Complications of Temporal Bone Infections

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CHAPTER 140 Complications of Temporal Bone Infections

Epidemiology

Table 140-1 presents the age distribution of extracranial, intracranial, and combined complications in a large series of patients. Nearly 80% of extracranial complications and 70% of intracranial complications occurred in children in the first 2 decades of life. Extracranial complications, led by postauricular abscess, most commonly occurred in children younger than 6 years.1 In a series of 93 intracranial and extracranial complications of otitis media, 58% were present in patients younger than 20 years.2 Low socioeconomic status and overcrowding confer either greater risk of or diminished resistance to an infection with an extended course and complications. Associations with inadequate health education and limited access to medical care likely contribute to heightened risk of complication. For this reason, most of the current reports of otogenic brain abscesses come from underdeveloped countries. Although the number of cases with immunodeficiency has increased, large series of patients with complications of otitis media have not been reported in patients with human immunodeficiency virus infection or acquired immunodeficiency syndrome, or in patients receiving immunosuppressive therapy after organ transplantation, even though such individuals do have heightened risks of suppurative ear disease.

Table 140-2 shows the classification of extracranial and intracranial complications, and Table 140-3 summarizes the relative frequencies of those complications. The dominant extracranial complication is postauricular abscess, and the dominant intracranial complication is meningitis. Complications tend to occur multiply, especially intracranial complications, as shown in Tables 140-4 and 140-5. Although all of the complications originate from infection in the pneumatized spaces of the middle ear and mastoid, the mechanisms by which complications occur in AOM differ from the mechanisms associated with COM. We discuss these two entities separately.

Table 140-2 Classification of Complications of Acute and Chronic Otitis Media

Extracranial Intracranial
Acute mastoiditis Meningitis
Coalescent mastoiditis Brain abscess
Chronic mastoiditis Subdural empyema
Masked mastoiditis Epidural abscess
Postauricular abscess Lateral sinus thrombosis
Bezold abscess Otitic hydrocephalus
Temporal abscess  
Petrous apicitis  
Labyrinthine fistula  
Facial nerve paralysis  
Acute suppurative labyrinthitis  
Encephalocele and cerebrospinal fluid leakage  

From Harker LA. Cranial and intracranial complications of acute and chronic otitis media. In: Snow JB, Ballenger JJ, eds: Ballenger’s Otorhinolaryngology Head and Neck Surgery. 16th ed. Hamilton, Ontario: Decker; 2003.

Acute Otitis Media

An estimated 85% of all children experience at least one episode of AOM, making it the most common bacterial infection of childhood.3 Predisposing factors include young age; male sex; receiving bottle feedings; and being exposed to a daycare environment, crowded living conditions, or smoking within the home. Medical conditions such as cleft palate; Down syndrome; and mucous membrane abnormalities such as cystic fibrosis, ciliary dyskinesia, and immunodeficiency states also predispose individuals to otitis media.

AOM is a bacterial infection of the middle ear space characterized by vascular dilation and proliferation (manifested externally by tympanic membrane edema and erythema), mucosal edema, exudation, bacterial proliferation, white blood cell infiltration, and pus formation. AOM here refers only to an acute infection that arises de novo, in a previously normal middle ear, rather than an acute clinical infection arising in long-standing otitis media with effusion. This distinction underscores that patterns of complications are different in AOM versus COM.

After the first few weeks of life, acute suppurative otitis media is caused primarily by three organisms: Streptococcus pneumoniae, Haemophilus influenzae, and Branhamella catarrhalis, composing roughly 30%, 20%, and 10% of isolates.3 Optimal treatment for acute suppurative otitis media with complications includes appropriate antibiotics in addition to myringotomy and placement of a ventilating tube. Tympanocentesis is used primarily to obtain material for culture and sensitivity to identify the offending organism, but it can also reduce the bacterial population. Myringotomy and tube placement also provide material to identify the involved organism. After treatment, the physician should document that the AOM has completely resolved by tympanometry and otoscopy if the tympanic membrane is intact, and by otoscopy if a ventilating tube is in place. If the complication was intracranial, a computed tomography (CT) scan or magnetic resonance imaging (MRI) study should be obtained.

