**Core Concept**
The management of periampullary carcinoma involves a multidisciplinary approach, but surgical resection remains the cornerstone of treatment for resectable tumors. The Whipple procedure, also known as pancreaticoduodenectomy, is a complex surgical operation that involves the removal of the tumor along with the surrounding tissues, including the head of the pancreas, the duodenum, and the bile duct.

**Why the Correct Answer is Right**
The Whipple procedure is the most appropriate treatment for this patient because it offers the potential for cure in the absence of metastasis. The procedure involves the removal of the tumor along with the surrounding tissues, which helps to ensure that all cancerous cells are eliminated. This is particularly important in periampullary carcinoma, where the tumor often arises from the ampulla of Vater, a region where the bile and pancreatic ducts converge. The Whipple procedure is a technically challenging operation that requires a high level of surgical expertise, but it offers the best chance of cure for patients with resectable tumors.

**Why Each Wrong Option is Incorrect**
**Option B:** Local excision and radiotherapy are not sufficient for the treatment of periampullary carcinoma, as they do not address the potential for microscopic spread of cancer cells to surrounding tissues. The Whipple procedure offers a more comprehensive approach to tumor removal.

**Option C:** External radiotherapy is not the most effective treatment for periampullary carcinoma, as it may not penetrate deeply enough to reach the tumor. The Whipple procedure, on the other hand, allows for the removal of the tumor along with the surrounding tissues, which helps to ensure that all cancerous cells are eliminated.

**Option D:** Internal radiation seeds via catheter are not suitable for the treatment of periampullary carcinoma, as they do not offer a high enough dose of radiation to effectively treat the tumor. The Whipple procedure, on the other hand, allows for the removal of the tumor along with the surrounding tissues, which helps to ensure that all cancerous cells are eliminated.

**Clinical Pearl / High-Yield Fact**
The Whipple procedure is a complex surgical operation that carries a high risk of complications, including pancreatic fistula, bleeding, and infection. Therefore, it is essential to carefully select patients for this procedure and to ensure that they are treated by experienced surgeons.

**✓ Correct Answer: A. Radical excision (Whipple procedure) where possible**