Effect of cochleostomy size on perilymph fistula control

Although the overall incidence of perilymphatic gushers is approximately 1%, patients with inner ear anomalies are at an increased risk for development of perilymphatic gushers. As cochlear implantation becomes more common in patients with inner ear anomalies (e.g., Mondini defect or common cavity defect), the ability to successfully seal such leaks becomes of paramount importance to reduce the risk of subsequent meningitis.

A 1.0-mm and a 1.5-mm cochleostomy were placed superior to the round window in two respective temporal bones. Cochlear implant electrodes (Cochlear [Lane Cove NSW, Australia], Med-El [Insbruck, Austria] and Advanced Bionics [Valencia, CA]) were placed in the cochleostomy and sealed with porcine periosteum. A fixed amount of pressure was applied to the inner ear, and the presence or absence of a leak was recorded for 10 different packings of each cochleostomy diameter at 0, 10, 15, 20, and 30 cm H(2)O.

For the Cochlear, Med-El, and Advanced Bionics electrode, no statistically significant difference was noted between the 1.0-mm and the 1.5-mm cochleostomy at 0, 10, 15, and 20 cm H(2)O. At 30 cm H(2)O, no leaks were noted with the 1.5-mm cochleostomy for any brand. For the 1.0-mm cochleostomy at 30 cm H(2)O, 6/10 of the Cochlear trials leaked (P = .004), 2/10 of the Med-El trials leaked (P = .24), and 5/10 of the Advanced Bionics trials leaked (P = .03).

The 1.5-mm cochleostomies are associated with a decreased risk of perilymphatic fistula as compared to 1.0-mm cochleostomies at 30 cm H(2)O; this likely represents a phenomenon of packing adequacy.