Splenic Sequestration

Background
Splenic sequestration is defined as sudden enlargement of the spleen and reduction in hemoglobin concentration by at least 2 g/dL below the baseline value. It is a major cause of acute anemia. During splenic sequestration, the reticulocyte count and circulating nucleated red blood cells are usually elevated, and the platelet count is generally decreased because both red cells and platelets are trapped in the spleen. Sequestration usually develops without warning or known cause. It may occur as early as several months of age, although it is more typical in children between the ages of 1 and 4 years old. Parents may note an enlarging mass in the left upper quadrant. Involution and autoinfarction of the spleen usually occurs by age 5, so sequestration events are less common in older children and adults with HbSS. In people with HbSS, the lifetime prevalence of acute splenic sequestration has been reported to be between 7 percent and 30 percent. In people with HbSC and HbSf­ thalassemia, splenic sequestration often occurs later in childhood or even during the adult years. Splenic sequestration in older patients is often accompanied by severe pain from splenic infarction, which can be documented by imaging studies.

Some people with SCD have a chronically enlarged spleen and may develop hypersplenism. This presents as a reduction in the white blood cell and platelet counts in addition to acute anemia. Such people are particularly prone to develop acute sequestration events.

In infants with HbSS, splenic sequestration may present acutely with severe anemia and hypovolemic shock. In older people, it may occur more insidiously. Although usual care for splenic sequestration consists of blood transfusion aimed at partial correction of the anemia, excessive transfusion (to hemoglobin values over 8 g/dL) should be avoided, as the sequestered erythrocytes in the enlarged spleen typically reenter the circulation several days later. The result could be hyperviscosity due to an excessively high hemoglobin concentration.

People with splenic sequestration must be monitored for recurrences. Thus, parents and patients are instructed to monitor splenic size and immediately report any marked increase above baseline. People with recurrent sequestration or a single life-threatening acute sequestration event most commonly have a splenectomy. Most people with chronic splenic sequestration accompanied by local pain and hypersplenism are also managed with splenectomy. Splenectomy for splenic sequestration does not further increase the risk of death or bacteremia since most patients are already functionally asplenic. Regularly scheduled transfusions aimed at avoiding the need for subsequent splenectomy have not been proven to be beneficial.

Summary of the Evidence
No RCTs were found that evaluated the treatment of splenic complications in SCD. Twenty observational studies (involving more than 950 people) and 39 case reports described various splenic complications in SCD. Reported complications in these observational studies included: splenic sequestration (n=16), hypersplenism (n=3), splenic abscess (n=2), and functional asplenia/splenic auto infarction (n=2). Overall benefits were reported for transfusion and splenectomy; however, since 75 percent of the studies had no comparative arm, the general quality of the evidence was considered low.

Only four studies, all involving children, had a comparative design. The first compared an intensive transfusion program (to achieve an HbS concentration <20 percent) to a conventional transfusion program in children with prior stroke. It reported the finding of normal or increased splenic size and improved function in the population receiving intensive transfusion, while all people receiving fewer transfusions had decreased splenic function (functional asplenia). A second study assessed three options for treating splenic sequestration: prompt splenectomy, a short-term transfusion program, or observation. Short-term transfusion was equivalent to observation and therefore of limited benefit in preventing recurrent splenic sequestration. The third comparative study did not report group-specific outcomes but rather overall mortality rates. The final comparative study included people with SCD with various splenic complications (splenic sequestration, hypersplenism) and compared outcomes in people who received splenectomy and those who did not.245 The remaining studies described splenectomy (n=l3), transfusion (n=3), an age-dependent approach (n=l),246 and hydroxyurea (n=l).

The splenectomy studies reported favorable outcomes following the surgery. Infection rates after splenectomy did not increase. Transfusion was reported to be effective in treating acute splenic sequestration. Recommendations In people with hypovolemia due to severe acute splenic sequestration, immediately provide IVfluid resuscitation. (Strong Recommendation, Low-Quality Evidence) In consultation with a sickle cell expert, transfuse people who have acute splenic sequestration and severe anemia to raise the hemoglobin to a stable level, while avoiding over-transfusion. (Strong Recommendation, Low Quality Evidence) In consultation with a sickle cell expert, address the performance and timing of splenectomy in people with recurrent acute splenic sequestration or symptomatic hypersplenism. (Moderate Recommendation, Low-Quality Evidence)

Seeing helps us learn. Explore the spleen with the model below.