Embryologic

Microtia and External Auditory Canal Dysplasias Microtia, meaning a small auricle, is more common in Navajo and Japanese populations as well as in fetuses exposed to thalidomide and retinoic acid.⁸Microtia has three degrees of severity, according to the Weerda classi- fication:⁹

• First degree: Microtia, prominent ear, pocket ear, absence of the upper helix, absence of the tragus, clefts, lobular deformities, and cup ear deformities type 1 and 2

• Second degree: Dysplasia as a cup ear deformity type 3 and mini-ear

• Third degree: Absence (i.e., anotia) of a normal auricular structure (unilateral or bilateral), or severely dysplastic ears displaced inferiorly due to incomplete ascension from the neck

In a study by Mayer et al, one third of patients had first- or second-degree microtia, and two thirds had third- degree microtia. Seventy-five percent of patients with mild microtia have associated bony or cartilaginous EAC stenosis, and 75% of those with major microtia exhibit EAC atresia.¹⁰

Maldevelopment of the first brachial arch affecting the EAC can occur syndromically or nonsyndromically and

can manifest as EAC atresia or stenosis as well as duplica- tion anomalies, including cysts, sinuses, and fistulas. These anomalies rarely occur together, but have been reported to coexist with one another occasionally.¹¹EAC atresia occurs in 1 out of 10,000 births and more commonly involves the lateral membranous or fibrocartilaginous portion of the EAC than its bony portion. EAC atresia may be associated with deletions in 18q, and 66% of individuals with these deletions have congenital aural atresia or EAC stenosis.¹²These anomalies may also be seen in Goldenhar, Treacher Collins, Pfeiffer, and Rasmussen syndromes.¹³ On physical examination, the right ear is more frequently affected, and patients have a conductive hearing loss.

Many of the severe cases may have a mixed hearing loss due to associated inner ear malformations. Because the EAC continues to grow during the first 2 years of life, the severity of the atresia may change during that time.

Patients with EAC stenosis or atresia usually present prior to discharge from the newborn nursery because of either an obvious visible deformity of the pinna or failure on a newborn hearing screening examination (Fig. 2.2). There is a three-stage grading system for severity for EAC atresia, as follows:¹⁴

1. Mild EAC atresia: Normal auricle, minimal ossicular deformity, and a normal middle ear cavity

2. Moderate EAC atresia: Small rudimentary pinna, small middle ear cavity, severely deformed ossicles, and an aberrant course of the seventh cranial nerve (Fig. 2.2) 3. Severe EAC atresia: Absent auricle and only a small

cleft for the middle ear cavity with absent ossicles.

This severe form can also have inner ear deformities.

Chapter 2 The External Auditory Canal and Pinna

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Fig. 2.1 Axial computed tomography scan shows incidentally found large bilateral preauricular cysts. These cysts may become sympto- matic due to infection; however, many small ones remain clinically silent throughout the life of the patient.

Fig. 2.2 Lateral patient photograph shows microtia with deformed residual pinna and atresia of the external auditory canal. (See Color Plate Fig. 2.2.)

There is also a classification by location and extent of severity for EAC atresia, as follows:¹⁵

• Type A (meatal): Fibrocartilaginous only with a small TM

• Type B (partial): Fibrocartilaginous and osseous. The malleus may be fixed, or the manubrium may be short or curved

• Type C (total): The EAC is absent, and there is a bony atretic plate with a normal-size middle ear cavity. The malleus is usually fused to the lateral wall.

• Type D (hypopneumatic total): The middle ear cavity is small, and there is little or no mastoid pneumatization.

The facial nerve is aberrant (common form with mandibulofacial dysostosis).

Nonsyndromic causes of EAC stenosis and atresia are due to failure of canalization. This failure can be com- plete, resulting in atresia, or incomplete, resulting in stenosis (Fig. 2.3). It is well known that severe microtia is often seen with EAC atresia, whereas milder microtia is typically seen with EAC stenosis (Fig. 2.4). Associated dys- plasia of the ossicles occurs in 98% of patients and in 72%

of them may involve all of the ossicles, including the stapes. Accompanying round window atresia is found in 6% of patients and labyrinthine malformations in 13%, but

Fig. 2.3 (A,B)Computed tomography (CT) three-dimensional reformations in a patient with nonsyndromic bilateral external auditory canal (EAC) atresia. In nonsyndromic EAC atresia, the zygomatic arch and mandible are normally formed, whereas they may be hypoplastic or even absent in syndromic EAC atresia. (C)Coronal CT view shows a thin atresia plate, small middle ear cavity, absent ossicles, and soft tissue filling the epitympanic space.

