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Understanding breast abscess formation requires one to understand the anatomy of the breast

Breast abscess among lactating women has a predilection for left breasts: Why?

I searched the operating registers at Gift Life Care Clinic from October 2016 to March 2021 for incision and drainage procedures for lactational breast abscess. Out of sixteen such, eleven (68.75%) were for left breast, two (12.5%) were for right breast, one (6.25%) for both breasts, and two (12.5%) procedures had lacked records for which breast side had been affected. The results showed that more than two-thirds of the patients had abscesses affecting the left breasts. In this article, we gain an insight into this fascinating observation.

A breast abscess is a localised collection of purulent material (pus) within the breast. It commonly follows untreated breast inflammation (mastitis). Breast abscess usually affects women aged 18 to 50 years. They are either lactational or non-lactational.

1-10% of lactating (breastfeeding) women suffer from mastitis. 3-11% of such women develop breast abscesses. The bacteria that commonly cause breast abscesses lie of the skin or inside the infants’ oral cavities – mainly staphylococcus aureus.

Understanding breast anatomy is key to delineating the mechanisms that underlie the likelihood of a breast abscess affecting the left breast than the right.

A breast has 15 to 20 lobes arranged like daisy petals. Within each lobe are multitudes of lobules that end in scores of bulbs that can produce milk. Interlinking the lobes, lobules, and bulbs are thin tubes (ducts) that align centripetally at the nipple, surrounded by a dark skin area (areola). Fat occupies the spaces within the lobules and ducts. Each breast rests on layers of muscles that cover the ribs of the anterior chest. Blood and lymph vessels traverse the breasts.

The breasts have lymph nodes into which lymph drains. We find them in the armpit, above the clavicular bone, and the chest.

When the nipple surface cracks, the skin barrier is breached, bacteria enter into the breast and end up into the lactiferous ducts containing milk. Milk provides an ideal environment for bacteria to grow. Due to the abundance of lactose in breast milk, bacteria rapidly multiply (replicate). Milk overproduction, as well as milk stasis, potentiates the process.  During this process, mastitis develops. When this is left untreated or poorly treated, well-circumscribed fluctuant masses form within the affected breast, following the destruction of the surrounding tissues.

Breast abscesses in lactating women form in the presence of breast inflammation, milk overproduction and stasis. The left breast is mostly affected by this eventuality because many lactating women tend to initiate breastfeeding using the right breast. Because of this phenomenon, the left breast is usually incompletely emptied. So, more milk is likely to stagnate in the left than the right breast. When milk stagnates, it becomes static; the breast distends, the overlying skin stretches and cracks – allowing bacteria to penetrate the skin.

With this, we recommend that health care workers educate lactating women on the proper techniques of breastfeeding.  To emphasise the ability to allow infants to evenly latch-on both breasts to avoid milk stagnation, overproduction and an increased propensity for the nipples to crack.

Note: Breast infection: A review of diagnosis and management by Boakes et al. and breast anatomy, Johns Hopkins Medicine were invaluable to this article!


MBChB (MUK), Graduate Fellow, Department of Physiology, Makerere University Founder and Content Creator Peer reviewer, Associate Editor

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