Evaluating the density of a mass is important in providing a differential diagnosis. Density should be
compared to the surrounding breast parenchyma or, as in this case of a fatty replaced breast, to the nipple. The differential diagnosis for a mass containing both radiolucent and radiopaque components would include: Hematoma, galactocele, intramammary lymph node, and hamartoma (fibroadenolipoma). Encapsulated lesions of mixed density (fat containing) are benign and require no additional evaluation or work up.
A. Incorrect. While fibroadenomas may be well circumscribed as in this case, they do not contain fat and are usually isodense to fibroglandular tissue.
B. Correct. Hamartomas, also known as fibroadenolipomas, are of mixed density and are composed of adipose and fibroglandular elements. These masses are unusual but have a characteristic appearance. Hamartomas are usually painless and asymptomatic.
C. Incorrect. While hematomas may appear well circumscribed, they tend to be of moderate to high density and present in patients with a history of trauma or surgery. The history does not support this diagnosis since this patient is an asymptomatic screening patient.
D. Incorrect. These milk-filled cysts may be well circumscribed with high fat content and demonstrate a mixed density appearance. However, history is again of importance, since this is a postmenopausal patient and galactoceles occur in younger nursing women.
Tabar L, Dean PB. Teaching Atlas of Mammography. 3rd ed. New York, NY: Thieme Stuttgart; 2001.
Kopans DB. Breast Imaging. 2nd ed. Philadelphia, Pa: Lippincott Raven; 1998.