**Core Concept**
Non-cirrhotic portal fibrosis (NCPF) is a rare cause of portal hypertension characterized by fibrosis of the small portal veins without underlying cirrhosis or other liver disease. This condition leads to increased pressure in the portal vein, causing splenomegaly and potentially resulting in variceal bleeding.

**Why the Correct Answer is Right**
In NCPF, the fibrosis of the small portal veins leads to obstruction of blood flow, causing portal hypertension. The increased pressure in the portal vein is shunted to the systemic circulation through the varices, leading to massive hematemesis and systemic hypotension. The presence of massive splenomegaly without hepatomegaly is a characteristic finding in NCPF due to the engagement of the spleen with the portal blood. The absence of fever or other significant history makes an acute infectious or inflammatory etiology less likely.

**Why Each Wrong Option is Incorrect**
**Option A:** Hepatocellular carcinoma (HCC) is a primary malignancy of the liver, which would typically present with hepatomegaly and potentially portal hypertension, but not typically massive splenomegaly without liver involvement.
**Option B:** Bleeding duodenal ulcer would present with upper gastrointestinal bleeding, but would not explain the massive splenomegaly or systemic hypotension.
**Option C:** Oesophageal varices can cause massive hematemesis due to portal hypertension, but would typically be associated with cirrhosis or other liver disease, and not NCPF.

**Clinical Pearl / High-Yield Fact**
NCPF is a rare but important cause of portal hypertension that can mimic cirrhosis clinically, but is distinguished by the absence of liver disease on biopsy. Remember to consider NCPF in the differential diagnosis of massive hematemesis and splenomegaly without liver disease.

**✓ Correct Answer: D. Non-cirrhotic portal fibrosis**