Splenomegaly

Overview

The spleen is not considered a vital organ, since the body can survive without it. However, the spleen is the largest lymphoid organ and has an important role in immunity and blood filtration.

Definition

A spleen is considered enlarged when it can be palpated 2 cm below the costal margin or when imaging shows that its size is above the upper limits of normal for age.

Normal physiology

Main functions:

• Filters the blood, removing old or damaged platelets and RBCs
• Acts as a reservoir for blood elements
• Filters and destroys encapsulated bacteria circulating in blood
• Produces lymphocytes and synthesizes antibodies

Blood enters the spleen via the splenic artery branching into central arterioles:

1. Arterioles end as capillaries surrounded by lymphatic tissue (white pulp).
2. White pulp has 3 structural elements responsible for mounting an immune response and antibody production:
   • Periarteriolar lymphocyte sheath (PALS): houses T cells and macrophages
   • Marginal zone: houses macrophages
   • Follicles: house B cells
3. Blood flows out of capillaries into surrounding venous sinusoids and cords (red pulp).
4. Red pulp is the storage site for platelets and contains macrophages that remove damaged or old RBCs.
5. Sinusoids drain into collecting veins, which carry blood to the splenic vein.
6. Filtered blood exits the spleen via the splenic vein.
7. The splenic vein joins the superior and inferior mesenteric veins to form the hepatic portal vein.

Pathophysiology

• Splenomegaly: enlargement of the spleen
  • 3 general mechanisms:
    • Passive congestion via compromise of hepatic portal vein 
    • Infiltration
    • Infection 
  • Splenomegaly can eventually lead to splenic rupture.
• Hypersplenism: increased functioning of the spleen that occurs with or without organ enlargement
  • Sequestration of blood elements leads to congestion.
  • Activation of reticuloendothelial system leads to thrombocytopenia and anemia.
  • Increased risk of splenic rupture
  • Clinical features:
    • Splenomegaly
    • Anemia
    • Leukopenia
    • Thrombocytopenia
    • Pancytopenia 
    • Compensatory bone marrow hyperplasia

Epidemiology and Etiology

Epidemiology

• Up to 5% of U.S. population affected
• Certain underlying causes associated with specific racial groups:
  • Sickle cell disease (African Americans)
  • Lysosomal storage diseases (Ashkenazi Jews)
• Geographic predisposition:
  • Areas with endemic malaria
  • Tropical splenomegaly 2 times more common in women
• Certain causes more likely in particular age groups:
  • Children: acute leukemia and storage diseases
  • Adults: chronic leukemia

Etiology

• Hematologic:
  • Polycythemia vera 
  • Anemia
  • Sickle cell disease
  • Thalassemia
• Oncologic:
  • Leukemia: 
    • CML
    • CLL
  • Lymphoma
  • Metastases
• Hepatic:
  • Cirrhosis
  • Portal vein hypertension
  • Portal or splenic vein thrombosis
  • Right heart failure
• Storage diseases:
  • Gaucher disease
  • Niemann-Pick disease
• Autoimmune diseases: 
  • Sarcoidosis
  • Systemic lupus erythematosus (SLE)
  • Rheumatoid arthritis (RA)
• Infectious:
  • Infectious mononucleosis (EBV)
  • Malaria
  • Typhoid
  • AIDS
  • Parasitic infections:
    • Leishmaniasis
    • Schistosomiasis
  • Septicemia secondary to encapsulated bacteria:
    • Streptococcus pneumoniae
    • Neisseria meningitidis
    • Haemophilus influenzae type B
• Genetic:
  • Histiocytosis X
  • Amyloidosis (may also be acquired)
• Structural:
  • Cyst(s)
  • Hemangioma(s)

Clinical Presentation

History and physical exam

• Obtain history.
• Physical exam:
  • Patient should be examined in the supine position.
  • Abdominal palpation:
    • Spleen should not be palpable in healthy individuals.
    • Gentle palpation below left costal margin
    • Ask the patient to take a deep breath. This maneuver causes the spleen to move up and down so that it can be felt when pressing below the left costal margin.
  • Abdominal percussion: Dullness to percussion may reveal presence of underlying solid tissue of the spleen.

Hackett’s grading system

The degree of splenomegaly is graded from 0 to 5, according to Hackett’s grading system:

• Grade 0: normal impalpable spleen
• Grade 1: spleen palpable only on deep inspiration
• Grade 2: spleen palpable on midclavicular line, halfway between umbilicus and costal margin
• Grade 3: Spleen expands toward the umbilicus.
• Grade 4: Spleen goes past the umbilicus.
• Grade 5: Spleen expands toward the pubis symphysis.

Causes categorized on the basis of degree of splenic enlargement

The differential diagnosis may be categorized on the basis of the degree of splenic enlargement.

Diagnosis

Splenomegaly is a clinical sign associated with multiple causes rather than a diagnosis. When splenomegaly is present, patients should be properly evaluated to identify the underlying cause.

Laboratory studies

• CBC with peripheral blood thick and thin films (for malaria)
• Liver function tests
• Viral hepatitis profile
• Autoimmune screening
• Inflammatory markers
• Cytogenetic tests 
• Karyotyping
• Tissue biopsy
• Bone marrow aspirate

Imaging

• Ultrasonography
• CT 
• MRI

Management

Management is based on the underlying cause and clinical status of the patient.

Conservative (treating underlying disorder)

• Antibiotics (therapeutic and/or prophylactic)
• Antimalarials
• Chemotherapy
• Blood transfusion or exchange transfer
• Low-dose radiotherapy for palliative care in patients with advanced hematologic problems

Splenectomy

• Indicated when underlying cause results in significant splenomegaly
• Splenic trauma and rupture
• Postsplenectomy vaccination is important to reduce the risk of overwhelming postsplenectomy infection (OPSI).

Clinical Relevance

• Asplenia: absence of a spleen. The most common anatomical reason for asplenia is surgical removal; only rarely is asplenia congenital. If asplenia is congenital, it is often associated with a malformation of the large thoracic vessels. Asplenic patients are at high risk for infection with encapsulated organisms and should be vaccinated for these whenever possible.
• Mononucleosis: Infectious mononucleosis, also known as “the kissing disease,” is a highly contagious disease caused by EBV. The common name for mononucleosis comes from its main method of transmission: spread of infected saliva via kissing. There is no treatment, but supportive care is usually sufficient.
• Rupture of the spleen: most common reason for rupture of spleen is blunt abdominal trauma. For individuals with splenomegaly, minimal trauma is already enough to cause a rupture of the capsule. Emergent surgery is usually necessary to prevent massive blood loss and shock from splenic rupture.