Infections of the Ear: Otitis Media and Externa, Mastoiditis
Rupal S. Jain
Candace E. Hobson
INTRODUCTION
Infections of the external and middle ear (otitis externa and otitis media) are common reasons for presentation to urgent care facilities or emergency departments (EDs). A foundational understanding of the anatomy of the ear and the pathophysiology of these infections is key to their successful management.
Anatomically, the ear is divided into the external, middle, and internal ear. The external ear consists of the auricle (pinna) and the external auditory canal (EAC). The auricle is the portion of the ear that protrudes from the head and is composed of cartilage covered by skin. The EAC, also known as the ear canal, is approximately 25 mm in length. The outer third of the EAC consists of an outer layer of skin with underlying skin follicles, cerumen and sebaceous glands, and cartilage. A thin layer of skin directly overlying bone comprises the medial two-thirds of the EAC. The tympanic membrane (TM) separates the external from the middle ear. The middle ear is an air-filled space containing the hearing ossicles (malleus, incus and stapes), the facial nerve, and the chorda tympani nerve. The middle ear communicates with the mastoid via the aditus ad antrum and with the nasopharynx via the eustachian tube. The inner ear consists of the cochlea and the vestibular labyrinth, the neural structures of hearing and balance.
THE CLINICAL CHALLENGE
Otitis Media
Acute otitis media (AOM) is a painful infectious process of the air-filled space of the middle ear, marked by the presence of both infected fluid and inflamed mucosa. It is a clinical diagnosis that is especially challenging owing to reliance on symptoms that are neither sensitive nor specific. Adding to the challenge, the physical examination is often limited owing to inadequate visualization of the TM secondary to obstructing cerumen, operator inexperience with otoscope, and/or lack of patient/child cooperation with examination. AOM is grossly overdiagnosed and unnecessarily treated, largely because of the aforementioned limitations, and this problem is compounded by the significant overlap of symptoms with the common cold, and patient preference for antibiotic treatment.1 Furthermore, the gold standard test for the diagnosis of otitis media is pneumatic otoscopy—a diagnostic maneuver not routinely taught to many providers.
MASTOIDITIS
Mastoiditis is a nonspecific term describing an inflammatory process of the mastoid. Because the middle ear and mastoid air spaces are confluent, AOM and serous otitis media typically result in some degree of mastoid inflammation. Technically, however, mastoiditis is a complication of otitis media caused by osteitis of the mastoid air cells resulting in breakdown of bony septations and coalescence of air cells. The full term for this condition, “acute coalescent mastoiditis,” is often simply referred to as “mastoiditis.”
Untreated, mastoiditis can lead to abscess formation, bone resorption, and invasive spread of the infection. Part of the diagnostic challenge is that initial findings may be subtle and variable based on the involved pathogen and patient age group. The classic postauricular symptom, tender and erythematous postauricular swelling as well as anteroinferior displacement of auricle, were present in only 10% of patients in a 2012 retrospective study.2 Accurate diagnosis relies on a combination of clinical symptoms, physical exam and otoscopic findings, and supportive evidence on computed tomography (CT) or magnetic resonance imaging (MRI).3
Otitis Externa
Acute otitis externa (AOE) affects patients of all ages with a lifetime prevalence of 10%.4,5 Otitis externa is inflammation or infection of the EAC, which may extend to involve the auricle or TM. AOE, also known as “swimmer’s ear,” is a cellulitis of the skin of the EAC. When otitis externa persists for over 3 months, it is considered chronic. Chronic otitis externa may be the result of inadequately treated AOE but is often associated with chronic dermatologic conditions. Distinguishing the nature and etiology of otitis externa is key to effective management.
PATHOPHYSIOLOGY
Otitis Media
AOM occurs most commonly in patients 6 to 24 months old, with most cases occurring in patients under the age of 5.6 In developed countries, the incidence of AOM in adults is less than 1%.7 Children are more susceptible to AOM owing to their shorter and more vertical eustachian tubes. Acute infection usually occurs in the setting of a recent viral upper respiratory infection, as inflammation and edema impede normal flow through the eustachian tube and allow pooling in the middle ear, creating conditions favorable for infection. In pediatric studies, AOM is most often associated with viral pathogens isolated from middle ear aspirates.8 The most commonly responsible bacterial pathogens are Streptococcus pneumoniae, nontypeable strains of Haemophilus influenzae, and Moraxella catarrhalis. In the less commonly infected adult population, further organisms include Group A Streptococcus, Pseudomonas aeruginosa, and Staphylococcus aureus.
Mastoiditis
The mastoid is an air-filled space of the temporal bone that lies posterior to the ear canal and middle ear. Acute coalescent mastoiditis is the most common intratemporal complication of AOM, which most typically occurs in young children following an episode of AOM. As purulent fluid from the middle ear collects in the mastoid air cells, osteitis, bony erosion, and coalescence of the mastoid air cells occurs. The most common offending organisms are S pneumoniae, Streptococcus pyogenes, S aureus, and P aeruginosa.9
By contrast, chronic mastoiditis is chronic inflammation of the mastoid air cells occurring in the setting of chronic otitis media; this sometimes requires elective surgical intervention. These patients present with chronic otorrhea, otalgia, and hearing loss and are not typically acutely ill.
Otitis Externa
AOE is an infection of the skin of the EAC that often occurs owing to a break in the EAC skin and cerumen barrier. Cerumen provides a protective lipid film overlying the skin of EAC that is slightly acidic and thus inhibits bacterial or fungi proliferation. Often, instrumentation of the ear, whether by a physician or by the patient with a Q-tip, fingernail, or bobby pen, disrupts this protective layer and, additionally, causes microtrauma to the underlying skin and allows for the entrance
of pathogenic organisms. The introduction of moisture (irrigation, swimming, sweat) further contributes by creating a moist, warm, dark space that is ideal for bacterial or fungal proliferation. P aeruginosa and S aureus are the most common AOE pathogens.2,5
of pathogenic organisms. The introduction of moisture (irrigation, swimming, sweat) further contributes by creating a moist, warm, dark space that is ideal for bacterial or fungal proliferation. P aeruginosa and S aureus are the most common AOE pathogens.2,5
APPROACH/THE FOCUSED EXAM
Acute Otitis Media
AOM is a clinical diagnosis; therefore, laboratory and imaging tests are not routinely necessary. Symptoms of AOM may include current or recently resolved upper respiratory infection (URI) symptoms (rhinorrhea, cough), unilateral or bilateral otalgia, decreased or muffled hearing, and otorrhea. On examination, the patient may have fever, retracted or bulging TM (Figure 4.1A), erythematous (from inflammation) or a yellow/white (from effusion) hue to the TM (Figure 4.1B), reduced TM motion on pneumatic otoscopy, and TM perforation (especially if the patient presents with otorrhea). Facial paralysis, meningismus, mastoid tenderness, or toxic appearance may be late signs suggestive of spread of the infection beyond the ear. In severe cases, intracranial complications may include meningitis, intracranial abscess, lateral sinus thrombosis, and otitis hydrocephalus.
