Splenic function: physiology and splenic hypofunction

A wide variety of disorders can result in diminished splenic function. The pathophysiology appears to be clearly defined in some instances, such as congenital asplenia and disorders of splenic vascular obstruction or congestion. In others, such as the autoimmune and GI disorders, the mechanism remains poorly defined. Further research is needed. The hyposplenia which occurs in many of these disorders has been associated with an increased risk of life-threatening, overwhelming bacterial sepsis. In other instances, this complication has not been reported. This certainly should not be interpreted to mean that it cannot occur. The risk of septicemia in hyposplenic disorders is rarely above 10 to 15%. In disorders with minimal inhibition of splenic function, the incidence of sepsis would presumably be less than the 1.5% incidence following surgical splenectomy for trauma. Considering these data, a very large number of patients would have to become asplenic before it would be likely that one would develop sepsis. Furthermore, the lack of awareness of the possibility of hyposplenia-related sepsis in many of these disorders may cause such occurrences to go unrecognized. Finally, since the risk of sepsis is probably less in hyposplenic adults as compared to children, studies on adults may underestimate the incidence of this complication in children. Many of the disorders reported to cause hyposplenia in adults have not been noted to do so in children. In instances such as celiac disease, it may take many years for the complication to manifest so that it would be unlikely for a child to manifest hyposplenia during childhood. However, in other instances, not enough children have been studied to be confident that the hyposplenia and its associated risk of sepsis are not complications that occur in children. Hyposplenia-related bacterial septicemia is a catastrophic complication. If a patient develops a disorder that is potentially associated with hyposplenia, the patient should be observed for signs of asplenia in the peripheral blood. If the technique is available, quantitation of red cell pits should be performed. If not, other studies of splenic function such as radionuclide scans should be considered, depending on the incidence of hyposplenia in that particular disorder. If evidence of asplenia develops, pneumococcal vaccine should be administered, penicillin prophylaxis should be considered, significant febrile episodes should be managed aggressively, and probably most importantly, the patient and family should be carefully educated about this complication. Most deaths from hyposplenia-related septicemia are preventable.     

Splenic hyperkinetic state and splenic artery aneurysm in portal hypertension.

Forty-eight out of six hundred and thirty patients with portal hypertension undergoing a celiac angiography series were diagnosed as cases of splenic artery aneurysm during the period 1977-1988. The case-control study of patients with portal hypertension with splenic artery aneurysms and those without was designed to characterize the angiological features. The splenic arterial flow was assessed by measuring the radii of the splenic arteries on celiac arteriograms. In the portal hypertensive patients with splenic artery aneurysms, the splenic artery was larger (p < 0.05) and the splenic arterial flow greater (p < 0.05), and these patients were in a more hyperkinetic state, than were those with no splenic artery aneurysm. The study suggests that splenic artery aneurysms in cases of portal hypertension may be the consequence of a hyperkinetic state in the spleen.     

Splenic lymphoma with circulating villous lymphocytes/splenic marginal-zone lymphoma.

Splenic lymphoma with villous lymphocytes (SLVL) represents a low-grade B-cell non-Hodgkin's lymphoma (NHL) that histologically is indistinguishable from splenic marginal-zone lymphoma (SMZL). Characteristic features of SLVL are splenomegaly, moderate lymphocytosis, nodular and intrasinusoidal pattern of bone marrow infiltration, serum monoclonal band, slow benign course, and response to splenectomy. The diagnosis is made by the morphology of the circulating villous cells and their immunophenotype, which is distinct from that of chronic lymphocytic leukemia (CLL) and hairy-cell leukemia (HCL), diseases with which SLVL may be confused. When treatment is indicated, splenectomy is the treatment of choice, but some patients may require additional chemotherapy to control progression. In those circumstances, fludarabine may be the agent of choice. Despite its unique features, which, compounded, suggest that SLVL is a clinicopathologic entity, there are no specific chromosome abnormalities and problems of differential diagnosis with other B-cell NHLs, chiefly mantle-cell lymphoma (MCL), remain in a minority of patients.     

Splenic infarction, splenic sequestration, and functional hyposplenism in hemoglobin S-C disease

Splenic atrophy or evidence of hyposplenism occurs in as many as one third of all patients with S-C hemoglobinopathy. Yet there are few reports in the literature of clinically apparent splenic infarction in this disease. We describe four instances of acute splenic infarction in three patients with hemoglobin S-C disease which illustrate a wide spectrum of clinical manifestations and severity. Of particular interest were the observations of coincident occurrences of splenic sequestration and functional hyposplenism with splenic infarction, suggesting a close pathophysiological relationship among these syndromes.     

The exchangeable splenic platelet pool in response to intravenous infusion of isoprenaline

8 healthy volunteers and 4 asplenic subjects, in whom autologous platelets had been labelled with radioactive sodium chromate, received i.v. infusions of isoprenaline in a dose of 0.03 microgram x kg-1 x min-1 over a period of 6 min. In the former group these infusions caused a significant decrease in the concentration of labelled as well as unlabelled platelets in the peripheral blood. Body surface countings showed that a significant increase in the count rate over the spleen occurred concomitantly with the decrease in the circulating platelet-bound radioactivity (PBR). In the group of asplenic subjects no change in PBR occurred. It is concluded that adrenergic beta-receptor stimulation causes a transitory trapping of platelets in the exchangeable splenic platelet pool.