Splenomegaly is enlargement of the spleen — the fist-sized lymphoid organ in the upper left abdomen that filters blood, removes aged red blood cells, and plays a central role in immune surveillance. The normal spleen measures up to approximately 12 cm in length on imaging; splenomegaly is defined as a length exceeding 13 cm. An enlarged spleen is not a diagnosis in itself but an imaging or physical finding that signals an underlying systemic condition — one that must be identified because treatment depends entirely on what is driving the enlargement.
Splenomegaly is one of the most reliable imaging markers of portal hypertension in the setting of cirrhosis — the spleen enlarges as blood backs up from the portal vein into the splenic vein when hepatic outflow resistance rises. It is also a cardinal feature of hematologic malignancies including lymphoma and leukemia, which may be detectable as focal splenic deposits on MRI before they are apparent on blood tests or bone marrow biopsy. Splenic artery aneurysm — a vascular condition that can complicate a chronically enlarged spleen — should be evaluated when splenomegaly is identified. MRI characterizes both the spleen's size and internal architecture and simultaneously evaluates the liver, portal venous system, and intra-abdominal lymph nodes — providing the complete picture needed to identify the underlying cause.
Causes
Infection.
The spleen enlarges rapidly in response to acute infection as it accelerates blood filtration and immune cell activation. Epstein-Barr virus (EBV) causing infectious mononucleosis is the most common cause of acute, sometimes dramatic, splenomegaly in young adults — the spleen can enlarge to 3–4 times its normal size within days, carrying a small but important risk of spontaneous or trauma-related rupture. Cytomegalovirus (CMV), HIV, and acute viral hepatitis produce milder splenomegaly. Bacterial endocarditis produces splenomegaly through a combination of immune activation and septic emboli that can cause splenic abscesses. Tuberculosis involves the spleen in disseminated disease. Parasitic infections — malaria (the most common global cause of massive splenomegaly), visceral leishmaniasis (kala-azar), and schistosomiasis (which causes hepatosplenic schistosomiasis with progressive portal hypertension) — produce some of the most severe degrees of enlargement seen in clinical practice.
Other causes.
Portal hypertension from cirrhosis is the most common cause of splenomegaly in Western countries, with the spleen serving as a pressure reservoir for the backed-up portal venous blood. Hypersplenism — the increased destruction of blood cells by an overactive enlarged spleen — produces thrombocytopenia and leukopenia that are reliable laboratory markers of significant portal hypertension. Hemolytic anemias (hereditary spherocytosis, autoimmune hemolytic anemia, sickle cell disease in early childhood before autosplenectomy, thalassemia major) chronically overload the spleen with abnormal red blood cells requiring removal. Hematologic malignancies — lymphomas (particularly splenic marginal zone lymphoma, which originates in the spleen), chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML), and myeloproliferative neoplasms (polycythemia vera, primary myelofibrosis) — infiltrate the spleen and cause progressive enlargement. Primary myelofibrosis produces the most extreme degrees of splenomegaly seen in developed-world medicine — spleens extending to the iliac fossa and weighing several kilograms. Gaucher disease (glucocerebrosidase deficiency) causes glucocerebroside accumulation in splenic macrophages producing massive splenomegaly. Systemic lupus erythematosus, sarcoidosis, and amyloidosis are inflammatory and infiltrative causes.
Symptoms
Many patients with moderate splenomegaly — particularly when caused by chronic portal hypertension — have no symptoms directly attributable to the spleen, and the finding is identified on physical examination or abdominal imaging. When the spleen is substantially enlarged, left upper quadrant heaviness or discomfort and early satiety from compression of the stomach fundus are the most common complaints. Left shoulder pain (Kehr's sign) from diaphragmatic irritation by a very large spleen or by a subcapsular hematoma can occur. Severe fatigue, pallor, easy bruising, and susceptibility to infections reflect the consequences of hypersplenism — low platelet counts and white cell counts from excessive splenic sequestration.
The most dangerous acute complication is splenic rupture — either spontaneous (most classically in infectious mononucleosis, where the capsule is acutely stretched) or from even minor abdominal trauma in patients with massive splenomegaly. Rupture causes sudden severe left upper quadrant pain radiating to the left shoulder, hemodynamic instability from intraperitoneal hemorrhage, and requires emergency surgery. This risk is the reason that contact sports are strictly contraindicated in patients with active mononucleosis splenomegaly.
