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Reproductive

Breast Anatomy

The breast is a modified apocrine gland composed of fibroglandular tissue, ducts, and supporting stroma embedded in fat, overlying the pectoralis major on the anterior chest wall. Imaging spans mammography, ultrasound, and dynamic contrast-enhanced MRI, each exploiting different tissue contrasts to detect and characterize disease. Knowledge of ductal-lobular architecture, Cooper ligaments, and lymphatic drainage underpins accurate BI-RADS interpretation and staging.

Key Structures

  • Terminal duct lobular unit (TDLU): the functional secretory unit and origin of most carcinomas and fibrocystic change
  • Ductal system: 15-20 lobes drain via lactiferous ducts converging on the nipple; ducts dilate in ectasia and harbor intraductal disease
  • Cooper ligaments: fibrous suspensory bands tethering skin to deep fascia; retraction/thickening signals underlying malignancy or edema
  • Nipple-areolar complex: retroareolar ducts and Montgomery glands; asymmetry or retraction is significant
  • Fibroglandular tissue and fat: BI-RADS density categories a-d; dense tissue lowers mammographic sensitivity
  • Pectoralis major and the retromammary fat plane posteriorly; axillary tail (of Spence) extends into the axilla
  • Intramammary and axillary (levels I-III) and internal mammary nodes—normal nodes reniform with a fatty hilum

Imaging Planes & Modalities

  • Digital mammography and tomosynthesis (DBT) in craniocaudal and mediolateral oblique projections screen and detect calcifications and masses; DBT reduces tissue superimposition
  • Ultrasound (high-frequency linear probe) characterizes masses as cystic vs solid, assesses margins/orientation, and guides biopsy; adds elastography and Doppler
  • Dynamic contrast-enhanced MRI (T1 fat-sat pre/post gadolinium with subtraction, plus T2 and DWI) evaluates extent of disease, high-risk screening, and implant integrity via kinetic curves
  • Contrast-enhanced mammography (CEM) provides functional vascular information as an MRI alternative
  • Image-guided biopsy: stereotactic for calcifications, US-guided for masses, MRI-guided for enhancement-only lesions

Landmarks & Normal Values

  • Retromammary space and the pectoral fascia mark the posterior boundary; chest-wall invasion is a staging concern
  • BI-RADS density: almost entirely fatty (a), scattered (b), heterogeneously dense (c), extremely dense (d)
  • Normal axillary node cortical thickness <3 mm with preserved fatty hilum; eccentric cortical thickening is suspicious
  • Nipple should be in profile on standard views; the inframammary fold defines the inferior extent
  • Background parenchymal enhancement (BPE) on MRI graded minimal to marked and influenced by hormonal/menstrual timing

Anatomical Variants

  • Accessory (ectopic) breast tissue and supernumerary nipples along the embryologic milk line, commonly axillary
  • Fibroglandular asymmetry and a prominent axillary tail that can simulate a mass
  • Sternalis muscle—a normal variant seen medially on the CC view that can mimic a lesion
  • Poland syndrome with hypoplasia/absence of the pectoralis major and breast
  • Intramammary lymph nodes—benign when reniform with a fatty hilum, common in the upper outer quadrant

Pathology Correlation

  • Most carcinomas arise in the TDLU; suspicious features include spiculated margins, non-parallel orientation on US, and washout kinetics on MRI
  • Fine pleomorphic or linear-branching calcifications in a segmental/ductal distribution suggest DCIS
  • Skin/trabecular thickening and Cooper ligament distortion indicate edema from inflammatory carcinoma, mastitis, or lymphatic obstruction
  • Lymphatic drainage is predominantly to the axilla (sentinel node), with internal mammary drainage for medial tumors—guides nodal staging
  • Fibroadenoma (oval, circumscribed, parallel) versus phyllodes; complicated cyst versus complex cystic-solid mass drives BI-RADS management
  • Architectural distortion without a mass may be radial scar or invasive lobular carcinoma, which is often occult and infiltrative

Pitfalls & Mimics

  • Dense breast tissue masks masses on mammography—correlate with US/MRI and pay attention to interval change
  • Do not dismiss developing focal asymmetry or architectural distortion; both can be the only sign of malignancy
  • Skin lesions, moles, and deodorant artifact can simulate calcifications—use skin markers
  • Invasive lobular carcinoma frequently underestimated in size; MRI helps map extent before surgery
  • Fat necrosis and post-surgical scar can mimic recurrence; oil cysts and dystrophic calcification are reassuring
  • Benign-appearing circumscribed masses in older women may be triple-negative or metastatic disease, not fibroadenoma

References

  • ACR BI-RADS Atlas, 5th edition. American College of Radiology
  • Ikeda DM, Miyake KK. Breast Imaging: The Requisites. Elsevier
  • Kopans DB. Breast Imaging. Lippincott Williams & Wilkins
  • Cardenosa G. Breast Imaging Companion. Wolters Kluwer

⚕️ Educational reference — correlate with clinical context and confirm with a qualified radiologist.