There are various classification techniques for hearing loss in children. Congenital (prelingual) hearing loss occurs before the child learns to speak. The prevalence of congenital hearing loss is 1 to 3 per 1,000 livebirths. Approximately 0.1% of children in the United States are born with profound deafness. The prevalence of late-onset (postlingual) hearing loss is about half of that of the prelingual form. About half of pediatric hearing loss is due to genetic factors, one-quarter of patients have acquired lesions, and one-quarter have idiopathic hearing loss. Seventy percent to 80% of instances of genetic deafness are nonsyndromic, that is, no associated anomalies in other parts of the body. Most patients with nonsyndromic deafness have abnormalities of the inner ear, that is, sensorineural deafness. Conductive hearing loss is due to abnormalities of the middle ear. If both sites are involved, the hearing loss is mixed.^1–3

The causes of congenital hearing loss are extensive. Congenital infections are responsible for many cases. Cytomegalovirus is a common congenital infection that can cause sensorineural hearing loss. Although there are multiple potential clinical manifestations of cytomegalovirus infection, hearing loss is the only finding in some affected infants. Hearing loss can also occur with congenital toxoplasmosis (15%), congenital rubella (50%), transplacental herpes simplex type 1 infection (50%), herpes simplex type 2 infection (uncommon), and congenital syphilis. Various maternal medications can cause congenital hearing loss, including aminoglycosides and chloroquine.

Postnatal infections can also cause hearing loss. Streptococcus pneumoniae meningitis carries a 15% to 20% risk for hearing loss, which is bilateral in more than half of patients. Other forms of bacterial meningitis can also lead to hearing loss. The most important viral agents associated with acquired hearing loss in infants are mumps and measles.

Mutations in GJB2, the gene that encodes connexin 26 (Cx26), are responsible for 25% to 50% of cases of autosomal recessive nonsyndromic hearing loss, with variations in prevalence by geographic population groups. Children with defective connexin 26 have prelingual hearing loss that is usually severe. Diagnostic imaging studies of the ear show no definable anatomic abnormalities. Mutations in SCL26A4 cause Pendred syndrome, which includes hearing loss; this may account for up to 10% of cases of syndromic hearing loss. There are hundreds of other causes of syndromic hearing loss, including osteogenesis imperfecta, Usher syndrome, Treacher Collins syndrome, Goldenhar syndrome, Turner syndrome, trisomy 21, otopalatodigital syndrome, branchio-oto-renal (BOR) syndrome, Kabuki syndrome, Opitz-Frias syndrome, Möbius syndrome, Duane syndrome, Alport syndrome, Refsum disease, Jervell and Lange-Nielsen syndrome, CHARGE association, Norrie syndrome, Cockayne syndrome, mucopolysaccharidosis, DiGeorge syndrome, achondroplasia, Wildervanck syndrome, Marfan syndrome, Apert syndrome, and Waardenburg syndrome.

High-resolution CT of the temporal bones is the imaging modality of choice for the evaluation of most pediatric patients with hearing loss. The most common finding is an enlarged vestibular aqueduct. Cochlear dysplasia is also a common CT finding in children with hearing loss. Other potential CT abnormalities include semicircular canal anomalies, narrow or absent internal auditory canals, enlarged internal auditory canals, and labyrinthitis ossificans (due to prior meningitis). Contrast-enhanced MR should be performed in patients with acquired hearing loss for whom acoustic schwannoma is a clinical consideration. High-resolution MR is also useful for detecting developmental abnormalities of the acoustic nerve, such as aplasia.

Congenital X-linked mixed hearing loss is a rare form of congenital deafness. Imaging studies are important for these patients because of inner ear anomalies that can complicate ear surgery. The internal auditory canals are wide and many patients have incomplete separation of the cochlear basal turns from the fundi of the internal auditory canals (see section Internal Auditory Canals). Other potential anomalies include hypoplasia of the bases of the cochleae, absence of the bony modioli, enlarged labyrinthine facial nerve canals, and widened vestibular aqueducts.^4,5

External Ear

Microtia

Microtia is the most common developmental anomaly of the external ear. The abnormality is bilateral in approximately 10% of patients. Microtia can occur as an isolated anomaly or as a component of an otofacial or craniofacial syndrome. Microtia is present in 70% of patients with Goldenhar syndrome. Most patients with microtia also have aural dysplasia and middle ear anomalies, and thus require evaluation with CT. Demonstration of the course of the facial nerve is clinically important for these patients.^6,7

External Auditory Canal Dysplasia

Dysplasia of the external auditory canal is usually due to failure of canalization of the meatal plate. The meatal plate is a solid core of epithelial cells that develops between the primary external meatus and the endodermal outpouching from the pharynx that gives rise to the middle ear cavity. Canalization of the meatal plate normally occurs during the 26th week of gestation.

