A patient presents with mediastinal mass with sheets of epithelial cells giving arborizing pattern of reactivity on keratin, along with interspersed lymphoid cells. The most probable diagnosis is:
**Core Concept**
The question describes a patient with a mediastinal mass composed of epithelial cells and interspersed lymphoid cells, which suggests a tumor with a mixed epithelial and lymphoid component. This type of tumor is known as a thymic carcinoma or a thymic tumor with a mixed epithelial and lymphoid component.
**Why the Correct Answer is Right**
The presence of sheets of epithelial cells with an arborizing pattern of reactivity on keratin staining is characteristic of thymic carcinomas. This pattern is often seen in thymic carcinoma cells, which express keratin markers. The interspersed lymphoid cells are also consistent with this diagnosis, as thymic carcinomas can arise from the epithelial component of the thymus, which is surrounded by lymphoid cells. The arborizing pattern of reactivity on keratin staining is a key feature that distinguishes thymic carcinomas from other types of tumors.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because thymomas typically have a more uniform epithelial component and less interspersed lymphoid cells compared to thymic carcinomas.
**Option B:** This option is incorrect because lymphomas typically have a more homogeneous population of malignant cells and less epithelial component compared to thymic carcinomas.
**Option C:** This option is incorrect because germ cell tumors typically have a more distinct population of malignant cells and less interspersed lymphoid cells compared to thymic carcinomas.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that thymic carcinomas can present with a wide range of clinical and pathological features, and a definitive diagnosis often requires a combination of histological, immunohistochemical, and molecular studies.
**Correct Answer: D. Thymic carcinoma**