Atresia and Hypoplasia

Congenital anomalies of the EAC are rather common, more so than middle ear abnormalities. The degree of congenital deformities of the EAC runs the gamut from total atresia to webs, to hypoplasia or stenosis of the EAC, to microtia (a small auricle of the ear) (Fig. 12-1 and Box 12-1).

Figure 12-1 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.

The degree of microtia tends to correlate with the extent of bony stenosis of the EAC. Middle ear malformations also vary with the severity of the auricular anomalies. Pneumatization of the middle ear often follows the degree of microtia: 67% of patients with major microtia (absence of normal auricular structures and anotia) have reduced pneumatization of the middle ear and mastoid. This is important to note because the surgeon needs to know how much drilling he will have to do and how large a space he will have to work in to reconstruct middle or inner ear structures. In addition, it is important to know whether the inner ear structures are normal. Thirteen percent of patients with microtia have dysplastic inner ear structures—usually a hypoplastic lateral semicircular canal.

In minor microtia (pocket ear, absence of upper helix, absence of tragus, mini-ear, clefts, and so on), 50% of the patients have a dysplastic malleus-incus complex, whereas with major microtia, 67% are dysplastic and 30% have absent ossicles altogether. The incudostapedial joint is commonly abnormal (>65%) in both minor and major microtia. Abnormalities of the stapes coexist in up to 70% of cases.

Thalidomide embryopathy accounted for a large blip in EAC dysplasias in the early 1960s; rubella infections still account for some these days. Bilateral EAC atresia is seen in 23% to 29% of cases. There is often concomitant abnormality in the temporomandibular joint, with EAC anomalies manifested by flattening or absence of the glenoid fossa. Dysplasia of the mandibular condyle (remember both the EAC and mandibular condyle are formed from first branchial apparatus structures and are associated with the fifth cranial nerve) and defects of the zygomatic arch may be seen. At the extreme, atresia of the EAC may be associated with hypoplasia of the malleus, fusion of the malleus and incus, or other anomalies of middle ear structures (in >50% of cases).

With a stenotic EAC, the slope of the EAC may be more vertically angulated. In addition, keratinous plugs and cholesteatomas may form. Rarely (11% to 30%) is there an associated anomaly of the inner ear, mainly because inner ear structures are derived from the neuroectoderm as opposed to the branchial system. In patients with EAC atresia, the facial nerve in its horizontal section may have an aberrant course in close proximity to the stapes footplate and may be anteriorly located in its descending portion. Evaluation of the facial nerve position (see Chapter 2), carotid and jugular anomalies, middle ear and mastoid air cell pneumatization, ossicular deformities, meningoencephaloceles, sigmoid sinus location, and other features is important for preoperative planning to prevent accidental surgical injury. The facial nerve may also be dehiscent in its tympanic course.

Surgery to correct the EAC is fruitless if the inner ear is nonfunctional. This must be evaluated. Surgery for external ear anomalies is difficult because it often requires grafts of bone and cartilage as well as drilling new canals. Thus, correction just for cosmetic purposes is usually delayed until after adolescence, when growth has slowed down. However, if the ear anomaly leads to learning disabilities it may be treated before schooling (Table 12-1).

Table 12-1 Checklist for Evaluating for EAC Atresia or Stenosis

First Branchial Cleft Cysts

First branchial cleft cysts occur around the ear or in the neighboring parotid gland (Fig. 12-2). A fistula from a first branchial cleft anomaly may drain to the EAC at the bone-cartilage interface. Second branchial cleft cysts are 10 times more common than first branchial cleft cysts, but the external ear would be an unusual site for a second branchial cleft cyst to drain.

Figure 12-2 First branchial cleft cyst. Axial T1-weighted image shows a cystic mass (C) in the right parotid gland near the external auditory canal. Rarely a first branchial cleft anomaly will communicate with the external ear.

Calcifications of the external ear or pinna occur in a variety of congenital and acquired lesions. Box 12-2 lists these entities.

