The Anatomy Of The Lactating Breast - Infant Journal

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2007 SNL All rights reservedBREASTFEEDI NGThe anatomy of the lactating breast:Latest research and clinical implicationsKnowledge of the anatomy of the lactating breast is fundamental to the understanding of itsfunction. However, current textbook depictions of the anatomy of the lactating breast arelargely based on research conducted over 150 years ago. This review examines the most recentliterature in an effort to update the current knowledge of the anatomy of the lactating breast.These findings provide insight into breast function and the breastfeeding process and havesignificant clinical implications that will ultimately allow for improved support of thebreastfeeding mother.Donna T Geddes (née Ramsay)PhDResearch FellowThe University of Western AustraliaSchool of Biomedical, Biomolecular andChemical SciencesFaculty of Life and Physical Sciencesdonna.geddes@uwa.edu.auKeywordsbreast; mammary gland; anatomy; duct;lactationKey pointsGeddes, D.T. (2007) The anatomy of thelactating breast: Latest research andclinical implications Infant 3(2): 59-63.1. The latest evidence suggests that theanatomy of the lactating breast isdifferent from current textbookdescriptions.2. The conventionally described lactiferoussinuses do not exist.3. The ratio of glandular to fat tissue is2:1, although both tissue types areintermingled and difficult to separate.4. The main milk ducts in the breast arefewer than previously thought, can besmall (2mm in diameter), superficialand easily compressed and are notuniformly distributed throughout thebreast.5. Clinically, this data is important forwomen undergoing breast surgery andthose seeking breastfeeding advice.infantVOLUME 3 ISSU E 2 2007It is well established that breast milkprovides the infant with optimalnutritional and developmental factors.Organisations such as the AmericanAcademy of Pediatrics recommendbreastfeeding (or the provision of mother’sown milk) for all infants, including highrisk and premature infants1. Indeed, manymothers, physicians and other healthprofessionals recognise this, however, manywomen still experience a variety ofbreastfeeding problems resulting in lowpercentages exclusively breastfeeding at sixmonths postpartum2,3, which is the currentrecommended duration for exclusivebreastfeeding4. Unfortunately, these ratesare even lower for those women whodeliver prematurely, even though thepremature infant stands to gain the mostfrom the provision of mother’s own milk5,6.This situation suggests that support for thebreastfeeding mother (term and preterm)is currently inadequate and indicates aclear need to bridge scientific investigationof breast function and clinical application.The knowledge of the anatomy of thelactating breast is fundamental to theunderstanding of its function. However,the current understanding of the anatomyof the lactating breast has largely beenbased on research conducted over 150years ago with little work performed since7.This review will examine the most recentliterature in an effort to update the currentknowledge of the anatomy of the breast.These findings have provided insight in tobreast function and the breastfeedingprocess and will ultimately allow for improved support of the breastfeeding mother.Anatomy and pregnancyTwo stages of breast growth occur duringpregnancy. During the first half ofpregnancy there is intense lobular-alveolargrowth (mammogenesis), resulting in bothincreased number and size of alveoli andextension and branching of the ductalsystem occurs8. The growth of themammary gland is influenced by a numberof hormones including oestrogen,progesterone, prolactin, growth hormone,epidermal growth factor, fibroblast growthfactor, insulin-like growth factor9,10 andmore recently parathyroid hormonerelated protein11.Montgomery glands, which are acombination of sebaceous glands andmammary milk glands, increase in size andsecretion during pregnancy, ranging innumber from 1 to 15. It is believed thesecretions protect the nipple from both themechanical stress of sucking andpathogenic invasion12. There is alsospeculation that the odour of the secretionmay act as a means of communicationwith the infant. It is of interest that a recentstudy has shown that increased numbers ofMontgomery glands are associated withincreased infant weight gain in the firstthree days after birth, increased infantlatching speed and sucking activity anddecreased time to onset of lactation inprimiparous mothers12, suggesting afunctional role of the Montgomery glandsduring lactation.Proliferation of the glandular tissue isbelieved to occur by invasion of theadipose tissue13. By mid-pregnancy there issome secretory development withcolostrum present in the alveoli and milk59

