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Pathology

Malignant otitis externa always commences with a focus of infection in the floor of the ear canal, at that point where the cartilage of the ear canal meets the bone which is situated more deeply (see anatomy, Chapter 2). There is always an area of granulation tissue-raw, red, fleshy tissue-at this point, and it may expand into quite a large, granular polyp. The underlying changes are those of severe inflammation, but, unlike the situation in otitis externa where this is confined to the ear canal skin and perhaps the surrounding soft tissues, the inflammatory and destructive changes here invade bone at an early stage, and the condition develops into an osteitis (bony infection) of the skull base, which spreads inward and involves cranial nerves adjacent to the area of initial infection. The first cranial nerve to be involved is the facial, or seventh, producing facial paralysis, and as the infection of the skull base advances other cranial nerves may also be involved. The invasive infection is potentially lethal, and cases advancing so far as to develop a facial palsy have a 50% mortality even with treatment. In fatal cases death is due to advancing infection of the skull base and infection which spreads into the cranial cavity. The poor prognosis in advanced cases relates not only to the disease itself, but to the generally enfeebled state of the patient.