Inflammatory

Otitis Externa

There are six forms of otitis externa (OE; also known as external otitis); acute, chronic, eczematous (dermatitis, psoriasis, lupus, or infantile eczema related), fungal, and necrotizing/malignant.

Acute Uncomplicated External Otitis

Acute uncomplicated external otitis or swimmer’s ear is the most common external ear infection. Patients with OE

present with pain, erythema, swelling, and severe tragal and auricular motion tenderness. Occasionally, a conduc- tive hearing loss may be present when canal swelling has obliterated the patency of the EAC.^64,65Most commonly, the condition is caused by a bacterial infection from Pseudomonas aeruginosaor Staphylococcus aureus. Oto- mycosis or fungal OE usually results from infection from either Candidaor Aspergillusspecies. Presentation usually follows the administration of multiple oral or topical anti- bacterial medications and can be quite refractory to conventional therapy.⁶⁶There is also an increased risk of otomycosis among diabetic and/or immunocompromised patients.⁶⁷When otomycosis complicates perforated otitis media or otitis media with a tympanostomy tube, therapy can be very challenging because most medications that are active against fungal species have not been approved by the U.S. Food and Drug Administration or are safe for middle ear usage. Uncommonly, acute OE can result from viral infection. Ramsay Hunt syndrome or herpes zoster oticus is due to infection of the seventh and eighth cranial nerves by reactivation of latent herpes zoster virus in the geniculate, spiral (i.e., cochlear), and/or Scarpa’s (i.e., vestibular) ganglia. Classically, this disease presents with acute facial palsy and a vesicular eruption in the distribu- tion of the somatosensory fibers of the facial nerve within the EAC and auricle.⁶⁸ When the vestibulocochlear nerve is involved, sensorineural hearing loss and vertigo may be present to varying degrees. Treatment of this disorder usually requires systemic corticosteroid therapy and an antiviral medication with efficacy against the offending agent (i.e., valacyclovir).

Imaging has a limited role in the diagnosis of acute OE unless it is recurrent or there is suspicion of an underly- ing benign or malignant lesion. Refractory OE may result from chronic EAC obstruction from a variety of lesions.

Similarly, malignant tumors may result in canal obstruc- tion or invasion, thereby mimicking clinical OE. CT may be very useful for assessing the anatomical details medial to a completely obstructed EAC. The presence of osseous erosion may be the only clue to an underlying neoplastic process. When facial paralysis complicates any EAC dis- ease, a comprehensive evaluation of the temporal bone including the facial nerve may be indicated. In some cases, this may require both MR and CT imaging. Specifi- cally, the osseous or intratemporal facial nerve is best evaluated with fine-cut images through the temporal bone. When IAC or cisternal involvement is suspected, MRI is more useful. For instance, when herpes zoster is suspected, MRI is the study of choice and demonstrates thickened seventh and eighth cranial nerves on high- resolution CISS images as well as fusiform enhancement of the nerves within the IAC. The entire intratemporal facial nerve (labyrinthine, tympanic, and mastoid segments) enhances along with the geniculate ganglion and the

Chapter 2 The External Auditory Canal and Pinna

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membranous labyrinth (especially the cochlea). The facial nucleus within the brainstem may also enhance.⁶⁹ Enhancement that is limited to the geniculate ganglion and to the labyrinthine segment of the facial nerve indi- cates a good prognosis whereas a widespread enhance- ment correlates with a poor prognosis.⁷⁰There can also be visible enhancement of the external ear vesicles.

Chronic External Otitis

Chronic external otitis leading to EAC fibrosis and exos- toses (see below) are two conditions that are commonly seen in swimmers, surfers, and divers who expose them- selves repeatedly to cold water. It is known that trauma, a low pH within the EAC, and cerumen insufficiency predispose to chronic external otitis.⁶⁷ As discussed previously, imaging studies serve to better assess the anatomical details deep to the obstructing lesion(s) as well as help to define the existence and extent of bony erosion.

Chronic Stenosing External Otitis

Another entity in the differential is chronic stenosing external otitis (also known as medial meatal fibrosis or postinflammatory acquired atresia). Medial canal fibrosis is a rare disorder found more frequently in males. Sixty percent are bilateral and present as a fibrous plug caus- ing stenosis or obstruction of the EAC. There may be associated TM thickening in late stages. This entity is sec- ondary to chronic OE or to recurrent otitis media with a perforated TM. It can also be secondary to trauma (often iatrogenic), radiation therapy for head and neck cancer, or tumor and inflammation, and usually develops at an average of 14 years after the insult.⁷¹Chronic inflamma- tion results in a subepithelial infiltration of inflammatory cells that causes fibrosis and medial EAC stenosis. The stratified epithelium of the TM and of the adjacent bony meatus is destroyed and replaced by fibrotic tissue, which has some similarity to the tissue seen with keloid formation. The fibrotic tissue can cover an underlying CH and may recur after surgery. This process occurs in sequential steps that include destruction of the epithe- lium, formation of granulation tissue, fibrosis, and, finally, lining of the EAC with new meatal skin.⁷²Patients with hearing aids are at risk for this disease because the pres- ence of the hearing aid, or of any other foreign body, may result in abnormal migration of epithelial cells. The gran- ulation tissue that forms ultimately results in the forma- tion of a fibrous plug. CHs can also form in this space;

