DR/ ABD ALLAH NAZEER. MD.

Radiological Imaging of Ear Microtia.

Anatomy of external ear and external auditory canal: The external ear is composed of an expanded cartilage called auricle or pinna. This is covered by a layer of thick skin. It serves to collect the sound waves from surrounding environment. The lateral surface of pinna is thrown into a number of undulations. Its major parts are helix, anti-helix, tragus and lobule. EAC is a curved tubular conduit measuring approximately 2.5 cm in length, outer 1/3rd of which is cartilaginous, with inner 2/3rd being bony. It is lined by skin having hair follicles and ceruminous glands. This serves to transmit sound waves from external ear to the tympanic membrane. 

Microtia refers to a small pinna of the ear, when is it completely absent it is termed anotia.EpidemiologyThe estimated incidence at around 1:9000 live births. It is more common in males and there is a recognized right sided predilection.PathologyAssociationsMicrotia can be associated with a wide spectrum of inner and middle ear anomalies. Isolated microtia is relatively uncommon. The most frequent associations include: ossicular dysplasiaexternal auditory canal stenosisexternal auditory canal atresiaWider organ associations include:renal anomalies

cross-fused ectopiarenal agenesis

Syndromic associations include:Down syndromeGoldenhar syndromeJacobsen syndromeNager syndromeTreacher-Collins syndrome

ClassificationIt is classified into four grades based on increasing severity:grade I: slightly small ear with identifiable structures; external auditory canal small but presentgrade II: partial or hemiear with a occluded or stenotic external ear canal producing a conductive hearing loss grade III: absence of the external ear with a small peanut like vestige structure and an absence of the external ear canal and eardrumgrade IV: complete absence (anotia)

Microtia is commonly associated with external and middle ear anomalies. Inner ear abnormalities are less consistent. The external and middle ear develop from first and second branchial arches. First arch contributes to incus, malleus, tensor tympani muscle, and mandible, and second arch to stapes, facial nerve canal, stapedius muscle, and the styloid process. Disorders of the first and second branchial arches also result in dysplasia of the auricular cartilage, leading to microtia in the 7th to 8th week, hence an association of microtia with anomalies of EAC and middle ear. Temporal bone HRCT is the investigation of choice for delineating these abnormalities. Anatomic abnormalities of the ear in microtia have been reported previously using HRCT imaging of temporal bone, but there is lack of such data for the Indian population.EAC atresia is commonly associated with microtia and usually presents as combined cartilaginous and bony atresia. Isolated cartilaginous or bony canal atresia, which was considered rare, had an incidence of 8.82% in our study. Surgical reconstruction of the EAC and ossicular chain is much easier when the EAC is present, even when it is very narrow and tortuous, because this acts as a landmark to help the surgeon reach the tympanic cavity more safely. Our study provides an incidence of EAC abnormalities in microtia, a parameter detailed in none of the published studies.

Small capacity middle ear was seen in 84.3% cases. Reduced middle ear space correlates with unfavorable surgical outcome. A tympanic cavity width <3 mm from the promontory to the atretic plate in the coronal plane is considered inadequate for reconstruction. Middle ear ossicles show variable anomalies ranging from absence, dysplasia, ossicles embedded in the atretic plate, and fusion abnormalities involving malleus and incus. We reported an incidence of combined ossicular dysplasia of 74.5% that is significantly lower as compared to previously reported values of more than 95%. However, the incidence of stapes dysplasia in our study population (74.5%) matched with the previously documented results.Atretic plate refers to the bony plate that separates the undeveloped external ear from the middle ear. Of the two commonly used surgical approaches, transmastoid and anterior, the latter involves drilling of the atretic plate. Hence, information regarding the pneumatization and thickness of the atretic plate is an important prerequisite in guiding the surgeon. We found a significant correlation between pneumatization of mastoid process and that of the atretic plate, similar to that documented in a study by Grassner,

Congenital cholesteatoma is commonly associated with microtia. Presence of soft tissue in the middle ear points to its presence. Our study showed a higher occurrence (38.4%) of cholesteatoma compared to previous studies. There was a significant association between the presence of cholesteatoma and poor mastoid and atretic plate pneumatization. None of the previous studies, to our knowledge, have documented this association.Facial nerve injury is the most substantial complication of microtia surgery. Thus, it is essential to determine the course of the facial nerve preoperatively. In patients with microtia, the facial canal tends to show an anterolateral displacement of its course, exposing it to the risk of injury during mastoid drilling. Such aberrant anatomy of facial canal was found in 8.22% of our patients, which is lower as compared to that in previous studies.The inner ear anomalies in microtia have a reported incidence of 10-52%. We found a much lower incidence (2.7%) with one patient having bilateral cochlear dysplasia. Patients with an atretic oval window are not considered candidates for surgical repair. These results are in consort with a different embryological origin of inner ear.

