Presbycusis is a disease characterized by hidden and slowly progressive bilateral sensorineural hear-ing loss.Its occurrence and development is a multifactorial process.The expression of each factor varies greatly a-mong individuals.Currently,there have been some studies on the pathogenesis of presbycusis,which can be catego-rized into ion channel abnormalities,cochlear synaptopathy,reactive oxygen species,hormone effects,mitochondrial abnormalities,genetic factors and vari other factors.This review summarizes the pathogenesis of presbycusis in re-cent years.

Objective To observe prenatal ultrasonic manifestations of fetal rhomboencephalosynapsis(RES).Methods Data of 15 singletons with RES were retrospectively analyzed,and the prenatal intracranial and extracranial ultrasonic manifestations were observed.Results All 15 fetuses were found with transverse cerebellar diameter lower than the 3rd percentile of normal value in the same gestational week and bilateral cerebellar hemisphere fusion(15/15,100％).Cerebellar vermis completely loss was observed in 14 fetuses(14/15,93.33％),while partially loss was noticed in 1 fetus(1/15,6.67％).Invisible of the fourth cerebral ventricle was detected in 4 fetuses(4/15,26.67％),while the fourth cerebral ventricular index(4Vi)＜1 was found in 11 fetuses(11/15,73.33％).No"split line"sign between vermis and cerebellar hemisphere was detected.A total of 14(14/15,93.33％)were found with combining intracranial or extracranial malformations,including 13(13/14,92.86％)with other intracranial malformations,10(10/14,71.43％)with extracranial malformations,whereas 1(1/15,6.67％)fetus had no other malformation.Conclusion Prenatal ultrasonic manifestations of fetal RES mainly included small cerebellum transverse diameter,complete or partial loss of vermis,invisible or dysplasia of the fourth cerebral ventricle,fusion of bilateral cerebellar hemispheres,as well as combining with other intracranial and extracranial malformations.