Splenomegaly 

A wide variety of diseases are associated with splenomegaly, or enlargement of the spleen, with many of the mechanisms leading to this condition being exaggerated forms of normal spleen function. (See Etiology.)

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.^[1]

The normal spleen is usually not palpable, although it can sometimes be palpated in adolescents and individuals with a slender build. However, an enlarged or palpable spleen is not necessarily of clinical significance. Moreover, certain individuals with broadly splayed costal margins have readily palpable, but small, spleens. (See Presentation.)

Spleens weighing 400-500 g indicate splenomegaly, and some authors consider spleens weighing more than 1000 g to indicate massive splenomegaly. Spleens that are prominent below the costal margin typically weigh 750-1000 g. 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. (See Treatment and Workup.)

In many instances, the spleen enlarges as it performs its normal functions. The 4 most important normal functions of the spleen are as follows:

• Clearance of microorganisms and particulate antigens from the blood stream
• Synthesis of immunoglobulin G (IgG), properdin (an essential component of the alternate pathway of complement activation), and tuftsin (an immunostimulatory tetrapeptide)
• Removal of abnormal red blood cells (RBCs)
• Embryonic hematopoiesis in certain diseases

As previously mentioned, 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, the following 6 etiologies of splenomegaly are considered primary:

• Immune response work hypertrophy - Such as in subacute bacterial endocarditis or infectious mononucleosis
• RBC destruction work hypertrophy - Such as in hereditary spherocytosis or thalassemia major
• Congestive - Such as in splenic vein thrombosis or portal hypertension
• Myeloproliferative - Such as in chronic myeloid metaplasia
• Infiltrative - Such as in sarcoidosis and some neoplasms
• Neoplastic - Such as in chronic lymphocytic leukemia and the lymphomas

Miscellaneous causes of splenomegaly include trauma, cysts, hemangiomas, metastasis, giant abscess (see the images below), and certain drugs (eg, RhoGAM).

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 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, that results from extramedullary hematopoiesis (ie, myeloproliferative disease).^[2]

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, splenic size may be increased as the abscess enlarges. This is a relatively uncommon, but important, process to recognize and treat.

In the United States, one large series reported a palpable spleen in 2% of patients, and another, in 5.6% of patients. Tropical splenomegaly syndrome has the highest predilection for indigenous persons of and visitors to the malarial belt of tropical Africa.

Race-related demographics

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.

Sex-related demographics

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.

Age-related demographics

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 prognosis for patients with splenomegaly is usually excellent and not substantially different from age-matched controls, but it is impacted by the underlying disease state rather than the presence of splenomegaly or the postsplenectomy state.

Morbidity and mortality

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.

Patients with splenomegaly need education with regard to decreasing their risk of splenic hemorrhage. These patients must be cautioned about contact sports and other activities that may acutely increase intra-abdominal pressure or place excessive forces on the left upper quadrant, left flank, or lateral back. This decreases the likelihood of splenic rupture in a patient with an abnormal splenic mass and capsule. The routine use of seat belts is essential while driving or riding in a motor vehicle.

Additional education regarding the signs and symptoms of postsplenectomy sepsis cannot be overstressed. Prompt antibiotic therapy may be lifesaving.

Education represents a mandatory strategy in the prevention of overwhelming postsplenectomy infection (OPSI). Asplenic patients should be encouraged to wear a Medi-Alert (Pinellas Park, Fla/Henderson, Nev) bracelet and carry a wallet card explaining their lack of a spleen. Patients should also be aware of the need to notify their physician in the event of an acute febrile illness, especially if it is associated with rigors or systemic symptoms.

For patient education information, see the Infections Center, as well as Mononucleosis (Mono).