Asplenia

• asplenia and splenic hypoplasia are terms used to indicate complete or partial lack of functioning splenic tissue
• absent (asplenia) or defective splenic function (hyposplenia)
  • associated with a high risk of fulminant bacterial infections (particularly with encapsulated bacteria)
    • hyposplenism is seen in patients with sickle-cell disease and is due to splenic infarction, but it may also occur in patients with coeliac disease or dermatitis herpetiformis. Occasionally it may be seen in patients with inflammatory bowel disease and chronic liver disease.
    • patients are at particular risk from Pneumococcus, Haemophilus influenzae, and meningococcus
• loss of splenic tissue usually occurs as a result of surgical removal or autosplenectomy (ie, infarction in patients with sickle hemoglobinopathies)
• in certain conditions, patients may lack normal splenic function despite having spleens that are normal in size or even enlarged
  • called functional asplenia and is also associated with fulminant bacterial sepsis risk
    
    
• causes of asplenia
  • congenital asplenia is rare
    • may be due to genetic disorders, heterotaxy syndrome, or exposure to environmental factors during gestation
      • most common of these genetic disorders associated with asplenia is the Ivemark syndrome, also referred to as asplenia syndrome, in which visceral heterotaxy is present with bilateral right-sidedness
      • congenital splenic anomalies are usually accompanied by abnormalities in other organ systems, especially cardiac abnormalities, but they may occur in isolation
        • patients with polysplenia have multiple spleens, and their splenic function is usually normal, but polysplenia is also frequently associated with congenital cardiac anomalies
        • congenital asplenia may be viewed as bilateral right-sidedness and is associated with dextrocardia in approximately one third of the cases
          • these conditions are extremely difficult to diagnose in the absence of other indicators, and morphologic anomalies of peripheral blood erythrocytes, such as Howell-Jolly (HJ) bodies, may be the only evidence of the presence of a nonfunctional spleen
  • acquired asplenia occurs for several reasons:
    • after splenectomy (surgical removal)
      • patients may require surgical splenectomy because of traumatic injuries to the spleen or conditions that cause splenic enlargement, such as hereditary spherocytosis or autoimmune lymphoproliferative syndrome (ALPS)
    • after splenectomy with the goal of interfering with splenic function
      • as a treatment for diseases (e.g. ITP, thalassemia, spherocytosis)
        • in these conditions the spleen's usual activity exacerbates the disease
    • due to underlying diseases that destroy the spleen (autosplenectomy), e.g. sickle-cell disease,
    • functional asplenia occurs when splenic tissue is present but does not work well, e.g. sickle-cell disease, polysplenia, coeliac disease
      • these patients are managed as if asplenic

Notes:

• polysplenia may be regarded as bilateral left-sidedness and may be associated with left atrial isomerism
• congenital cardiac anomalies are more common and are often more severe in asplenia than in polysplenia
  • include endocardial cushion defects, pulmonary atresia or pulmonary stenosis, transposition of the great vessels, total anomalous pulmonary venous return, and a double-outlet right ventricle
  • cyanotic heart diseases, including severe atrioventricular canal defects, tend to be more common in asplenia, whereas acyanotic defects, which usually occur with increased pulmonary blood flow, are more common in polysplenia

References

1. Kirkineska L et al. Functional hyposplenism. Hippokratia v.18(1); Jan-Mar 2014.
2. Yi S et al. Splenectomy. Treasure Island (FL): StatPearls Publishing. 2024 Jan.