**Question:** Onion skin spleen is seen in -

A. Malaria
B. Leishmaniasis
C. Hepatitis
D. Typhoid fever

**Core Concept:** Onion skin spleen is a histopathological feature characterized by multiple layers of red pulp surrounded by white pulp. This occurs due to increased blood flow and splenic enlargement in response to infections or other conditions.

**Why the Correct Answer is Right:** Onion skin spleen is a characteristic feature seen in typhoid fever, specifically Salmonella typhi infection. The increased blood flow and splenic enlargement lead to the formation of multiple layers of red pulp, resulting in this histopathological finding.

**Why Each Wrong Option is Incorrect:**

A. Malaria: Onion skin spleen is less commonly seen in malaria, particularly Plasmodium falciparum infection, as compared to typhoid fever. In malaria, the spleen primarily demonstrates hyperplasia of the red pulp and white pulp, rather than onion skin appearance.

B. Leishmaniasis: Onion skin spleen is not a common finding in Leishmaniasis, caused by Leishmania parasites. In Leishmaniasis, the spleen demonstrates focal or diffuse lymphoid hyperplasia with sinusoidal dilatation, but not the onion skin appearance characteristic of typhoid fever.

C. Hepatitis: Onion skin spleen is rarely seen in hepatitis, caused by viral infections. In hepatitis, the spleen demonstrates lymphoid hyperplasia, but not the onion skin appearance associated with typhoid fever.

D. Typhoid fever: This is the correct answer, as mentioned earlier. Onion skin spleen is a characteristic feature observed in typhoid fever due to Salmonella typhi infection, resulting from the increased blood flow and splenic enlargement.

**Clinical Pearl:** Onion skin spleen is an important diagnostic clue in clinical practice, especially when diagnosing typhoid fever in endemic areas, where other infectious diseases also present with splenomegaly and lymphoid hyperplasia.

**Correct Answer:** D (Typhoid fever)

**Explanation:** In cases of typhoid fever caused by Salmonella typhi, the spleen experiences increased blood flow and enlargement in response to the infection. This leads to the formation of multiple layers of red pulp, resulting in the onion skin appearance. This characteristic histopathological finding is aids in the diagnosis of typhoid fever in endemic areas, where other infectious diseases can also present with splenomegaly and lymphoid hyperplasia.

**Why This is Important:** Understanding the onion skin spleen is crucial for medical students, interns, and physicians, as it aids in accurately diagnosing typhoid fever, which is prevalent in endemic areas. This knowledge helps in differentiating it from other splenomegaly conditions and infections.