Complications of Temporal Bone Infections

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. 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 also predispose individuals to otitis media (OM).

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. Here, AOM refers only to an acute infection that arises de novo in a previously normal middle ear rather than an acute clinical infection that arises in long-standing OM with effusion. This distinction underscores that patterns of complications are different in AOM versus COM.

After the first few weeks of life, suppurative AOM is caused primarily by three organisms— Streptococcus pneumoniae, Haemophilus influenzae, and Branhamella catarrhalis —and these compose roughly 30%, 20%, and 10% of isolates, respectively. Despite routine administration of conjugated pneumococcal vaccine to infants and young children, S. pneumoniae remains one of the most commonly isolated pathogens in the setting of AOM and acute mastoiditis. Optimal treatment for acute suppurative OM with complications includes appropriate antibiotics in addition to myringotomy and placement of a ventilating tube. Tympanocentesis alone or myringotomy with tube placement can be used to obtain material for culture and sensitivity to identify the offending organism, and it can also reduce the bacterial population. After treatment, the physician should document that the AOM has completely resolved. This can be done in the office by tympanometry and otoscopy. 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 inflammation and infection of the middle ear space and mastoid that persists longer than the 3 weeks usually necessary for resolution of AOM in a previously healthy ear. COM can occur with or without cholesteatoma. Without cholesteatoma, a tympanic membrane perforation is typically present. A third type of COM is evident in young children with persistent otorrhea who have 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 blocks the normal pathways for aeration and decreases 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, which reflects the loss of aeration.

COM is characterized by distinct bacteriology compared with AOM, with COM being highly likely to harbor multiple bacteria of anaerobic and aerobic types. Harker and Koontz 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. Lampikoski and colleagues found an increased incidence of biofilm formation in ears affected with COM, particularly in those with cholesteatoma formation, and this likely contributes to the resistance of COM to medical management with antibiotics alone.

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 that includes treatment with ototopical and/or oral antibiotics, repeated contamination, repeated cultures, 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. With persistent otorrhea, secondary fungal infection of the external auditory canal and/or the middle ear and mastoid should be considered.

History

The clinician must establish when the patient's ear was last free of disease and perfectly normal to differentiate AOM from COM. This is crucial because the bacteriology, medical treatment, and most probable complications are different for each. Key questions relate to (1) prior evaluation of the involved ear, (2) history and treatment of the OM, (3) the order of appearance and magnitude of symptoms, and (4) objective evidence that the ear was normal recently (e.g., tympanogram, radiographic study that included the ears).

Intracranial complications may present differently in children as compared with adults. Children with intracranial complications are more likely to present with headache, nausea, and vomiting, whereas adults are more likely to present with decreased level of consciousness. Establishing the chronology of this alteration of sensorium helps the physician differentiate among diagnoses of brain abscess, meningitis, and subdural empyema. A brain abscess takes weeks to develop, whereas it takes only a few hours to several days for meningitis and subdural empyema to become fulminant and progress to coma.

Box 141.2 outlines historical features that are suggestive of complications of OM.

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 come to medical attention 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 many patients.

Patients with intracranial or multiple complications often appear more systemically ill than patients with otitis alone. They can be seen with toxicity or with obtundation, manifesting depressed levels of consciousness that can vary from lethargy to total unresponsiveness.

A complete neurologic examination is essential as focal neurologic signs may be absent, subtle, or florid. The clinician should evaluate the mental status and the station and gait of the patient. The motor and sensory function of the extremities should be evaluated, and a complete cranial nerve evaluation should be performed that includes assessment of vision, extraocular muscle function, facial nerve function, and facial sensation. The presence of nystagmus should also be assessed, and the clinician should evaluate cerebellar function by checking for dysmetria or dysdiadochokinesia. In addition, ocular saccades and smooth pursuit should be assessed.

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

The physical examination of the ear itself usually does little to pinpoint a specific complication, unless an obvious postauricular, cervical, or temporal abscess is present. Nonetheless, the otologic examination should begin with an assessment of the color, size, shape, and position of the pinna compared with that of the opposite side, particularly making note of any protrusion outward or downward. The clinician must also assess the regions adjacent to the auricle for any swelling, erythema, tenderness, purulent drainage, or fluctuation.

The external auditory canal and tympanic membrane should be examined thoroughly, ideally using a microscope and fine suction. If purulent secretions are present, a sample for culture should be obtained. The clinician should document the presence of any edema and whether it primarily affects the posterosuperior bony canal wall or the entire canal circumference. Any perforation, granulation tissue, epithelial debris, and erosion of the scutum should be documented. Pneumatic otoscopy should determine whether conjugate deviation of the eyes is apparent, which suggests a labyrinthine fistula.

The tympanic membrane reflects only the status of the middle ear and can appear normal or nearly normal, even when an otologic complication is suspected. Although mastoid infection always begins with a middle ear infection, suppuration in these two locations can proceed differently, and the middle ear may revert to normal or nearly normal under treatment, whereas the mastoid may not. Specifically, this may occur when an aditus block exists (see the section on masked mastoiditis ). When evaluating a patient with a normal otologic examination and an infectious complication that could be caused by AOM or COM, a CT scan can evaluate for the possibility of an aditus block as the cause.

Imaging Techniques

CT scanning is essential for all patients suspected of having complications of OM. CT is a fast and reliable method for assessing the status of the middle ear and the mastoid air cell system and for diagnosing intracranial complications of OM. CT reveals bony details of the middle ear, epitympanic and mastoid structures, and it 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 it can reveal erosion of the bony plates that cover the sigmoid sinus, cerebellum, or tegmen of the middle ear, mastoid, and bony labyrinth.

CT scans can help to establish the specific primary otologic diagnosis (e.g., AOM, COM, and cholesteatoma), and it can help the clinician discern several of the specific cranial and intracranial complications of OM. CT has been reported to have a sensitivity of 97% and a positive predictive value of 94% in detecting complications of AOM. In addition to their diagnostic value, CT scans are useful in assessing the results of therapy, and they provide a baseline study of the mastoid for posttreatment 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. For a febrile, stuporous patient with meningeal irritation, CT scanning, even without enhancement, can be an adequate diagnostic tool to rule out intraparenchymal brain abscess or communicating hydrocephalus before performing lumbar puncture to establish the diagnosis of meningitis. Intravenous (IV) 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 but not on CT scanning, in which the adjacent bony skull often obscures the meninges. T2-weighted MRI can show intraparenchymal edema from subtle brain infection much earlier than a CT scan. Diffusion-weighted MRI may also be useful in confirming intratemporal or intracranial abscess formation, as well as evaluating for underlying cholesteatoma disease in the temporal bone. When otitic complications are suspected, CT scans and MRI provide valuable complementary information.

Lumbar Puncture

To detect meningitis, the physician must perform a lumbar puncture, measuring the cerebrospinal fluid (CSF) pressure when starting and ending the procedure. The CSF is examined for bacteria on direct smear and is measured for glucose, chloride, and protein to compare with their concentrations in serum. Lumbar puncture should be undertaken only after clinical assessment, ophthalmoscopic examination (noting that papilledema sometimes requires hours to develop), and CT scan have ruled out significantly increased intracranial pressure that can result in herniation of the cerebellar tonsils during or after the procedure. Lumbar puncture is contraindicated in the presence of elevated intracranial pressure with brain abscess and subdural empyema.