Invisible saccule in 3T MRI: insights into inner ear vulnerability and fluid dynamics.

Background: The trabecular mesh of the inner ear plays a critical role in maintaining the structure of the vestibular organs, particularly within the pars superior. Cases have been reported in which the saccule cannot be visualized in the pars inferior lacking this structure.

Objectives: To investigate the clinical features and endolymphatic hydrops (EH) and perilymphatic enhancement (PE) on MRI in ears with an invisible saccule (IS) and to clarify the mechanism of IS.

Materials And Methods: Retrospective study of 89 IS ears and 71 contralateral visible saccule (VS) ears from 406 patients with hearing impairment and vertigo between 2021 and 2024. Middle ear disease, schwannoma, perilymphatic fistula, and ears after intratympanic injection were excluded.

Results: Compared with VS ears, IS ears had worse hearing, especially in the low-frequency range, and higher PE. Cases diagnosed with Meniere's disease accounted for 13% of IS, all of which showed EH limited to the cochlea, and PE showed higher in IS ears with vertigo than in those without.

Conclusions And Significance: The development of IS is associated with loss of anatomical support and subsequent collapse and fistula of the membranous labyrinth, which may cause the breakdown of the blood-labyrinth barrier and changes in lymphatic flow.