Which of the following causes severe anemia in sickle cell disease and is characterized by a rapidly enlarging spleen?

Sickle cell disease is associated with various complications, one of the most concerning being splenic sequestration crisis, which is characterized by a sudden and severe enlargement of the spleen due to the rapid pooling of sickled red blood cells. In this situation, blood flow to the spleen becomes compromised, leading to engorgement and a consequential decrease in the circulation of red blood cells, resulting in severe anemia.

During a splenic sequestration crisis, children, particularly those with sickle cell disease, may present with significant abdominal pain, a noticeably enlarged spleen (splenomegaly), and symptoms of anemia such as fatigue, pallor, and rapid heartbeat. The spleen normally helps filter out old or dysfunctional red blood cells; however, due to the sickling and vaso-occlusive nature of the disease, it can become a site of drastic red blood cell trapping.

In contrast, other causes listed—such as aplastic crisis and hemolytic crisis—have different underlying mechanisms. Aplastic crisis is mainly caused by an infection (often parvovirus B19) that disrupts the bone marrow's ability to produce red blood cells, leading to anemia but not specifically splenic enlargement. Hemolytic crisis involves increased destruction of red