The cause of pain in the left quaternary region is pain in the organs or tissues of the left quaternary region due to lesions such as trauma, inflammation or tumors. It is common in left upper abdominal diseases, left chest diseases and left posterior peritoneal diseases. 1. Left upper abdominal diseases: stomach, spleen, pancreas and other organs are located in the left quaternary rib area, gastritis, gastric cancer, splenomegaly, pancreatitis, duodenal ulcer and other diseases can cause pain, which can be manifested as left quaternary rib area pain. 2. Left thoracic diseases: costochondritis, intercostal neuritis, fracture, left lung infection, pleurisy and other diseases produce inflammatory media stimulation, which can cause pain in the left quarter rib area. 3. Left posterior peritoneal diseases: left kidney stone, hydronephrosis and other diseases can cause left quarter rib pain. It is recommended to go to the hospital for further examination and diagnosis.