How do lymph nodes appear on imaging?

On mammography, they are one of the circumscribed fat-containing masses. The cortex of the nodes are equal density and usually uniform thickness. The hila are fat density.

On ultrasound, they are both hypoechoic (the cortex) and hyperechoic (the fatty hilum).
Normal nodes have a uniform thin cortex measuring <=2.5 to 3 mm and preservation of the fatty hilum.
Abnormal nodes will have focally or diffusely thickened cortex and/or a compressed or absent fatty hilum.