**Core Concept**
Splenomegaly refers to enlargement of the spleen, often due to chronic hemolysis, storage of abnormal RBCs, or infiltration by immune cells. In sickle cell anemia, repeated vaso-occlusive crises and hemolysis lead to splenic sequestration and chronic enlargement.

**Why the Correct Answer is Right**
In sickle cell anemia, sickled red blood cells obstruct small vessels, causing recurrent episodes of vaso-occlusion and hemolysis. This results in increased RBC trapping in the spleen, especially in children, leading to **splenic sequestration** and **splenomegaly**. The spleen acts as a filter, trapping and destroying sickled cells, which is a hallmark of the disease. This is particularly prominent in infants and young children and is a key clinical feature.

**Why Each Wrong Option is Incorrect**
Option A: Megaloblastic anemia is caused by vitamin B12 or folate deficiency and typically presents with macrocytic anemia and **mild or no splenomegaly**; splenomegaly is not a feature.
Option C: Thalassemia also involves chronic hemolysis, but splenomegaly is **not a consistent feature**—it may occur in some cases, but it is less prominent than in sickle cell disease.
Option D: G6PD deficiency causes acute hemolysis triggered by oxidants, but **splenomegaly is rare** and usually absent; it is more associated with acute crises than chronic enlargement.

**Clinical Pearl / High-Yield Fact**
Splenomegaly in sickle cell anemia is most common in **infants and young children** and is a sign of **severe vaso-occlusion**. It can lead to acute drop in hemoglobin and requires urgent intervention.

✓ Correct Answer: B. Sickle cell anemia