Chronic Otitis Media

AOM is primarily a middle ear infection that extends into the contiguous mastoid, whereas COM reflects persistent mastoid infection with concurrent otitis media. COM is present when an infectious process persists for longer than the 1 to 3 weeks usually necessary for resolving AOM in a previously healthy ear. COM can occur with or without cholesteatoma. Without cholesteatoma, there is typically a tympanic membrane perforation. A third type of COM is evident in young children with persistent otorrhea with a patent middle ear ventilating tube.

If infection in the middle ear and mastoid does not resolve, mucosal edema and exudation increase, and mucous glands and secretory elements proliferate. Mucosal edema in the spaces between the middle ear and the epitympanum and in the aditus between the epitympanum and mastoid antrum block the normal pathways for aeration and decrease oxygenation and vascularity. At the same time, the blockage prevents pharmacologic agents from reaching the attic and mastoid. Radiographically, the mastoid air cell system is partly or completely opaque, reflecting the loss of aeration.

COM changes are accompanied by a characteristic bacteriology compared with acute conditions. Harker and Koontz4 cultured 30 cholesteatomas at surgery and isolated at least one anaerobic organism in 67% of the cases, at least one aerobic organism in 70%, and both organisms in 50%. In 57% of the cholesteatomas, multiple organisms were cultured; in 30%, five or more bacteria were identified. Even without clinical infection, anaerobes, such as Propionibacterium acnes, were frequently isolated. An ear with COM is highly likely to harbor multiple bacteria of anaerobic and aerobic types.

COM that develops in patients with indwelling middle ear ventilating tubes has a different bacterial flora. In most instances, these cases begin with an upper respiratory infection or with water contamination. A series of events, including treatment with antibiotic drops, treatment with oral antibiotics, repeated contamination, repeated culture and sensitivity tests, increasing patient and physician frustration, decreasing patient compliance, and fungal overgrowth, frequently results in resistant organisms developing. The resistant bacteria most often found are Pseudomonas aeruginosa, Achromobacter xylosoxidans, and methicillin-resistant Staphylococcus aureus, although the etiologic importance of individual organisms identified on swab culture is unclear. A fungal component of the external auditory canal and the middle ear and mastoid should be considered.

Pathophysiology

Complications associated with AOM may occur during the first few days of the infection as a result of associated bacteremia. Alternatively, bacteria can extend infection to a new location. A patient may develop partial or complete facial paralysis because of dehiscence of the bony fallopian canal in the tympanic segment. If there are preformed pathways leading to the meninges or the labyrinth, patients with AOM are at risk to develop meningitis, subdural effusion, or suppurative labyrinthitis. Developmental anomalies, such as an enlarged vestibular aqueduct or Mondini’s deformity, present such a risk. Bacteria can propagate along preformed pathways left from previous surgery or temporal bone fractures. With AOM, there is no granulation tissue formation or bone destruction; complications develop by hematogenous dissemination or by direct extension along preformed pathways. The usual medical treatment of the AOM resolves the otitis, and mastoidectomy is unnecessary. It is crucial to know whether the middle ear was normal before the current AOM began.

In COM and mastoiditis, complications occur with bone destruction, granulation tissue formation, or the presence of cholesteatoma. Bacteria gain access to the involved structures most commonly by direct extension from mastoid infection, and by infecting and propagating along veins leading from the mastoid to adjacent structures. Direct extension can come about as a result of bone resorption from cholesteatoma or osteitis, or it can occur without bone erosion if the patient has preformed pathways from previous mastoid surgery, temporal bone fracture, congenital dehiscences, or other conditions that removed the intervening bone. The mechanisms by which bone is actively resorbed, although incompletely understood, probably include enzymatic degradation, suppuration, and decreased blood supply.

Diagnosis

Physical Examination

The vital signs, especially the temperature, provide a pretreatment baseline and one parameter for following the course of the disease and the treatment; however, if the patient has previously received oral or parenteral antibiotics, he or she may present without a fever. Although some patients with extracranial or intracranial complications remain afebrile during the entire course of their illnesses, the temperature curve can provide useful information in other patients.

