Objective To investigate the pathological mechanism of delayed endolymphatic hydrops(DEH) , and clarify the clinical value of endolymphatic space imaging after intratympanic injection of gadolinium in the diag_nosis of delayed endolymphatic hydrops .Methods Twenty -four hours after bilateral intratympanic injection of gadolinium ,the locations and severity of endolymphatic hydrops of all patients were evaluated by using three dimen_sional fluid-attenuated inversion recovery (3D -FLAIR) and three dimensional real inversionrecovery (3D -real IR) .ResuIts All patients had unilateral or bilateral endolymphatic hydrops .Among 9 ipsilateral DEH patients , only 1 (11 .1% ) patient was identified as mild endolymphatic hydrops and the rest (88 .9% ) examined had signifi_cant endolymphatic hydrops in vestibule of their affected ears ;Endolymphatic hydrops appeared in cochlea of the af_fected ear in 8 (88 .9% ) patients ,except for 1 patient .Endolymphatic hydrops were not observed in the contralater_al ears of 9 ipsilateral DEH patients .Mild endolymphatic hydrops in bilateral vestibule ,severe in right cochlear and none in left cochlea of contralateral DEH patient were identified .ConcIusion Endolymphatic hydrops is the primary pathological factors of DEH .Endolymphatic space imaging after intratympanic injection of gadolinium can intuitively reflect the locations and severity of endolymphatic hydrops in DEH patients .