**Core Concept:** Colorectal cancers are a common cause of lower gastrointestinal (GI) bleeding in elderly patients. Sigmoidoscopy is a diagnostic tool used to visualize the lower GI tract.

**Why the Correct Answer is Right:**
The correct answer is D: Proctectomy (rectosigmoid resection) as it addresses the primary site of the mass (sigmoid colon) and eliminates the source of bleeding. This surgical procedure involves removing the affected segment of the colon along with adjacent healthy tissue. In this case, the mass is located 3.5 cm above the anal verge and is approximately 4 cm in size.

**Why Each Wrong Option is Incorrect:**
A. Resection (rectopexy) is incorrect as it only involves securing the rectum to the surrounding tissues without removing the affected tissue. This would not resolve the source of the bleeding and might worsen the condition.
B. Resection (rectosigmoid colectomy) is incorrect as it involves removing the entire sigmoid colon, causing more significant morbidity and is not specific enough for the precise location of the mass.
C. Resection (sigmoid colectomy) is incorrect as it only removes the sigmoid colon, which is still inadequate to address the bleeding issue since the mass is closer to the anal verge.

**Why the Correct Answer is Right:**

Proctectomy is the correct answer because it removes the affected segment of the colon (rectosigmoid) and ensures the mass is completely resected, preventing further bleeding and allowing for proper healing. Additionally, this procedure is tailored to the specific location of the mass in the sigmoid colon, minimizing the risk of complications associated with more extensive procedures like rectopexy, rectosigmoid colectomy, and sigmoid colectomy.

**Core Concept:** The management of lower gastrointestinal bleeding involves addressing the primary site of the mass and removing the affected segment of the colon to prevent further bleeding and allow for proper healing.

**Why the Correct Answer is Right:**

Proctectomy is the appropriate surgical procedure for treating lower gastrointestinal bleeding due to the mass in the sigmoid colon. This procedure ensures the complete removal of the affected segment of the colon, preventing further bleeding and allowing for proper healing. Furthermore, proctectomy is tailored to the specific location of the mass (sigmoid colon), minimizing the risk of complications associated with more extensive procedures such as rectopexy, rectosigmoid colectomy, and sigmoid colectomy.

**Why the Correct Answer is Right:**

Proctectomy is the correct surgical procedure for treating lower gastrointestinal bleeding caused by a mass in the sigmoid colon. By removing the affected segment of the colon (rectosigmoid), the procedure prevents further bleeding and allows for proper healing. Additionally, proctectomy is suitable for the specific location of the mass, reducing the risk of complications related to more extensive procedures like rectopexy, rectosigmoid colectomy, and sigmoid colectomy.

**Why the Correct Answer is Right:**

Proctectomy is the appropriate surgical procedure for treating lower gastrointestinal bleeding resulting from a