The “normal” mature female breast ranges from 50 g to greater
than 400 g. A typical nonlactating breast weighs between 150 and
250 g, while the lactating breast may exceed 400 g. The size and
density of the breast are influenced by the individual’s body
habitus. The average breast measures 10–12 cm in diameter, and
its average thickness centrally is 5–8 cm. The adult breast lies between
the 2nd and 6th ribs in the vertical axis and between the
sternal edge and the midaxillary line in the horizontal axis. The
breast is attached to the dermis by fibrous bands called suspensory
(Cooper’s) ligaments anteriorly, and the posterior surface is
the pectoral fascia.Approximately three-quarters of the breast is
on the pectoralis major muscle (superior and medial portions).
The breast tissue is divided into upper outer, upper inner, lower
outer, and lower inner quadrants; the subareolar area; and the
axillary tail of the upper outer quadrant. The arterial blood supply
is derived from the axillary, intercostal, and internal mammary
arteries, and venous drainage is into the axillary and internal
mammary veins. Lymphatic drainage is to the axillary, subclavicular,
and internal mammary lymph nodes.While drainage
from the upper outer quadrant is predominantly to the axillary
lymph nodes, drainage from the inner quadrants is to the internal
mammary chain of nodes. The nerves are branches of the
thoracic segmentals.