**Core Concept**
The question is testing the clinical correlation between bilateral hilar lymphadenopathy (BHL) and a negative Mantoux test. BHL is a radiographic finding often associated with sarcoidosis, a systemic granulomatous disease. A negative Mantoux test, which measures the body's response to tuberculin, suggests that the patient is not infected with Mycobacterium tuberculosis.

**Why the Correct Answer is Right**
Sarcoidosis is a condition characterized by the formation of non-caseating granulomas in various organs, including the lungs. In sarcoidosis, BHL is a common finding, often accompanied by symptoms such as cough, dyspnea, and chest pain. The presence of BHL with a negative Mantoux test should raise suspicion for sarcoidosis rather than tuberculosis, which typically presents with a positive Mantoux test. The lack of a significant cellular response to tuberculin in a patient with BHL suggests that the lymphadenopathy is not due to tuberculosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because tuberculosis is less likely in the presence of a negative Mantoux test. A positive Mantoux test would be more consistent with tuberculosis.
**Option B:** This option is incorrect because histoplasmosis is a fungal infection that can cause BHL, but a negative Mantoux test would not be expected in this case, as histoplasmosis would not affect the tuberculin response.
**Option C:** This option is incorrect because lymphoma is a possibility in patients with BHL, but a negative Mantoux test would not be a characteristic feature of lymphoma.

**Clinical Pearl / High-Yield Fact**
BHL with a negative Mantoux test should prompt consideration of sarcoidosis as the underlying diagnosis. Sarcoidosis is a systemic disease that can affect multiple organs, including the lungs, skin, eyes, and heart.

**Correct Answer: C. Sarcoidosis.**