Ultrasound is commonly used to diagnose or characterize fluid collections. Fluid collections can occur in many different parts of the body. There are many different types of collections that can be diagnosed with ultrasound. Some collections are simple looking made up of dark fluid whereas others look more complex inside.
Seromas are collections that are found after surgery or trauma. These are common in the breast after surgery but can occur in other areas. Seromas are sterile and not infected. They do not have blood in them. They tend to decrease in size over time. They can look more complex if you image them when they are chronic.
Hematomas are also commonly imaged with ultrasound. These are basically collections of blood. They can occur from trauma, surgery or spontaneously, especially in those who have disorders of blood clotting or are on blood thinners. The appearance of hematomas depends on the age but they usually look complex without blood flow inside. They can sometimes get infected. This is possible to diagnose with sampling.
Urinomas are collections of urine from a leak. They occur around the kidneys or urinary tract after injury, trauma or surgery. Bilomas are localized leaks of bile outside of the bile ducts, usually from some sort of injury or instrumentation. Bilomas and urinomas will be hard to differentiate from other collections. The clinical context and additional testing may be needed.
Abscesses are collections of pus that look like thick walled complex collections. Abscesses often have surrounding blood flow. There can be bubbles of gas inside. They can be treated by draining them, using ultrasound as guidance.
Fluid in the lungs is called an effusion. In the scrotum, fluid is called a hydrocele. A hygroma is fluid accumulating adjacent to the covering of the brain. A fluid collection adjacent to the pancreas in the setting of prior pancreatitis is called a pseudocyst.
Fluid collections occur throughout the body and are often imaged with ultrasound. Fluid collections can range from benign and resolving on their own, to those that require emergent treatment like abscesses (infected collections). Fluid collections may need sampling for definitive diagnosis. It is often not possible to say if a collection is infected based on its appearance. In some rare cases, what seems like a collection may represent a cyst or even a mass.