when this occurs, the rate of recurrence is high.^73,74A his- tory of dermatitis (eczema or psoriasis) or other chronic skin condition may predispose to this disease. This is a rare condition in children.

Patients with sclerosing external otitis are treated surgically if recurrent infection and otorrhea are present, conductive hearing loss from EAC obstruction occurs, or when the clinician suspects other pathologies, such as squamous cell carcinoma. Clinical suspicion in these cases must be high, and the threshold for imaging these patients is very low. Associated chronic, unremitting pain is a clue to more ominous pathology. CT shows a soft tissue mass within the medial EAC that is inseparable from the TM and has a crescentic appearance laterally without mastoid or middle ear involvement. There is no bone erosion, and contrast enhancement is minimal and usually appears along the thickened and edematous walls of the EAC.

There can be intense associated bony reaction and thick- ening of the EAC. MRI displays similar findings, with the mass exhibiting intermediate-to-low T2-weighted signal intensity. Lower T2-weighted signal intensity is expected if fibrous components are extensive. Postcontrast images demonstrate mild EAC wall enhancement. The differential diagnosis is extensive, the most common causes being cerumen and debris in the EAC. In these cases, there will usually be air located between the EAC wall and the soft tissue mass, as well as lack of enhancement of the mass.

Alternatively, soft tissue in the EAC with otorrhea may be due to CH, but these patients have bony erosion of the EAC and usually unilateral disease as well. The most wor- risome diagnosis that one must consider is carcinoma, which may present in the setting of long-standing chronic otitis.⁷⁵Other conditions occurring secondary to chronic OE include auricular cellulitis, chondritis, parotitis, and development into malignant external otitis (MEO).⁶⁷Enti- ties such as tuberculosis, syphilis, lupus, carcinoma, and histiocytosis may have mastoid and/or middle ear involvement.⁷⁶Surgical treatment includes excision of the fibrous tissue with a wide canaloplasty and a meato- plasty, followed by reconstruction with a fascial graft and/or split skin grafts.⁷⁷

Malignant External Otitis

MEO or necrotizing otitis externa (NOE) generally presents with otorrhea and severe otalgia in diabetics and immuno- compromised patients. This condition can also be associ- ated with a history of trauma. In most diabetics, the causes of infection are gram-negative rods such as Pseudomonas aeruginosa.⁷⁸However, there are other immunosuppressed patients who have an increased incidence of MEO, such as those with hematological neoplasms, postchemotherapy, and AIDS. In the immunocompromised host, such as AIDS patients, MEO is often due to microorganisms other than Pseudomonas, and, unlike diabetics, there is no granula- tion tissue formation. MEO in AIDS patients also has a more fulminant course, with a mortality rate of 42%

compared with 4% in diabetics. Sometimes, MEO occurs

after cerumen removal and irrigation with tap water because these organisms thrive in moist environments.

On physical examination, there is granulation tissue in the inferior EAC, along the bony-cartilaginous junction.

Commonly, the infection spreads inferiorly into the soft tissues and TMJ. MEO readily spreads via the fissures of Santorini from the EAC into the mastoid and subsequently into the TMJ and middle cranial fossa, causing sigmoid sinus thrombosis and secondary venous infarction. Mid- dle cranial fossa involvement can also result in meningi- tis, subdural empyema, and brain abscess. Spread through the TM is unlikely; instead, middle ear involvement is usually secondary to mastoid extension. MEO can also extend insidiously along the skull base, resulting in multi- ple cranial neuropathies, osteomyelitis, and death.^79,80 Most commonly, involvement of the facial nerve occurs at the level of the stylomastoid foramen.⁸¹If spread along the skull base occurs posteriorly and inferiorly into the region of the jugular foramen, the infection can involve CN IX to XII, resulting in jugular foramen syndrome. MEO has been classified into the following stages:^82,83

• Stage I: Confined to the EAC with or without facial nerve paralysis (Fig. 2.11)

• Stage II:Superior extension, skull base osteitis, and/or multiple cranial nerve involvement

• Stage III: Extension beyond the temporal bone or intracranially and contralateral involvement

Imaging of MEO can be performed with CT and/or MRI to evaluate the initial extent of disease. CT is superior for evaluation of bone destruction, but MRI is superior for eval- uation of soft tissue extension, cranial nerve involvement,

osseous marrow changes, meningeal disease, and parotid extension.^84,85In cases where MEO cannot be differenti- ated from uncomplicated OE, technetium 99m methylene diphosphonate (Tc 99M MDP) may be useful in helping make the diagnosis. Tc 99M MDP may show positive areas where CT and MRI show little if any changes. Conversely, Tc 99M MDP scanning is positive with bone erosion or new bone formation with healing, and thus it is not effec- tive for differentiation of continued disease or healing.

