The spleen is the largest immune organ in the body and normally cannot be palpated under the rib cage. If the lower edge of the spleen can be palpated, it is considered to be enlarged. However, it is important to note that the soft edge of the spleen can be palpated in a few thin women and in those with flaccid abdominal walls. In addition, patients with visceral prolapse, as well as left-sided pleural effusions and the lowering of the transverse septum in the case of pneumothorax, may cause the spleen to prolapse, and these are not considered splenomegaly. Splenomegaly can also be clinically determined by means of ultrasound or CT. ultrasound images with a long diameter of more than 10-11 cm and a thick diameter of more than 4 cm can be considered splenomegaly. CT or MRI images with a long diameter of the spleen of more than 5 rib units are considered splenomegaly. I. The spleen has the following functions: 1. Hematopoiesis: The spleen is an important hematopoietic organ in the embryonic stage and becomes a lymphoid organ in the post-embryonic stage. However, there are still a small number of hematopoietic stem cells in the adult spleen, which can restore hematopoietic function and produce red blood cells, granulocytes and platelets when the animal body is severely ischemic or in certain pathological states. 2. Blood storage: The spleen is an important reservoir of blood, especially blood cells, which are concentrated in the splenic cords and sinuses. In certain emergency situations, the spleen contracts to release blood cells into the circulating blood. 3. Blood filtering: The spleen is also an effective filtering organ for blood. Bacteria, foreign bodies, antigen-antibody complexes and senile blood cells are phagocytosed and digested by a large number of macrophages as they flow through the spleen. 4. Immunity: The spleen has the important function of generating immune responses. Antigens in the blood can cause potent cellular and humoral immune responses in the spleen. The limbic zone is an important site for the initiation of the immune response. The cellular immune response causes a marked enlargement of the arterial lymphatic sheath and an increase in the output of immunologically active cells. Humoral immune response causes an increase in plasma cells in the white marrow lymph nodes and splenic cords, as well as an increase in the concentration of antibodies in the blood output from the spleen. Five major causes of splenomegaly: 1. Infectious diseases causing splenomegaly (1) Acute infectious diseases: Infectious mononucleosis, infectious lymphocytosis, viral hepatitis, typhoid and paratyphoid fever, scrub typhus, leptospirosis, dengue fever, epidemic hemorrhagic fever, cytomegalovirus infection, sepsis, subacute infective endocarditis, regression fever, etc. In acute infections, the spleen is reactive and enlarged, usually to a lesser extent, with a softer texture and mild tenderness. As the infection is controlled, the spleen gradually returns to normal. (2) Chronic infectious diseases: disseminated tuberculosis, brucellosis, syphilis, fungal infections, vertebral worm disease, malaria, schistosomiasis, and black fever. Chronic recurrent infections with sustainable enlargement and hard texture of the spleen. (3) Infections of the spleen: splenic abscess and tuberculous granuloma of the spleen, etc. Splenic abscess is a rare complication of abdominal purulent infection, sepsis, typhoid fever, etc. It has chills, fever, abdominal muscle tension, splenomegaly with tenderness and fluctuating sensation, and elevated leukocytes; when combined with peripleural inflammation, frictional sounds may appear in the splenic area, and it needs to be differentiated from left subdiaphragmatic abscess and abdominal wall abscess with the help of ultrasonography and nuclear imaging. Chronic congestive cardiac insufficiency, chronic constrictive pericarditis, hepatic venous obstruction (Budd-Chiari syndrome), cirrhosis of the liver due to various causes, as well as inflammation of the portal vein and splenic vein, thrombosis, and cancer embolism. Congestive splenomegaly is caused by increased splenic vein pressure, obstruction of splenic blood return and spleen stasis formation, often accompanied by ascites and hypersplenism. IV. Splenomegaly caused by abnormal immune response Systemic lupus erythematosus, rheumatoid arthritis, rheumatic fever, desiccation syndrome, dermatomyositis, periarteritis nodosa, adult Still’s disease, leukoaraiosis, serum sickness, Felty’s syndrome, idiopathic thrombocytopenic purpura. V. Splenomegaly due to blood disorders 1. Hemolytic anemia: seen in thalassemia, hemoglobinopathy, autoimmune hemolytic anemia, hereditary spherocytosis, hereditary elliptocytosis, and sickle cell anemia. There are manifestations of anemia, jaundice, and splenomegaly. 1, malignant blood diseases: ① acute and chronic leukemia such as acute myeloid leukemia, acute lymphoblastic leukemia, chronic granulocytic leukemia, chronic lymphocytic leukemia, juvenile lymphocytic leukemia, hairy cell leukemia. ② chronic myeloproliferative diseases such as true erythroblastosis, chronic myelofibrosis, and primary thrombocythemia. ③Lymphoma, myeloma, malignant histiocytosis, hemophagocytic syndrome ④Amyloidosis, lipid-like storage disease such as Niemann-Pick disease. Patients mostly have anemia, hemorrhage, fever, progressive enlargement of liver and spleen lymph nodes, bone pain, abnormal blood cells and other manifestations, and often appear giant spleen. Sixth, primary splenic tumors are rare clinically. Benign mismatched tumors, hemangiomas, lymphangioleiomas, splenic cysts and fibromas have no symptoms other than splenomegaly. Malignant tumors are mostly lymphoma, splenic sarcoma, plasmacytoma, fibrosarcoma, angiosarcoma, and metastatic carcinoma. Lymphoma is the most common. VII. Others such as nodular disease, certain acute and chronic poisoning.