Splenic anatomy and function1
The spleen is a functionally diverse organ with active roles in immunosurveillance and hematopoiesis. It lies within the left upper quadrant of the peritoneal cavity and abuts ribs 9-12, the stomach, the left kidney, the splenic flexure of the colon, and the tail of the pancreas. A normal spleen weighs 150 g and is approximately 11 cm in craniocaudal length.
The normal spleen is usually not palpable, although it can sometimes be palpated in adolescents and individuals with a slender build. Spleens that are prominent below the costal margin typically weigh 750-1000 g. Spleens weighing 400-500 g indicate splenomegaly, and some authors consider spleens weighing more than 1000 g to indicate massive splenomegaly. Poulin et al defined splenomegaly as moderate if the largest dimension is 11-20 cm and severe if the largest dimension is greater than 20 cm.
In many instances, the spleen enlarges as it performs its normal functions. The 4 most important normal functions of the spleen are: (1) clearance of microorganisms and particulate antigens from the blood stream; (2) synthesis of immunoglobulin G (IgG), properdin (ie, an essential component of the alternate pathway of complement activation), and tuftsin (an immunostimulatory tetrapeptide); (3) removal of abnormal red blood cells (RBCs); and (4) embryonic hematopoiesis in certain diseases.
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Related eMedicine topics:
Splenomegaly [in the Pediatrics: General section]
Tropical Splenomegaly Syndrome
Related Medscape topics:
Specialty Site Allergy & Clinical Immunology
Specialty Site Hematology-Oncology
Many of the mechanisms leading to an enlarged spleen are exaggerated forms of normal spleen function. Although a wide variety of diseases are associated with enlargement of the spleen, 6 etiologies of splenomegaly are considered primary, including: (1) immune response work hypertrophy, such as in subacute bacterial endocarditis or infectious mononucleosis; (2) RBC destruction work hypertrophy, such as in hereditary spherocytosis or thalassemia major; (3) congestive such as in splenic vein thrombosis or portal hypertension; (4) myeloproliferative, such as in chronic myeloid metaplasia; (5) infiltrative, such as in sarcoidosis and some neoplasms; and (6) neoplastic, such as in chronic lymphocytic leukemia and the lymphomas.
Miscellaneous causes of splenomegaly include trauma, cysts, hemangiomas, metastasis, giant abscess, and certain drugs (eg, RhoGAM).
Two large series report the presence of a palpable spleen in 2% and 5.6% of patients. An enlarged or palpable spleen is not necessarily of clinical significance. Certain individuals with broadly splayed costal margins have readily palpable, but small, spleens.
Tropical splenomegaly syndrome has the highest predilection for indigenous persons and visitors of the malarial belt in tropical Africa (see Sex).
Morbidity and mortality in cases of splenomegaly principally stem from associated disease states or surgical procedures, rather than from the splenomegaly itself. The rates for morbidity and mortality are highly variable and relate to the presence or absence of comorbidities, hemorrhage, and organ failure.
Patients with enlarged spleens are more likely to have splenic rupture from blunt abdominal or low thoracic trauma. These patients are unlikely to undergo nonoperative management of their splenic injury or splenic salvage maneuvers, because their spleen is abnormal with regard to architecture, capsule tensile strength, and, commonly, hemostatic function.
No race predilection is recognized for splenomegaly. However, note that blacks may have hemoglobin SC disease, a disorder related to sickle cell disease. Unlike sickle cell disease that results in a small, autoinfarcted spleen, patients with hemoglobin SC disease may have splenomegaly that accompanies their pigment gallstones.
Tropical splenomegaly syndrome (or hyperactive malarial syndrome) has a female-to-male incidence ratio of 2:1. Otherwise, no sex predilection is documented for splenomegaly.
No age predilection is recognized for splenomegaly. Nonetheless, the capsules of older spleens are much thinner than their younger counterparts. The combination of capsular thinning with increased spleen weight and size makes splenic injury more common in elderly persons. These factors account for the increased likelihood of splenectomy for trauma in this subgroup.
The most common history in patients with splenomegaly is mild abdominal pain that is vague in nature. Pain may be referred to the left shoulder. Increased abdominal girth is less common. Early satiety from gastric displacement occurs with massive splenomegaly. Associated symptoms or signs are typically related to the underlying disorder and may include the following:
Febrile illness (infectious)
Pallor, dyspnea, bruising, and/or petechiae (hemolytic process)
History of liver disease (congestive)
Weight loss, constitutional symptoms (neoplastic)
Pancreatitis (splenic vein thrombosis)
Alcoholism, hepatitis (cirrhosis)
Related Medscape topics:
Specialty Site Gastroenterology
Specialty Site Infectious Diseases
Spleen size is not a reliable guide to splenic function, and palpable spleens are not always abnormal. Patients with chronic obstructive pulmonary disease (COPD) and low diaphragms commonly have palpable spleens. In one study, 3% of college freshmen had palpable spleens; an additional study showed that 5% of hospitalized patients with normal spleens based on scan results were thought to have palpable spleens by their physicians.
The physical examination should include palpation with the patient in the supine and right lateral decubitus position, with knees up and hips flexed. Apply light fingertip pressure as the patient slowly inspires. The use of the reverse Trendelenburg position may aid in bringing the spleen into contact with the examiner’s fingers. This is especially helpful in patients with morbid obesity.
The spleen moves with respiratory patterns and may only be palpable at the end of inspiration.
In extreme splenomegaly, the lower splenic pole may extend into the pelvis or cross the abdominal midline. In these circumstances, palpating at the pelvic brim or the right upper quadrant may be necessary to delineate spleen size and location.
Percussion of the abdomen may disclose caudal displacement of the gastric bubble in massive splenomegaly.
Additional signs that identify possible etiologies of splenomegaly include the following:
Signs of cirrhosis (eg, asterixis, jaundice, telangiectasias, gynecomastia, caput medusa, ascites)
Heart murmur (endocarditis, congestive failure)
Scleral icterus (spherocytosis, cirrhosis)
Petechiae (any cause of thrombocytopenia)
The causes of splenomegaly are diverse, but they may be conveniently grouped into the following categories:
Inflammatory splenomegaly: This is an acute enlargement of the spleen that develops in association with various infections or inflammatory processes and results from an increase in the defense activities of the organ. The demand for increased antigen clearance from the blood may lead to increased numbers of reticuloendothelial cells in the spleen and stimulate accelerated antibody production with resultant lymphoid hyperplasia. Examples include splenomegaly from lupus and Felty’s syndrome, and from viral infections such as Ebstein Barr Virus–induced mononucleosis.
Hyperplastic splenomegaly: In this setting, splenomegaly is thought to reflect work hypertrophy that results from the removal of abnormal blood cells from the circulation (either cells with intrinsic defects or cells coated with antibody) or, in some cases, as the result of extramedullary hematopoiesis (ie, myeloproliferative disease).
Congestive splenomegaly: This condition develops as a result of cirrhosis with portal hypertension, splenic vein occlusion (thrombosis), or congestive heart failure (CHF) with increased venous pressure.
Infiltrative splenomegaly: In this setting, splenomegaly is the result of engorgement of macrophages with indigestible materials (eg, sarcoidosis, Gaucher disease, amyloidosis, metastatic malignancy).
Infectious splenomegaly: Splenic filtering of blood-borne pathogens, especially encapsulated organisms, may lead to abscess formation. Because many splenic abscesses may be indolent in presentation, spleen size may be increased as the abscess enlarges. This is a relatively uncommon but important process to recognize and treat.