arrest, and nor-mal development (Table 97.8).

Variations of the cochleaAccording to Sennaroglu and Saatci (2002), cochlear malfor-mations can be subdivided into Michel anomaly/complete


labyrinthine aplasia, cochlear aplasia, common cavity, cochlear hypoplasia, and incomplete partition types I and II on the basis of anatomical features and the time of arrest of development during intrauterine life.

Michel anomaly/complete labyrinthine aplasiaA Michel anomaly is characterized by complete aplasia of the labyrinthine structure, where there is complete absence of inner ear structure. It accounts for 1% of the congenital anomalies of the inner ear. It is generally bilateral but unilateral cases have also been reported. Congenital absence of inner ear structure is due to otic placode arrest before the third week of embry-onic development. Michel (1863) described this anomaly in an autopsy report of a 12‐year‐old male with the bilateral defect.

Cochlear aplasiaIn this anomaly there is complete absence of the cochlea. The vestibule and semicircular canal can be normal, dilated, or hypoplastic. It can occur as a bilateral or unilateral anomaly. On examination of the anterior part of the internal auditory canal, it presents as a dense otic bone. The absence of the cochlea results in anterior displacement of the labyrinthine segment of the facial canal from its usual course. This anomaly should be differentiated from common cavity and cochlear ossification. In cochlear ossification there is bulge in the promontory caused by the basal turn of the cochlea, which is absent in cochlear aplasia. It can be differentiated from common cavity by the absence of a cavity in the cochlear location, anteroinferior location of the internal auditory canal in relation to the malformed cavity, and bony sclerosis at the location of the absent cochlea (Sennaroglu and Saatci 2002).

Common cavityCommon cavity malformation results from arrested devel-opment during the fourth week of intrauterine life. In this

anomaly there is no differentiation between the cochlea and vestibule and a common cavity forms. The internal auditory canal dimensions are abnormal and vary among patients, as described by Sennaroglu and Saatci (2002). Enlarged internal auditory canals were found in patients with large common cav-ities, and small dimensions were present in patients with small common cavities.

Incomplete partition type IThis anomaly, also known as cystic cochleovestibular malfor-mation, is characterized by cystic dilatation of the cochlea and vestibule. The cochlea is empty. The cochlea and vestibule have normal dimensions but lack internal structures. The cochlea lacks the modiolus and cribriform areas, so the cystic cavity is empty. The cause is arrest of development at the fifth week of intrauterine life (Sennaroglu and Saatci 2002).

Cochleovestibular hypoplasiaThis anomaly is believed to result from developmental arrest at the sixth week of intrauterine life. The cochlea is hypoplastic/smaller in size and the vestibule is either hypoplastic or absent. The dimensions of the internal auditory canal vary from normal to smaller (Sennaroglu and Saatci 2002).

Incomplete partition type IIThis anomaly, also known as Mondini malformation, results from developmental arrest later than type I because the coch-lea and vestibule have normal size and their internal struc-tures are better developed. The vestibule has minimal dila-tation. It contributes to 50% of cochlear deformities, and is believed to be a result of arrested development at the seventh week of intrauterine life. The cochlea has 1.5 turns and its apex between the middle and apical turns has an interscalar defect. The basal part of the modiolus is developed in the cochlea so there are more nerve endings and spiral ganglia than in the incomplete partition type I malformation (Sennaroglu and Saatci 2002).

Variations of the semicircular canalAplasia of semicircular canalAplasia of the semicircular canal can present as an isolated anomaly or part of a syndrome. The patient usually presents with sensorineural hearing loss. It is a common associated anomaly in patients with CHARGE syndrome. The associa-tion of aplastic semicircular canals with CHARGE syndrome was first reported by Guyot et al. (1987) in a study based on histopathological findings of temporal bones. Its association with Noonan syndrome has also been reported. Superior semicircular canal development is usually complete at the 19th week of intrauterine life and the horizontal semicircular canal by 22 weeks. The semicircular canal can develop any time up to 24 weeks. In Noonan syndrome, patients usually present with mixed‐type bilateral severe hearing loss. The lit-erature reports 20% low‐frequency and 50% high‐frequency hearing loss.

Table 97.8 Classification of inner ear anomalies. Adapted from Sennaroglu and Saatci (2002).

