Breast anatomy

Position and coverings

• Base extends from the 2nd to the 6th rib and from the sternal edge to the midaxillary line. Two-thirds lies on pectoralis major, the lateral third on serratus anterior, the lower part on the external oblique aponeurosis.
• The axillary tail (of Spence) passes through the deep fascia into the axilla and can be missed clinically.
• Behind the breast lies the retromammary space (loose areolar tissue over the pectoral fascia): it gives mobility and takes an implant. A cancer that becomes fixed when pectoralis major contracts has invaded the pectoral fascia.
• Suspensory ligaments (Cooper) run from the deep fascia to the skin; a tumour shortening them causes skin dimpling. Blocked dermal lymphatics give peau d'orange.
• On the mediolateral oblique mammogram pectoralis major shows as a triangular band along the upper posterior edge.

Lobes, ducts, development and the male breast

• A modified apocrine sweat gland of 15–20 lobes, each drained by one lactiferous duct opening on the nipple; galactography of a discharging duct fills a single lobe.
• The terminal duct lobular unit is the secreting unit and where most cancers, ductal and lobular, begin.
• The male breast has ducts but no lobules; male cancer is usually subareolar ductal carcinoma. Pubertal gynaecomastia is a tender subareolar disc, from oestrogen rising faster than testosterone.
• Development: ectoderm of the mammary ridge (milk line) from axilla to groin; accessory nipples lie on this line. Poland syndrome: hypoplastic breast with absent sternocostal pectoralis major.
• Breast growth needs ovarian oestrogen, not a uterus. In Müllerian agenesis (46,XX) the ovaries are normal, so breasts and pubic hair are normal, but there is no uterus and a short blind vagina, giving primary amenorrhoea.

Hormones, pregnancy and lactation

• After delivery the placenta goes, oestrogen and progesterone fall, and prolactin can act: milk comes in over 2–3 days. Suckling sends afferents to the hypothalamus: dopamine falls so prolactin rises, and oxytocin is released (also contracting the uterus).
• High prolactin in lactation suppresses GnRH, so periods stop (lactational amenorrhoea).
• Sheehan syndrome: pituitary infarction after postpartum haemorrhage; failure to lactate is often the first sign, later hypothyroidism and adrenal failure.
• Lactational mastitis and abscess: usually Staphylococcus aureus entering through a cracked nipple.

Age and hormone changes on imaging

• Adolescent breast tissue is very radiosensitive: women given mantle radiotherapy as teenagers need early MRI screening.
• Breast MRI is timed to days 7–14 of the cycle, when background enhancement is least. Cancer enhances fast and washes out because its new vessels are leaky.
• Lactation is not a reason to delay imaging a persistent lump; pregnancy-associated cancer is often found late.
• Tamoxifen blocks oestrogen receptors in the breast but is a partial agonist in the endometrium and bone: risks are endometrial carcinoma and venous thromboembolism; it protects against contralateral breast cancer.

Reading mammographic lesions

• Fat necrosis follows trauma or surgery: injured fat cells release lipid that is saponified and walled off by foamy macrophages. Early it can look spiculated and mimic cancer; only the oil cyst stage is clearly benign.
• Bloody or serous nipple discharge from one duct: commonest cause is intraductal papilloma.

Blood supply and nerves

• Intercostal veins connect with the vertebral venous plexus (Batson), the valveless route for vertebral metastases.
• Nipple sensation: lateral cutaneous branch of the 4th intercostal nerve.
• Nerves at axillary surgery: long thoracic on serratus anterior (winging; loss of overhead abduction because the scapula cannot rotate up), thoracodorsal to latissimus dorsi, medial and lateral pectoral nerves, intercostobrachial (numb inner arm).
• Halsted radical mastectomy removed pectoralis major: weakest movements are adduction and medial rotation of the arm. Modified radical mastectomy keeps the muscle.
• Reconstruction: latissimus dorsi flap on the thoracodorsal artery; pedicled TRAM flap on the superior epigastric artery; a free lower abdominal (free TRAM or DIEP) flap needs the deep inferior epigastric vessels joined to the internal thoracic vessels.

Lymph drainage

• About 75% to axillary nodes, mainly the anterior (pectoral) group first. The medial quadrants drain largely to parasternal (internal mammary) nodes beside the internal thoracic vessels.
• The subareolar plexus collects lymph from the nipple and much of the gland, so sentinel tracer can be injected around the areola.
• If the axilla is blocked, lymph crosses the midline to the other breast or axilla; the lower inner quadrant can reach subperitoneal lymphatics via the rectus sheath.

• Groups: anterior, posterior (subscapular), lateral (humeral), central, apical (all lymph finally passes through the apical group).
• Grade versus stage: grade describes the cells (tubule formation, nuclear pleomorphism, mitoses); stage is size, skin or chest wall involvement and node count. A tumour with skin involvement is T4; 4–9 axillary nodes is N2.

Risk and genetics

• BRCA1 (17q) and BRCA2 (13q): autosomal dominant tumour suppressors with breast and ovarian cancer (BRCA2 also male breast). A relative with ovarian cancer or several young relatives with breast cancer suggests them.
• Other risks: early menarche, late menopause, nulliparity, late first pregnancy, HRT, obesity after menopause, radiation. Breastfeeding is protective.

Remember Oestrogen grows ducts and fat; progesterone grows lobules; prolactin makes milk; oxytocin ejects it.

Exam trap Axillary levels are defined by pectoralis minor, not pectoralis major.

Exam trap Teacup calcifications that change shape between views are benign milk of calcium.

How FCPS asks about this

• Hormone for duct growth and fat deposition: oestrogen; lobules and alveoli: progesterone.
• Dense breasts in a lactating woman: proliferated alveoli distended with milk.
• Lucent lesion with rim calcification after surgery: oil cyst from fat necrosis.
• Failure to lactate after postpartum haemorrhage: Sheehan syndrome.
• Weak arm after Halsted mastectomy: adduction and medial rotation (pectoralis major removed).
• Vertebral metastasis from breast: valveless vertebral venous plexus.
• Young relatives with breast and ovarian cancer: BRCA1 or BRCA2 mutation.