**Core Concept**
The most common type of pancreatic endocrine neoplasm, also known as pancreatic neuroendocrine tumor (PNET), arises from the islet cells of the pancreas. These neoplasms are characterized by excessive production of hormones such as insulin, gastrin, or vasoactive intestinal peptide (VIP).

**Why the Correct Answer is Right**
The correct answer is **Insulinoma**. Insulinomas are the most common type of pancreatic neuroendocrine tumors, accounting for approximately 60-70% of all PNETs. They are typically benign and arise from the beta cells of the pancreas, leading to excessive insulin production and resulting in hypoglycemia. Insulinomas are often diagnosed in patients with a history of recurrent hypoglycemic episodes, and treatment usually involves surgical resection.

**Why Each Wrong Option is Incorrect**
**Option A:** Glucagonoma is a rare type of PNET that produces glucagon, leading to hyperglycemia and a characteristic rash. It is not the most common type of pancreatic endocrine neoplasm.

**Option B:** Gastrinoma is a type of PNET that produces gastrin, leading to excessive acid production in the stomach. While gastrinomas are common in patients with Zollinger-Ellison syndrome, they are not the most common type of pancreatic endocrine neoplasm.

**Option C:** VIPomas are rare type of PNET that produce vasoactive intestinal peptide (VIP), leading to watery diarrhea and hypokalemia. They are not the most common type of pancreatic endocrine neoplasm.

**Clinical Pearl / High-Yield Fact**
The Whipple procedure (pancreaticoduodenectomy) is a surgical treatment for pancreatic neuroendocrine tumors, including insulinomas. It involves the removal of the head of the pancreas, duodenum, and gallbladder.

**Correct Answer: A. Insulinoma.**