Dehiscent jugular bulb

Right side Dehiscent jugular bulb 

A high riding jugular bulb is a normal anatomical variation, present very close to middle ear and the intervening sigmoid plate between a high riding jugular bulb and the middle ear may be thin and intact but when it is absent, allowing the wall of the vein to bulge into the middle ear cavity is termed as Dehiscent jugular bulb is a known causes of pulsatile tinnitus.
Can present as a retrotympanic vascular mass and turn out disasterous if mistaken for a middle ear tumour and biopsied.