Ménière's disease primarily affects the endolymphatic sac, a structure responsible for regulating endolymph fluid volume and pressure within the inner ear. Dysfunction or impaired absorption in the endolymphatic sac leads to endolymphatic hydrops, causing the hallmark symptoms of Ménière's disease: vertigo, tinnitus, hearing loss, and aural fullness. Surgical approaches often target the endolymphatic sac to decompress it or enhance fluid drainage, relieving symptoms. This key pathophysiological site differentiates Ménière's from disorders involving the cochlear nerve, ossicles (like the stapes), or the tympanic membrane.

Reference: Cummings Otolaryngology, Paul W. Flint et al., 6th Edition.