The most frequent form of external auditory canal dysplasia is external canal atresia, either fibrous or bony. Congenital stenosis can also occur, but is less common. The anomaly is bilateral in approximately 30% of patients. External auditory canal atresia is slightly more common in males. The auricle is nearly always deformed; severe dysplasia of the outer ear tends to be associated with external auditory canal atresia, whereas less severe auricular deformities may be accompanied by stenosis. Dysplasia of the external auditory canal is associated with an increased risk of congenital and acquired cholesteatomas and epidermoids. A number of malformation syndromes include external auditory canal dysplasia as a component.

In the fibrous form of external auditory canal dysplasia, a soft tissue plug occupies the expected location of the tympanic membrane. With the osseous form of atresia, the tympanic membrane is replaced by a bony plate (Figure 33-1). With severe dysplasia, the cartilaginous and osseous portions of the external auditory canal are absent. A malformed auricle terminates on a bony overgrowth that arises from the squamous portion of the temporal bone; this is referred to as the atresia plate. A stenotic external auditory canal frequently follows an abnormal superiorly angulated course. The narrowing can be focal or diffuse.

Anomalies of the middle ear and mastoid process are commonly associated with dysplasia of the external auditory canal. This is likely related to the common embryological origins of the external auditory canal and the middle ear. The severity of ossicular deformities tends to correlate with the severity of the external auditory canal dysplasia. Potential ossicular deformities in these patients include dysplasia, hypoplasia, abnormal rotation, and focal ossicular defects. The manubrium of the malleus is often absent, and the short process of the malleus may be fused to the atresia plate. In some patients, there is fusion of the incus to the attic wall. Pneumatization of the middle ear cavity is often reduced.^8–10

The facial nerve canal often follows an anomalous course in children with external auditory canal dysplasia. Accurate definition of the anatomy of the facial nerve is important for patients who will be undergoing temporal bone surgical procedures. Most often, the tympanic and mastoid segments of the facial nerve canal are predominantly affected. There is an abnormal caudal location of the tympanic segment, whereas the mastoid segment is displaced anterolaterally. The facial nerve may exit the temporal bone at the level of the round window.¹¹

Because of common embryological origins, anomalous development of the mastoid process is common in patients with dysplasia of the external auditory canal. The tympanic portion of the temporal bone can also be affected. The bony deformities can be in the form of aplasia or hypoplasia. The ipsilateral mandibular condyle is often small and deformed. The temporomandibular joint is shallow and occupies a more superior and posterior position than normal. The carotid canal is sometimes abnormal, and may be associated with hypoplasia or aplasia of the internal carotid artery.

Absence of the oval window can occur in association with dysplasia of the external auditory canal; occasionally, this occurs concomitantly with absence of the round window. Anomalies of the inner ear are uncommon in patients with external auditory canal dysplasia. Potential inner ear abnormalities in these patients include cochlear hypoplasia, hypoplasia or enlargement of the lateral semicircular canal, and enlargement of the vestibule and vestibular aqueduct. Occasionally, the internal auditory canal is hypoplastic or follows an anomalous course.

Middle Ear

Anomalies of the middle ear most often occur in association with dysplasia of the external auditory canal. Isolated anomalies of the middle ear are less common. Some of these lesions have an autosomal dominant pattern of inheritance. Middle ear anomalies can also occur in association with various syndromes, such as Goldenhar and Treacher Collins syndromes. The ossicles that are most commonly dysplastic are the incus and stapes.

Potential anomalies of the incus include aplasia, a hypoplastic long process, fusion of the short process to the lateral semicircular canal, and a fibrous union or absence of the incudostapedial joint. Anomalies of the stapes include aplasia, hypoplasia, absence of the head and crura, fusion of the head to the promontory, and foot plate fixation. Malleus anomalies include aplasia, fusion of the incudomalleal joint, and fusion of the manubrium to the incus and stapes. Other developmental lesions of the middle ear include a hypoplastic tympanic cavity, aplasia of the stapedius muscle, and malformation of the pyramidal eminence. Most middle ear anomalies result in substantial conductive hearing loss.

