Gallstones are hardened deposits of digestive fluid that can form in the gallbladder, a small organ located beneath the liver. While some individuals with gallstones experience no symptoms, others may encounter significant discomfort. An ultrasound examination is the primary and most effective diagnostic tool for identifying these deposits. This article explains how ultrasound works and what gallstones typically look like on a scan.
How Ultrasound Detects Gallstones
Ultrasound technology utilizes high-frequency sound waves to create images of internal body structures. A device called a transducer emits these sound waves, which then travel through tissues and organs, including the gallbladder. When these sound waves encounter a structure, such as a gallstone, they bounce back as echoes. The transducer captures these echoes, and a computer processes them to generate a real-time image on a monitor.
Ultrasound is particularly well-suited for detecting gallstones because it is a non-invasive procedure that does not involve radiation. It provides excellent visualization of soft tissues and fluid-filled organs like the gallbladder. Real-time images allow medical professionals to observe the movement and characteristics of structures within the gallbladder.
Identifying Gallstones on Ultrasound
Gallstones present distinct characteristics on an ultrasound image that help differentiate them from other structures. They typically appear as bright, highly reflective areas within the gallbladder, a feature known as hyperechogenicity. This brightness occurs because the sound waves are strongly reflected by the dense composition of the stones.
A diagnostic sign for gallstones is acoustic shadowing. This phenomenon occurs when the sound waves are almost completely blocked by the gallstone, creating a distinct dark area or “shadow” directly behind the stone on the ultrasound image. The presence of this shadow confirms the bright spot is a solid object.
Most gallstones are mobile, shifting their position within the gallbladder when the patient changes posture. For instance, if a patient rolls, gallstones can be observed moving to the dependent portion of the gallbladder. This mobility helps distinguish gallstones from gallbladder polyps, which are typically fixed to the gallbladder wall and do not move.
Gallstones can vary considerably in size, ranging from tiny specks as small as 2 millimeters to several centimeters. They can also vary in number, with a patient having a single large stone or numerous smaller ones. These specific visual characteristics on ultrasound allow healthcare providers to accurately identify gallstones.
What to Expect During a Gallbladder Ultrasound
Undergoing a gallbladder ultrasound is a straightforward and painless procedure. Patients are asked to fast for a period before the exam, usually 4 to 12 hours. This fasting ensures the gallbladder is distended with bile, allowing for clearer visualization and preventing it from contracting after a meal.
During the procedure, the patient lies down, usually face-up, on an examination table. A sonographer or radiologist applies a clear, water-based gel to the upper right side of the abdomen. This gel helps the transducer make good contact with the skin and eliminates air pockets that could interfere with the sound waves. The sonographer moves the handheld transducer across the skin over the gallbladder area, applying slight pressure to capture images.
The entire scan takes 10 to 30 minutes. It is a non-invasive test, and patients experience little to no discomfort, though some mild pressure from the transducer may be felt. After the scan, the gel is wiped off, and patients can resume their normal activities immediately as there is no recovery period. Images are reviewed by a radiologist, and results are sent to the referring doctor, who will discuss them with the patient.