Patients with intracranial or multiple complications often appear more systemically ill than patients with otitis alone. They can present with toxicity or with obtundation, manifesting depressed levels of consciousness that can vary from lethargy to total unresponsiveness. Focal neurologic signs may be absent, subtle, or florid. The physical examination of the ear itself usually does little to pinpoint a specific complication, unless there is an obvious postauricular, cervical, or temporal abscess.

A complete neurologic examination is essential. The clinician should evaluate the mental status and evaluate the station and gait along with the Romberg and sharpened Romberg tests. The motor and sensory function of the extremities should be evaluated, and a complete cranial nerve evaluation should be performed, including an assessment of vision, extraocular muscle function, facial nerve function, and facial sensation. The presence of nystagmus should be assessed. The clinician should evaluate cerebellar function by checking the alternate motion rate of the extremities, determining whether past pointing is present or absent, and performing the finger-to-nose test. Ocular saccades and smooth pursuit should be assessed.

It is crucial to determine whether nuchal rigidity is present, and if so, Kernig’s and Brudzinski’s signs must be sought. The optic discs should be observed with an ophthalmoscope to determine whether papilledema is present.

The otologic examination should begin with an assessment of the color, size, shape, and position of the pinna compared with the opposite side. The clinician should make note of any erythema, tenderness, or drainage, and any evidence of trauma, excoriation, or protrusion outward or downward. Next, the clinician should observe the regions adjacent to the auricle and note any swelling, erythema, tenderness, purulent drainage, or fluctuation.

The external auditory canal and tympanic membrane should be examined using a microscope and fine suction. If purulent secretions are present, a culture test should be performed. The clinician should document the presence of any edema, and whether it primarily affects the posterosuperior bony canal wall or the entire canal circumference. A drawing of the tympanic membrane should be made, illustrating any perforation, granulation tissue, or epithelial debris, and any erosion of the scutum. Pneumatic otoscopy should determine if there is conjugate deviation of the eyes suggesting a labyrinthine fistula.

The tympanic membrane can appear normal or near-normal even when an otologic complication is suspected because it reflects only the status of the middle ear. Although mastoid infection always begins with a middle ear infection, suppuration in these two locations can proceed differently, in that the middle ear may revert to normal or near-normal under treatment, whereas the mastoid may not.

We make special notation of the problem of an aditus block. The middle ear can appear normal after several courses of antibiotics while symptoms from the mastoid persist (see section on masked mastoiditis). When evaluating a patient with any infectious condition that could be caused by AOM or COM, a CT scan can evaluate the possibility of an aditus block as the cause, even if the tympanic membrane appears normal.

Imaging Techniques

CT scanning is essential for all patients suspected to have complications of otitis media. CT is a fast and reliable method for assessing the status of the middle ear and the mastoid air cell system and diagnosing intracranial complications of otitis media.5,6 CT reveals bony details of the middle ear, epitympanic, and mastoid structures, and documents pneumatization versus opacification by inflammatory process. CT can show progressive demineralization and loss of the bony septa of air cells in coalescent mastoiditis, and reveal erosion of the bony plates covering the sigmoid sinus, cerebellum, or tegmen of the middle ear, mastoid, and bony labyrinth itself.

CT scans can help to establish the specific primary otologic diagnosis (e.g., AOM, COM, cholesteatoma), and several of the specific cranial and intracranial complications of otitis media. In addition to their diagnostic value, CT scans are useful in assessing the results of therapy, and provide a baseline post-treatment study of the mastoid for comparison in case of further complications.

When the patient is somnolent or unstable, and when intracranial complications are suspected, CT may be the study of choice because it is fast and gives the health care team better access to the patient during the study than MRI does. Even without enhancement, CT scanning can be an adequate diagnostic tool for a febrile, stuporous patient with meningeal irritation when ruling out the presence of an intraparenchymal brain abscess or communicating hydrocephalus before performing lumbar puncture to establish the diagnosis of meningitis. Intravenous injection of an iodinated contrast agent is essential, however, when using CT to diagnose cerebritis, cerebral abscess, subdural empyema, and ventriculitis.

