Peritonitis is an inflammation of the peritoneum, the membrane made up of two layers that surround and protect the organs of the abdomen. This condition is very often secondary to a perforated abdominal organ, which then leaks its contents into the normally empty space between the layers. One of the most common causes is associated with a progressed appendicitis that remains unnoticed for too long. The symptoms are severe pain, typically beginning in the lower right abdomen and quickly spreading to the rest of the abdomen, and fever, often accompanied by vomiting and constipation. In these cases the abdomen becomes hard to the touch and contracted, with diagnosis confirmed by blood test and an ultrasonograph. Treatment requires surgery along with antibiotics.