Long thought of as an unessential organ that could be removed without adverse effects, the spleen and its significance in 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 post-splenectomy sepsis. This chapter will provide an overview of the basic functions of the spleen and the infectious complications associated with asplenia.
A child may be asplenic for anatomic or functional reasons. Anatomic reasons include: (1) congenital asplenia, which can be isolated, or part of Ivemark syndrome, which is associated with cardiovascular defects and heterotaxy and (2) splenectomy. Splenectomy may be performed for various reasons. In children, the most common reasons are trauma-associated splenic rupture, malignancy, hypersplenism, and splenomegaly associated with persistent anemia and/or thrombocytopenia.2 Functional asplenia results from having an anatomically intact but poorly working spleen. There are various conditions that can cause functional asplenia, including sickle cell disease (Table 57–1). Some of the mechanisms leading to functional asplenia include infarction, infiltration, and impaired phagocyte function.2–4
Table 57–1. Causes of Asplenia |Favorite Table|Download (.pdf)
Table 57–1. Causes of Asplenia
- Congenital asplenia
- Functional asplenia
- Hematologic—sickle cell disease, thalassemia
- Autoimmune—biliary cirrhosis, chronic active hepatitis, Graves disease, Hashimoto's thyroiditis, rheumatoid arthritis, Sjogren's syndrome, systemic lupus erythematosis, polyarteritis nodosa
- Gastrointestinal—celiac disease, Crohn's disease, ulcerative colitis, dermatitis herpetiformis, intestinal lymphangiectasias, Whipple's disease
- Infiltrative—amyloidosis, sarcoidosis, storage diseases (Gaucher, Niemann Pick)
- Therapy-induced—radiation therapy, corticosteroid therapy, intravenous IgG (transient)
- Other—bone marrow transplant (chronic graft versus host disease)
Rates of overwhelming infection in asplenic children vary, depending on age and underlying reason for asplenia. Past studies have found that younger age, underlying illnesses including hemoglobinopathies, and splenectomy within the prior 3 years are associated with increased risk.2,5,6 However, it is important to note that there is a lifelong risk for overwhelming infection.
The spleen is comprised of a fibrous capsule, a trabecular framework of fibers and smooth muscle, cell-rich red and white pulp interspersed among this framework, and a blood supply arising from the splenic artery2,7,8:
- Fibrous capsule: The splenic capsule is highly elastic, containing smooth muscle that allows for the distension and splenomegaly seen in many pathologic states.
- White pulp: White pulp contains aggregates of lymphoid follicles (B-lymphocytes) found in the periarterial sheaths of the medium-sized splenic arteries. These follicles can form germinal centers with antigenic stimulation. At the edge of each follicle is a region called the marginal zone, where antigen trapping and processing occur.
- Red pulp...