Stomach ulcers are open sores in the lining of the stomach wall, and during an endoscopy they typically appear as round or oval craters with a whitish or yellowish base, surrounded by a rim of inflamed, reddened tissue. Most are relatively small, under 3 centimeters across, though they can range from a few millimeters to well over 4 centimeters in severe cases. Because you can’t see your own stomach lining, these ulcers are visualized through an endoscope, a thin camera threaded down the throat, and their appearance tells doctors a great deal about severity, healing stage, and even whether cancer might be involved.
Shape, Size, and Location
A typical stomach ulcer looks like a well-defined crater punched into the pinkish stomach lining. Benign ulcers tend to have smooth, regular edges and a flat, even base. The surrounding tissue folds taper neatly inward toward the crater, almost like the spokes of a wheel converging on a center point. The crater floor is often coated in a thin layer of whitish or yellowish material, which is a mix of dead tissue and fibrin, a protein your body uses during wound repair.
Most stomach ulcers sit in the lower portion of the stomach called the antrum, and specifically along the inner curve known as the lesser curvature. This location isn’t random. Research shows that nearly all gastric ulcers develop right at the boundary between the acid-producing upper stomach and the antrum below, almost always on the antral side of that line. Out of 499 gastric ulcers examined in one study, only 21 were found more than 2 centimeters away from this border.
Size varies considerably. Many ulcers are a centimeter or less across. A “giant” gastric ulcer is defined as a crater exceeding 3 centimeters in diameter, and these account for roughly 10 to 15 percent of all gastric ulcers. In extreme cases, ulcers can grow much larger. One surgical case report documented a perforated ulcer measuring 4 by 3.5 centimeters.
What the Base of the Ulcer Reveals
The floor of the crater is one of the most important visual features. Doctors classify what they see there because it predicts how likely the ulcer is to bleed or rebleed. A system called the Forrest classification breaks this down into distinct categories based on appearance.
- Active bleeding: A spurting or oozing stream of blood coming from the ulcer base. This is the most urgent finding.
- Visible vessel: A raised, often reddish or dark bump on the ulcer floor. It’s a blood vessel stump that isn’t actively bleeding but could start at any moment.
- Adherent clot: A dark red or maroon blood clot stuck to the base that won’t wash off easily.
- Flat pigmented spot: A small dark dot, red or black, on the ulcer floor. This signals a previous small bleed that has largely stopped.
- Clean base: A smooth, white or yellowish crater floor with no blood, clots, or visible vessels. This is the lowest-risk appearance.
Clean-based ulcers and those with only a flat spot carry low rebleeding risk. Ulcers with visible vessels, active bleeding, or adherent clots are considered high-risk and typically need treatment during the endoscopy itself.
Signs of H. pylori Infection
Most stomach ulcers are caused by a bacterial infection called H. pylori, and the surrounding stomach lining often shows telltale signs. The mucosa around the ulcer may appear uniformly red, a pattern called diffuse redness, rather than the normal pale pink. The tissue can look swollen and thickened.
One of the most distinctive markers is nodularity: the stomach lining takes on a bumpy, granular texture that looks like goose flesh. This is especially common in younger patients. In children with H. pylori infection, nodularity appears in over 90 percent of cases. In young adults, it drops to about 32 percent, while other signs like tissue thinning (atrophy) and scattered red spots become more prominent. Spotty redness, patchy discoloration, and small raised or depressed erosions scattered across the stomach lining are all visual clues that this bacterium is at work.
How Ulcers Look as They Heal
Stomach ulcers don’t heal all at once. The process moves through four visually distinct stages. In the initial healing phase, the sharp edges of the crater begin to soften and the surrounding redness starts to fade. New tissue begins creeping inward from the edges. During the proliferative stage, the crater floor fills in with fresh, reddish tissue, and the ulcer visibly shrinks in diameter. The base becomes smoother and less coated with dead tissue.
Once the crater closes over, it enters the scar stages. First comes the “red scar” phase, where the healed area looks like a patch of reddish, slightly raised tissue with a striped or palisade pattern. Over weeks to months, this transitions into the “white scar” phase, where the surface develops a pale, cobblestone-like texture. Healing isn’t considered truly complete until this final cobblestone pattern, with tiny pit formations in the surface, has fully developed. Some patients retain a visible scar indefinitely, though it causes no symptoms.
Benign vs. Cancerous Ulcers
One of the key reasons doctors examine ulcer appearance so carefully is to distinguish a simple peptic ulcer from an ulcerated stomach cancer. The visual differences can be subtle but important.
Benign ulcers have smooth, round or oval shapes with regular, clearly defined edges. The base is even, and the surrounding tissue folds converge symmetrically toward the crater like rays toward a center point. Cancerous ulcers, by contrast, tend to have irregular, angulated, or oddly shaped outlines. Their edges are uneven or asymmetric, sometimes with one side heaped up higher than the other. The base looks lumpy or uneven rather than smooth. Perhaps the most telling sign is what happens to the surrounding tissue folds: instead of tapering neatly toward the crater, they appear disrupted, eaten away, or fused together near the edge.
Any ulcer that looks irregular, fails to heal after 8 to 12 weeks of treatment, or has heaped-up borders will typically be biopsied to rule out malignancy. The visual assessment alone isn’t enough for a definitive answer, but it guides the next steps.
What a Perforated Ulcer Looks Like
In roughly 2 to 14 percent of peptic ulcer cases, the ulcer erodes completely through the stomach wall, creating a perforation. This is a surgical emergency. On a CT scan, a perforation appears as a visible gap or defect in the stomach wall, often with free air or fluid visible in the abdominal cavity that shouldn’t be there.
During surgery, the perforation looks like a hole punched through the stomach, often in the lower front portion of the stomach near where it meets the small intestine. The surrounding abdominal cavity is typically inflamed, with a fibrous coating (fibrinous peritonitis) covering nearby organs from the leaking stomach contents. The tissue around the hole is thickened and inflamed, and in severe cases the ulcer may have adhered to neighboring structures like the liver’s round ligament or the abdominal wall itself. About 4 million people worldwide are diagnosed with peptic ulcers each year, and perforation carries mortality rates as high as 30 percent, making it one of the most dangerous complications.