An uncommon “third window” in retrofenestral otosclerosis

Otosclerosis is an otologic disease characterized by disordered resorption and deposition of the otic capsule bone. It can lead to progressive conductive, mixed or sensorineural Hearing Loss (HL). In rare cases, it manifests itself with a tendency for massive bone resorption with subsequent formation of cavities (“cavitating otosclerosis”). Cavities can sometimes realize communication between the Cerebrospinal Fluid (CSF) at the Internal Auditory Canal (IAC) and the cochlear duct. In these uncommon cases, a “third-window” phenomenon may be established as a concomitant cause of conductive HL. Therefore, the feasibility of stapes surgery should be evaluated, without underestimating the risk of gusher complications. In this report, we discuss the case of a female patient affected by cavitating otosclerosis realizing a connection between IAC and cochlear duct, with mixed hearing loss.