Posterior sinus of middle ear cavity is one of the recently identified anatomical sinus inside the middle ear cavity.
Serial temporal bone dissections have shown that it is present in nearly 90% of dissected bones.
Position: It lies just posterior to the oval window.
Depth: 1mm or less
Width: 1.5 mm or less
In nearly 60% of dissected specimen a ridge of bone arising from the floor of middle ear cavity separates it from sinus tympani.
In 8% of dissected specimen, the sinus tympani and posterior sinus merged together to form one confluent sinus.
It has been demonstrated that cholesteatoma / granulation tissue may lie within this sinus making removal difficult leading on to
Retraction pockets may also occur close to this area.