A pseudocyst is an encapsulated collection of fluid that lacks the true epithelial lining found in genuine cysts. The term is most commonly used to refer to pancreatic pseudocysts, which form after episodes of pancreatitis when pancreatic enzymes leak and become walled off by inflammatory tissue. However, pseudocysts can occur in other locations as well. On ultrasound, a pseudocyst appears as a well-defined, round or oval, predominantly anechoic structure, often with smooth walls of variable thickness. Internal debris or septations may be seen in more complex cases. Sonography is used for initial detection, serial monitoring to track size changes, and guidance during drainage procedures when the pseudocyst is symptomatic or complicated.