Head and Neck ImagingMalignant otitis externa
(also called necrotizing otitis externa), severe infection of the
external ear, usually caused by
Pseudomonas aeruginosa. Most patients are suffering from diabetes or are otherwise immunocompromised. The infection rapidly spreads to involve surrounding bone and soft tissues. The exact pathogenesis is unknown;
ischaemic conditions or decreased activity of white blood cells can be contributory factors. The disease may erode into the bone of the mastoid, anteriorly into the temporomandibular joint and parotid gland, and anteromedially towards the infratemporal space.
Facial nerve palsy may develop and is considered to be a bad prognostic sign; it is usually caused by infratemporal spread of the infection towards the stylomastoid foramen (
Fig.1) (
Fig.2). Other cranial neuropathies can result as the infection spreads below the skull base. Intracranial extension may occur in advanced cases.
CT and
MRI are excellent techniques for visualizing the disease extent;
MRI is the preferred
modality if intracranial spread is suspected. Treatment consists of surgical d
pbridement of the external auditory canal, drainage of collections and
intravenous antibiotics.
Malignant otitis externa used to have a grave prognosis, but with the advent of more effective antibiotics, the infection can be controlled in the majority of cases.
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Axial CT images through skull base show destruction of the bony external auditory canal, erosion of the mastoid bone and invasion of the temporomandibular joint (a). The contrast-enhanced image reveals extension of the infection into the soft tissues of the infratemporal fossa (b, arrows).
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Malignant otitis externa, Fig.1 | | Malignant otitis externa, Fig.2 (a) | | Malignant otitis externa, Fig.2 (b) |