What is the procedure used to examine the sigmoid colon by means of a flexible tube inserted through the anus?

The procedure used to examine the sigmoid colon with a flexible tube inserted through the anus is known as sigmoidoscopy. This procedure specifically targets the sigmoid colon, which is the last part of the large intestine before it connects to the rectum. During sigmoidoscopy, a sigmoidoscope—a slender, flexible tube with a light and camera—allows the healthcare professional to visualize the lining of the sigmoid colon, checking for abnormalities such as polyps, inflammation, or signs of disease.

Sigmoidoscopy is less invasive compared to other procedures that examine the entire colon, such as colonoscopy, which examines the entire length of the colon from the rectum to the cecum. Endoscopy is a broader term that encompasses various procedures using flexible tubes to examine different parts of the digestive tract but does not specifically refer to the sigmoid colon. Proctoscopy, while also involving inspection of the rectum, is focused on the rectal area and does not extend into the sigmoid colon. Thus, the correct answer is sigmoidoscopy, as it directly pertains to the examination of the sigmoid colon.