Re-evaluation of the role of the human endolymphatic sac in Menière's disease.

The role of endolymphatic sac (ES) dysfunction in the etiopathogenesis of Meniere's disease has remained controversial since the early 1900s. The first reports of the ultrastructural (transmission electron microscopy, TEM) pathology of the human ES in Meniere's disease have been published only in the last decade. These studies have been based on biopsies of the extraosseous (intradural) ES and in no cases has the TEM appearance of the intraosseous ES been described. Likewise the control material used has been from biopsies of extraosseous ES taken from patients with acoustic schwannomas. To date, no reports have compared the ultrastructure of the intrasosseous ES from normal control patients to patients with Meniere's disease. Since the intraosseous ES is believed to be the most active portion of the entire ES, studies were made of the ultrastructure of ten normal interosseous human ESs fixed immediately after death and obtained at autopsy (control material). Fourteen patients undergoing translabyrinthine (TL) neurotologic procedures (10, TL resection of acoustic schwannoma; 4, TL eighth cranial nerve section for Meniere's disease) had the entire vestibular aqueduct, containing the endolymphatic duct and the intraosseous ES, removed and processed for TEM. The roles of the epithelium, subepithelial space, and vasculature were morphologically studied to evaluate possible ES pathology in Meniere's disease and in patients with acoustic schwannoma. Wide anatomic variation in the distribution and density of the subepithelial connective tissue was observed in all groups. There was no difference in the TEM appearance of the intraosseous ES from normal controls and patients with eighth nerve schwannoma, nor was there any difference in the ES collagen deposition in patients with Meniere's disease. The ESs from two patients with Meniere's disease showed evidence of abnormal glycoprotein metabolism; one with possible hypersecretion and one with possible alteration of degradation of resorbed glycoprotein. The results of this preliminary study suggest that "perisaccular fibrosis" of the intraosseous ES was not a pathologic feature in these four cases of Meniere's disease and that alteration of ES glycoprotein secretion/resorption may be of etiopathologic significance.