The spleen culls aged and abnormal cells from the blood; removes intraerythrocytic inclusions through a process called pitting; sequesters approximately one-third of the normal intravascular platelet pool; removes bacteria, foreign particles, and tumor cells from the blood; and by virtue of the T and B lymphocytes and macrophages in the white pulp, plays a role in immune surveillance and antibody formation. Splenomegaly can occur as a result of vascular engorgement or cellular infiltration, and it is frequently associated with a combination of neutropenia, thrombocytopenia, and anemia. Hypersplenism is defined as one or more blood cytopenias in the setting of splenomegaly. Hypersplenism can occur with moderate or minimal splenic enlargement as a result of exaggerated removal of physically abnormal (e.g., as in hereditary spherocytosis) or antibody-coated blood cells (e.g., as in autoimmune hemolytic anemia). The presence of splenomegaly in a patient with blood cytopenias is useful to narrow the cause of the cytopenias, although the cause of the blood cytopenias may not be solely or principally as a result of hypersplenism (e.g., as in hairy cell leukemia). Thrombocytopenia in the setting of cirrhosis and splenomegaly is the result of pooling in the enlarged spleen and a relative decrease in thrombopoietin. The role of the spleen in the anemia and neutropenia associated with cirrhosis with splenomegaly is poorly understood, but a relative reduction in erythropoietin levels and decreased marrow myeloid progenitor cells have been proposed. Splenectomy has been used in cases of severe thrombocytopenia requiring chronic platelet transfusions or leading to bleeding. Thrombopoietin receptor agonists are another option in the management of thrombocytopenia, and nonpeptide thrombopoietin receptor agonists have been shown to increase platelet counts in patients with thrombocytopenia associated with hepatitis C virus–related cirrhosis and splenomegaly. Splenectomy may be justified in the case of massive splenomegaly, infarction, or disabling symptoms of pain and compression of neighboring structures. In some circumstances, benefit can be achieved by partial destruction of splenic tissue by embolization using intraarterial infusion of gel microparticles. Hyposplenism can result from agenesis, atrophy, surgical removal of the spleen, or reduction of splenic function by disease. In the latter case, disturbance in splenic circulation disrupts the specific architecture required for the spleen’s culling, phagocytic, and pitting functions. Hyposplenism may be suspected by alterations in red cell morphology, such as target cells or acanthocytes; red cell inclusions, specifically Howell-Jolly and Pappenheimer bodies (siderotic granules highlighted with polychrome stains); pitted red cells; or an elevated platelet count. The presence of pitted red cells identified by interference-contrast microscopy is perhaps the most specific blood finding of hyposplenism, followed by Howell-Jolly bodies. The most devastating consequence of hyposplenism is sudden overwhelming sepsis by encapsulated bacteria. Immunizations and prophylactic antibiotics can decrease the risk of sepsis. A high awareness and prompt antibiotic treatment of febrile episodes are warranted.
Acronyms and Abbreviations:
G-CSF, granulocyte colony-stimulating factor; Ig, immunoglobulin; TPO-RA, thrombopoietin-receptor agonist.