BREASTFEEDI NGducts and this increases throughout thesecond half of pregnancy. Branching of theductal system continues during this timebut this is less marked than the first half ofpregnancy8. It is of interest that this is thestage that mothers who deliver preterminfants are required to initiate theirlactation. It is therefore possible thatdevelopment of the breast is interruptedprematurely and this may impact on milkproduction14.While development of the breasttypically leads to an increase in breast sizeduring pregnancy, the proportion ofgrowth varies greatly between womenranging from little or no increase to aconsiderable increase in size. Although themajor increase in breast size is usuallycompleted by week 22 of pregnancy, it isclear that for some women significantbreast growth occurs during the lasttrimester of pregnancy and some womencan undergo significant growth postpartum15. The increase in size of themother’s breast during pregnancy ispositively correlated with the increase inthe concentration of human placentallactogen in the mother’s blood suggestingthat this hormone may be integral instimulating breast growth in women15.However, breast growth during pregnancyshould not necessarily be used as a proxyof future lactation success as, while Coxand colleagues showed great variability inbreast growth between women, allsuccessfully breastfed for at least 12months15.Anatomy and lactationDescriptions of the anatomy of thelactating breast have changed little since SirAstley Cooper’s meticulous dissections ofthe breasts of women who had died duringFIGURE 1 Artist’s representation of the ductalsystem of a cadaver injected with colouredwax (Cooper, 1840).60lactation (FIGURE 1) werepublished over 160 yearsago7. As a result of this workit is well accepted that thebreast is composed ofglandular and adiposetissue, supported by a looseframework of fibrousconnective tissue calledCooper’s ligaments.Descriptions of the breastdescribe the glandular tissueas consisting of 15-20 lobes,themselves comprised ofFIGURE 2 Ultrasound image of the lactating breast showinglobules, each containing 10- milk ducts (dark, hypoechoic) within the breast, under the100 alveoli that areareola. Note the superficiality of the duct, the early branchingapproximately 0.12mm inand the lack of a sinus.diameter16. The alveoli arethe sites of milk synthesis and storage. Theultrasound is able to delineate very smallsmallest elements of the alveoli are thestructures of the breast with the addedsecretory cells. These epithelial cells areadvantage of being non-invasive, thusarranged in a single layer around a lumen,allowing the breast to be examined withoutdistortion. (FIGURE 2).thus giving form to the alveolus. Eachalveolus is surrounded by a network ofAnatomy of the lactating breaststarlike, branching myoepithelial cellsresponsible for contracting (under theaction of oxytocin) and ejecting the milkfrom the alveoli lumen into the ductulesleading from each alveolus16.Research methodology issuesInvestigation of the lactating breast sinceCooper has been slow, mainly due tolimitations of imaging techniques. Forexample, mammography of the lactatingbreast is hindered due to a marked increasein glandular tissue causing a subsequentincrease in radio-density thus making theimages of the breast difficult to interpret17.Galactography (the injection of radioopaque contrast media into the duct orificeat the nipple and subsequent radiography)is not ideal in the lactating woman as it islimited to imaging one ductal system (thatmay not be outlined completely) and therisk of introduced infection is increased.Computed tomography (CT) andmagnetic resonance imaging (MRI) arepromising modalities that may, in thefuture, provide more informationregarding mammary gland anatomy. Tworecent studies have used MRI to image thebreast – one was able to identify somecentral ducts in the breasts of lactatingwomen18, whilst another attempted toquantify fatty and glandular tissue volumesin the breasts of non-lactating women19.Ramsay et al recently re-investigated theanatomy of the lactating breast using highresolution ultrasound20. High resolutionIt is widely believed that the predominanttissue in the lactating breast is glandular.Ramsay et al. found there to beapproximately twice as much glandulartissue as fatty tissue in the lactating breast20.However, the proportion of tissues variedgreatly between women with some womenhaving up to half of the breast comprisedof fatty tissue and conversely others up to80% of the breast comprised of glandulartissue. In addition, the glandular tissue wasnot evenly distributed throughout thebreast with the vast majority (over 66%)being found within a radius of 30mm fromthe base of the nipple. The fatty tissue wasalso not evenly distributed with fatty tissuebeing found within the glandular tissue(intraglandular), at the back of the breast(retromammary) and subcutaneously.Indeed, the amount of fat intermingledwith the glandular tissue (intraglandularfat) was highly variable, similar to thatobserved in the non-lactating breast21.Furthermore, most of the fatty tissue in thebreast was subcutaneous (approximatelytwo thirds) and was also not uniformlydistributed, with little subcutaneous fatfound at the base of the nipple and areola.Ultrasound imaging has also providedfurther information on the ductal anatomyof the lactating breast. It is commonlyquoted that the glandular tissue is drainedby 15-20 ducts22 and is based on Cooper’soriginal work7. It is however possible thatnot all ducts emanating from glandularVOLUME 3 ISSU E 2 2007infant