A

C

B

not atresia of the oval window.^10,16 Common ossicular abnormalities include a short or absent manubrium of the malleus, a more pronounced deformity of the head of the malleus than that of the incus, and misshapen stapes crura. Ossicular fusion is seen in 54% of EAC atresia patients and most commonly involves the malleoincudal joint (76%), followed by fusion of the ossicles to the atresia plate.

The atresia plate may be bony or membranous (soft tissue) and of variable thickness (Fig. 2.5). Also, the middle

ear cavity may be small (68%), and the facial nerve may be displaced.^17,18Less commonly, accessory ossicles can be seen with a type 2 first branchial cleft anomaly.¹⁹ The association of incus and malleus abnormalities with EAC stenosis/atresia occurs due to the common (i.e., branchial) embryologic origin of all of the ossicles except for the stapes footplate. EAC atresia and mallear manubrium development are related, a finding that has been substan- tiated in a knockout mouse model.²⁰Also associated with microtia and EAC atresia are poor pneumatization of the

Chapter 2 The External Auditory Canal and Pinna

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Fig. 2.4 (A)Coronal computed tomography (CT) scan shows severe right-sided soft tissue and distal bony external auditory canal stenosis.

The long process of the incus is mildly deformed but not fused. The size

of the middle ear cavity is normal. (B)On the left, CT shows similar findings in this patient with bilateral microtias.

Fig. 2.5 (A)Coronal computed tomography scan shows right-sided membranous atresia (note absence of bony atresia plate). The malleus and incus are deformed and fused laterally. The middle ear cavity is

slightly small. (B)On the left side, similar findings are seen. The deformed incus is laterally fused.

A B

A B

mastoid, mandibular condyle dysplasia, zygomatic arch defects (50%), eustachian tube dysplasia (20 to 40%), ten- sor tympani muscle hypoplasia (20 to 40%), oval window absence (33%), labyrinthine dysplasia (13%), and/or round window absence (6%). Associated hypoplasia or aplasia of the internal carotid artery is rare.¹⁰There can be associ- ated CH of the middle ear medial to the atresia plate.

More commonly, CH can develop in the EAC medial to a stenosis (Fig. 2.6). The presence of a CH correlates with smaller EAC size, so that the rate of CH is 50% if the EAC is 4 mm or less in diameter.²¹

Of the syndromes resulting in microtia and EAC atresia, Goldenhar syndrome or hemifacial microsomia is the most common and is also the second most common cra- niofacial anomaly after cleft lip and palate. There are four major components to Goldenhar syndrome: deformity of the auricle, EAC atresia, malformation of the tympanic cavity, and ossicular abnormalities causing conductive hearing loss. Occasionally, there is also sensorineural hearing loss due to stria vascularis and semicircular canal or cochlear abnormalities as well as hypoplastic or atretic oval window.^21,22Pfeiffer syndrome is another cause of EAC stenosis/atresia that results in moderate to severe conductive or mixed hearing loss in patients with cranio- facial abnormalities. In addition to the stenosis and/or atresia of the EAC, there is hypoplasia of the middle ear cavity and occasionally hypoplastic ossicles. Typically, the inner ear anatomy is normal, but middle ear effusions are frequently seen. Therefore, when Pfeiffer syndrome patients receive CT for craniofacial anomalies, examina- tion of the temporal bones should also be performed.²³ Treacher Collins syndrome is an autosomal dominant genetic disorder that is also associated with temporal bone abnormalities. Eighty-five percent of these patients

present with bilateral microtia as well as bilateral abnor- malities of the EAC, TM, ossicles, and middle ear cavity.

These patients will also have midface hypoplasia and micrognathia.^24,25

Pierre Robin syndrome (also known as Pierre Robin sequence) demonstrates retrognathia, glossoptosis, and bilateral cleft palate, as well as ear abnormalities. The ear abnormalities include an abnormal pinna and ossicles, as well as abnormal stapes footplates in 50% of patients.

Aplasia of the lateral semicircular canals (LSCCs), large vestibular aqueducts, and unusually large otoconia are also seen, but not EAC atresia or stenosis.²⁶Because the middle ear arises from the branchial arches, whereas the inner ear does not, labyrinthine abnormalities such as aplasia and partitioning deficiencies are typically not associated with microtia and EAC atresia/stenosis.

