Uterine polyps are soft, fleshy growths that project from the lining of the uterus into the uterine cavity. They range from a few millimeters (about the size of a sesame seed) to several centimeters (golf-ball-size or larger), and they can appear as round, oval, elongated, or angular shapes that conform to the space inside the uterus. What they look like depends on whether you’re viewing them through a camera inside the uterus, on an ultrasound screen, or under a microscope.
Appearance During Hysteroscopy
The clearest view of a uterine polyp comes from hysteroscopy, where a thin camera is inserted through the cervix into the uterus. Seen this way, polyps look like smooth, glistening, pinkish-red or reddish-tan projections growing from the uterine wall. They’re covered by the same tissue as the uterine lining itself, which gives them a moist, velvety surface.
Most polyps are pedunculated, meaning they hang from the uterine wall on a narrow stalk, somewhat like a teardrop or a tiny balloon on a string. Others are sessile, sitting directly on the wall with a broad, flat base. Both types have smooth surfaces. Compared to the surrounding uterine lining, polyps tend to look slightly different in color or texture because they contain a denser mix of glands, supportive tissue, and blood vessels packed beneath that outer layer. Think of them less like a hard lump and more like a soft skin tag. They’re pliable and can sway within the uterine cavity.
How They Look on Ultrasound
On a standard transvaginal ultrasound, polyps appear as bright (hyperechoic) focal masses within the uterine lining. They may distort the normal thin-line appearance of the endometrium, creating what’s called an “interrupted mucosa sign,” where the smooth contour of the lining looks disrupted. Most polyps show a uniform brightness on the screen, though some contain small fluid-filled cysts (typically 2 to 3 millimeters) that appear as tiny dark spots within the bright mass.
The challenge with a standard “dry” ultrasound is that polyps are made of the same mucosal tissue as the uterine lining, so they can blend in. A polyp may simply look like thickened endometrium rather than a distinct growth. This is why a standard ultrasound alone can’t always distinguish a polyp from other conditions like endometrial hyperplasia, since both appear bright and may contain cystic areas.
When a clearer picture is needed, a saline infusion sonogram offers a much better view. During this procedure, sterile saline is injected into the uterine cavity, which expands the space and outlines the lining with fluid. A polyp then stands out dramatically: it appears as a defined mass surrounded by dark fluid on all sides, making its shape, size, and point of attachment easy to see. Doppler imaging can also reveal blood flow within the polyp, sometimes showing a characteristic “feeding vessel” running up the stalk into the growth.
Under the Microscope
After a polyp is removed, a pathologist examines it under a microscope to confirm the diagnosis and check for abnormal cells. At this level, the polyp’s interior architecture becomes visible. The hallmark features are clusters of endometrial glands (the same tube-like structures found in normal uterine lining) surrounded by supportive connective tissue called stroma. Threading through this tissue are thick-walled, dilated blood vessels, which is one of the key features pathologists look for to confirm a polyp rather than just an overgrown patch of lining.
The glands inside a polyp can vary. Some look normal, some appear enlarged or cystic, and in rare cases, the glandular tissue is highly proliferative, which raises concerns about precancerous changes. Some polyps are made almost entirely of stromal cells with very few glands. This microscopic evaluation is the definitive step in diagnosis, which is why hysteroscopy with guided biopsy is considered the gold standard for confirming uterine polyps.
How Polyps Differ From Fibroids
Polyps and fibroids can look similar on a standard ultrasound, which is one reason they’re sometimes confused. But they’re quite different in texture and composition. Fibroids are dense, firm, rubbery growths made of muscle tissue. They can change the shape of the entire uterus. Polyps, by contrast, are soft and fragile, made of the same delicate mucosal tissue as the uterine lining. A helpful comparison: fibroids are like firm rubber balls, while polyps are more like skin tags.
On a saline-enhanced ultrasound or during hysteroscopy, the distinction becomes clearer. A polyp sits entirely within the uterine cavity, covered by endometrial tissue, and moves freely if it has a stalk. A submucosal fibroid, even when it protrudes into the cavity, typically has a firmer, more rounded appearance and is anchored more deeply into the uterine wall. The fibroid’s surface may also look different because it’s covered by stretched, thinned-out lining rather than the normal-looking mucosa that coats a polyp.
Size Variation and Why It Matters
The size range for uterine polyps is enormous. Some are just a few millimeters across, barely visible even on enhanced imaging. Others grow to several centimeters and can fill a significant portion of the uterine cavity. Most fall somewhere in between. You can have a single polyp or multiple ones at the same time.
Size alone doesn’t determine whether a polyp needs to be removed. If a polyp isn’t causing symptoms like abnormal bleeding, heavy periods, or fertility problems, observation without treatment is a reasonable approach regardless of size. When symptoms are present or when there’s concern about the risk of abnormal cells, surgical removal through hysteroscopy is the standard approach. The decision depends on your symptoms and individual risk factors rather than on a specific size cutoff.