Necrotising otitis externa
Necrotising otitis externa (NOE), also known as malignant otitis externa, is a severe invasive infection of the external auditory canal (EAC) which can spread rapidly to involve the surrounding soft tissue, adjacent neck spaces and skull base.
Predisposing conditions for NOE include diabetes and immunosuppression (i.e., diabetes or patients receiving chemo- and/or radiation therapy). Pain can be out of proportion for typical otitis externa.
Pseudomonas aeruginosa is the pathogen in 98% of cases. The route by which the infection spreads is variable. It can spread anteroinferiorly to involve the suprahyoid neck spaces (parotid space and masticator space). Alternatively, the infection can also erode the cartilaginous-bone of the EAC resulting in a direct intracranial spread with resultant serious intracranial complications.
Serious complications include:
On contrast-enhanced CT, there can be thickening and enhancing soft tissue in the region of the external auditory canal with or without formation of phlegmon/abscess. In cases of abscess, cartilaginous bone ring enhancing collection with a necrotic low attenuation centre can be observed.
Technetium-99m bone scanning is sensitive to osteoblastic activity and is highly sensitive for bony infection, with uptake in the temporal bone and skull base differentiating NOE from typical acute otitis externa 4.
Follow up imaging using gallium-67 citrate and indium-111 labelled leukocyte scans, in addition to serum ESR levels can gauge treatment response 4.
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