What diagnostic criteria would a radiologist have to fulfill in order to definitively diagnose diverticulitis on a ct without contrast scan?

Pneumopertioneum: Making this diagnosis, or just about any other definitive intestinal diagnosis is very difficult to impossible based on a ct scan without contrast. Sometimes the intestine is already filled with enough fluid that makes the diagnosis easier, but it still may not be 100% accurate. If the radiologist sees outpouchings along the sigmoid colon with small amounts of air outside the bowel, that's clear.

Inflammation : Without contrast it is hard, but on occasions they can see the inflammation surrounding the colin and air pockets or diverticuli in the colon around an area of inflammation.