Semilunar syndrome is an imaging definition, often an imaging manifestation of ulcerative lesions in the stomach.1. Niche shadow is commonly seen in ulcerative lesions, and the niche shadow of semilunar syndrome is often irregular in shape, half-moon shaped, with a clearer, curved outer edge and an uneven inner edge, with multiple sharp corners near the gastric lesser curvature, with the direction of the sharp corners pointing to the gastric lesser curvature, located within the gastric contour, and with a transparent band of varying width at the periphery, i.e., the ring tit. 2. It is a kind of niche shadow, with irregular shape and mostly acupressure filling defect, which appears in the gastric lesser curvature and mainly refers to ulcerated gastric cancer of gastric lesser curvature. 3. Half-moon syndrome usually appears in advanced gastric cancer or gastric cancer with metastases, and at this time, the treatment of advanced gastric cancer is mainly based on conservative treatment.