In an ultrasound, what does the radiologist mean by 'in a subtle finding' ?

X ray: A report of a subtle finding on an X ray usually means something that is not clinically significant or would not be known to be present if the X ray had not been done. A radiologist will recommend that repeat films or another imaging study such as a CT or MRI be done for an abnormality that should be followed.

Subtle means: difficult to visualize. It may or may not be a significant finding, so best to talk to your doc about the results.