Infection and Inflammation

Chapter 11


Infection and Inflammation



Infectious and inflammatory disorders commonly involving the temporal bone; external, middle, and inner ear; and the facial nerve are discussed in this chapter.


The auricle, the cartilaginous canal, and the bony external canal comprise the external ear, with the tympanic membrane representing the division between the external and middle ear.


The middle ear is predominately composed of the tympanic cavity and its contents. The eustachian tube connects the middle ear to the nasopharynx and can be a path for the spread of infection. All air spaces are lined with mucosa, which makes them susceptible to the spread of infection and inflammation. The membranous and bony labyrinths make up the inner ear, with potential communications present within the subarachnoid space.



External Ear



External Otitis






Imaging: The diagnosis of otitis externa should be made clinically; however, the diagnosis can be made in the evaluation for possible mastoiditis. Soft tissue swelling and inflammation of the external canal in isolation, without evidence of involvement of the parotid or mastoids, may be demonstrated on computed tomography (CT) (e-Fig. 11-1). The acute inflammatory stage can be classified from mild to severe, and when infection spreads to surrounding tissues, the condition is then termed malignant or necrotizing otitis externa.2 Langerhans cell histiocytosis can infiltrate the soft tissue of the external canal but is more often associated with bony involvement (Box 11-1).







Malignant (Necrotizing) Otitis Externa







Imaging: CT shows more extensive inflammation within the external canal and can demonstrate bony destruction. Magnetic resonance imaging (MRI) with gadolinium demonstrates osteomyelitis, with increased signal on fat-suppressed T2-weighted images and abnormal enhancement, within bone. MRI is useful in confirming central skull base involvement, especially in the presence of multiple cranial nerve palsies, and in evaluating for intracranial complications. Facial nerve paralysis, intracranial extension, and additional cranial nerve involvement may result.5


Single photon emission CT (SPECT) technetium-99m bone scan is an effective way to confirm or exclude bone involvement in a patient whose condition evokes high clinical suspicion, and bone scan can be positive in the absence of osseous destruction on CT.6




Other Lesions Encountered Within the External Auditory Canal


Acquired cholesteatoma may present as debris or a mass within the external auditory canal (e-Fig. 11-2), as can keratosis obturans.8 Exostoses of the external canal may result from chronic inflammation caused by prolonged exposure to water. These lesions tend to be bilateral, broad based, and of bony density.




Foreign bodies and osteomas can also occur in the external canal, with osteomas appearing pedunculated and very dense (e-Fig. 11-3).9





Mastoid and Middle Ear



Acute Infections



Otitis Media




Clinical Presentation and Etiologies: Otitis media is the most common childhood infection that is treated with antibiotics. The otoscopic findings are critical to the diagnosis. Acute otitis media typically presents with fever, ear pain, and a red tympanic membrane.10 The initial cause of the infection is likely viral, but it may be bacterial or represent a secondary bacterial infection. Antibiotic therapy does appear to be moderately more effective than no treatment. Complications may occur in up to 10%, and this rate may be increasing; this could be associated with more conservative treatment.11




Mastoiditis





Imaging: Mastoid air fluid levels can be seen in uncomplicated acute mastoiditis; however, the diagnosis remains a clinical diagnosis. Imaging becomes useful in evaluating for possible complications of acute mastoiditis, with CT being the primary acute imaging modality. CT facilitates the diagnosis of complications of mastoiditis with a high sensitivity and positive predictive value.16 MRI and magnetic resonance venography (MRV) are valuable in assessing intracranial involvement and associated dural sinus thrombosis.


The initial CT finding is decreased definition of the mastoid trabeculae caused by inflammatory hyperemia. As the trabeculae are absorbed and periostitis develops, coalescent mastoiditis develops with infected fluid within the mastoid.17 The subsequent development of a subperiosteal abscess is, by far, the most common complication and typically occurs in the postauricular region where bone is thin, termed the Macewen triangle. CT demonstrates a rim-enhancing fluid collection that is adhering close to bone; underlying bone is usually intact but may show focal destruction (Fig. 11-4). The abscess rarely may arise from the zygomatic root and present with an abscess anterior to the ear. The infection may also progress inferiorly through the mastoid tip, resulting in a Bezold abscess (e-Fig. 11-5). The eustachian tube allows infection to spread into the retropharyngeal space, and children with mastoiditis may present with a retropharyngeal abscess.





Mastoid infection may extend to the petrous apex and central skull base though the continuous mucosal spaces, resulting in petrous apicitis and osteomyelitis, respectively. Petrous apicitis classically presents as the clinical Gradenigo triad of purulent otorrhea, pain in the distribution of the fifth cranial nerve, and ipsilateral sixth cranial nerve palsy.18 CT demonstrates bony destruction and associated epidural empyema, but normal asymmetric pneumatization may make evaluation difficult. MRI demonstrates a peripherally enhancing fluid collection within the apex, and diffusion-weighted images show restricted diffusion with associated empyema or, less commonly, brain abscess (Fig. 11-6).



The major pathways that allow infectious intracranial extension include bone erosion, thrombophlebitis, and preformed pathways. The oval and round windows, cochlear and vestibular aqueducts, internal auditory canal, dehiscent tegmen, and patent petrosquamosal suture are preformed pathways that allow early or late intracranial extension. These pathways may lead to the development of suppurative labyrinthitis, as shown by abnormal enhancement of the internal auditory canal and membranous labyrinth (e-Fig. 11-7). Meningitis can occur via these pathways by spread to the subarachnoid space.17




Meningitis, epidural empyema, dural sinus thrombosis, and cerebellar or cerebral abscesses are the most common intracranial complications. Bony erosion commonly involves the relatively thin sigmoid plate (Trautmann triangle) and may result in an epidural empyema or anterior lateral cerebellar abscess. Usually, significant compression of the adjacent sigmoid sinus occurs, and it may be difficult to distinguish between extrinsic mass effect and thrombosis of the sinus. Erosion through the tegmen results in a middle cranial fossa epidural empyema and or temporal lobe abscess (Fig. 11-8). Veins allow organisms to readily traverse both bone and dura, resulting in thrombophlebitis and spread of infection. The sigmoid sinus is the most common to become thrombosed; however, the lateral, petrosal, and cavernous sinuses may be involved, especially with infection of the petrous apex.17,19,20 Venous sinus thrombosis may lead to venous infarctions or otitic hydrocephalus caused by impaired venous drainage.21 MRI and gadolinium-enhanced MRV can be helpful in diagnosing dural sinus thrombosis (e-Fig. 11-9). Diffusion-weighted images show purulent material to have increased signal, which may be especially helpful in postoperative imaging (Fig. 11-10 and Box 11-2).19




Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on Infection and Inflammation
Premium Wordpress Themes by UFO Themes