**Core Concept**
Miliary tuberculosis (TB) is a form of disseminated TB characterized by the widespread presence of tiny tubercles in the lungs and other organs. This condition occurs when TB bacteria spread through the bloodstream, leading to the formation of numerous small, millet seed-like lesions in the lungs and other parts of the body.

**Why the Correct Answer is Right**
The pathognomonic finding in miliary TB is the presence of numerous, small, well-defined nodules or "miliary" lesions in the lungs, typically less than 2-3 mm in diameter. These lesions are a result of the hematogenous spread of TB bacteria and are often seen on chest radiographs as a fine, reticular pattern or a "pavement stone" appearance. The lesions are composed of a central area of caseation necrosis surrounded by a ring of epithelioid cells and lymphocytes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not describe a characteristic finding in miliary TB. While lymphadenopathy can be present in TB, it is not specific to miliary TB.
**Option B:** This option is incorrect because it refers to a different radiographic pattern seen in pulmonary TB. The "Galaxy sign" is a characteristic finding in pulmonary TB, but it is not specific to miliary TB.
**Option C:** This option is incorrect because it refers to a different type of TB. Constrictive pericarditis is a complication of tuberculous pericarditis, but it is not a characteristic finding in miliary TB.

**Clinical Pearl / High-Yield Fact**
Miliary TB can be a challenging diagnosis, especially in immunocompromised patients. A high index of suspicion and a detailed radiographic evaluation are essential for diagnosing this condition.

**Correct Answer:** C.