What is the organ under the left rib?

Left subcostal pain is mainly caused by pancreas and splenic flexure of colon. Acute pancreatitis should be considered first if the patient has left subcostal pain, which is often accompanied by abdominal distension, nausea, vomiting and back pain. At the same time, left subcostal pain may also occur when tumors of splenic flexure of colon occur.