**Core Concept**
The fat halo sign is a radiological finding that refers to the appearance of a high-attenuation rim surrounding a mass or lesion on computed tomography (CT) scans. This phenomenon is primarily observed in the context of fatty replacement or infiltration of tissues, particularly in the liver and other abdominal organs.

**Why the Correct Answer is Right**
The fat halo sign is typically associated with hepatocellular carcinoma (HCC), a primary malignancy of the liver. The sign is thought to result from the accumulation of fat within the tumor cells, which creates a high-attenuation rim on CT scans. This finding is often seen in the context of HCC, especially in patients with underlying liver disease, such as cirrhosis. The presence of a fat halo sign can help differentiate HCC from other liver lesions, such as metastases or benign tumors.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the fat halo sign is not typically associated with metastatic disease to the liver. While metastases can cause a range of appearances on CT scans, the fat halo sign is more specific to primary liver tumors like HCC.
**Option B:** This option is incorrect because the fat halo sign is not a characteristic feature of benign liver lesions, such as hemangiomas or cysts. These lesions typically have distinct imaging features that do not include a high-attenuation rim.
**Option C:** This option is incorrect because the fat halo sign is not a result of inflammation or infection within the liver. While certain infections, such as abscesses, can cause changes in liver attenuation, the fat halo sign is more specific to neoplastic processes.

**Clinical Pearl / High-Yield Fact**
When interpreting CT scans of the liver, remember that the fat halo sign is a high-yield feature for hepatocellular carcinoma, particularly in patients with underlying liver disease. This sign can help narrow the differential diagnosis and guide further management.

**Correct Answer: A. Hepatocellular carcinoma.**