Figure 14.

(A) Principal drawing of the human utriculo-endolymphatic valve (Bast's valve) based on SR-PCI. The valve is structurally associated with the opening of the vestibular aqueduct through a laminar disc (interrupted line) emerging from the vertical crest of the vestibular aqueduct to the lip of the valve. The outer wall of the utricular duct faces the disc and forms the utricular fold. Between the inner and outer wall at the base of the lip, there is loose tissue allowing the valve to open (small arrows). (B) Hypothetical representation of the role of Bast's valve and UD in generating acute endolymphatic hypertension and hydrops in patients with MD. Increased endolymph pressure is caused by reduced reabsorption or hypersecretion in the ES, leading to a “backflow” of endolymph. It compresses the wall of the utricular duct and pushes the valve to open (inset), leading to acute EH and vertigo. Experimentally, secretion in the ES may be provoked within a short timeframe (41, 42).