**Delta Sign in CT Scan**

**Core Concept**
The delta sign is a radiological finding on non-contrast computed tomography (CT) scans, indicative of a specific vascular structure. It refers to the appearance of a triangle or delta shape formed by the confluence of contrast material in the superior mesenteric artery (SMA) and the splenic artery, against the background of the portal vein and its tributaries.

**Why the Correct Answer is Right**
The delta sign is characteristic of a splenic artery aneurysm. When an aneurysm occurs in the splenic artery, it can cause the artery to dilate and become visible on a non-contrast CT scan. The contrast material outlines the aneurysm, forming a triangular shape at the confluence of the SMA and the splenic artery, which is known as the delta sign. This sign is particularly useful in identifying splenic artery aneurysms, which are often asymptomatic and can be life-threatening if ruptured.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the delta sign is not typically associated with liver hemangiomas. Liver hemangiomas are usually identified by their characteristic "light bulb" appearance on CT scans.
* **Option B:** This option is incorrect because the delta sign is not related to portal vein thrombosis. Portal vein thrombosis would typically present with a more diffuse filling defect within the portal vein, rather than a delta-shaped appearance.
* **Option C:** This option is incorrect because the delta sign is not characteristic of pancreatic pseudocysts. Pancreatic pseudocysts are usually identified by their well-defined, fluid-filled appearance on CT scans.

**Clinical Pearl / High-Yield Fact**
The delta sign is a classic radiological finding in splenic artery aneurysms, and its recognition is crucial in identifying this potentially life-threatening condition. It is essential to be aware of this sign when interpreting non-contrast CT scans, especially in patients with a history of trauma or hypertension.

**Correct Answer: C. Splenic artery aneurysm.**