This patient has evidence of acute cholecystitis. She has a dilated CBD, gallstones and developed fever while in the ED. She went to the OR for cholecystectomy.
The images depict a Wall Echo Shadow Sign. Her gallbladder is so full of stones that the posterior wall is completely shadowed out. You will notice that the anterior wall and the anterior surface of the stones are visible, but everything posterior to that is anechoic due to the acoustic shadowing of the dense stone.
The WES sign can often lead one to think that the gallbladder is not present because the the characteristic anechoic sacular gallbladder is absent. Others have inaccurately concluded that the WES sign is a rib shadow. However, if there is difficulty in visualizing the gallbladder, have the patient roll onto their left side. This should bring the gall bladder more anterior and move the bowel gas away. If you see a large shadow arising from the middle of the screen, take a closer look because it could be a WES.