**Core Concept**
Mesenteric vein thrombosis is a rare but life-threatening condition that occurs when a blood clot forms in the mesenteric veins, impairing blood flow to the intestines. This can lead to bowel ischemia, necrosis, and potentially life-threatening complications.

**Why the Correct Answer is Right**
The correct answer highlights the potential complication of surgery in mesenteric vein thrombosis. When bowel resection is performed due to necrosis, it can result in short-bowel syndrome, a condition characterized by malabsorption of nutrients due to the reduced length of the small intestine. This is a critical consideration in surgical planning and patient counseling. The mesenteric veins drain the small intestine, and thrombosis in these veins can lead to bowel ischemia and necrosis, which may necessitate surgical resection. The resulting short-bowel syndrome is a well-documented complication of such surgery.

**Why Each Wrong Option is Incorrect**
**Option A:** Peritoneal signs are not always present in mesenteric vein thrombosis, as the condition can initially present with non-specific symptoms such as abdominal pain and nausea. Peritoneal signs, such as rebound tenderness, may develop as the condition progresses and bowel ischemia worsens.

**Option B:** Involvement of a long length of bowel is not a characteristic feature of mesenteric vein thrombosis. The condition typically affects a segment of bowel rather than the entire large or small intestine.

**Option C:** I.V. heparin is not the treatment of choice for mesenteric vein thrombosis. Anticoagulation therapy is often used, but the initial treatment typically involves supportive measures such as fluid resuscitation and bowel rest. Surgery may be necessary if bowel resection is required.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize the potential for short-bowel syndrome in patients undergoing surgery for mesenteric vein thrombosis. This can have significant implications for long-term nutritional support and management.

**✓ Correct Answer: D. Surgery can lead to short-bowel syndrome**