1) extent - a pseudomeningocele will extend further out laterally than a diverticulum 2) boundaries - usually the pseudomeningocele remains ill-defined, whereas the diverticulum has smooth, well-defined edges

This is controversial. I like to have contrast because I can better see neuritis, tumor spread, and contusion. But there are many radiologists who feel comfortable without it unless those entities are specifically on the clinical differential. If the patient or referring physician doesn't want to use contrast, I generally don't put up a fight. But if they ask, I say yes.