What is the significance of cm differentiation on kidney ultrasounds? e.g. is it a marker or inflammation or kidney function? just trying to improve my understanding?

CM diferentiation = CorticoMedullary differentiation. By renal US, the cortical and medullary sections (outer and inner) have different echogenic charaters and that difference is showed as corticomedullary differentiation. If the cortical section (renal parenchyma) is damaged and scarring (chronic) the echo character changes so there is no more echo differentiation between the two sections.

I assume you are talking about the kidney dimensions usually length. Normally the Left is larger. You need to know what is the average and 2 SD for length differences between the two kidneys in women of you age and ethnic background and height. If they are significantly different is size the some thing is usually wrong in the smaller kidney. Most commonly renal artery stenosis to the small kidney.