**Core Concept:** The hot rim sign is a radiological phenomenon seen in hepatobiliary scintigraphy using Tc99m-labelled iminodiacetic acid (HIDA). It indicates an increase in tracer activity in the periportal region, suggesting biliary obstruction.

**Why the Correct Answer is Right:** The hot rim sign is a result of impaired biliary excretion due to a blockage in the biliary system. In hepatobiliary scintigraphy, Tc99m-HIDA is injected into the bloodstream, and it is taken up by the liver cells (hepatocytes) and transported into the bile ducts. When the bile duct is obstructed, the tracer accumulates in the periportal region, causing an increase in tracer activity.

**Why Each Wrong Option is Incorrect:**

A. In this scenario, the hot rim sign is not seen, as the bile duct obstruction would cause the presence of the hot rim sign.
B. The hot rim sign is present, as the explanation above explains its presence and not its absence.
C. This option contradicts the explanation provided, as the hot rim sign is present in cases of bile duct obstruction.
D. Similarly to option B, the explanation provided discusses the presence of the hot rim sign, not its absence.

**Why This is Important:** The hot rim sign is crucial in diagnosing bile duct obstruction, as it helps differentiate between obstructive and non-obstructive jaundice. This can significantly impact diagnosis and treatment planning for patients.

**Clinical Pearl:** A positive hot rim sign on hepatobiliary scintigraphy should prompt further evaluation for bile duct obstruction, including imaging studies like ultrasound, MRCP, or ERCP, and may lead to the diagnosis and management of obstructive jaundice.