MRI provides sensitive imaging for diagnosing intracranial complications because paramagnetic contrast agents such as gadolinium-DTPA (pentetic acid) cross the blood-brain barrier in areas of cerebritis or abscess. Meningeal enhancement is easily seen with MRI (and not on CT scanning, in which the adjacent bony skull often obscures the meninges). T2-weighted MR images can show intraparenchymal edema from subtle brain infection much earlier than a CT scan can. When otitic complications are suspected, CT scans and MRI provide valuable complementary information.

Fibrous tissue in the mastoid that is a result of previous (nonactive) COM or prior surgery enhances on MRI and may be misinterpreted by the radiologist as “mastoiditis.” In such cases, the enhancement reflects the increased vascularity of this fibrous tissue and is analogous to the routine observation of enhancement of the highly vascular nasal turbinates with gadolinium.

Treatment

Although each complication has its own separate treatment, there are certain general management principles for treating the underlying otitis. For each patient, the treatment of the underlying acute or chronic otitis and the treatment of any complications can be medical or surgical, and can be administered sequentially or concurrently. In nearly all instances of complications resulting from AOM, appropriate antibiotic therapy is sufficient to resolve the otitis without any need for surgery. This usually includes aspiration by tympanocentesis or myringotomy, as previously discussed.

When complications have resulted from COM and mastoiditis, initial antibiotic therapy should involve broad-spectrum antibiotics effective against anaerobic and aerobic organisms. In all of these cases, some form of mastoidectomy is required. When surgery is necessary for intracranial complications, the neurosurgeon operates first. Temporal bone management is considered separately. A mastoidectomy may be performed at the same sitting if the patient’s condition permits. In most instances (except for brain abscess and subdural empyema), the COM and its complications are treated entirely through the mastoid. When intracranial and otologic surgical procedures are necessary, the surgeons must plan the order of procedures, preparation, draping, and incisions to limit duration of anesthesia and optimize surgery.

A mastoidectomy under these circumstances is hampered by inflammation, and landmarks can be obscured. When no cholesteatoma is associated with the mastoiditis, the external auditory canal wall can be left intact unless visibility is inadequate. An open cavity, canal wall down procedure is preferred in the presence of cholesteatoma.1

Alternatively, these cases can be operated as canal wall up procedures, wherein the cholesteatoma is debulked and infection is cleared. Several months later, after the inflammation has resolved, the residual cholesteatoma is removed at definitive surgery. Allowing the inflammation to resolve may improve the effectiveness of cholesteatoma removal. With this approach, a second-stage operation (third procedure) is often required.

Postoperative follow-up is an essential part of the general treatment of patients who experienced life-threatening complications of AOM or COM. Even when the patient responded perfectly, the surgeon should consider follow-up CT scan to confirm objectively the status of the mastoid at the termination of treatment because there is a risk of recurrence or emergence of new intracranial complications. In patients who have experienced lateral sinus thrombosis, epidural abscess, subdural empyema, or brain abscess, follow-up evaluation with enhanced MRI 2 to 4 weeks after treatment is recommended.

Extracranial (Intratemporal) Complications

Acute Mastoiditis

Acute mastoiditis can develop when AOM fails to resolve. According to Luntz and colleagues,7 acute mastoiditis exists when there are signs of AOM on otoscopy and local inflammatory findings over the mastoid process (e.g., pain, erythema, tenderness, auricular protrusion), or when the mastoid inflammatory changes coexist with radiographic or surgical findings of mastoiditis with or without evidence of AOM. Other authors insist on the concomitant presence of AOM, mastoid physical findings, and radiologic findings.8

Luntz and colleagues7 reported results of a multicenter retrospective study of 223 such patients that provided valuable insight into the process. Of patients, 28% were younger than 1 year at diagnosis, 38% were 1 to 4 years old, and 21% were 4 to 8 years old. Although one third of patients experienced signs and symptoms of AOM immediately preceding the mastoiditis, two thirds did not. Thirty percent of the patients had a history of recurrent AOM, and 5% (all of whom had recurrent AOM) had a prior episode of acute mastoiditis.

