I was told of this funny bit of medical jargon yesterday by a psychiatrist friend of mine, which, apparently, is occasionally used by physicians when they want a medical sounding way of saying that the patient’s symptoms exist only in their imagination.
Luckily I found a great definition on Urban Dictionary:
A word used by doctors and nurses to imply that a patient’s problems are all in their mind. The tentorium is a membrane just under the brain, so “supratentorial” refers to what is above that, namely the brain. This term can be used in front of the patient or patient’s family because it sounds like technical jargon.
Patient: “Every time Dr Phil comes on TV, my arms and legs start twitching!”
Doctor, quietly to nurse: “Seems to be a supratentorial problem.”
Then to patient, condescendingly: “Sorry, dear, we’re just talking shop. Go on.”
Link to Urban Dictionary definition (thanks Quinton!)