Ossicular anomalies frequently are accompanied by abnormal development of the facial nerve. In children with middle ear anomalies that are not associated with dysplasia of the external auditory canal, dehiscence of the tympanic segment of the facial nerve is common. The nerve may be in an abnormal anterior and medial location. When the dehiscent facial nerve overlies the oval window or stapes, the oval window may be congenitally absent.

Inner Ear

Anomalies of the inner ear involve the internal auditory canal, cochlea, semicircular canals, vestibule, or vestibular aqueduct/endolymphatic sac (Table 33-1). The most common of these otic capsule dysplasias are dilation of the vestibular aqueduct and dysplasia of the semicircular canals. The pattern of dysplasia and the severity correlate with the gestational age at which arrest of inner ear development occurred, that is, the earlier the insult, the greater the severity of dysplasia. Most of these anomalies result in sensorineural hearing loss.⁹

Dilated Vestibular Aqueduct

A dilated vestibular aqueduct (large vestibular aqueduct syndrome) is the most common imaging finding in children with sensorineural or mixed hearing loss. The causative insult presumably occurs during the seventh gestational week. Approximately 15% of these patients have a pendrin gene mutation. Dilated vestibular aqueduct can be an isolated anomaly (15%), or occur in conjunction with cochlear dysplasia (especially the Mondini malformation), vestibular dysplasia, or anomalies of the semicircular canals. Both forms are typically bilateral. Modiolar deficiencies of the cochlea are present in nearly all patients with a dilated vestibular aqueduct. The “Cincinnati criteria” define a dilated vestibular aqueduct as being more than or equal to 1.0 mm in diameter at its midpoint, or more than or equal to 2 mm at the operculum. On CT, the anomalous vestibular aqueduct is larger than the normal adjacent posterior semicircular canal (Figure 33-2). Children with dilated vestibular aqueduct are at risk for progressive hearing loss.^1,12–14

Although CT optimally demonstrates the morphology of the vestibular aqueduct, abnormalities of the endolymphatic duct and sac can be visualized with high-resolution MRI (Figure 33-3). In patients with a dilated vestibular aqueduct, the endolymphatic sac frequently bulges into the posterior fossa (i.e., large endolymphatic sac anomaly). The adjacent portion of the temporal bone often has a scalloped configuration. A portion or all of the endolymphatic duct and sac sometimes has lower signal intensity than that of clear cerebrospinal fluid (CSF) on T2-weighted MR images, due to the presence of fibrous or epithelial tissue. An enlarged endolymphatic sac is a component of Pendred syndrome, which includes congenital deafness and thyroid dysfunction.

Cochlear Anomalies

There is a spectrum of cochlear anomalies that includes cochlear hypoplasia, incomplete partition, common cavity, and cochlear aplasia. Most cochlear anomalies can be classified according to a system proposed by Jackler et al, which is based on the concept of arrested maturation at different stages of organogenesis. These range from complete labyrinthine aplasia caused by arrested development during the third gestational week to incomplete partition of the cochlea caused by an insult during the seventh week. In the normal embryo, complete formation of the cochlea is typically established by the eighth week of development. The Sennaroglu classification is a more recently developed system that also correlates cochlear anomalies with stages of organogenesis (Table 33-2).^1,15–17

Complete labyrinthine aplasia, or Michel deformity, is due to developmental failure during the third gestational week. There is essentially no inner ear development (Figure 33-4). Some patients have a rudimentary cystic cavity or multiple small cavities. This is a very rare anomaly.

Cochlear aplasia is due to failure of development during the later part of the third gestational week. The vestibule and semicircular canals are present, and may or may not have structural abnormalities. There is no cochlear development.

The common cavity deformity is a severe cochlear anomaly in which the cochlea and vestibule comprise a large cystic cavity with no other differentiation (Figure 33-5). There are no cochlear turns. This anomaly is due to developmental failure during the fourth gestational week. Anomalies of the semicircular canals may or may not be present in these patients. The common cavity anomaly accounts for approximately 25% of cochlear malformations. When this anomaly is accompanied by a history of recurrent meningitis, an associated perilymphatic fistula is likely.

