An ultrasound of the bladder is a non-invasive imaging technique used to examine this organ. It allows healthcare professionals to visualize the bladder’s structure and function. Understanding how images are produced and what a normal bladder looks like can help prepare individuals for this common medical test.
How Ultrasound Visualizes the Bladder
Ultrasound technology creates images using high-frequency sound waves, which are beyond the range of human hearing. A device, called a transducer, sends these sound waves into the body, where they bounce off internal structures as echoes. The transducer receives these echoes, which a computer processes to generate real-time pictures. Unlike X-rays, ultrasound does not use ionizing radiation, making it a safe imaging option. The bladder is well-suited for ultrasound because it is fluid-filled, allowing sound waves to travel efficiently and provide clear images.
What a Normal Bladder Looks Like on Ultrasound
A properly filled bladder appears clearly on an ultrasound image. In a transverse view, it looks rectangular or box-shaped with rounded edges. In a sagittal (longitudinal) view, it takes on an oval or dome-shaped appearance. The urine within a normal bladder appears anechoic, meaning it looks black on the ultrasound screen because fluid does not reflect sound waves back to the transducer. This creates a clear, dark space, allowing good visualization of the bladder walls and any contents.
The bladder wall should be thin and smooth, measuring less than 5 millimeters (mm) when adequately distended, and potentially around 3 mm when well-distended. A full bladder is important for optimal imaging because it pushes adjacent organs, like the bowels or uterus, out of the way, providing an unobstructed view and improving image quality. The fluid also enhances sound wave transmission, resulting in clearer images.
Common Conditions Identified on Bladder Ultrasound
Ultrasound can reveal various abnormalities that differ from a normal bladder appearance. Bladder stones, for instance, appear as bright, highly reflective objects (hyperechoic) within the bladder. They cast a dark shadow behind them (acoustic shadowing) because they block sound waves, and may exhibit a “twinkling artifact” on Doppler imaging. Stones are mobile and can be seen shifting position with patient movement.
Tumors or masses appear as irregular thickenings or projections from the bladder wall. These soft-tissue lesions may extend into the bladder and show vascular flow with Doppler ultrasound. Ultrasound helps assess the size and location of these masses, though it cannot definitively determine if a tumor is cancerous or detect very small lesions. Incomplete bladder emptying, known as post-void residual (PVR) volume, measures the amount of urine remaining after urination. A normal PVR is below 50 mL, though levels between 50 and 100 mL can be normal for older patients.
Preparing for a Bladder Ultrasound
Preparation is important for a successful bladder ultrasound. The primary instruction is to arrive with a full bladder. A full bladder serves as an “acoustic window,” allowing sound waves to travel more effectively and providing a clearer view of the bladder and surrounding structures. To achieve this, individuals are advised to empty their bladder about 90 minutes before the appointment, then drink about 1 liter (32 ounces) of water within 30 to 60 minutes of the exam, and refrain from urinating until the procedure is complete.
During the ultrasound, a technician applies a water-based gel to the skin over the lower abdomen. This gel helps transmit sound waves from the transducer into the body. The technician moves the transducer across the skin to capture images of the bladder. Patients lie down, and comfortable clothing enhances ease during the procedure.