BREASTFEEDI NGFIGURE 3 3D representations of the tissues of the lactating breast based on the ultrasound findings of Ramsay et al20. A) Ductal network,B) Distribution of glandular tissue and C) Complete 3D representation of all tissues. Copyright Medela AG, 2006. Used with permission.tissue open on to the nipple or vice versa23.Love and Barsky observed an average offive nipple openings (range 1-17), mostfrequently in the central portion of thenipple, in a group of 219 expressingwomen23. Similarly, 10 mastectomy (nonlactating) nipples in the same studyshowed 5-7 patent ducts. Going andMoffatt’s dissection of one lactating nippleshowed only four patent ducts24. Ramsayand coworkers, using ultrasound toexamine the lactating breast, have alsoshown lower numbers of main milk ducts(mean 9; range 4-18) than the 15-20commonly reported20. Importantly theresults of these recent studies comparefavourably with Cooper who, although hestated finding 15-20 openings at thenipple, also wrote that he could usuallyonly cannulate 7-12 patent ducts7.Furthermore, both Going and Moffat24 andLove and Barsky23 found no evidence ofductal communication between the lobesof the breast (non-lactating) in contrast toOhtake who demonstrated twoconnections between lobes in themastectomised breast of a 69 year oldwoman25. Whilst these results wereobtained from studies on non-lactatingbreasts they agree with Cooper’sobservations that each glandular lobeexited the breast from its own duct.Ramsay and coworkers have also shownthat the milk ducts in the lactating breastare small (mean 2mm in diameter),superficial and easily compressed20. Inaddition they do not display the typical saclike appearance of the ‘lactiferous sinus’(FIGURE 2). Instead branches drainglandular tissue located immediately belowthe nipple and often merge into the maincollecting duct very close to the nipple20(FIGURE 2). Furthermore, ultrasoundstudies have demonstrated that the milkducts increase in diameter at milk ejectionleading to the conclusion that the mainfunction of the ducts is likely to be theinfantVOLUME 3 ISSU E 2 2007transport of milk rather than storage26.This is in agreement with Cardenosa andEklund who concluded that the ducts arenot, in general, enlarged during lactation27.In addition the paths of the ducts from thenipple into the breast are erratic and theyare intertwined much like the roots of atree20 (FIGURE 1) making them difficult toseparate surgically22.Clinical implicationsThe new findings with regard to theanatomy of the breast have allowed for thedevelopment of new anatomical diagrams(FIGURE 3) and have many clinicalimplications for lactating women. Of mostimportance is that they have provided theclinician with a better understanding of thenormal function of the breast and, at thesame time, greater insight to the‘abnormal’ function of the breast. Indeed,these anatomical findings may help inproviding physiological explanations foroften observed clinical phenomena.Breast surgeryThe number of women electing to havebreast surgery is increasing annually. In theUK, anecdotal reports suggest that breastaugmentation in 2005 increased by 51percent from 200428. Alarmingly, studieshave shown that as many as 50 percent ofwomen who have undergone breastaugmentation may experience low milkproduction29,30. Moreover, periareolarincisions were associated with an increasedlikelihood of lactation insufficiency29,31. It isreasonable to assume that the severing ofducts and glandular tissue will diminishthe amount of milk producing tissue that isable to drain freely through the nipple,especially since the breast has a lowernumber of patent ducts than previouslythought20,23. In addition, the pressure of animplant upon the glandular tissue maycause compression of the ducts thus raisingthe possibility of obstruction of milk flow.Similarly, reduction mammoplasty canimpact on lactation with 0-82% of womenable to breastfeed (at least partially)depending on the surgical techniqueused32,33. A possible explanation of whythese mothers may have low milkproduction includes the obvious removalof large quantities of glandular tissue.Unfortunately the co-distribution ofglandular and fatty tissue demonstratedwithin both the lactating20 and nonlactating breast21 would make it difficult topreferentially remove fatty tissue duringthis procedure. Furthermore, it is possiblethat the reduction surgery may impair theoutflow of milk, perhaps more severelythan augmentation, given that the breasthas fewer patent ducts than previouslyquoted20,23.Low milk productionWhilst there is little information regardingthe incidence of verified low milk supply, itis certainly recognised as a significantproblem for mothers of preterm infantswho must express their milk in order tofeed their baby and maintain lactation34.Clinically, pharmacological intervention(metoclopramide, domperidome) toincrease prolactin levels and boost milkproduction may be trialled. This usuallyoccurs without prior measurement ofmaternal serum or milk prolactin levelsand not unexpectedly, provides varyingsuccess. Another reason for low milkproduction may be insufficient glandulartissue. Ramsay and coworkers20 showedthat the ratio of glandular tissue to adiposetissue was 2:1 and quantification of thevolume of glandular tissue in the breast(possibly by ultrasound, CT or MRI) ofmothers experiencing milk supplyproblems would be valuable to exclude amaternal, physiological cause for low milkproduction. Further investigation couldthen be directed towards the effectivenessof milk removal by either the infant or61