Aplasia or hypoplasia of the tympanic part or mastoid process of the temporal bone, mandibular condyle, and zygomatic arch is also associated with microtia. Bifid mandibular condyle is a rare association with an incidence of 0.5%. It is thought to be developmental and is due to presence of fibrous septum or vascular structure impeding the fusion of condylar ossification center. IAC anomalies can range from mild asymmetry and narrowing to replacement by thin neural canal. One case of IAC narrowing was documented in our study.Carotid canal anomalies are not uncommon in the setting of microtia. Aberrant course of carotid artery in mesotympanum confers surgical risk. Absent carotid canal is usually unilateral and can be associated with persistent stapedial artery. High riding jugular bulb is an uncommon association with microtia. Vascular anomalies in our study showed an overall incidence of 5.5%.

Grades of Microtia and Atresia (courtesy of Dr. Sheryl Lewin, MD (Medpor surgeon)

Sonogram of bilateral microtia on auricular parasagittal section.

Sonogram of bilateral microtia on retrocolic transverse section.

Sonogram of unilateral microtia on auricular parasagittal section.

Three-dimensional sonogram of bilateral microtia.

Axial HRCT image showing partial EAC atresia on left side (white arrow) and complete atresia on right side (white arrowhead) showing an aberrant anterior course of right facial nerve (white arrow), which is seen at the same level (dotted black line) as the rudimentary pit for right external auditory canal (black arrow). 3D volume-rendered CT image showing right microtia (white arrow) showing loss of normal undulations with absent opening for the external auditory meatus (black arrow).

EAC anomalies. (A) Coronal HRCT shows EAC with cartilaginous and bony component in a normal ear (arrow). (B) Coronal HRCT of grade I microtia shows combined cartilaginous and bony EAC atresia (arrow). (C) Coronal HRCT shows isolated atresia of cartilaginous EAC (arrow). (D) Axial HRCT section shows stenotic cartilaginous EAC (arrow)

Middle ear anomalies. (A) Axial HRCT section shows small capacity middle ear (arrow). (B) Axial HRCT section shows dysplastic malleus and incus. Also note an associated cholesteatoma. (C) Axial HRCT section shows incudomalleal ankylosis (white arrow). Also seen is non-pneumatized atretic plate (black arrow). (D) Axial HRCT section in microtia shows normal stapes

Facial canal anomalies. (A) Coronal HRCT section shows anterior location of facial canal (arrow). Also note the shortened vertical course of the nerve. (B) Sagittal HRCT section of same patient shows similar findings (arrow). (C) Axial HRCT section shows intimate course of facial nerve to the round window (arrow).

Inner ear anomalies. (A) Axial HRCT section shows narrowed left internal acoustic meatus (arrow). (B) Coronal HRCT of same patient shows similar finding. Note normal right IAC. (C) Axial HRCT section shows globular cochlea (arrow) with dysplastic modiolus. (D) Coronal HRCT of same patient shows bilateralism of cochlear dysplasia (arrows)

Vascular anomalies. (A) Serial coronal HRCT sections shows aberrant course of left internal carotid artery in the middle ear (black arrows). (B) Axial section of same patient shows similar finding (arrow). (C) Axial HRCT section shows absent carotid canal on right side (white arrow). Note the normal carotid canal on left side (black arrow). (D) Coronal HRCT section shows high riding jugular bulb on right side (arrow).

