Usefulness of CT scans in malignant external otitis: effective tool for the diagnosis, but of limited value in predicting outcome

Computerized tomography (CT) scanning is a well recognised tool for the diagnosis of malignant external otitis. To investigate the degree of correlation between CT findings scan and the patients clinical status focusing on a subgroup of patients with cranial nerve palsies. Diagnosis of malignant external otitis was confirmed in 23 patients (average age 71 years, age range 39–87) based on criteria of severe pain, otitis externa refractory to conventional treatments and possibly diabetes mellitus and pseudomonas detection. CT was performed on 23 of these patients. Results from these scans were analysed and correlated with patient clinical status. Retrospective analysis of CT images and medical notes were used for data analysis.The CT scans of all 23 patients showed evidence of involvement of disease outside the external auditory canal, confirming the diagnosis. Sixteen out of 23 patients (70%) demonstrated evidence of bone erosion. Four of the 16 showed involvement of the petrous apex. From our subset of ten patients with cranial nerve involvement, eight demonstrated evidence of bone erosion and two showed mastoid and middle ear involvement without bone erosion. All four patients with petrous apical involvement presented with cranial nerve palsies (two lower cranial nerve palsies, one seventh nerve palsy and one combined lower and seventh nerve palsy). CT scanning was found to be a fast and economical tool in the initial assessment of patients with malignant external otitis. Petrous apex involvement was constantly associated with cranial nerve palsies, usually the lower cranial nerves. CT findings of temporal bone in itself however, were not closely correlated to the clinical outcome of the patients.