Malignant Otitis Externa

The most severe inflammatory condition affecting the EAC is malignant otitis externa, a Pseudomonas infection of the EAC seen in elderly diabetic patients (93% of cases). HIV-infected patients may also be at risk. Patients present with putrid-smelling, purulent discharges coming from their ear. The infection usually begins at the junction of the cartilaginous and bony portion of the EAC along the fissures of Santorini, which lead to the parapharyngeal space. Irrigation of the ear under pressure will drive the inflammatory process out of the EAC, leading to a potential aggressive infection extending into the infratemporal fossa, the nasopharynx, the parapharyngeal space, the adjacent bone, the temporomandibular joint, the middle and inner ear structures, and intracranially in the extradural space. Palsies of cranial nerves VI, VII, and IX through XII may reflect extension of the disease at the skull base and neural foramina. Venous sinus thrombosis is a complication. The process may mimic an aggressive neoplasm in many respects and often is difficult to control with antibiotics. CT will identify soft tissue in the EAC, bony erosion of the EAC walls, and osteitic changes at the skull base. Magnetic resonance (MR) imaging may demonstrate edema of the external ear, the parapharyngeal fat may be obliterated as the infection extends anteriorly and medially, and the tissue planes around the carotid sheath may be infiltrated (Fig. 12-3). The signal intensity of the skull base may be abnormal and the bone may enhance. Technetium-99m bone scans and gallium-67 citrate scans show uptake of radiotracers and may be useful to assess activity of disease.

Figure 12-3 Malignant otitis externa. A, computed tomography (CT) shows a soft-tissue mass in right external auditory canal (EAC, asterisk) with opacification of middle ear and mastoid air cells. B, Lower section demonstrates bone reaction secondary to osteitis of the clivus (arrows). C, Obliteration of tissue planes in the nasopharynx and parapharyngeal space by infectious mass (M). Open arrows indicate the osteomyelitis. D, The fat-suppressed T1-weighted image (T1WI) shows enhancing tissue in the EAC, mastoid, petrous tip, right side of clivus, and parapharyngeal space. E, High signal on T2WI is present in the clivus and longus musculature. F, This CT section through the same level as D section shows the difference between what magnetic resonance can show versus the bony details afforded by CT.

Keratosis Obturans

Keratosis obturans, caused by plugs of keratin in the EAC, is hard to distinguish from a congenital cholesteatoma, which may infiltrate from the middle ear to the EAC. Keratosis obturans, however, is very painful and is usually seen bilaterally in middle-aged adults with histories of bronchiectasis or sinusitis. Acquired cholesteatomas are usually unilateral and are seen in older patients. A duller, less severe pain is noted and there is more bone erosion, often extending into the middle ear and mastoid bone.

Swimmer’s Ear and Surfer’s Ear

Swimmer’s ear (acute external otitis) is usually due to Pseudomonas infection. Rarely, mastoiditis or osteomyelitis may complicate swimmer’s ear. Patients who swim in cold water are prone to exostoses of the EAC (surfer’s ear). Recurrences will occur if the swimmer returns to the frozen pool or frigid oceans (Fig. 12-4). Relapsing chondritis, frostbite, and severe sunburns may affect the auricle of the ear, particularly the upper helix.

Figure 12-4 Exostosis of the external auditory canal (EAC). Coronal computed tomography reveals a dense EAC exostosis (arrow).

Of course, the most common EAC mass is due to benign wax buildup.

Squamous Cell Carcinomas

Squamous cell carcinomas of the EAC are the most common neoplastic processes in this location. This is essentially a skin cancer with the associated risk from sun exposure. The lesion may invade the middle ear and temporal bone. Cartilaginous invasion of the external ear or middle ear extension portends poor prognosis and must be treated aggressively. The 5-year prognosis for EAC squamous cell carcinomas without middle ear disease is 59%, but it is 23% if the cancer extends into the middle ear. Deep lesions in the bony canal have the worst prognosis (Fig. 12-5). Pain occurs early because of periosteal spread or extension to the temporomandibular joint, where trismus may also arise. Facial nerve involvement also occurs early in the course.

Figure 12-5 External auditory canal (EAC) squamous cell cancer. A, Coronal T1-weighted image of a patient with an extensive squamous cell carcinoma of the EAC reveals considerable spread into the mastoid air cells and the suprazygomatic portion of the masticator space (arrow). B, Extensive destruction in the temporal bone by the cancer is seen on computed tomography.

