THIS IS A VERY LONG POST, BUT WORTH TAKING THE TIME TO READ
Yes I am aware there is a similar old thread On This Back in 2005
GYNECOMASTIA: ETIOLOGY, DIAGNOSIS, AND TREATMENT
Chapter 14 - Ronald S. Swerdloff, MD, Jason Ng, MD, and Gladys E. Palomeno, MD,
March 1, 2004
In this thread we will review: the ontogeny and physiology of breast development; factors that influence breast enlargement in the male; the differential diagnosis of gynecomastia; the process of diagnostic investigation; and treatment of gynecomastia.
BREAST DEVELOPMENT
Male breast development occurs in an analogous fashion to female breast development. At puberty in the female breast, complex hormonal interplay occurs resulting in growth and maturation of the adult female breast.
In early fetal life, epithelial cells, derived from the epidermis of the area programmed to later become the areola, proliferate into ducts, which connect to the nipple at the skin's surface. The blind ends of these ducts bud to form alveolar structures in later gestation. With the decline in fetal prolactin, placental estrogen and progesterone at birth, the infantile breast regresses until puberty.
During thelarche, the initial clinical appearance of the breast bud, growth and division of the ducts occur, eventually giving rise to club-shaped terminal end buds, which then form alveolar buds. Approximately a dozen alveolar buds will cluster around a terminal duct, forming the type 1 lobule. Eventually, the type 1 lobule will mature into types 2 and 3 lobules, called ductules, by increasing its number of alveolar buds to as many as 50 in type 2 and 80 in type 3 lobules. The entire differentiation process takes years after the onset of puberty and, if pregnancy is not achieved, may never be completed.
HORMONAL REGULATION OF BREAST DEVELOPMENT
The initiation and progression of breast development involves a coordinated effort of pituitary and ovarian hormones, as well as local mediators (see Figure 1).
Figure 1. Hormones affecting growth and differentiation of breast tissue. (GH= Growth Hormone; ER= Estrogen Receptor; Page Ranking= Progesterone Receptor; AR= Androgen Receptor)