This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Suppuration in the mammary gland is usually due to infection which has entered the gland either through the lymphatics or the lactiferous ducts. The starting point of the infection is thought to be an ulcerated crack or fissure of the nipple. Infection travelling into the gland by way of the lymphatics would cause pus primarily in the pericanalicular tissue but it would soon involve the lactiferous ducts and then pus might exude from the nipple. Infection travelling up the ducts might reach the ultimate lobules and therefore give rise to widespread and multiple abscesses. Suppuration in this gland resembles that in the parotid gland, already described. When the body of the gland is involved it is apt to be so in more than one spot. The infection follows the branching of the ducts and usually there are several small abscesses instead of one large one. If there is a large collection of pus it is not contained in one cavity but more likely in several. This is so often the case that in treating these abscesses it is advised that they should not only be incised but the finger should then be introduced and the partitions separating the various abscess cavities broken through.
In its incipiency a lymphatic infection may cause a single collection of pus, but this soon breaks through into the canaliculi and infects and involves the glandular structure. In an early stage of duct infection several inflammatory areas may start up about the same time. The pus soon breaks through the canaliculi and involves the periglandular tissue so that in each mode of infection the condition soon becomes the same. It is for this reason that it is difficult to say whether the infection originated in the lymphatics or the ducts.
When the ducts are inflamed the pus often finds a vent at the nipple. The frequency of this is the reason why direct infection of the ducts is regarded as the more common mode. In incising a mammary abscess the incisions should follow the course of the ducts, that is, they should be made in a direction radiating from the nipple towards the circumference and not transversely, otherwise healthy ducts will be divided.
As has been pointed out some of the glandular tissue dips down. to the pectoral fascia, hence when some of these deepest lying lobules are inflamed the pus instead of breaking laterally into the adjoining lobules or tissue breaks into the submammary tissue and bursa. Here it spreads rapidly beneath the gland and raises the gland above it. As the pus accumulates it sinks downward and works its way outward to the lower outer quadrant along the edge of the anterior axillary fold. Here is where it should be opened. As the cavity is single one incision is sufficient to drain it. Tumors of the Mammary Gland. Benign Tumors. - There are two main kinds of benign mammary growths, Cystic and adenomatous or fibro-adenomatous. Cystic growths due to retention of secretion of the ducts occur as small, rounded mors, painful and tender to the touch, and are seen between the ages of 25 and 35 years. They are not in any way dangerous. They are composed of a number of dilated acini. Another form is degenerative in character, occurring in the decline of life, and consists of a large number of various sized, usually small, cysts located mostly toward the deep surface of the gland. They contain mucoid and degenerated material produced by the lining membrane of the acini. The whole breast is apt to be studded with small shot-like cysts and both breasts are usually involved. This affection in itself is not malignant, but it may become so by intracanalicular growths springing up from the walls of the cysts.
Adenomatous growths are encapsulated, usually single, and are composed of three distinct elements. These are glandular tissue more or less normal in character, glandular tissue cystic in character, and fibrous tissue. The fibrous tissue forms the capsule as well as the stroma in the meshes of which latter glandular tissue, nearly normal, occurs. These are called fibro-adenomata and if the glandular tissue is quite abundant they may be called adenomata. If the glandular acini are dilated so as to overshadow the fibrous portion, then it is called a cystic adenoma. These cystic growths may be quite large.