When we interpret CT studies of the temporal bones performed in patients with congenital abnormalities, our report addresses the following:

• Extent of EAC atresia and its nature (membranous, bony, or a combination of both)

• Thickness of the atresia plate

• Amount of mastoid pneumatization

• Normal or abnormal middle cranial fossa level (especially if too low)

• Temporomandibular joint location

• Presence or absence of CH (Fig. 2.7)

• Ossicular fusion—incudomallear and incudostapedial joint maintenance, and if the ossicles are fused to the atresia plate (Fig. 2.8). (Rotation of the long incus process resulting in an obtuse angle to the lenticular process and the incudomallear and incudostapedial joints being visible on the same axial slice should also be mentioned.) Fig. 2.6 (A)Axial computed tomography (CT) scan shows bone stenosis

of the medial external auditory canal (EAC) with a small soft tissue mass medial, proven to be a cholesteatoma. (B)Axial CT in a different patient

shows bone stenosis of the lateral aspect of the EAC with a large soft tissue mass medially, also proven to be a cholesteatoma.

A B

• Stapes present, dysplastic, or absent (may be useful information if a prosthesis placement is required)

• Size of the oval window (normal size is 2 mm in vertical diameter)^27,28

• Size of the middle ear cavity in all three axes (if 3 mm in width from the lateral margin to the cochlear promontory, surgery may be precluded)²⁸

• Inner ear structures and size of the internal auditory canal (IAC; rarely affected with EAC dysplasia, but if

abnormal may exclude surgical intervention. If the IAC is small, there can be associated cochlear nerve defi- ciency, but deficiency of the cochlear nerve can also be present with a normal-size IAC, and MRI may be indi- cated to assess the status of the cochlear nerve).^29,30

• Course of the facial nerve with special attention to its horizontal portion in the middle ear and its descend- ing portion (location of the stylomastoid foramen) (Fig. 2.9)

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Fig. 2.7 (A)Three-dimensional computed tomography (CT) surface rendering in a patient with hemifacial microsomia shows an absent external auditory canal, a hypoplastic zygomatic arch, and a thin, small vertical mandibular ramus. (B)In a different patient also with hemifacial microsoma, CT surface rendering of bone shows an absent EAC, a partially absent zygomatic arch, and a hypoplastic ipsilateral mandible.

(C)In the same patient, CT surface rendering of skin shows hypoplasia of the right side of the face and an absent pinna on that side. (See Color Plate Fig. 2.7.)

A

C

B

Surgical reconstruction for auricular and EAC atresia are considered separately. Usually, microtia is a cosmetic procedure that is undertaken prior to entering grade school. A variety of approaches and materials have been used, but currently autogenous rib grafting using a mul- tistage operation produces excellent results when per- formed by a highly experienced surgeon. Others have used alloplastic materials with very good results as well.

The creation of an EAC with an intact conductive hearing mechanism usually follows the auricular surgery so there is no interference with the healing of the skin flaps and the implanted framework. EAC reconstruction is undertaken either to improve hearing or when CH is present. Thus, bilateral involvement represents a clear indication for surgical intervention. Following early identification, these children are fit with a bone conduc- tion hearing aid to ensure normal auditory receptive abilities prior to surgical intervention. With this device, speech and language acquisition usually proceeds nor- mally. Atresiaplasty in unilateral cases is reserved for those patients where the anatomy is favorable, the fam- ily expectations are appropriate, and the child is very cooperative. Favorable anatomy is generally present when inner ear and facial nerve morphology is normal, temporal bone pneumatization is good, and the ossicular chain is only mildly deformed. Jahrsdorfer et al²⁴ has created a classification system to help in decision mak- ing in this regard.

For atresiaplasty, the EAC is created by drilling poste- rior to the glenoid fossa and anterior to the mastoid air cells, entering the epitympanum and superior aspect of the middle ear space just below the level of the middle cranial fossa dura.²⁸The ossicular chain is mobilized from the atresia plate, and a TM is created using a temporalis fascia graft. Finally, the canal is lined with a split-thickness skin graft, and a meatoplasty is created by attaching the skin graft to a newly created meatal opening.¹⁴Good hearing results (air–bone gap 25 dB) can usually be obtained in 75% of patients and are dependent on favorable anatomical factors. In cases where good hearing is not realized from the procedure, a conventional hearing aid can be used with excellent results. For children where anatomical factors preclude EAC reconstruction or the risks seem unacceptable to the family, an osseointegrated cochlear stimulator (BAHA device, Cochlear Corp., Englewood, CO) can be considered.

Postoperative complications from EAC atresia recon- struction include facial paralysis, sensorineural hearing loss, conductive hearing loss, TM perforation, cerebrospinal fluid (CSF) leak, and meatal stenosis secondary to bony regrowth or soft tissue stenosis. This latter complication is widely considered the most frequently occurring.³¹The Fig. 2.8 Coronal computed tomography scan shows severe bony

stenosis and membranous atresia. The small external auditory canal is vertically oriented. The malleus and incus are fused and deformed, and this ossicular mass is fused laterally. The facial nerve is directly behind the deformed ossicles, and the middle ear cavity is small.

