Omental cyst torsion is a clinical manifestation of omental cysts. Omental torsion refers to the twisting of the greater omentum along its longitudinal axis and causes its blood circulation to become impaired. It is generally classified as primary or secondary. The torsion is often clockwise and can be twisted multiple times. What are the causes of omental cyst torsion? Torsional onset is more acute, with the possibility of remission and later recurrence. In mild cases, it causes only edema and venous stasis in the distal omental tissue. In severe cases, it causes impaired blood flow, purplish-black infarct hemorrhage and necrosis of the omentum, and a small amount of bloody exudate in the abdominal cavity, with varying sizes of infarcts, the larger ones up to 20 cm or more in diameter. The torsionally infarcted omental segment may gradually form a fibrotic mass, which may even be dislodged and become free in the abdominal cavity. Small cysts are usually mostly asymptomatic and are often found incidentally during open surgery. Large cysts can be symptomatic and are characterized by a feeling of abdominal distention and abdominal pain. Patients themselves often occasionally find a mass in the abdomen at night, with a feeling of heavy pressure in the abdomen when lying supine, and severe abdominal pain when complicated by intestinal obstruction or intestinal torsion. Abdominal examination: a mass can be found in the abdomen, which is mostly located in the upper abdomen, soft, cystic in nature, relatively mobile, without pressure pain or with deep induration. Medium and small cysts occurring in the greater omentum have clear boundaries that are easily palpable and have a wide range of activity. In contrast, in giant cysts or those with complications, palpation is unclear and they are easily misdiagnosed as tuberculous peritonitis and ascites, etc. In giant omental cysts in supine position, the whole abdomen is percussed with turbid sounds, only the two hypochondrium or lumbar areas are bulged, and intestinal sounds are heard in the depths, and there is a sense of vibrating water throughout the abdomen, but no mobile turbid sounds. There are two types of large omental cysts: true cysts and pseudocysts. True cysts are rare and are due to congenital abnormal development of ectopic lymphoid tissue or obstruction of lymphatic vessels. The cysts are thin-walled, covered with a single layer of endothelial cells, and may be single- or multi-housed, and the contents are mostly pale yellow plasma and celiac fluid. Pseudocysts are mostly secondary to traumatic hematoma, inflammation, fat necrosis or foreign body reaction of the greater omentum. They have thick walls, only fibrous tissue, no lining endothelial cells, and are mostly unicompartmental, containing cloudy inflammatory exudate or blood.