Not every anechoic thing in the pelvis is urine!
In this pelvic area sonogram, the Foley balloon (arrow) appears to be located outside the urinary bladder suggesting malposition of the catheter. However, the fluid collection anterior to the Foley is pelvic ascites and the Foley is in appropriate position as shown by the green dot in the illustration. Blood, serous fluid, and urine are all black on ultrasound. Note the margins of this ‘bladder-like’ structure are irregular which should make us suspect something isn’t right. To confirm the diagnosis, we should perform a long axis scan which will show that this fluid collection is in continuity with the peritoneal cavity. Moreover, a patient’s medical history should alert to the presence of pelvic ascites. It’s interesting to note that the bedside bladder scanning devices that are available in most hospitals these days can wrongly display ascitic fluid volume as bladder volume in this scenario.
Here is another example demonstrating pelvic ascites and urinary bladder (No catheter). Note the irregular nature of the ascites with bowel loops and well circumscribed urinary bladder.