AQP2 and endolymphatic hydrops: Immunohistochemical and ultrastructural studies showed that the endolymphatic sac of MD patients had excessive secretion of glycoprotein (13, 14), and the overexpression of aquaporin-2 in the endolymphatic sac epithelium was also involved in the formation of endolymphatic hydrops (15), suggesting that the endolymphatic sac secretion exceeded absorption, increasing the inner ear pressure.