CT Findings in the External Auditory Canal after Transcanal Surgery

BACKGROUND AND PURPOSE:Middle ear surgery is often performed through the external auditory canal, and the CT appearance of the external auditory canal after transcanal middle ear surgery can mimic erosive pathology such as carcinoma, external auditory canal cholesteatoma, or necrotizing external otitis. We reviewed the CT findings in a group of patients following transcanal surgery to highlight this potential pitfall in interpretation.MATERIALS AND METHODS:Twenty-seven temporal bones in 25 patients with a history of a transcanal approach to the middle ear and available postoperative CT imaging were identified. Images were assessed for changes along or involving the walls of the external auditory canal, including widening, irregularity, bony defects, and soft tissue opacification.RESULTS:Osseous changes along the floor of the external auditory canal were demonstrated in 25 of 27 (92.6%) temporal bone CT scans. Similar changes were present in the superior and anterior walls of the external auditory canal in 21 and 18 temporal bones, respectively. The anterior wall was the most common site for complete bony defects (10 of 27 temporal bones). The posterior wall was the least often involved, with osseous changes in 15 of 27 temporal bones and bony defects in 3 cases. Soft tissue thickening was seen most commonly along the floor. No patient was found to have a superimposed pathologic process of the external auditory canal.CONCLUSIONS:CT findings in the external auditory canal after transcanal surgery include thinning, irregularity and/or flattening of the bone, soft tissue thickening, and bony wall defects. Although these changes may be subtle, they may mimic pathology and should be included in the differential diagnosis of osseous abnormality of the external auditory canal.

Middle ear surgery performed through the external auditory canal (EAC) often involves drilling a portion of the bony canal wall to provide access and necessary exposure.^1–3 In the absence of associated transmastoid surgery (such as a canal wall down mastoidectomy), the postoperative status may not be immediately obvious to the interpreting radiologist, and relevant history may not be provided. On CT, such postoperative changes in the external canal can mimic bony and soft tissue changes typically associated with neoplasms, external canal cholesteatoma, or aggressive infections of the EAC. Prior literature has predominantly focused on the appearance of the middle ear after surgery.^4–11 We describe the CT appearance of the EAC after transcanal surgery so that postoperative change can be included in the differential diagnosis, even in the absence of available history, and erroneous diagnoses may be avoided.