In glomus tumour

In glomus tumour , why does the tumour blanch on increasing pressure of eac and again starts pulsating on releasing/ decreasing the pressure ( here the tympanic membrane is intact so the pressure changes cant be transmitted to the middle ear , then how the eac pressure change affects the tumour ?

The changes of pressure in the EAC do affect the middle ear through a normal TM ( that is the cause of barotrauma )When the ET is normal , the pressure changes get normalised . An increase in pressure in the EAC will push the TM inwards , leading-to blanching of the vascular mass .