Cystic cochleovestibular malformation, or incomplete partition type I, refers to lack of the entire modiolus and cribriform area, resulting in a cystic appearance on high-resolution CT (Figure 33-6). There is variable enlargement of the vestibule, sometimes resulting in a cystic appearance.

Cochlear hypoplasia is due to arrested development at approximately the sixth week of embryogenesis. There is rudimentary development of the cochlea. The vestibule and semicircular canals may be normal or have a variable degree of dysplastic development.

Mondini dysplasia (incomplete partition type II) is an incomplete partition anomaly of the cochlea. There is a range of severity, but the basal (first turn) is intact by definition. The apical and middle turns are confluent, and form a common cavity. The overall size of the cochlea is diminished. The interscalar septum is absent or there is incomplete partitioning, such that there are fewer than the normal 2½ to 2¾ turns. Most often, the cochlea consists of 1.5 turns. The defect involves both the interscalar septum and the osseous spiral lamina. There is enlargement of the vestibule and vestibular aqueduct. Other anomalies of the inner ear, such as semicircular canal dysplasia, occur in approximately 20% of individuals with Mondini dysplasia. Imaging studies usually show a single basal cochlear turn and a distal sac (Figure 33-7). Mondini dysplasia is due to arrest of development of the cochlea at about week 7 of embryonic development. The Mondini malformation is a common form of genetic deafness. Mondini dysplasia and dilated vestibular aqueduct are associated with Pendred syndrome and less commonly with BOR syndrome. Because of the intact basal turn, some hearing is possible in patients with Mondini dysplasia.

A variety of additional patterns of cochlear maldevelopment can occur, some of which do not fit into the standard Jackler or Sennaroglu classification systems. The bony modiolus (the conical central pillar of the cochlea, around which winds the cochlear canal) can be hypoplastic or absent. This can occur as a combination of hypoplasia of the cochlear base, widening of the lateral portion of the internal auditory canal, and fixation of the stapes footplate as an X-linked disorder. A dwarf cochlea with a normal number of turns but markedly diminished size is a rare cochlear anomaly. Asymmetry of the scalar chambers is also rare, usually characterized by enlargement of the anterior chamber; high-resolution MRI is required for detection of this cochlear dysplasia.

Semicircular Canal Anomalies

Anomalies of the semicircular canals include absence or dysplasia of 1 or more of the canals in isolation, in association with a vestibular abnormality, or in association with both vestibular and cochlear abnormalities. The commonest labyrinthine anomaly and the second most common congenital deformity of the inner ear is a dilated dysplastic lateral semicircular canal; these patients often have normal cochlear function. Semicircular canal anomalies most commonly involve the lateral semicircular canal because it is the last to form during embryonic development; anomalies of the superior and posterior semicircular canals can occur concomitantly, but are only rarely involved in isolation. Semicircular canal dysplasia most often occurs in the form of widening and foreshortening of the canal; hypoplastic narrowing is less common (Figure 33-8). With severe dysplasia, the lateral semicircular canal forms a common lumen with a dilated vestibule; this is termed lateral semicircular duct-vestibule dysplasia.^1,18

Aplasia of 1 or all of the semicircular canals is much less common than the deformities described above. Complete semicircular canal aplasia can occur in individuals with CHARGE syndrome. Alagille syndrome and Waardenburg syndrome are associated with aplasia of the posterior semicircular canal. The major clinical manifestation of semicircular canal aplasia is vertigo. An additional rare anomaly of the semicircular canals is that of dehiscence of the roof of the superior canal; these patients may suffer a form of vertigo that is induced by sound (Tullio phenomenon).

Internal Auditory Canals

Anomalies of the internal auditory canals include hypoplasia (stenosis), duplication, and atresia. The normal internal auditory canal diameter should be at least 2 mm. Anomalous development of the vestibulocochlear or facial nerves can coexist with dysplasia of the bony canal or occur despite the presence of a normal canal. As described above, enlarged internal auditory canals and cochlear anomalies occur in some patients with X-linked mixed hearing loss (Figure 33-9). The anatomy of the internal auditory canals is best demonstrated with CT, whereas MR allows imaging of the vestibulocochlear and facial nerves (Figure 33-10).¹⁹

The vestibulocochlear nerve can be hypoplastic or aplastic. In some patients, dysplasia is confined to the cochlear branch; a labyrinthine malformation sometimes coexists with this finding. Developmental hypoplasia or aplasia can also involve the facial nerve. This is a component of Möbius syndrome; the clinical manifestations include facial diplegia and bilateral lateral rectus muscle paralysis. Duplication of the facial nerve (bifid facial nerve) is an additional potential facial nerve anomaly, most often characterized by bifurcation of the proximal aspect of the tympanic segment.

