Breast Cyst

Breast cysts are fluid-filled, epithelial-lined cavities located within the breast parenchyma. They can range in size from microscopic to large palpable cysts with 20 – 30 mL of fluid.

Epidemiology

• Women
• > 35 years old
• Premenopausal 
• Increases until menopause, then sharply declines
• New breast cyst formation in older women is associated with exogenous hormone replacement therapy

Pathogenesis

• 50% are multiple or recurrent 
• Thought to arise from destruction and dilatation of lobules and terminal ductules
• Influenced by ovarian hormones

History

• Asymptomatic 
• Breast mass that changes with menstrual cycle
• Variable size, larger size prior to menstruation and smaller in size after menstruation

Physical Exam

• Breast mass characteristics
  • Soft
  • Mobile 
  • Round
  • Smooth
  • Well circumscribed

Imaging

• Cyst can be confirmed by direct aspiration OR US
• Breast US
  • Simple cyst
    • Cyst with smooth borders, no solid intracystic components
    • Always noncancerous
    • Direct aspiration is not necessary
  • Complex cyst
    • Cyst with mix of fluid and solid intracystic components
    • Direct aspiration may be necessary
  • Complicated breast cyst
    • Cyst with fluid; may have cloudiness to fluid or border may be irregular
    • Direction aspiration may be used
• Direct aspiration
  • Fluid can be straw-colored, opaque, or dark green and may contain debris
  • If cyst resolves with aspiration and contents aren’t grossly bloody → fluid doesn’t need to be sent for cytologic analysis
  • If cyst recurs multiple times (> 2 times) → core needle biopsy should be performed
• Core needle biopsy
  • Evaluate solid elements

Treatment

• Usually doesn’t require treatment. Simple breast cysts usually resolve. Complex breast cysts may require aspiration and more follow-ups.
• Direct aspiration (see above)
• Surgical removal
  • Isn’t usually indicated 
  • May be considered if cyst recurs multiple times or if needle biopsy reveals atypia, incompletely removes the mass, or if the cyst is large and painful

Relevant Information

• No evidence of increased risk for breast cancer

• Breast anatomy
  • Lies between subdermal layer of adipose tissue and superficial pectoral fascia
  • Cooper ligaments
    • Provide structural support and shape (anchored into the skin)
    • Infiltration by tumors can produce tethering, resulting in dimpling on the breast tissue
• Lymphatics
  • Lymph nodes
    • Level 1: located lateral to the lateral border of the pectoralis minor muscle
    • Level II: located posterior to the pectoralis minor muscle as well as anterior to the pectoralis minor and posterior to the pectoralis major (Rotter or interpectoral nodes)
    • Level III: located medial to pectoralis minor muscle and include subclavicular nodes
  • Most drains to axillary nodes (97%)
  • Any quadrant can drain into internal mammary nodes
  • Supraclavicular nodes → N3 disease
  • Primary axillary adenopathy → ≤ 1 is lymphoma
• Nerves
  • Long thoracic nerve
    • Innervates serratus anterior muscle 
    • Injury → winged scapula 
    • Lateral thoracic artery supplies serratus anterior muscle
  • Thoracodorsal nerve
    • Innervates latissimus dorsi muscle
    • Injury → weak arm pull-ups and adduction
    • Thoracodorsal artery supplies latissimus dorsi
    • Arises from posterior cord of brachial plexus; enters axillary space under axillary vein (close to long thoracic nerve)
  • Medial pectoral nerve: innervates innervates pectoralis major and pectoralis minor muscles
  • Lateral pectoral nerve: innervates pectoralis major muscle
  • Intercostobrachial nerve
    • Lateral cutaneous branch of second intercostal nerve
    • Sensation to medial arm and axilla
    • Most common injured nerve with modified radical mastectomy (MRM) or axillary lymph node dissection (ALND)
• Arterial supply: branches of
  • Internal thoracic (mammary) artery
  • Intercostal arteries
  • Thoracoacromial artery
  • Lateral thoracic artery
• Batson’s plexus: valveless vein plexus, allows direct hematogenous metastasis of breast cancer to spine
• Costoclavicular ligament (Halsted ligament): defines axilla apex
• Breast development
  • Formed from ectoderm milk streak
  • Hormone influence
    • Estrogen: duct development (double layer of columnar cells)
    • Progesterone: lobular development
    • Prolactin: synergizes estrogen and progesterone
    • Cyclic changes
      • Estrogen → increased breast swelling, growth of glandular tissue
      • Progesterone → increased maturation of glandular tissue, withdrawal causes menses
      • FSH, LH surge → ovum release
      • After menopause, less estrogen and progesterone results in atrophy of breast and vulvar tissue
• Microscopic anatomy
  • Three tissue types
    • Glandular epithelium
      • Branching system of ducts arranged in a radial pattern extending from the nipple-areolar complex
      • Each major duct has branches and ultimately ends in terminal ductules or acini (acini are milk-forming glands of lactating breasts)
    • Fibrous stroma and supporting tissues
    • Adipose tissue 
  • Basement membrane
    • Contains laminin, type IV collagen, proteoglycans
    • Differentiates in situ from invasive breast cancer

Complications

• Infection
• Pain

Differential Diagnoses

• Fibrocystic changes
• Papilloma
• Breast abscess
• Phyllodes tumor
• Radial scar
• Intracystic carcinoma