Labeled white blood cell scans can also be helpful. Gal- lium scans are sensitive for monitoring therapy.⁸²Therefore, gallium-67 single-photon emission computed tomogra- phy (SPECT) is advocated for follow-up and evaluation of treatment.⁸⁶

The differential diagnosis of MEO includes OE, chronic otitis media (COM) with CH, EAC CH and keratosis obtu- rans (KO), chronic granulomatous diseases, Langerhans cell histiocytosis, and carcinoma of the EAC. Characteristic among most of these pathologies is granulation tissue within the EAC. Differentiation among these varied pathologies ultimately may require microscopic evalua- tion, culture, and biopsy of the offending tissue. This should only be considered when imaging has assessed the involvement of the underlying middle ear, inner ear, and facial nerve.

Other Causes of Inflammatory External Auditory Canal Pathology

Tuberculosis (TB) in the head and neck region usually presents as cervical lymphadenopathy (95%). In 2% of patients with head and neck involvement, TB presents in the larynx, and in 1% of cases, it will present in the cervical spine, oropharynx, ear, or as a retropharyngeal abscess.

Only 9% of patients will have a history of previous or sub- sequent TB.⁸⁷ Tuberculous OE has been described as a punched-out ulcerative lesion on the tragus, an edema- tous and inflamed EAC, or a purulent nonmucoid dis- charge with facial palsy.⁸⁸Tubercular mastoiditis, petrous apicitis, and otitis media also occur.⁸⁹Typically, patients with EAC involvement present with otorrhea, hearing loss, and dizziness, and may have facial palsy. TB at imag- ing, in particular with CT, appears as an aggressive osteo- destructive process (Fig. 2.12).⁹⁰

Wegener granulomatosis is a nonneoplastic, aseptic, necrotizing vasculitis that typically affects the sinonasal cavities, the orbits, oral cavity, nasopharynx, larynx, tem- poral bone, and skull base. In 70% of patients, there is an elevated erythrocyte sedimentation rate, and antineu- trophil cytoplasmic antibody (C-ANCA) is present.⁹¹There is respiratory and renal tract involvement in most patients;

19 to 38% of patients have otologic involvement, which may mimic relapsing polychondritis. Patients typically present with ear pain, otitis media with effusion (40 to 70%),

Chapter 2 The External Auditory Canal and Pinna

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Fig. 2.11 Coronal computed tomography scan shows soft tissue filling the external auditory canal (EAC) in this diabetic patient with stage 1 (confined to the EAC) malignant otitis externa. The tympanic membrane is thickened.

sensory neural hearing loss (8%), and tinnitus. Patients are usually men 40 to 60 years of age. There is an increased risk of superimposed infection and mastoiditis. Because this disease is indolent, it can be present for years prior to diagnosis, but the prognosis is poor if left untreated.

C-ANCA titer elevations are 85 to 98% specific and are used to follow up the response to corticosteroids and immuno- suppressive agents. If renal disease is present, serum crea- tinine levels are high.⁹²Imaging studies may show bone destruction generally accompanied by soft tissue thicken- ing throughout the temporal bone (Fig. 2.13). Unfortunately, the imaging features are nonspecific and may be identical to those seen in EAC carcinoma or chronic otitis.

Langerhans cell histiocytosis (LCH), if limited to bones, is commonly referred to as eosinophilic granuloma. It is characterized by an accumulation of abnormal histio- cytes, together with lymphocytes and eosinophils. Histio- cytosis can involve the temporal bone region in as many as 25% of patients⁹³and may mimic acute or chronic in- fectious ear disease.^93,94Ear involvement occurs in 13.5%

of childhood cases and is associated with a younger age at diagnosis, multisystem disease (93.8%), and a higher risk of poor response.⁹⁵The disease is often located adjacent to or within the area of the endolymphatic sac.⁹⁶ At imaging, there are destructive bone lesions involving the mastoid bone (Fig. 2.14). The squamous portion of the temporal bone and the middle ear are less commonly affected.⁹⁷ At CT, the lesions produce significant bone destruction and enhance homogeneously. CT is the pre- ferred study of choice for diagnosis, determining the extent of temporal bone involvement, and for monitoring response to treatment. Bone scans are less sensitive than CT for detec- tion of lesions.⁹⁷With MRI, the lesions are bright on T2- weighted sequences, isointense to marrow on T1-weighted sequences, and enhance intensely.⁹⁸MRI is useful for evalua- tion of intracranial extent and assessment of vascular involvement, and thus is complementary to CT.⁹⁹Treatment can be with surgery, radiotherapy, and/or chemotherapy;

preservation of hearing is the goal. The posttreated temporal bone re-ossifies and remodels.

