CT and MRI of the external auditory canal

ABSTRACT

The most dangerous inflammation of the external ear is malignant otitis externa. Pseudomonasaeruginosa is the commonest organism, however early diagnosis requires culture of the ear secretions beforeosteomylitis occurs. Radiological diagnosis can help in the diagnosis and estimation of the prognosis. Thirty three patients with positive radiological findings were chosen, all were referred from theoutpatient clinic complaining of ear discharge, otalgia or swelling .The cases had some difficulties in their clinicaldiagnosis or uncertain differential diagnosis. They were twenty two males and eleven females. The average agewas forty seven years old . The oldest patient was eighty five, while the youngest was nine years old. MRI and CTwere done for all patients beside the culture of ear discharge. History of long term DM or immune-suppressedconditions was registered. The aim of this work is to illustrate the role of CT and MRI in delineation of differentpathological entities of the external ear, with special emphasis on the evaluation of necrotizing otitis externa andits early radiological signs, complications and differential diagnosis.The patients were divided into four groups .The first one contains sixteen cases with malignant otitisexterna, the second one was middle ear infection with mastoiditis and external ear involvement, it includes sixpatients. The third group is three patients with external ear cholesteatoma. The fourth group contains eightpatients with different rarer external ear pathology for the first and largest group Positive findings in all CT andMRI studies. Laboratory studies of these radiologically proven cases reveal positive fungal infection in ten casesand negative cultures in the remaining six.The cases of malignant otitis externa show erosions in the external auditory canal in all patients, involvement ofthe petrous bone and middle ear in half of the cases while seven patients show skull base and or tempomandibularjoint osteomylitis. Facial nerve canal involvement occurs in six patients, while carotid canal was only involved inonly tow patients. We conclude that CT and MRI are the best imaging modalities for evaluating the extent and characterof bony and soft-tissue abnormalities of the EAC. CT scan is more helpful in bony evaluations, while MRI is morehelpful in evaluating the soft tissue involvement. Radiological imaging including combined CT scan and MRI is ofgreat value in early diagnosis of malignant otitis externa [before involvement of-the facial nerve] and so it candecrease the high mortality rate associated with late diagnosis of that aggressive infection