An ultrasound finding of a gallbladder contains shadowing; this likely indicates:

When an ultrasound finding reveals shadowing associated with the gallbladder, it typically suggests the presence of gallstones, also known as cholelithiasis. The shadowing occurs because gallstones are denser than the surrounding fluid and soft tissue, creating an acoustic shadow that is visible on the ultrasound. This phenomenon helps differentiate gallstones from other potential gallbladder abnormalities.

Cholecystitis, which is inflammation of the gallbladder, may present with other ultrasound findings such as thickening of the gallbladder wall and the presence of fluid around the gallbladder, but the presence of shadowing is more indicative of gallstones. Gallbladder sludge, which consists of thickened bile, might not produce significant shadowing and typically just appears as a homogeneous echogenicity with no clear borders. Meanwhile, portal vein thrombosis is unrelated to shadowing in the gallbladder and would manifest with different ultrasound characteristics, usually related to the portal system rather than the gallbladder itself.

Thus, the presence of shadowing clearly aligns with the presence of cholelithiasis as the best interpretation of the ultrasound findings.