Cholesteatoma

Both CH and KO arise from exfoliation of squamous ep- ithelium into the EAC, but these processes occur in dif- ferent age groups; generally CH is found in individuals over age 40, and KO in those under age 40.¹⁰⁰With CH,

A B

Fig. 2.12 (A)Axial computed tomography (CT) scan shows aggressive process (proven tuberculosis) with destruction of the walls of the exter- nal auditory canal and extension into the mastoid posteriorly, to the tem-

poromandibular joint anteriorly, and medially into the middle ear. The ossicles show irregular borders due to early involvement. (B)Coronal CT shows the degree of extension, particularly into the mastoid bone.

Fig. 2.13 Axial computed tomography scan in a patient with Wegener granulomatosis shows destructive process centered in the right mas- toid. There is extension of the disease into the middle ear cavity and the ossicles show marginal erosive changes.

A

C D

E F

B

Fig. 2.14 (A)Axial computed tomography (CT) scan in a young child shows “punch-out” aggressive soft tissue mass involving the lateral as- pect of the right temporal bone and extending into the middle ear cav- ity. Biopsy show eosinophilic granuloma. In a child, a middle ear rhab-

domyosarcoma may have a similar appearance. (B)Axial CT in a differ- ent and older child shows too a punch-out lesion involving the posterior wall of the right external auditory canal (EAC). Soft tissue fills the EAC.

This was also eosinophilic granuloma.

there is unilateral, dull, chronic ear pain and pruritus, typ- ically accompanied by otorrhea. There is erosion of the posteroinferior wall of the EAC and a normal-appearing TM. EAC CH usually presents with normal hearing, unless large, when it produces conductive hearing loss. Histolog- ically, CH arises from hyperplastic epithelium containing inflammatory cells. Subsequently, there is invasive growth of the lesion into the mesenchymal tissues with accumu- lation of necrobiotic keratin debris and bone erosion with bony sequestra formation.¹⁰¹There are several different causes of EAC CH with the congenital form occurring with patients with EAC stenosis/atresia and the acquired form probably related to periostitis (Fig. 2.6). After EAC sur- gery, there is approximately a 1% chance that CH may arise from inclusion cysts along the incision.¹⁰²

EAC CH is best assessed with CT, which demonstrates bone erosion. EAC erosion is smooth or irregular and tends to be focal. CH shows a soft tissue mass and erosion within the bony portion of the EAC (Fig. 2.15). When this process is associated with acute periostitis, it may be difficult to differentiate from carcinoma (Fig. 2.16). On MRI, recurrent CHs have restricted diffusion and are

bright on diffusion weighted images.¹⁰³The staging aris- ing in the EAC is as follows¹⁰¹:

• Stage I:Hyperplasia of the canal epithelium

• Stage II:Hyperplasia with periostitis

• Stage III:Necrosis/erosion of the bony canal

• Stage IV:Erosion of structures beyond the EAC

Treatment of EAC CH includes débridement with exci- sion of the matrix. Removal of necrotic bone adjacent to the soft tissue mass may be needed to prevent osteitis and recurrence, as well as to allow for normal squamous epithelial migration. Because of its characteristic posterior and inferior location within the EAC, the descending seg- ment of the facial nerve is at risk during treatment of this disorder. Great care must be exercised when removing CH matrix in this location. CT imaging is of paramount importance in determining the extent of involvement, and supplementary facial nerve monitoring is recommended during surgery in this region. Although the middle ear space is usually spared in this disease, occasionally canal erosion can extend inferior to the tympanic annulus and

A B

C

Fig. 2.15 (A)Coronal computed tomography (CT) scan in a patient with a cholesteatoma of the right external auditory canal (EAC).

There is erosion of the floor of the EAC, and the soft tissue mass is contiguous with the pars tensa of the tympanic membrane.

(B)Coronal CT in a patient with a typical pars flaccida acquired cholesteatoma. The rounded mass protrudes mostly into the EAC rather than into Prussak’s space. The tip of the scutum is blunted.

(C)Axial CT in the same patient shows the rounded cholesteatoma in the anterior aspect of the EAC.