Patterns of Failure in Canal Wall Down Mastoidectomy Cavity Instability

Objective: To evaluate patterns of failure for canal wall down mastoid cavities requiring surgical revision. Study Design: Retrospective review. Setting: Academic tertiary referral center Patients: Adults and children that underwent revision of an unstable open mastoid cavity from 1995 to 2010. Intervention(s): Review of demographic data, tympanomastoid pathology, and plausible risk factors for an unstable cavity. Available computed tomography (CT) scans were reviewed for indicators of suboptimal cavity shape. Spearman's correlation analysis was undertaken. Findings were classified as Type 1 (primary tympanomastoid pathology), Type 2 (cavity shape/size), or Type 3 (negative host environment). Main Outcome Measure(s): Frequency of risk factors and correlation. Results: Approximately 130 cases were reviewed. Stapes erosion (49.2%), absent malleus (26.2%), cholesteatoma (44.6%), tympanic membrane perforation (34.6%), and fibrotic middle ear mucosa (20.8%) were common. CT scans often demonstrated an intact open mastoid tip (87.5%) and a high facial ridge (54.2%). Notable correlations were discovered between the facial ridge height proximally and the height distally (r = 0.46437, p = 0.0256) and tympanic membrane perforation and absent malleus (r = -0.17944, p = 0.0419). Approximately 68% of the subjects had at least 1 Class 1 risk factor present among cholesteatoma, tympanic membrane perforation/atelectasis, and extruded prosthesis. All CT scans reviewed demonstrated at least 1 Class 2 factor. Conclusion: Although primary tympanomastoid pathology is quite common, some aspect of suboptimal mastoid cavity size and shape is pervasive. Correlation analysis suggests that surgeons tend to either lower the facial ridge completely or not at all and that an absent malleus seems to be associated with a tympanic membrane perforation.