Other Skin Tumors

Other skin tumors such as basal cell carcinomas or melanomas may also affect the external ear in the same manner as squamous cell carcinomas. In rare cases, they develop perineural spread via cranial nerves V and VII (Fig. 12-6). Lymphatic drainage may be to intraparotid, retropharyngeal, occipital, and skull base lymph nodes. Kaposi sarcoma in HIV-positive individuals could affect the ear. Carcinomas of the parotid gland commonly invade the temporal bone and EAC, particularly if perineural growth occurs along cranial nerve VII. Adenoid cystic carcinoma of the parotid is the classic histology for this eventuality.

Figure 12-6 Invasion of temporal bone by basal cell carcinoma (B) of the skin. Note the extensive medial extent of this mass, which arose from the skin around the ear in a south Florida sun worshipper.

(Courtesy of Stuart Bobman.)

Pediatric Tumors

In children, rhabdomyosarcomas and lymphomas may present as external ear masses. Spread to the middle ear or along the eustachian tube is not uncommon, and in fact, tumors arising in the nasopharynx can present as ear masses because of retrograde growth along this route. Invasion of the petrous and mastoid portions of the temporal bone is not uncommon (Fig. 12-7).

Figure 12-7 Retrograde spread of nasopharyngeal cancer. A, Patient had pain and discharge emanating from right ear. T1-weighted image shows a soft-tissue mass (M) in the right mastoid region that eroded into the external auditory canal (EAC). B, The ear was the tip of the iceberg. The mass (M) arose in the nasopharynx and grew retrograde into the middle ear and EAC via the eustachian tube. Note the parapharyngeal fat and torus tubarius (t) obliteration, as well as invasion of the pterygoid muscle (p).

Metastases

Metastases are rare to affect the EAC portion of the temporal bone.

Hypoplasia and Fusion

The middle ear is also a site of congenital dysplasias that may be associated with EAC stenosis or atresia (Fig. 12-11). Ossicular fusion, hypoplasia, or maldevelopment may occur and may coexist with anomalies of the facial nerve as it runs through the middle ear cavity. Isolated middle ear congenital abnormalities are not as common as those of the EAC or inner ear. When they occur in the absence of external ear anomalies, the distal incus (especially the long process) and the stapes are most commonly affected in concert, followed by the stapes alone and incus alone. These components of the ossicular chain are derived from the second branchial arch. Absence, hypoplasia, and fixation to the attic may be seen.

Figure 12-11 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 maldeveloped 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.

Epidermoids

To prevent confusion with acquired cholesteatomas, use the term epidermoids rather than the older terms congenital cholesteatomas, epidermoidomas, or primary cholesteatomas. Epidermoids may arise in a variety of locations within the temporal bone (Fig. 12-12) from aberrant epithelial rests. The temporal bone is, in fact, the most common skull base site of congenital epidermoids. The classic locations for these lesions include the petrous apex, Koerner’s septum (the petrosquamosal suture), mastoid air cells, eustachian tube opening, geniculate ganglion region, middle ear-epitympanum junction, incudostapedial joint, sinus tympani, and facial nerve recess. Intracranial locations for epidermoids are in the IAC and the basal and cerebellopontine angle cisterns. These lesions are pearly white to the surgeon’s eye and are usually hypointense on T1-weighted images (T1WI) and hyperintense on T2-weighted images (T2WI). As in the brain, they are as bright as cerebrospinal fluid (CSF) on T2WI but are more intense than CSF on T1WI. They are brighter than CSF on fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted images (DWI). On CT, they appear as noninvasive, low-density, erosive, well-circumscribed lesions in the temporal bone with scalloped margins (Fig. 12-13). Although they may be whitish lesions that simulate acquired cholesteatomas, these lesions are not associated with perforation of the tympanic membrane, and the patients have no history of antecedent ear infections or previous surgeries. Presentation often is with deafness, vertigo, or facial nerve palsy. The scutum is usually intact. Epidermoids may be solid or cystic. Epidermoids do not enhance, whereas acquired cholesteatomas may enhance perip herally. Treatment for both is surgical excision.

