To develop a radiologic classification of severity of round window involvement in otosclerosis and describe the impact of each class on hearing and outcome of stapes surgery.Retrospective chart review with radiologic review of computed tomographic scans.Hospital and private otolaryngology clinics.We reviewed computed tomographic scans of 930 ears with clinical otosclerosis; 121 (13%) had round window involvement, with no pericochlear involvement in 41 of these-the primary subjects of the study. A control group consisted of 15 ears with stapedial otosclerosis.Round window involvement was classified into 5 groups from isolated round window edge hypodensity (RW-I) to overgrowing obliteration with possible extension to the cochlea (RW-V). Hearing measures included 4-frequency pure-tone average air conduction, bone conduction, and air-bone gap (ABG).Of the 41 ears, 17.1%, 31.7%, 34.1%, and 17.1% were classified as RW-I to RW-IV, respectively. Patients with RW-I and RW-II otosclerosis, compared with the controls, showed no statistically significant differences in preoperative hearing or in ABG after stapes surgery. Patients with RW-III otosclerosis had significantly poorer hearing and a larger postoperative ABG (mean, 15 dB) than controls and groups RW-I and RW-II, whereas the RW-IV group showed the most severe hearing loss and poorest surgical outcome (all p's ≤ 0.001).The proposed classification for round window otosclerosis is a valuable clinical tool that can help in decisions regarding, and counseling about, stapes surgery. Classes RW-I and RW-II have no clinical impact. Patients with RW-III otosclerosis may have a mild residual gap after surgery; those with RW-IV have dramatically poorer results.
