Galactocoele: presentation, prevalence, pathophysiology

Presenting signs and symptoms

A galactocoele presents as a painless, soft, cystic breast mass, presenting either

• During lactation, or

• After cessation of lactation.

Galactocoeles are typically asymptomatic, and are not infected.

Here is how the signs and symptoms of a galactocoele presentation may be recorded using the NDC Classification of Benign Lactation-related Breast Inflammation.1 You can find out more about the NDC Classification system here.

Location of inflammation	Dimensions (millimetres)	Erythema	Pain	Systemtic signs + symptoms
Generalised - bilateral		None	None	Feels well
Generalised - unilateral		Mild	Mild when touched only	Fever
Localised WITHOUT lump		Moderate	Mild constant	Myalgia
Localised WITH lump		Severe	Moderate when touched only	Rigor
			Moderate constant
			Severe

Prevalence

There is no prevalence data. It has been estimated that galactocoels occur in approximately 4% of breastfeeding women.2

Pathophysiology: inactive, end-stage breast inflammation (unilateral, localised)

A galactocoele is most accurately conceptualised as a milk retention cyst, containing non-infected milk. Applying the NDC Classification, It is made up of

• A dilated terminal lactiferous duct, which is

• Surrounded by a layer of epithelial cells and myoepithelial cells, and which

• Contains either milk or, if chronic, semi-solid material.3

Although the pathophysiology of a galactocele remains controversial, it's clear that inadequate outflow leads to collection of milk.

The causative mechanisms that result in this are yet to be formally defined. However, the key consideration is that it is a retention of milk. It is stagnant, uninfected fluid. Over time, galactocoeles may calcify.

The NDC mechanobiological model of breast inflammation

The NDC mechnobiological model (here and here) hypothesizes that a galactocoele develops in an area where the alveoli have been subject to very high internal hydrostatic compression pressures.4, 5 This aetiological model is supported by murine studies 5 and human weaning studies.4

This intra-alveolar hydrostatic compression of the lactocytes results from either obstruction to outflow or from inadequate amounts of outflow. Resultant high intra-alveolar pressure may result in tight junction rupture between lactocytes, rupture of the basement membranes, and involution of the alveolus. When this occurs on a scale of alveolar rupture which has not been able to repair with tissue remodeling, a galactocoele results. Clinical symptoms of inflammation either subside or do not emerge, and the collection of fluid remains quiescent.

Analysis of the Academy of Breastfeeding Medicine's Clinical Protocol #36 hypothesised pathophysiology of galactocoeles

The Academy of Breastfeeding Medicine's Clinical Protocol #36 'The Mastitis Spectrum' states:

“A galactocele develops when ductal narrowing obstructs the flow of milk to the extent that a significant volume of obstructed milk collects in a cyst-like cavity … Galactoceles, which can result from unresolved hyperlactation, can become infected … An infected galactocele requires drainage as well as antibiotics.” 6

This ABM CP #36 pathophysiological theory of galactocoele development is unconvincing, because it does not take into account the alveolar rupture, associated apoptosis and resultant tissue destruction that necessarily occurs in the subclinical (or occasionally clinical) inflammatory development of galactocoele.7

Moreover, a galactocoele which becomes infected has become an abscess, so the diagnosis ‘infected galactocoele’ is unnecessary and lacks clinical meaning.

Clinical Protocol #36 does not describe the pathophysiological mechanism by which galactocoeles are hypothesised to result from ‘hyperlactation'. The only realistic model for explaining why 'hyperlactation' might result in a galactocoele is that high intra-alveolar milk volumes have intra-alveolar pressure effects, consistent with the NDC mechanobiological model

You can read more analysis of ABM CP #36 here.

References

1. Douglas PS. Re-thinking benign inflammation of the lactating breast: classification, prevention, and management. Women's Health. 2022;18:17455057221091349.

2. Stevens K, Burrell HC, Evans AJ et-al. The ultrasound appearances of galactocoeles. Br J Radiol. 1997;70 : 239-41.

3. Geddes DT. Ultrasound imaging of the lactating breast: methodology and application. International Breastfeeding Journal. 2009;4:doi:10.1186/1746-4358-1184-1184.

4. Douglas P. Re-thinking benign inflammation of the lactating breast: a mechanobiological model. Women's Health. 2022;18:17455065221075907.

5. Kobayashi K, Han L, Lu S-N, Ninomiya K, Isobe N, Nishimura T. Effects of hydrostatic ompression on milk production-related signaling pathways in mouse mammary epithelial cells. Experimental Cell Research. 2023;432:113762.

6. Mitchell KB, Johnson HM, Rodriguez JM, Eglash A, Scherzinger C, Cash KW, et al. Academy of Breastfeeding Medicine Clinical Protocol #36: The Mastitis Spectrum, Revised 2022. Breastfeeding Medicine. 2022;17(5):360-375.

7. Douglas PS. Does the Academy of Breastfeeding Medicine Clinical Protocol #36 'The Mastitis Spectrum' promote overtreatment and risk worsened outcomes for breastfeeding families? Commentary. International Breastfeeding Journal. 2023;18:Article no. 51 https://doi.org/10.1186/s13006-13023-00588-13008.