Figure 12-12 Epidermoid (E) of bone. A, A lytic oblong bone lesion is seen along the posterior margin of the top of the petrous bone. B, Note how bright the mass is on T2-weighted image. The diagnosis was an intraosseous epidermoid. Contrast this case with that of the enlarged vestibular aqueduct on computed tomography and magnetic resonance imaging (see Fig. 12-32).

Figure 12-13 Epidermoid of petrous apex. Axial computed tomography displays a well-defined mass in the petrous apex with a thin bony margin (arrowheads). This was a congenital cholesteatoma (epidermoid).

Otitis Media

Inflammatory disease of the tympanic cavity is common in children. Opacification of the epitympanic recess with thickening of the tympanic membrane is often seen in patients with otitis media. The most frequent causes of otitis media are Streptococcus, Moraxella catarrhalis, Haemophilus influenzae, and Pneumococcus. Obstruction of the eustachian tube from nasopharyngeal lymphoid hypertrophy caused by upper respiratory tract infections is responsible for this condition in children. Otitis media generally responds well to antibiotics. Rarely, ossicular erosions, usually a marker for acquired cholesteatoma, can occur in association with acute otitis media. When they occur, they usually affect the long process of the incus and can lead to conductive hearing defects. The erosions appear on CT as tiny, lytic, punched-out areas in the ossicle. The middle ear is filled with fluid density and intensity on CT and MR, respectively, in uncomplicated otitis media (Fig. 12-14). Although pneumolabyrinth is more commonly seen in cases of barotrauma or in the postoperative setting, occasionally you may see air in the inner ear structures with infections, presumably from a labyrinthine fistula. Gas-producing organisms may be at fault.

Figure 12-14 Acute otomastoiditis. A, An air-fluid level is seen in the epitympanic space with complete opacification of the mesotympanum. The mastoid air cells are also opacified. B, Air in the vestibule and in the cochlea (pneumolabyrinth), seen in this patient with otomastoiditis, implies an open connection between the middle ear and the inner ear.

Ossicular disruptions may be caused by trauma or infection (Fig. 12-15). A gap of greater than 1 mm between the long process of the incus and the head of the stapes is suspicious for disruption. This finding is equally well displayed on axial or coronal sections. Usually the inflammatory causes are due to erosion of the long process of the incus. Fibrosis may ensue. Because the incus is not well suspended by the anchoring ligaments, the incudostapedial joint is most commonly affected by trauma. Therefore, dislocations and subluxations are common between the incus and stapes. Incudal disarticulation accounts for more than 80% of post-traumatic conductive hearing loss.

Figure 12-15 Ossicular dislocation. A, Note that the head of the malleus seems to be “falling off” of the short process of the incus on this axial scan. This is incudomalleolar dislocation, most often found in the setting of trauma. B, The presence of both the incus and the malleus in the same slice on a coronal scan is ABNORMAL! Usually the incus lies posterior to the malleus head.

Effusions

Middle ear effusions may be present with both infectious and noninfectious processes. They appear as nonerosive opacification of the middle ear cavity. One may identify an air-fluid level. The process may be due to a pressure phenomenon and can be seen in patients after air travel in poorly pressurized compartments. Radiation therapy may also be a culprit. Alternatively, look for the long-standing nasogastric tube as a predisposing factor. This may also lead to mastoid air cell opacification.

Mastoiditis

Infection may travel from the middle ear via the aditus ad antrum (the narrow channel connecting the middle ear cavity to the mastoid antrum) to the mastoid air cells. Mastoiditis may occur as a complication of otitis media; coalescence of mastoiditis portends a poor prognosis because it represents bony infection rather than mucositis. β-Hemolytic streptococci and pneumococci are usually the pathogens involved. CT reveals opacification of air cells; bone destruction constitutes a criterion for coalescent mastoiditis. The infection is very bright on T2WI. Occasionally, air-fluid levels within the small mastoid air cells can be seen. Middle ear or petrous apex opacification may coexist. Coalescent mastoiditis may also be a complication of cholesteatoma formation (Fig. 12-16).

Figure 12-16 Coalescent mastoiditis. Note the destroyed mastoid air cell septations and the dehiscent area at the transverse sinus anterolateral margin (open arrow). This is a set-up for septic thrombophlebitis. The anterior margin of the petrous bone is also eroded focally (arrowheads).

