|
Pathophysiology
of the Breast
The human breast develops as a series of thickenings along the
mammary ridge (or "milk line") extending from axilla to groin.
The caudal two thirds of these thickenings disappears in humans,
leaving a single pectoral thickening bilaterally that becomes
the primitive breast. Extra or supranumerary breasts are rare.
More commonly, extra nipples occur along the mammary ridge,
usually on the inferior aspect of the breast or on the chest
wall (Bland).
"Milk line" extending from axilla to groin. From Bates B: A guide
to physical examination and history taking, ed 6, Philadelphia,
1995, Lippincott-Raven.
|
Normal breast: structure, function, and epidemiology.
From Powell.
|
The female breast remains essentially dormant
until puberty. During adolescence girls develop breast buds
in response to the increased levels of follicle-stimulating
hormone and luteinizing hormone. The areola elevates and ducts
begin to elongate and branch while fibrous tissue is laid down.
Lobule formation is dependent on ovulation. In young adulthood
the breast has multiple lobes, each with a main branching duct
and supported by fibrous tissue (Osuch).
The ducts behind the areola dilate and form sinuses that can
be palpated as bumps beneath the areola on CBE. The areola develops
raised glands, Montgomery’s tubercles, which lubricate the nipple
during lactiation (Osuch).
During pregnancy the breast lobules proliferate
and undergo further maturation and breast size increases. The
nipple and areola become more darkly pigmented. Further into
pregnancy the lobular cells become distended with colostrum.
Several days before delivery, lactation is stimulated by high
levels of prolactin and placental hormones. After breast feeding
stops, the lobules regress and the breast slowly returns to
a mature resting state. The ductal tree remains intact.
|
A. Adolescence, B. Pregnancy, C.
Lactation, and D. Post-menopausal period. From
Bland KI, Copeland EM: Breast. In Shwartz SI, Shires GT
et al, eds: Principles of surgery, ed 6, New York,
1994, McGraw-Hill.
|
In the postmenopausal breast, both the ductal
structures and the lobular structures slowly recede and are
replaced by adipose tissue. Some lobules remain, but they are
small and scattered within the adipose tissue. CBE in postmenopausal
women is easier to interpret because of this reduced nodularity.
Of note, in postmenopausal women taking hormone replacement
therapy the breast structure may return to a more premenopausal
appearance (Osuch).
|