Fig. 2.9 Drawing showing microtia, bony atresia, and deformed ossicles. The facial nerve descends anteriorly under the lateral semi- circular canal and in front to the stapes and thus is prone to injuries when drilling the atresia plate to gain access to the middle ear cavity.

(Courtesy of Suresh Mukherji, MD, Ann Arbor, MI.) (See Color Plate Fig. 2.9.)

most dreaded complication of EAC atresia surgery is facial nerve injury. Although rare, the facial nerve is at risk of injury in both its descending segment and in the extracranial portion. In the intratemporal portion, anterior displacement of the descending segment is the norm, mak- ing it most vulnerable while drilling the ear canal inferi- orly. The extratemporal portion of the facial nerve is at risk of injury during meatoplasty, especially when the cartilagi- nous framework from the microtia repair lies anterior to the newly created ear canal, requiring mobilization for realignment. Other complications of atresiaplasty include persistent conductive hearing loss from ear canal stenosis, TM perforation or lateralization, and ossicular chain dis- continuity or fixation. Sensorineural hearing loss can occur from inadvertent labyrinthine injury while drilling around the ossicular chain. We have recently started to use a laser to lyse the final attachments of the ossicular chain to avoid such drill-induced trauma.³⁰

Brachial Cleft Cyst

A brachial cleft cyst (BCC) is a congenital lesion that can occur in the area of the EAC, and is the cause of one third of pediatric nonmalignant lesions in the region of the parotid gland requiring surgery.³²BCCs arise from lack of involution of structures from the first through fourth branchial arches and are classified by location. Pathologi- cally, BCCs are composed of a thin fibrous pseudocapsule with central squamoid epithelium and occasionally lym- phocytic and germinal tissues. The majority of BCCs are simple cysts (two thirds) with thick mucous contents, no cutaneous or airway opening, and 3 cm or less in size.

Due to their histologic components, BCCs are similar in their imaging appearance, regardless of their location.

Rarely, a BCC undergoes malignant transformation into squamous cell carcinoma.³³On physical examination, a BCC is compressible due to its fluid components and usu- ally painless. These lesions have a tendency to enlarge with upper respiratory tract infections due to lymphoid secretions from follicles in the wall of the cyst and may become painful even in the absence of infection.

BCCs are readily evaluated with CT. Their appearance is that of a well-circumscribed mass with fluidlike compo- nents centrally (Fig. 2.10).³⁴On MRI, a BCC is of low T1- and high T2-weighted signal and may exhibit rim enhancement following contrast administration. Increased proteinaceous contents may lead to higher T1-weighted signal and occa- sionally low T2-weighted signal intensity. In the absence of infection, FLAIR imaging will demonstrate the central fluid to have low signal. If there is accompanying infection, sur- rounding soft tissue edema (stranding of fat) will be present on CT and MRI, and the rim has a tendency to be thicker, nodular, and to enhance. MRI may be useful for locating a sinus/fistula. CT better assesses bony abnormalities.³⁵

Fistulography can also be performed to better assess the course, anatomy, and topography of a fistulous tract, which helps improve the rates of complete resection of a fistula associated with a BCC.³⁶

In this chapter, we will concentrate on first BCCs because these occur in the region of the EAC. First BCCs are less common than second BCC cysts and account for less than 8% of all BCCs. A first BCC arises in a periauricular location, often parallels the EAC in orientation, and can be enveloped by the parotid gland. A congenital tract or sinus from the BCC may communicate with the EAC. Due to this embryological development, a first BCC can be associated with other first cleft anomalies, including het- erotopic salivary gland tissue, which has a predisposition for malignant transformation,³⁷or CH.³⁸Although there are two possible subtypes of a first BCC, there are no strict or well-defined histological and anatomical features for each one. The probability of an associated sinus with a first BCC is 56%, and a fistulous tract to the EAC at the cartilaginous–bony junction occurs in 31%, with the remain- ing first BCCs having a simply cystic appearance.³⁹A first BBC usually presents while the patient is a child, one third of patients presenting acutely due to infection and two thirds presenting with asymptomatic swelling, but may also present in teenagers or young adults if the lesion is purely cystic and not infected.⁴⁰On rare occasions with any BCC, there can also be communication with the skin surface, producing a fistula.

Commonly, a BCC is treated by complete resection to prevent recurrence and reduce complications.⁴¹Because many BCCs present as an abscess, they can be improperly diagnosed and treated with simple incision and drainage rather than complete excision.⁴² The surgeon must be

Chapter 2 The External Auditory Canal and Pinna

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Fig. 2.10 Axial computed tomography (CT) scan shows a cystic rounded mass in the lateral external auditory canal (EAC). This is a proven type 1 branchial cleft cyst, which extended into the EAC via a defect in its floor.