Complications of acute otomastoiditis include sigmoid sinus thrombosis (see Chapter 4), thrombophlebitis, epidural abscesses, meningitis, subperiosteal abscesses, fistulas, and osteomyelitis. Cerebellar or temporal lobe encephalitis is uncommon. Bezold’s abscess is an inflammatory collection that occurs inferior to the mastoid tip as the infection spreads from the bone to the adjacent soft tissue (Fig. 12-17). It can spread down the plane of the sternocleidomatoid muscle to the lower neck.

Figure 12-17 Bezold’s abscess. A, The T2-weighted image shows the opacified mastoid air cells as well as inflammation extending into the subcutaneous tissue. B, The coronal enhanced scan is fantastic; see the ring-enhancing abscess (arrow) just below the opacified mastoid tip? Note the meningeal enhancement as well.

Another complication of chronic otitis media (“COM” on the pediatrician’s chart) is ossicular fixation. This may cause a conductive hearing loss and may be fibrous (soft tissue around the ossicles) or tympanosclerotic (calcification around ossicles or ossicular ligaments).

Acquired Cholesteatomas

Long-standing otomastoiditis may result from chronic eustachian tube dysfunction. This may lead to recurrent otitis media and acquired cholesteatomas; these two entities are easier to distinguish in textbooks than in real life, where imaging characteristics may overlap (Table 12-2). Acquired cholesteatomas are erosive collections of keratinous debris from an ingrowth of stratified squamous epithelium through a perforated tympanic membrane. The critical features in identifying a lesion as a cholesteatoma are the presence of mass effect, bony erosion, or expansion (Fig. 12-18). The cholesteatoma most often arises from a perforation in the pars flaccida of the tympanic membrane. Once the pars flaccida (Shrapnell’s membrane) has been violated, the inflammatory process proceeds into Prussak’s space, which is located lateral to the middle ear ossicles but medial to the scutum in the epitympanic space. One often sees a soft-tissue mass causing erosion of the scutum and medial displacement of the malleus and incus with pars flaccida cholesteatomas. The head of the malleus and body of the incus are the areas most susceptible to erosion by a pars flaccida cholesteatoma; lysis of all the middle ear ossicles is uncommon. From Prussak’s space the lesion often spreads through the aditus ad antrum, expanding its waist as the inflammatory process proceeds into the mastoid air cells. On MR, cholesteatomas are hypointense on T1WI and intermediate on T2WI, and do not enhance, as opposed to granulation tissue (postoperative), which does enhance.

Table 12-2 Cholesteatoma versus Otitis Media

Figure 12-18 Acquired cholesteatoma. This rampant cholesteatoma has eroded the ossicles as well as the posterior wall of the mastoid air cells. Remnants of malleus and incus are present, and the middle ear cavity is opacified.

Pars tensa cholesteatomas are much less common than pars flaccida cholesteatomas. They arise from perforation through the posterosuperior-most portion of the pars tensa, which is the inferior portion of the tympanic membrane. From this location the sinus tympani, pyramidal eminence, and facial recess may be expanded or eroded. Pars tensa cholesteatomas present with a mass in the middle ear, erosion of the long process of the incus or stapes, epitympanic spread, and ossicular displacement. The scutum is usually intact.

Complications of cholesteatomas include fistulization into the semicircular canals (from 4% to 25% of cases), with the lateral semicircular canal most commonly affected. This may be identified as a dehiscence in the bony labyrinth with a soft-tissue mass expanding the region of the oval window or lateral margin of the lateral semicircular canal. Alternatively, cholesteatomas may erode the tegmen tympani (the roof of the epitympanic space) and subsequently invade the intracranial compartment (Fig. 12-19). Another area of potential erosion is the lateral or inferior wall of the tympanic portion of the facial nerve (Fig. 12-20). If there is dehiscence or skeletization of the facial nerve canal or the sinus tympani, the surgeon must know this preoperatively so that removal of the cholesteatoma is done in a careful fashion so as not to injure the underlying structures.

Figure 12-19 Tegmen tympani erosion. This example of a cholesteatoma shows erosion of the roof of the epitympanic space and the scutum. There is opacification of Prussak’s space and middle ear cavity as well as the hypotympanum.