Category Types

Malformations of cochlea Michel deformity: complete aplasia of inner ear structures

Aplasia of cochlea: complete absence of cochlea

Common cavity malformation

Hypoplastic cochlea

Incomplete partition I; II

Malformations of vestibule Hypoplastic, dilated or absent vestibule, common cavity and Michel deformity

Malformations of semicircular canal

Absence, hypoplasia or enlargement of semicircular canal

Malformations of internal auditory canal

Absence, narrowing or enlargement of internal auditory canal

Malformations of vestibular and cochlear aqueduct

Vestibular and cochlear aqueduct, either normal or enlarged


Variations of the vestibular and cochlear aqueduct

Enlargement of vestibular aqueduct (VA)This is the most common radiologically detected anomaly in children affected by sensorineural hearing loss. It is a bilat-eral anomaly with normal to mild impairment of hearing in childhood and it deteriorates with age. Almost 40% of patients develop sensory hearing loss. Valvassori and Clemis (1978) defined the enlarged VA using hypocycloidal polytomogra-phy. According to them the aqueduct should have dimensions greater than 1.5 mm at the midpoint.

Arenberg et al. (1984) first proposed a classification of the VA on the basis of radiological findings. They divided the VA into five types (Table 97.9): type I, the VA measures 1–2 mm in the distal one‐third of its course; type II measures less than 1 mm in the distal two‐thirds of the aqueduct course; type III VA is greater than 2 mm in the distal one‐third and in close proximity to the external aperture; in type IV the external aperture meas-ures 1–2 mm; type V lacks an external aperture.

Dewan et al. (2009) recently proposed new “Cincinati crite-ria” based on CT findings from children with normal hearing. According to these criteria, a vestibular aqueduct with a 1.0 mm midpoint and 2.0 mm opercular width, greater than the 95 per-centile, is regarded as enlarged. They compared the Cincinnati criteria with the Valvassori criteria. According to their study, the Cincinnati criteria identified enlargement of the vestibular aqueduct in 44% patients and the Valvassori criteria identified it in only 16%. Among those patients, 45% had unilateral and 55% bilateral anomaly with the Cincinnati criteria, and 64% were unilaterally affected and 36% bilaterally with the Valvassori cri-teria. According to Dewan et al. (2009), the Cincinnati criteria were superior to the Valvassori criteria in identifying patients with enlargement of the vestibular aqueduct.

Enlargement of cochlear aqueductControversy exists regarding the existence of enlargement of the cochlear aqueduct (CA). Jackler and De la Cruz (1993) published a study based on the CT appearance of the CA. They divided the CA into four parts: (1) the lateral orifice segment, which has a narrow bony aqueduct opening into the cochlear

basal turn; (2) the segment of the labyrinthine capsule with the CA running medially through it; (3) petrous apex segment; and (4) medial orifice segment.

According to the study, the CA diameter is not consistent and is cochlear‐segment specific. The petrous and labyrinthine seg-ments with diameters up to 2 mm were considered normal by Jackler and De la Cruz (1993). The median orifice segment has a variable diameter in the range 0–11 mm with mean 4.5 mm. Migi-rov and Kronenberg (2005) published a classification of the coch-lear aqueduct based on CT findings (Table 97.10). They divided the CA into four types: (I) basal turn of cochlea and its opening into subarachnoid space is clearly visible; (II) cochlear aqueduct defined in the medial two‐thirds; (III) only the medial third and/or external aperture can be defined; and (IV) undefined CA.

In the literature, Mukherji et al. (1998) described a case of enlargement of the cochlear aqueduct in an 18‐month‐old patient with severe bilateral hearing loss. The mid‐portion diam-eter was 1.2 mm and was considered enlarged. To justify their findings, the author examined 50 temporal bones radiologically using 1‐mm‐thick contiguous axial CT sections. The diameter of the mid‐otic segment of the CA was 0.56±0.26 mm. Stimmer (2010) published a report of radiological findings from 400 tem-poral bones using spiral CT. A diameter greater than 1 mm in the whole otic capsule segment was considered enlarged. How-ever, they found no diameter greater than 1 mm.

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Table 97.9 Classification of vestibular aqueduct. Adapted from Arenberg et al. (1984).

Type Description

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Table 97.10 Classification of cochlear aqueduct based on CT findings. Adapted from Migirov and Kronenberg (2005).

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