**Core Concept**
Hepatocellular carcinoma (HCC) is a primary malignant tumor of the liver, often arising in the setting of chronic liver disease. Imaging techniques, such as contrast-enhanced computed tomography (CECT), play a crucial role in diagnosing HCC. The Liver Imaging Reporting and Data System (LI-RADS) is a widely accepted algorithm for the diagnosis and management of HCC.

**Why the Correct Answer is Right**
The rapid wash-in and washout of contrast on CECT is a characteristic feature of HCC, which is attributed to the high vascularity and rapid blood flow within the tumor. This phenomenon is often seen on arterial phase imaging. LI-RADS provides a standardized framework for the interpretation of liver imaging studies, incorporating key features such as arterial phase enhancement, washout, and size to predict the likelihood of HCC. Alpha-fetoprotein (AFP) is a tumor marker that is elevated in approximately 70% of HCC cases, although levels can be normal in up to 30% of cases, particularly in early disease or in individuals with chronic liver disease.

**Why Each Wrong Option is Incorrect**
**Option A:** HCC is not the most common primary malignant tumor of the liver. The most common primary malignant tumor of the liver is actually cholangiocarcinoma.
**Option B:** Fibrolamellar HCC does not have a better prognosis compared to conventional HCC. Fibrolamellar HCC is a rare subtype of HCC that tends to occur in younger individuals and is often associated with a better prognosis, but it is not necessarily better than conventional HCC.
**Option C:** LI-RADS is not an algorithm for the diagnosis of HCC, but rather a system for the standardized reporting and management of liver imaging studies. While LI-RADS incorporates key features for the diagnosis of HCC, it is not a diagnostic algorithm per se.

**Clinical Pearl / High-Yield Fact**
It is essential to note that AFP levels can be normal in up to 30% of HCC cases, particularly in early disease or in individuals with chronic liver disease. Therefore, a normal AFP level does not rule out HCC.

**Correct Answer: D.**