Saw a show on tv and they mentioned something called cavernous sinus tumor. What is that?

The cavernous. Sinus location is exactly as dr oro defines, it can be affected by infectio, extrinsic masses (pituitary tumors, meningiomas, aneurysm). The cranial nerves moving the eye (iii, IV but not vi, and two branches of the vth nerve pass through it, and their functional loss is what brings it to attention!
A skull base tumor. The cavernous sinus is a large vein sinus draining venous blood from the brain. It is located on the base of the skull just behind each eye. The sinus contains important nerves for eye movement (the third and fourth cranial nerves), and for facial sensation (the first and second branches of the fifth cranial nerve). It also surrounds the carotid artery. Different tumors can grown within the sinus.