Mandibular condyle anomaly. (A) Volume rendered image shows bifid right mandibular condyle (arrow). (B) Coronal HRCT section of same patient shows double temporal articular fossa on right side (arrow)

A 17-year-old male with grade I microtia on the right side. (A) Volume rendered image shows grade I microtia. There is preservation of helix with preauricular tag (arrow). (B) Axial HRCT section shows small capacity middle ear with dysplastic ossicles (arrow). (C) Coronal HRCT section of same patient shows similar findings (arrow). (D) Coronal HRCT section also depicts non-pneumatized atretic plate with normal inner ear (arrow)

A 2-year-old male child with bilateral grade III microtia. (A) Volume rendered image shows left-sided grade III microtia, with bud like pinna (arrow). (B) Axial HRCT section of same side shows preserved middle ear capacity, pneumatization, and ossicles (arrow). (C) Volume rendered image shows right sided grade III microtia (arrow). (D) Axial HRCT section of right side shows small middle ear and dysplastic ossicles (arrow). Also noted is associated cholesteatoma (arrowhead).

HRCT scan: A–C: axial cuts; D: coronal reformat of right ear; showing bilateral mixed external auditory canal atresia (arrows) with deformed right pinna (notched arrow) and small middle ear cavities with hypoplastic deformed ossicles, more severe on the right side (chevrons), non-pneumatized mastoids (curved arrows), normal left ear pinna (star) and normal inner ear structures (striped arrows).

 External auditory canal (EAC) atresia. A, Axial computed tomography demonstrates absence of EAC on the left side (arrow). The middle ear ossicles are deformed. B, The finding is confirmed on the coronal image, where one can see the normal right EAC (arrow), the absent EAC on the left (asterisks), and the lateralized left middle ear ossicles.

Left microtia and external auditory canal (EAC) atresia. A, Axial computed tomography (CT) scan through the temporal bone shows an absent left EAC and malformed auricle (arrows). B, The ossicles on the left are fused and there is no incudomalleolar joint (arrowhead). The position of the facial nerve second genu on the left is anterior to the right (arrows), which puts it in potential danger during the ossicular reconstruction procedure. Note decreased air space of left middle ear. C, Coronal reconstruction of axial CT images shows the mal developed left pinna with microtia (compare white arrows), the absence of an EAC on the left (see E on the right), with a poorly aerated left middle ear (black arrowhead) and fused ossicles (black arrow). D, When the EAC and ossicles are congenitally malformed, the temporomandibular joint (arrow) on the same side is also typically maldeveloped as seen on the left here—shallow and maloriented.

Abnormal fixation of the handle of the malleus along with increased distance of the handle of malleus to the cochlear promontory in a 4-year-old boy with right-sided CHL (patient 9). Axial HRCT of the temporal bones, superior-to-inferior. A and B, There is abnormal fusion of the right malleus and incus (long arrow) superiorly. The inferior image shows fixation of the handle of the malleus anteriorly (short arrow). Note an increased distance of the handle of the malleus to the cochlear promontory (arrowhead). C and D, Normal separation of the left ossicles is present superiorly. Inferiorly, there is a normal distance of the handle of the left malleus to the promontory in the normal ear (between arrows).

A 10-year-old with left conductive hearing loss and microtia. A, Coronal high-resolution computed tomography shows bony atresia of the external auditory canal and fusion of the malleus to the atretic plate (arrow). B, The stylomastoid foramen is positioned anteriorly (arrow).

High-resolution computed tomography temporal bone. (a) Axial image showing right external auditory canal atresia (arrow) in an 18-year-old female. (b) Axial image in a 1-year-oldboy showing external auditory canal atresia (arrow) of mixed bony and soft tissue on left side with dysplastic malleus and incus (arrowhead). (c) Axial image in the same patient shows descending facial nerve canal (arrow) noted within posterior aspect of bony septum of external auditory atresia. (d) Axial image showing bilateral mixed bony and soft tissue external auditory canal atresia (arrow) with dysplastic malleus and incus in 4-year-old boy. (e) Coronal image showing right bony external auditory canal atresia (arrow) in a 4-year-old boy. (f) Axial image showing left external auditory canal atresia (arrow) including the bony and membranous portion in a 2-year-old male and (g) Axial image shows fusion of malleus and incus (arrow) in the same patient. (h) Coronal image showing right external auditory canal atresia (arrow) of mixed bony and soft tissue with dysplastic malleus and incus (arrowhead) in an 11-month-old male. (i) Coronal image showing, right external auditory canal atresia (arrow) involving both membranous and bony portions in a 5-year-old female

(a) A transversal computed tomographic view of a right ear microtia and complete absence of the external auditory canal, atretic bony plate (white arrows). The mastoid segment of the facial nerve (thick black arrow) is displaced anteriorly, facing the round window (thin black arrow). M microtia. (b) Coronal view of an atretic ear showing the mastoid segment of the facial nerve (arrowheads) displaced anteriorly at the level of the vestibule (V)

Atresia of the left external auditory canal with ossicular fusion.