There are various potential anomalous courses of the facial nerve, sometimes occurring in combination with other ear malformations. Accurate localization of the facial nerve is essential for preoperative planning. An anomalous course of the facial nerve is common in patients with vestibulocochlear nerve hypoplasia or aplasia. An abnormal anterior position of the facial nerve can occur in association with various cochlear malformations. Anomalous positions of the tympanic and mastoid segments of the facial nerve sometimes accompany malformations of the ossicles or external auditory canals.

Congenital Cerebrospinal Fluid Fistulas

Congenital CSF fistulas from the subarachnoid space to the inner ear or middle ear cavity are classified into perilabyrinthine and translabyrinthine types. The translabyrinthine variety is more common, and is associated with severe labyrinthine dysplasia and deafness. The perilabyrinthine type is quite rare. A congenital CSF fistula typically occurs via the internal auditory meatus, which is abnormally tapered laterally.²⁰

Translabyrinthine CSF fistula can occur via deficiencies of the lamina cribrosa or cochlear modiolus that allow communication between the CSF in the internal auditory canal and the perilymph in the vestibule and/or cochlea. If there is perforation of the stapes footplate, CSF and perilymph can enter the middle ear cavity via the oval window. Communication via the round window is much less common. Translabyrinthine fistulas are usually associated with severe labyrinthine dysplasia.

Patients with congenital CSF fistula may suffer recurrent episodes of meningitis; this anomaly is potentially fatal. If the tympanic membrane is intact, there may be CSF rhinorrhea due to escape of fluid via the eustachian tube. CSF otorrhea occurs if there is an opening in the tympanic membrane.

Imaging for Cochlear Implants

Cochlear implants are used to treat selected patients with profound sensorineural hearing loss. The cochlear implant electrically stimulates remaining auditory nerve tissue in the cochlea and creates a sensation of hearing. Deaf children who are treated with cochlear implants at a young age are usually able to develop auditory and verbal communication skills. The external components of the system consist of a microphone, speech processor and a transcutaneous transmitter. The signal is transmitted to an internal receiver stimulator that is connected to an electrode that is implanted in the cochlea.²¹

Diagnostic imaging studies serve an important role in screening candidates for cochlear implants, as well as for presurgical planning. The middle ear is assessed for aeration, signs of otitis media, and developmental anomalies that might complicate insertion of the device. The cochleostomy site is adjacent to the round window recess. Assessment of cochlear anatomy is essential. Complete occlusion of the neural foramen indicates absence of the cochlear nerve, and is a contraindication to cochlear implantation. Patients with a normal cochlear canal tend to experience better hearing performance with cochlear implants than those with a hypoplastic canal. The bony anatomy is best demonstrated with CT, whereas the status of the vestibulocochlear nerve can be determined with high-resolution MR.²²

MR evaluation of the internal auditory canals consists of high-resolution axial and coronal T2-weighted images, as well as reconstructed sagittal oblique images that are perpendicular to the canals. Steady-state free precession (SSFP; fast imaging employing steady-state [FIESTA]; constructive interference in steady state [CISS]) images provide high spacial resolution and high contrast between CSF and nerves. The facial and vestibulocochlear nerves emerge from the lateral aspects of the pons and traverse the cerebellopontine angle cistern. Within each internal auditory canal, the facial nerve courses superior and anterior to the vestibulocochlear nerve. The vestibulocochlear nerve enters the canal as a single linear structure and separates into individual nerves in the lateral portion of the canal: cochlear, superior vestibular, and inferior vestibular branches. In the lateral aspect of the internal auditory canal, sagittal oblique images usually show 4 nerves in cross-section: the facial nerve anterosuperiorly, the superior vestibular nerve posterosuperiorly, the cochlear nerve anteroinferiorly, and the inferior vestibular nerve posteroinferiorly (Figure 33-11). Incomplete separation of the vestibular nerves is a common variation. The connection of the cochlear nerve to the cochlear aperture is usually discernible on axial images (Figure 33-12).^23,24

