This sign is extremely specific and shouldn’t be overlooked. A growing tumor acts like a stricture (a narrowing) inside the colon. As stool passes this blockage, it is forced into an unusually narrow shape—often described as pencil-thin, ribbon-like, or stringy.
This change is persistent, lasting for more than a few days, and indicates a possible obstruction in the lower bowel. If the diameter of your stool consistently decreases, it’s a physical indication that something is blocking the normal passage.
4. Feeling of Incomplete Emptying (Tenesmus)
This is arguably the most important signal related to the rectum and lower sigmoid colon. Tenesmus is the persistent, painful feeling that you need to pass stool, even immediately after a bowel movement, coupled with the sensation that you cannot fully empty your bowel.
This occurs when a tumor is located near the rectum or anus. The tumor creates a mass that triggers the nerves, making the rectum feel full, yet nothing (or very little) can be passed. Because this symptom is often mistaken for severe constipation or hemorrhoids, it is frequently ignored—but it is a key red flag that requires immediate examination.