Figure 1: On the right, the mastoid air cells are under pneumatized. There is no identifiable external auditory canal.Figure 2: A thick bony plate is visualized in the expected area of the external auditory meatus.Figure 3: The facial nerve is identified.Figure 4: There is a small amount of bone in the attic of the middle ear cavity but no formed malleus or incus is identified. This suggests rudimentary and/or hypoplastic ossicles. However, a normal morphology and location of the stapes is seen. The internal auditory canal is normal in caliber.Figure 5: The apical and basal turns of the cochlea are within normal limits.

Diagnosis: Microtia

Bilateral dysplastic pinnae. Note preauricular skin tag on right side (circle). Axial HRCT (C and D) showing bilateral mild narrowing of cartilaginous EAC (arrows) and normal bony EAC (dotted arrow) with ear wax. Also seen are the thickened sclerotic calvarial bones with loss of normal medullary cavity (asterisk). EAC: External auditory canal.

Axial high resolution computed tomography images. (A and B) showing soft tissue opacification in bilateral middle ears (A) with erosion of head of head of malleus (arrows). Coronal reformatted CT image (C) showing thinning and erosion of tegmen tympani (dotted arrows) secondary to cholesteatoma.

Coronal reformatted high resolution computed tomography. (A) image showing thickened sclerotic bones causing narrowing of bilateral internal auditory canal (arrows); normal cochlea and vestibule seen in both ears on axial high resolution computed tomography image (B).

3D reconstruction of left normal external ear B. 3D reconstruction of right external ear, showing auricular microtia C (coronal plane) and D (axial plane), 2D CT images from the same patient show external auditory canal agenesia and absence of the tympanic bone

Right-sided Goldenhar syndrome in a 12-year-old patient. a–d Axial CT images through right temporal bone. The facial nerve canal shows a relatively long labyrinthine segment (a, arrowhead); note the associated hypoplastic appearance of the ossicular chain (a, arrow). Short tympanic segment of facial nerve (b, arrowheads); a second genu cannot be clearly identified, but the mastoid segment of the facial canal is running posterolaterally to the tympanic cavity (c, arrowhead). At a lower level, the mastoid segment of the facial nerve can be seen to run lateral to the middle ear cavity (d, arrowhead). e–h For comparison, the corresponding heterolateral structures are labelled on axial CT images of the normal left temporal bone at similar levels. i Coronal CT image through right temporal bone. The short mastoid segment of the facial nerve canal (arrowheads) can be seen to run inferolaterally, just lateral from the middle ear cavity (asterisks) (the opacification of the right middle ear cavity is presumably caused by chronic dysfunction of the Eustachian tube)

(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) 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.

Axial CT Scan of the external auditory canal abnormalities, A, stenosis(arrow) is seen on the right B, Atresia and formation of an atretic plate (arrow head) are in the right , A normal external auditory canal is on the left (arrow).

CT scan in the axial plane of right unilateral external auditory canal atresia (EACA) is shown. The right external auditory canal (EAC), to the left of this photo, is not developed compared to the normally developed left EAC. The image is slightly tilted in the horizontal plane.

Microtia – congenital anomaly of external and middle ear, resulting in conductive hearing loss. External auditory canal is not patent (arrow), mastoid process is underdeveloped (arrowhead)

There is complete absence of the pinna, with soft tissue density filling the distal portion of the external auditory canal. There is some �degree of stenosis of the more proximal external auditory canal, which is vertically oriented. Also �noted is incomplete pneumatization of the left mastoid air cells and asymmetric enlargement of the left mandibular condyle.

Diagnosis: Anotia.

Atresia. CT three-dimensional reformations in a patient with unilateral microtia with deformed residual pinna (C) and external auditory canal atresia (D).

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