GROSS ANATOMY OF THE NON-LACTATING BREAST
For the past 160 years, the descriptions of the anatomy of
the breast have changed little since Sir Astley Cooper’s
meticulous dissections of breasts of women who were
lactating when they died (Figure 1).
The breast is composed of glandular (secretory) and
adipose (fatty) tissue, and is supported by a loose
framework of fibrous connective tissue called Cooper’s
ligaments. Traditional descriptions of breast anatomy
describe the glandular tissue as consisting of 15 to 20
lobes that are comprised of lobules containing between
10 and 100 alveoli that are approximately 0.12 mm in
(Figure 2). The size of each lobe is extremely
variable, and some lobes may differ by 20-to 30-folD.
Although it is generally thought that each lobe is a single
entity, a recent study that created three-dimensional
reconstructions of the entire ductal system (16 lobes) of
a mastectomized breast of a 69-year-old female was able
to demonstrate two connections between lobes.
generally believed that 15 to 25 ducts drain the alveoli
and merge into larger ducts that eventually converge into
one main milk duct which dilates slightly to form the
lactiferous sinus before narrowing as it passes through
the nipple and opens onto the nipple surface (Figure 2).
Recent histologic sections of mastectomy nipples have
shown more than 17 ducts on average
; however, it is
not known whether these are all patent, and others
suggest the average number of ducts is lower (5–9).
The diameters of the main ducts in the non-lactating
breast as measured by ultrasound are between 1.2 mm
and 2.5 mm in diameter. Dilated ducts in the non-
lactating breast may be caused by conditions such as
polycystic ovarian disease
or ductal ectasia. The nipple
pores are 0.4 mm to 0.7 mm in diameter and are
surrounded by circular muscle fibres.
The heterogeneous distribution of glandular and adi-
pose tissue in the breast has hindered measurement of
these tissues. However, the ratio of glandular to adipose
tissue estimated by mammography is 1:1 on average, and
it is well documented that the proportion of glandular
tissue declines with both advancing age
and increasing breast size