**Core Concept:** Pehe's disease is a rare genetic disorder characterized by the accumulation of copper in the liver, resulting in liver damage and portal hypertension. It is caused by mutations in the ATP7B gene, which encodes a copper transporter protein called ATP7B. This protein helps to transport copper out of the liver cells, but in Pehe's disease, it malfunctions, leading to copper accumulation.

**Why the Correct Answer is Right:** The correct answer (D) refers to the radiological sign of "Bridge Sign" in Pehe's disease. This sign is characterized by the presence of a prominent "bridge" of dilated veins connecting the spleen to the stomach on abdominal ultrasound or CT scan. The Bridge Sign is indicative of portal hypertension, which is a common complication of Pehe's disease due to the liver damage and abnormal copper accumulation.

**Why Each Wrong Option is Incorrect:**

A. "Spleen Sign" (Option A) is not a specific radiological sign for Pehe's disease. It might be present in conditions causing portal hypertension, but it is not a unique feature of Pehe's disease.

B. "Spleen Atrophy" (Option B) does not directly reflect the disease process in Pehe's disease. While splenomegaly may be present due to portal hypertension, splenomegaly alone is not specific to Pehe's disease.

C. "Portal Vein Thickening" (Option C) is a common radiological finding in various liver diseases causing portal hypertension. It is not specific to Pehe's disease either.

**Clinical Pearl:** Pehe's disease is a useful example of how genetic disorders can present with a unique combination of clinical, biochemical, and radiological findings. Understanding these signs helps in narrowing down the differential diagnosis and confirms the diagnosis when combined with appropriate clinical and laboratory findings.