One third of the patients exhibited symptoms for 48 hours or less before diagnosis, and another third had symptoms for 2 to 6 days before presenting with acute mastoiditis. Spontaneous tympanic membrane perforation occurred in less than one fourth of patients; the tympanic membrane was bulging or erythematous in two thirds. Twenty-two percent of the patients presented with complications on admission, the most common of which was subperiosteal abscess (Fig. 140-1), followed by meningoencephalitis and occasional cases of other complications.

Despite parenteral antibiotics, 8% of the patients who had been free of complications on admission developed complications of acute mastoiditis during hospitalization. The most common was subperiosteal abscess, but three patients developed intracranial complications, and two developed facial paralysis while receiving parenteral antibiotics. One third of patients required surgery because they had extracranial or intracranial complications on admission, failed to exhibit satisfactory clinical improvement, or developed complications despite adequate antibiotic treatment during hospitalization.

Bak-Pedersen and Ostri9 reviewed the records of 79 patients who underwent acute cortical mastoidectomy for acute mastoiditis. All patients had erythema and swelling and pain over the mastoid associated with a current or recent episode of AOM that did not improve after 24 to 48 hours of intravenous antibiotics. The average age in the series was 16 months, and the average duration from the onset of disease (AOM) until admission for acute mastoiditis was 9 days. Only one third of the patients exhibited an asymptomatic interval between AOM symptoms and the mastoiditis.

Both of the aforementioned studies established that acute mastoiditis is a disease of the very young. Also, they dispelled the classic notion that acute mastoiditis develops only after an asymptomatic period of 3 to 4 weeks.

Van Zuijlen and colleagues10 pointed out that in countries such as the Netherlands, where it is unusual to prescribe antibiotics as first-line treatment for AOM, the incidence of acute mastoiditis is considerably higher than in countries where antibiotics are routinely prescribed for AOM. Lower overall costs and reduced incidence of allergic reactions resulting from withholding antibiotics in routine AOM must be weighed against heightened risks of mastoiditis and other complications.

Coalescent Mastoiditis

Pathophysiology

As the infection grows, elevated pressure within the mastoid may extend the infection beyond the confines of the mastoid. In the presence of intense inflammation and infection, phlebitis and periphlebitis are common and spread the infection to the adjacent meninges, sigmoid sinus, cerebellum, and temporal lobe.12 Infection may extend to the meninges, sigmoid sinus, labyrinth, or facial nerve. The most common pathway for infection to extend beyond the mastoid is through the lateral cortex behind the ear. Less commonly, it can extend to the soft tissues in the upper portion of the neck (see section on Bezold’s abscess) and, rarely, to the soft tissue anterior and superior to the auricle either by direct extension through eroded bone or by phlebitis and periphlebitis. Go and coworkers13 found only 8 of 118 patients in whom the mastoiditis had caused an intracranial complication.

Treatment

Treatment for coalescent mastoiditis can be either medical or surgical. Without question, complete mastoidectomy with ventilating tube placement in conjunction with appropriate antibiotic therapy provides prompt, precise eradication of all infected tissue in an expeditious and cost-effective manner. This approach is the most conservative management of this potentially serious complication. Because the increased vascularity and granulation tissue greatly increase the difficulty of the operation, however, it should not be undertaken lightly. Another consideration is that pneumatization has not progressed to incorporate the mastoid tip in children younger than 2 years, so there is risk of surgical injury to the facial nerve. The primary author’s experience with cochlear implant surgery in children 12 to 24 months old suggests, however, that the facial nerve does not exit through the lateral surface of the mastoid in this age group as is commonly taught, and the risk of facial nerve injury in this age group is not substantial.

Appropriate intravenous antibiotics for a minimum of 3 to 6 weeks also eradicate the disease process in most infected infants who have no additional complications. The therapeutic choice for a specific patient depends on the clinical factors present and regional preferences. At the end of medical therapy, it is essential to document that the disease process has been completely eradicated. The patient should continue receiving antibiotic therapy until a CT scan documents that the mastoid air cell system is no longer opacified, and the middle ear is normally aerated.