AN9.1-3 | Pectoral region — Glossary

A large fan-shaped muscle of the anterior chest wall with three heads (clavicular, sternocostal, abdominal); adducts, medially rotates, and flexes the arm

A thin triangular muscle deep to pectoralis major; originates from ribs 3-4-5 and inserts on the coracoid process; key landmark for axillary lymph node levels

A sheet of deep fascia extending from the clavicle, enclosing subclavius and pectoralis minor; the costocoracoid membrane is the portion above pectoralis minor

The part of the clavipectoral fascia between subclavius and pectoralis minor; pierced by the lateral pectoral nerve, cephalic vein, thoracoacromial artery, and lymphatics (LCTA)

The continuation of the clavipectoral fascia below pectoralis minor that attaches to the axillary fascia; creates the hollow of the armpit

A nerve from the lateral cord of the brachial plexus (C5-C7); supplies the clavicular head of pectoralis major; pierces the costocoracoid membrane

A nerve from the medial cord of the brachial plexus (C8-T1); supplies pectoralis minor and the sternocostal head of pectoralis major

Fibrous septa (suspensory ligaments) running from the pectoral fascia through the breast to the skin; cancer invasion causes skin dimpling

One of 15-20 ducts that drain each breast lobe; converges toward the nipple; dilates to form a lactiferous sinus near the nipple

A dilation of the lactiferous duct just before it opens at the nipple; temporary storage of milk during lactation

An embryological ectodermal ridge from the axilla to the inguinal region; only one pair of breasts develops at the 4th intercostal space; persistence elsewhere causes polythelia or polymastia

An extension of breast tissue toward the axilla; drains directly to Level I axillary nodes; a lump here may be breast tissue rather than lymphadenopathy

Orange-peel appearance of breast skin caused by lymphatic obstruction from cancer; oedema around tethered hair follicle pits creates the dimpled pattern

The first lymph node draining a tumour; identified by blue dye or radiotracer injection; biopsy determines whether cancer has spread to regional nodes

Parasternal lymph nodes along the internal thoracic vessels behind the costal cartilages; drain the medial breast; clinically silent (harder to detect)

A loose connective tissue plane between the breast and pectoral fascia allowing breast mobility; cancer can spread through this space to the chest wall

Supernumerary (extra) nipples along the milk line; the most common congenital anomaly of the breast

Supernumerary (extra) breast tissue along the milk line; may enlarge during pregnancy

Congenital absence of pectoralis major (sternal head) with ipsilateral breast hypoplasia/amastia and hand anomalies (syndactyly, brachydactyly)

A branch of the axillary artery that pierces the costocoracoid membrane and divides into pectoral, acromial, deltoid, and clavicular branches

A superficial vein of the upper limb ascending in the deltopectoral groove; pierces the costocoracoid membrane to drain into the axillary vein

Areolar glands (modified sebaceous glands) on the areola that secrete a lubricating, protective substance during lactation

Enlargement of male breast tissue; physiological (neonatal, pubertal) or pathological (liver cirrhosis, drugs like spironolactone, Klinefelter syndrome)