Acute splenic sequestration is the sudden pooling of blood in the spleen resulting in anemia, which may be life threatening. This type of crisis occurs most often in young children between 10 and 27 months of age in whom autoinfarction of the spleens has not yet happened.
The cause of this syndrome is unclear; it may be seen in the setting of concurrent bacterial or viral infection.

Diagnostic criteria
The diagnostic criteria for acute splenic sequestration include an acutely enlarging spleen, a decrease in hemoglobin level of at least 2 g per dL below baseline, thrombocytopenia often with a platelet count <100,000 per mm,³ leukopenia, and evidence of bone marrow compensation with reticulocytosis.

In its most severe form, acute splenic sequestration results in life-threatening anemia, hypovolemia, and shock. Decreases in the levels of hemoglobin <4 g per dL are associated with 35% mortality rates. It is estimated that as much as 50% of the patient’s red cells can be sequestered in the spleen. Approximately 50% of patients who survive an episode of acute splenic sequestration will experience a recurrence.

Mangement
Emergency management is aimed at restoring circulatory blood volume and hemodynamic stability. Although
therapy may begin with crystalloid resuscitation, red blood cell transfusions must be given promptly.

Long-term management is complicated because there is a high rate of recurrence of either acute or subacute sequestration. Splenectomy has been advocated when recurrent episodes occur.

Hereditary spherocytosis may be a cause of hemolytic disease in the newborn and may present as anemia and hyperbilirubinemia sufficiently severe to require phototherapy or exchange transfusions. Hemolysis may be more prominent in the newborn because hemoglobin F binds 2,3-diphosphoglycerate poorly, and the increased level of free 2,3-diphosphoglycerate destabilizes spectrin-actin-protein 4.1 interactions in the RBC membrane .

The severity of symptoms in infants and children is variable. Some children remain asymptomatic into adulthood, but others may have severe anemia, with pallor, jaundice, fatigue, and exercise intolerance. Severe cases may be marked by expansion of the diploë of the skull and the medullary region of other bones, but to a lesser extent than in thalassemia major.

After infancy, the spleen is usually enlarged, and pigmentary (bilirubin) gallstones may form as early as age 4–5 yr. At least 50% of unsplenectomized patients ultimately form gallstones, although they may be asymptomatic. Because of the high RBC turnover and heightened erythroid marrow activity, children with hereditary spherocytosis are susceptible to aplastic crisis, primarily as a result of parvovirus infection, and to hypoplastic crises associated with various other infections .

The erythroid marrow failure may result rapidly in profound anemia (hematocrit <10%), high-output heart failure, hypoxia, cardiovascular collapse, and death. White blood cell and platelet counts may also fall .