The integrity of the vestibulocochlear nerve has important implications for planning of a cochlear implant. Vestibulocochlear nerve dysplasia is categorized into 3 types. With type 1, there is no identifiable vestibulocochlear nerve on MRI and the internal auditory canal is stenotic on CT. A cochlear implant is contraindicated in these children. Type 2 indicates the presence of a common vestibulocochlear nerve and aplasia or hypoplasia of the cochlear branch. When there is a labyrinthine malformation, it is termed type 2A. Type 2B refers to dysplasia of the cochlear branch without labyrinthine malformation. Children with a type 2 malformation often have some degree of hearing in the affected ear. This anomaly does not contraindicate cochlear implantation.

Postoperatively, standard radiographs and CT are useful to visualize the implanted electrode (Figure 33-13). This allows determination of the depth of insertion into the cochlea, and identifies kinking or incorrect placement of the electrode. With radiography, the most useful projection is the modified Stenvers view.

Potential complications of cochlear implantation include infection, facial nerve dysfunction, device failure, fracture of the electrode, and electrode misplacement. CT is often indicated in the work-up of a suspected complication. Kinks or fractures of the electrode are easily demonstrated with CT, and may also be visible on standard radiographs. Fluid in the middle ear cavity is suggestive of infection, although a CSF leak is a rare complication that can lead to the accumulation of sterile fluid. Chronic infection may lead to bone resorption adjacent to the implant. Facial nerve stimulation occurs in some patients with cochlear implants, and CT evaluation of the proximity of the electrode to the facial nerve is helpful in this situation.

Vascular Anomalies

Developmental variations of the jugular bulb are relatively common. The most frequent variation is elevation of the roof of the jugular bulb above the inferior tympanic ring or floor of the internal auditory canal, that is, high jugular bulb. Dehiscence of the floor of the middle ear can lead to protrusion of the jugular bulb into the hypotympanum. Patients with this anomaly can suffer pulsatile tinnitus and ipsilateral hearing loss. A bluish middle ear cavity mass is usually visible otoscopically. Other potential jugular bulb anomalies include diverticulum, agenesis, and stenosis. CT is the optimal technique for defining the osseous anatomy in these patients, whereas MR or contrast-enhanced CT examinations allow assessment of the venous structures.

An aberrant internal carotid artery is a rare anomaly in which the internal carotid artery enters the tympanic cavity through an enlarged tympanic canaliculus. There is dehiscence of the carotid plate. CT is the optimal diagnostic technique for evaluation of this anomaly. Imaging studies show a “mass” in the hypotympanum that extends toward the oval window, indents the promontory, and displaces the tympanic membrane laterally. The lateral and posterior walls of the carotid canal are absent. Patients with an aberrant internal carotid artery may have pulsatile tinnitus, hearing loss, otalgia, and vertigo.²⁵

A persistent stapedial artery is a rare anomaly that most often occurs in association with the above-described form of aberrant internal carotid artery. In these patients, the anomalous vessel arises from the aberrant internal carotid artery and enters the middle ear cavity via a small canaliculus. It extends through the crura of the stapes and enters the canal of the tympanic portion of the facial nerve or runs parallel to the facial nerve in a separate canal. CT demonstrates a small enhancing “mass” in the middle ear cavity. Because the persistent stapedial artery supplies the middle meningeal artery, the foramen spinosum is absent. In patients with a persistent stapedial artery and a normal internal carotid artery, the anomalous vessel arises from the vertical petrous segment of the internal carotid artery.^26,27

A wide variety of syndromes and bone dysplasias are associated with anomalies of the temporal bones and ears. As noted above, many of these conditions result in congenital hearing loss. Depending on the constellation of anomalies, many of the dysostoses in which ear malformations occur concomitantly with malformations of other organs can be classified as otofacial, otocervical, otoskeletal types. Ear anomalies occur in various chromosomal syndromes, such as trisomy 18, trisomy 21, and trisomy 13. Temporal bone involvement, with or without ear anomalies, is an important component of various skeletal dysplasias. For example, abnormal skull base development in children with achondroplasia results in a predisposition to middle ear disease. This is in part, due to shortening of the eustachian tubes.