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DEFINITIONS

Once regarded as an unessential organ that could be removed without adverse effects, the spleen and its significance in host defense against infections were not well recognized until 1952, when King and Shumacker published a seminal paper describing an association between splenectomy and subsequent susceptibility to overwhelming infection.1 Since then, severe infection in asplenic individuals has become a well-known entity, termed postsplenectomy sepsis or overwhelming postsplenectomy infection. This chapter provides an overview of the basic functions of the spleen and the infectious complications associated with asplenia and hyposplenia.

Asplenia can arise from anatomic or functional causes. Anatomic asplenia, partial or total, results from either (1) congenital asplenia, which can be isolated or part of a syndrome such as Ivemark syndrome, which is associated with cardiovascular defects and heterotaxy; or (2) splenectomy. In children, the most common reasons for splenectomy are trauma-associated splenic rupture, malignancy, hypersplenism, and splenomegaly associated with persistent anemia and/or thrombocytopenia.2,3 Functional asplenia or hyposplenia results from having an anatomically intact but poorly working spleen. Mechanisms leading to functional asplenia include splenic infarction, infiltration, and atrophy.2,3 Polysplenia, which can occur with heterotaxy, may be associated with reduced splenic function due to the presence of nonfunctioning splenules (Figure 61-1). A wide range of conditions can cause functional asplenia or hyposplenia (Table 61-1).

TABLE 61-1Causes of Asplenia and Hyposplenia
FIGURE 61-1.

Computed tomography of abdomen in a 4-year-old patient with pneumonia and a prior episode of pneumococcal sepsis. The liver is midline. There are multiple splenules, indicating a diagnosis of polysplenia. The patient also had dextrocardia with a right-sided aortic arch. [Used with permission from Samir S. Shah, MD, MSCE]

EPIDEMIOLOGY OF INFECTION

Rates of overwhelming infection in asplenic/hyposplenic children vary, depending on age and underlying reason for asplenia. Risk factors for overwhelming infection in these children include younger age, underlying hemoglobinopathy, and splenectomy within the prior 3 years.2,4,5 The incidence of bloodstream infection has decreased significantly among children with sickle cell disease since the introduction of Streptococcus pneumoniae and Haemophilus influenzae type b (Hib) conjugate vaccines, as well as penicillin prophylaxis.6,7...

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