We searched Medline by using the medical subject heading terms “asplenia”, “hyposplenism”, “pneumococcal vaccination”, “splenectomy”, “splenic atrophy”, and “splenosis” for articles published between January, 1998, and June, 2010, but we did not exclude commonly referenced and highly regarded older publications. We also searched the reference lists of review articles on splenectomy and hyposplenism for additional papers we judged to be relevant to this Review.
ReviewPost-splenectomy and hyposplenic states
Introduction
The initial experimental evidence of the protective role of the spleen against infections was provided in the early 1900s by Morris and Bullock,1 who indicated that splenectomised rats had a significantly higher post-surgical mortality than did rats who had sham operations, and this high mortality was attributed to sepsis by the bacillus that causes rat plague. Many years afterwards, the crucial function of the spleen in immune defence emerged as a result of two brief studies. King and Schumacker2 reported a series of cases of overwhelming post-splenectomy infections (OPSI) caused by encapsulated bacteria in a cohort of children who had had splenectomy. Dameshek3 coined the term hyposplenism to describe a patient with coeliac disease in whom Howell-Jolly bodies were detected on peripheral blood smear and an atrophic spleen was confirmed at post-mortem examination. Hyposplenism is now regarded as an acquired disorder, potentially associated with several diseases and sometimes accompanied by a reduction in spleen size. Asplenia refers to the absence of the spleen, a disorder that is rarely congenital and is more frequently a result of surgery.
Although basic research has provided detailed information on the role of the spleen in the immune response,4, 5 and data from many studies have confirmed the association of asplenia or impaired splenic function with increased morbidity and mortality from infectious complications,6 this information has not been sufficiently translated into appropriate clinical practice. Most physicians are unaware of the diseases for which a systematic search for splenic dysfunction should be done, what the clinical predictors of this dysfunction and the means for assessing it are, what the real risks of sepsis are, and what would be the best ways to prevent sepsis. Treatment of post-splenectomy thrombotic complications has been recently reviewed;7 in this Review, we clarify the risk factors for spleen dysfunction, clinical signs, diagnostic techniques, and prophylaxis options against infection.
Section snippets
Immunological function of the spleen
The spleen consists of three functional inter-related compartments—the red pulp, white pulp, and marginal zone (figure 1).4 The red pulp is a sponge-like structure filled with blood flowing through sinuses and cords. The white pulp is distributed along the central arteriole branching from the splenic artery. T cells form an envelope (the periarteriolar lymphoid sheath) around the central arteriole, and also surround the B-cell follicle in a thin layer. This thin layer is formed by an outer dark
Diagnosis of spleen dysfunction
Diagnosis of spleen dysfunction is generally based on assessment of the spleen's filtering function by radioisotopic methods or quantitation of erythrocyte morphological abnormalities (table 1). Radioisotopic methods enable a morphofunctional assessment of the spleen by injection, uptake, and clearance of particulate substances or radiolabelled tracers.16, 17 However, their use in clinical practice is limited by their high costs and some technical difficulties. Detection methods of
Splenectomy
In tertiary referral centres, the frequency of splenectomy for haematological, immunological, or oncological reasons (54%) is substantially higher than that for trauma surgery (16%),27 although this ratio might be different in non-academic settings. The increasing awareness of the risk of OPSI28 has led to a more conservative approach, and a notable reduction in the incidence of splenectomy for trauma was recorded in children between 1970 and 2000.29 In 2005, the Society for Surgery of the
Hyposplenism
The natural history of many diseases, including congenital, haematological, immunological, gastroenterological, infectious, and iatrogenic disorders, can be complicated by splenic abnormalities ranging from a reversible mild hyposplenism to severe splenic atrophy (panel).6 In most of these conditions, the pathogenesis of hyposplenism is mostly unknown.8 Table 2 describes the main clinical aspects of the most frequent diseases complicated by splenic hypofunction or atrophy. Because of the
OPSI
The term OPSI defines fulminating sepsis, meningitis, or pneumonia triggered mainly by S pneumoniae, N meningitidis, and H influenzae type b in splenectomised and hyposplenic individuals.29 Although data from several studies6 have confirmed that asplenia and hyposplenism are major risk factors for sepsis, prevention of these infections is often overlooked. Nevertheless, extrapolation of definite figures on the epidemiology of OPSI from a series of retrospective studies is difficult because of
Education
Up to 84% of splenectomised individuals are thought to be unaware of their increased susceptibility to severe sepsis,80 and provision of proper information reduces infectious complications.81 In particular, patients and relatives should be instructed to notify their physicians of any acute febrile illness, especially if associated with rigor and systemic symptoms,81 and of visits to tropical countries because of the high risk of parasitic infections, such as malaria or babesiasis. In
Conclusions
Although post-splenectomy and hyposplenic states might predispose individuals to thromboembolic complications, the main adverse events are immunological and infectious. Spleen-preserving surgical techniques have become increasingly common both for emergency and elective splenectomy; however, the morbidity and mortality associated with the absence and the dysfunction of the spleen are still unacceptably high. In disorders associated with hyposplenism, spleen function should be assessed by means
Search strategy and selection criteria
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