**Core Concept**
Sickle cell anemia is a genetic disorder characterized by the production of abnormal hemoglobin, leading to red blood cell deformity and dysfunction. The condition involves chronic hemolysis, vaso-occlusion, and compensatory mechanisms that affect multiple organs and systems.

**Why the Correct Answer is Right**
Splenomegaly is not typically seen in sickle cell anemia due to autosplenectomy, a process where the spleen becomes fibrotic and non-functional as a result of repeated infarctions and scarring. This occurs because the spleen is one of the organs most affected by vaso-occlusion and hemolysis, leading to its eventual atrophy and functional loss. In contrast, other organs like the heart, kidneys, and lungs are also affected, but the spleen's unique susceptibility to damage results in its premature demise.

**Why Each Wrong Option is Incorrect**
**Option A:** Fish vertebra, also known as biconcave vertebrae, is a common radiological finding in sickle cell anemia due to marrow hyperplasia and bone deformity.
**Option B:** Enlarged heart is a common complication of sickle cell anemia, resulting from chronic anemia, vaso-occlusion, and subsequent cardiac strain.
**Option D:** Leukocytosis, or elevated white blood cell count, can be seen in sickle cell anemia as a response to chronic inflammation and infection.

**Clinical Pearl / High-Yield Fact**
In sickle cell anemia, the spleen's premature atrophy can lead to an increased susceptibility to infections, particularly those caused by encapsulated organisms like Streptococcus pneumoniae and Haemophilus influenzae.

**✓ Correct Answer: C. Splenomegaly usually seen**