A 52-year-old intellectually disabled man who had previously undergone a left canal wall down mastoidectomy with cartilage graft tympanoplasty for cholesteatoma 20 years ago presented with new-onset discharge in the contralateral ear. He did not have any symptoms, particularly recurrent discharge, in the post-operative ear, despite infrequent and irregular clinic follow-up for periodic cleaning of the cavity. Clinical examination of the post-operative ear revealed the presence of retained cerumen which was easily removed. The mastoid cavity was noted to have a healthy skin lining, an intact neotympanum, and a smooth bowl-like appearance with no areas that could not be adequately visualized through the surgically widened external auditory meatus. He underwent computerized tomographic imaging of the temporal bone to evaluate the nature and cause of the new-onset discharge in the contralateral ear. This imaging study provided the opportunity to present and describe key post-operative radiologic features of a symptom-free canal-wall down mastoidectomy with tympanoplasty.

A canal-wall down mastoidectomy is a more extensive type of mastoidectomy which, in addition to the resection of the mastoid cortex, all mastoid air cells and Körner septum, is characterized by the resection of the posterior wall of the external auditory canal and scutum. Among the most common causes of failure following this type of surgery are incomplete removal of tegmental air cells and incomplete lowering of the facial ridge.1These two factors can and should be purposefully assessed in a post-operative imaging study.

Adequacy of bone removal in the epitympanum to address the issue of tegmental air cell disease is evaluated on axial CT images at the level of the malleus head-incus body complex and the proximal portion of the tympanic segment of the facial nerve. (Figure 1) All of the bone lateral to the ossicles, especially that overlying the malleus head and anterior epitympanic recess, should have been surgically removed.

On coronal CT images, this same adequacy is demonstrated by the surgical removal of all bone lateral to the epitympanum, from the scutum to the outer cortex, such that there is a clear line of sight from the external auditory meatus to the epitympanum. This helps ensure that there are no pockets of soft tissue medial to any bony ridges; soft tissue that may represent residual or recurrent disease. (Figure 2)