Diagnosis
Physical examination — finding a palpable spleen tip below the left costal margin — is present only when the spleen has enlarged significantly (the normal spleen is not palpable). Blood tests are essential: complete blood count (evaluating for thrombocytopenia and leukopenia from hypersplenism, anemia from hemolysis or marrow infiltration), peripheral blood smear (identifying abnormal red cell morphology), liver function tests, EBV and CMV serology, HIV testing, and specific markers based on clinical context. Bone marrow biopsy is performed when hematologic malignancy is suspected and peripheral blood findings are indeterminate.
An MRI of the abdomen is the most accurate imaging study for splenomegaly evaluation. MRI precisely measures splenic dimensions and volume, identifies focal lesions within the splenic parenchyma (lymphoma deposits appear as T1-hypointense, T2-hyperintense nodules with restricted diffusion; abscesses show ring enhancement; hemangiomas show characteristic fill-in enhancement; infarcts appear as wedge-shaped non-enhancing peripheral defects), and simultaneously characterizes the liver for cirrhosis and the portal venous system for portal hypertension. MRI evaluates intra-abdominal and retroperitoneal lymph nodes for lymphoma staging. When a vascular cause is suspected — particularly splenic artery aneurysm or splenic vein thrombosis — MR angiography characterizes the splenic vasculature. The combination of spleen size, internal architecture, hepatic findings, and lymph node status on MRI frequently narrows the differential and directs appropriate laboratory or biopsy confirmation.
Classification
Splenomegaly is classified by degree of enlargement and by the mechanism of splenic involvement.
- Mild splenomegaly (13–15 cm): Common with acute viral infections, early portal hypertension. Often resolves with treatment of the underlying cause.
- Moderate splenomegaly (15–20 cm): Chronic liver disease, hematologic disorders, lymphoma. Associated with clinically significant hypersplenism and thrombocytopenia.
- Massive splenomegaly (>20 cm or crossing the midline): Myeloproliferative neoplasms (especially primary myelofibrosis), advanced lymphoma, malaria, visceral leishmaniasis, Gaucher disease, thalassemia major. Associated with severe symptoms, high rupture risk with trauma, and often a dominant management challenge independent of the underlying disease.
Treatments
Treatment targets the underlying cause — reducing or eliminating the stimulus for splenic enlargement — rather than the enlarged spleen itself in most cases.
Treatment of the underlying condition: Antiviral or antimicrobial therapy for infectious causes; treatment of cirrhosis and portal hypertension (including TIPS for refractory complications); chemotherapy, immunotherapy, or targeted therapy for hematologic malignancies; enzyme replacement therapy (imiglucerase) for Gaucher disease; immunosuppression for autoimmune causes. All typically reduce spleen size over weeks to months as the driving stimulus is addressed.
Activity restriction.
Patients with acute splenomegaly — particularly from infectious mononucleosis — must avoid contact sports, vigorous exercise, and activities risking abdominal trauma until the spleen has returned to normal size on follow-up imaging, typically 3–4 weeks after symptom onset. Return-to-sport decisions should be guided by imaging confirmation of size normalization rather than symptom resolution alone, as the spleen may remain enlarged after symptoms resolve.
Splenectomy.
Surgical spleen removal is indicated for: hereditary spherocytosis and other hereditary hemolytic anemias where the spleen is the primary site of red cell destruction; immune thrombocytopenic purpura (ITP) refractory to medical therapy; splenic marginal zone lymphoma as a primary treatment; symptomatic massive splenomegaly in myelofibrosis (though the benefit must be weighed against significant surgical risk); and splenic rupture as an emergency. Patients undergoing elective splenectomy receive vaccination against encapsulated organisms (pneumococcus, meningococcus, Haemophilus influenzae type b) at least 2 weeks before surgery and often lifelong penicillin prophylaxis, given their permanent susceptibility to overwhelming post-splenectomy infection (OPSI) — a rare but rapidly fatal sepsis syndrome.
Partial splenic embolization.
Interventional radiologists can selectively occlude branches of the splenic artery using embolic particles, reducing functional splenic volume by 50–70% while preserving residual immune function. This reduces hypersplenism-related cytopenias and can allow chemotherapy to proceed safely in patients whose thrombocytopenia would otherwise preclude treatment. It is also used in patients with portal hypertension-related splenomegaly who are not surgical candidates.
Get an MRI to Confirm Your Diagnosis
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