Final answer:
The pre-existing condition you must have before developing diverticulitis is diverticulosis, which is the condition where diverticula form in the wall of the large intestine. It is more common in people who are obese and is thought to be due to a combination of genetic and environmental factors.
Step-by-step explanation:
Diverticulitis is a digestive disease in which tiny pouches in the wall of the large intestine become infected and inflamed. These pouches, known as diverticula, are usually pre-existing and are part of a condition called diverticulosis. Therefore, the pre-existing condition one must have before developing diverticulitis is diverticulosis. Diverticulosis is a condition where diverticula form in the wall of the large intestine. It is more common in people who are obese and is thought to be due to a combination of genetic and environmental factors.