BREASTFEEDI NGbreast pump (in the case of the motherexpressing for the preterm infant) or themanagement of breastfeeding/expressingregimes. Finally, knowledge of the normalfeatures of the ductal system is integral todiagnosing ductal abnormalities that mayaffect milk flow and drainage of theglandular tissue and manifest themselves aslow milk production.Milk ejection and milk removalMilk ejection is critical for a successfullactation as only small volumes of milk (110mL) can be either expressed35 orremoved by the breastfeeding infant36 priorto milk ejection. Stimulation of the nippleinitiates milk ejection by conveyingnervous impulses to the hypothalamus,which causes the posterior pituitary glandto release the hormone oxytocin into thebloodstream37. Oxytocin causes themyoepithelial cells surrounding the alveolito contract thereby forcing (ejecting) milkinto the ducts. This results in increasedintra-ductal pressure38, duct dilation36,39 andincreased milk flow rate39. Multiple milkejections almost always occur duringbreastfeeding (mean 2.5; range 0-9)36 andbreast expression (mean 3-6 for a 15minute expression period)39 and althoughmany women are able to sense the firstmilk ejection, few are able to sensesubsequent milk ejections.Effective milk removal from the breastby either the infant or breast pump isnecessary to avoid the down regulation ofmilk synthesis by local control mechanismsand eventual weaning40. While it is wellknown that stress can influence milkejection, resulting in diminished amountsof milk removed by both the infant37 andbreast pump41, it is often the subtle stresswhich affects maternal confidence andsubsequently milk ejection that isoverlooked. Therefore it is important toprovide positive support to the motherduring both breastfeeding and pumping.The effect of breast anatomy on theexpression of milk is largely unexplored,however there is an indication that largermilk duct diameters are associated withlonger milk ejection episodes and moreavailable milk expressed during pumping39.It is possible to image the milk ducts in thenipple with ultrasound and markeddifferences in duct size between womenhave been observed20,42. Thus milk duct sizeor nipple integrity may indeed affect milkflow during expression or breastfeeding.These observations may explain thedifferences in pumping success experienced62by different women. Also, since the ductsare superficial and compressible it may bepossible that an ill fitting breast shield usedto apply vacuum to the breast maycompress some ducts and therebycompromise milk flow. This emphasisesthe need for the mother to use a correctlyfitted breastshield.The absence of lactiferous sinuses ormilk reservoirs leads one to reconsider themechanism by which the infant removesmilk from the breast. It is evident thatcorrect positioning and attachment of theinfant to the breast is important forsuccessful breastfeeding, however therationale for this is not fully explained.Mechanistically, it is commonly believedthat the infant uses a peristaltic motion ofthe tongue to strip milk from the nipple43.However, Ramsay et al, have recentlyshown that milk flow into the infant'smouth occurs when the tongue is loweredand vacuum in the mouth is increased44.In addition, the absence of the lactiferoussinuses further emphasises the criticalnature of milk ejection for successful milktransfer as it is well documented that onlysmall amounts of milk are available priorto the stimulation of milk ejection35,36, thussuggesting that the main function of theducts is the transport of milk, not storage.Finally, the mother using a breast pumpshould attempt to optimise milk removalduring the initial milk ejection periods asmilk ejection is a discrete event with asmuch as 45% of the removed milk beingobtained during the first milk ejection39.ConclusionTo date, few studies have activelyinvestigated the anatomy of the lactatingbreast despite the obvious importance aclear understanding of the lactatingmammary gland has to both mother andinfant. Perhaps this lack of information is apart of the greater reason why manywomen continue to

The anatomy of the lactating breast: Latest research and clinical implications Knowledge of the anatomy of the lactating breast is fundamental to the understanding of its function. However, current textbook depictions of the anatomy of the lactating breast are largely based on research conducted over 150 years ago. This review examines the most .

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