Dense breasts have more fibrous and glandular tissue than fatty tissue, which can also make it difficult for a radiologist to detect cancer on a mammogram. Dense tissue, like cancer, shows up white on the mammogram. Fatty tissue is dark, so any cancer is more visible. Also, ultrasound is significant in differentiating cystic from solid breast masses. Ultrasound is also important in detecting suspicious breast masses and should therefore be used in the evaluation of symptomatic breast masses.