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.

Breast Anatomy

🧩 Key Structures

🎞️ Imaging Planes & Modalities

📏 Landmarks & Normal Values

🔀 Anatomical Variants

🧠 Pathology Correlation

💡 Pitfalls & Mimics