Thoracic Wall and Mammary Gland

Thoracic Anatomy

  • Thorax Description:

    • Shaped like a cylinder between the neck and the abdomen

    • Superior thoracic aperture: Open to the neck

    • Inferior thoracic aperture: Closed by the diaphragm

    • Key structures:

      • Sternum (subcutaneous)

      • Right pleural cavity

      • Left pleural cavity

      • Vertebral column

      • Mediastinum

      • Diaphragm

      • 1st rib

      • Ribs

Thoracic Wall Landmarks

  • Junctions and Anatomic Landmarks:

    • Jugular notch (suprasternal notch): Opposite intervertebral disc between T2 & T3

    • Manubrium sterni: Opposite T3 & T4 vertebrae

    • Sternal angle (Angle of Louis): Lies at T4-T5 disc; marks the level of the 2nd pair of costal cartilages. Rib counting starts here.

    • Body of the sternum: Opposite T5-T9 vertebrae

    • Xiphisternal joint: Level of T9 vertebra

  • Important Lines:

    • Midsternal line: Vertical through the midline of the body

    • Parasternal line: Along the lateral border of the sternum

    • Midclavicular line: Vertical from the middle of the clavicle

    • Axillary lines:

    • Anterior axillary line: Along anterior axillary fold

    • Posterior axillary line: Along posterior axillary fold

    • Midaxillary line: Between anterior and posterior axillary lines

    • Scapular line: Through the inferior angle of the scapula (T7)

    • Mid-vertebral line: Along the spinous processes of the vertebrae

Dermatomes of the Thoracic Wall

  • Dermatomes:

    • Area of skin innervated by specific spinal nerve root; used for assessing neurological issues through sensation tests (light touch/pin prick):

    • Skin at clavicle level: C5

    • Anterior chest wall below C5: T1

    • T4: Includes nipple area

    • T7: Includes xiphoid process

    • T10: Includes umbilicus

Female Mammary Gland Anatomy

  • Structure and Function:

    • Modified sweat gland in superficial fascia

    • Rudimentary in males; well-developed in females

    • Shape influenced by fat content

    • Glandular tissue engorges during pregnancy and lactation; atrophies with age

    • Structure: Milk-secreting alveoli arranged around lactiferous ducts in lobules

  • Dimensions:

    • Extent:

    • Transversely: Lateral border of sternum to midaxillary line (MAL)

    • Vertically: 2nd to 6th rib

    • Axillary tail of Spence: Extension towards axilla; may enlarge menstrual cycle giving false lump impression

Components of Mammary Gland

  • Nipple: Projection with no fat, hair, or sweat glands, usually at 4th intercostal space, lactiferous ducts open at the tip

  • Areola: Pigmented area around the nipple

  • Mammary Bed:

    • Deep relations: Rest on pectoral fascia, pectoralis major, serratus anterior, external oblique, and rectus abdominis

  • Retromammary Space:

    • Loose connective tissue space allowing breast movement

Lobular Organization

  • Gland divided into 18-20 lobules;

    • Each lobule has a lactiferous duct opening separately at the nipple with a dilated portion (lactiferous sinus) beneath areola

Development and Anomalies of Mammary Gland

  • Milk Line: Linear ectodermal thickening during embryonic development extending from axilla to groin

    • Failure to disappear can result in supernumerary nipples (polythelia) or breasts (polymastia)

  • Amastia: Absence of mammary glands due to milk line failure

  • Gynecomastia: Enlargement of male breasts due to drug-induced, hormonal imbalance, or genetic causes (e.g., Klinefelter syndrome)

Blood Supply of Mammary Gland

  • Arterial Supply:

    • Lateral part: Lateral thoracic artery & 3rd, 4th, and 5th posterior intercostal arteries

    • Medial part: Perforating branches & anterior intercostal branches from internal thoracic artery

  • Venous Drainage:

    • Drains to axillary, internal thoracic, and intercostal veins

Nerve Supply of Mammary Gland

  • Includes:

    • Lateral and anterior cutaneous branches of 3rd, 4th, and 5th intercostal nerves

Breast Quadrants & Clinical Significance

  • Surface of breast divided into four quadrants:

    • Utility:

    • Understanding lymphatic drainage

    • Assisting in identification of distant cancer metastasis

    • Explaining anatomical location of tumors

    • E.g., tumor at 10 o'clock position suggests superior lateral quadrant involvement

Lymphatic Drainage of Mammary Gland

  • Groups:

    • Parasternal (Internal thoracic) group

    • Axillary group

    • Clinical Relevance: Predicting breast carcinoma metastasis

    • Lateral quadrants drain to pectoral lymph nodes

    • Medial quadrants to parasternal lymph nodes;

      • Some cross midline to opposite side

    • Nipple and areola drain to pectoral lymph nodes

Carcinoma of the Breast

  • Clinical Features:

    • Skin retraction or dimpling caused by fibrosis of Cooper's ligaments

    • Peau d'orange sign: Edema presenting "orange peel" skin due to lymphatic obstruction

    • Nipple retraction may occur due to fibrosis of lactiferous ducts

  • Mammography: Radiographic evaluation focusing on high-density areas indicating lesions (cancerous or benign)

Mastectomy

  • Radical Mastectomy: Removal of:

    • Entire breast, all lymph nodes under the arm, fat, fascia, and chest wall muscles

    • Risk of injury to three major nerves:

    1. Long thoracic nerve: Supplies serratus anterior; injury results in winging of scapula and weakness in arm abduction

    2. Intercostobrachial nerve (T2): Causes numbness in axilla and medial arm

    3. Thoracodorsal nerve: Supplies latissimus dorsi; may also be injured

Thoracic Wall Overview

  • Structure of thoracic cage comprised of:

    • Posterior: Vertebral column

    • Sides: Ribs and intercostal spaces

    • Anterior: Sternum and costal cartilages

    • Superior: Suprapleural membrane

    • Inferior: Thoracic diaphragm

    • Functions: Protect lungs & heart, provide muscle attachment, and assist in breathing via volume changes in thoracic cavity

Thoracic Inlet & Outlet

  • Superior Thoracic Aperture:

    • Boundaries: anterior (superior border of manubrium sterni), posterior (1st thoracic vertebra), lateral (1st pair of ribs)

    • Contains: Trachea, esophagus, nerves, blood vessels

    • Suprapleural membrane (Sibson's fascia) protects apex of lung

  • Inferior Thoracic Aperture:

    • Boundaries: anterior (xiphisternal joint), posterior (12th thoracic vertebra), lateral (costal margin)

    • Closed by diaphragm with passage openings for aorta, esophagus, and inferior vena cava

Thoracic Outlet Syndrome (TOS)

  • Compression of C8 & T1 nerve roots or subclavian artery due to cervical rib or Pancoast tumor leading to symptoms:

    • Numbness, pain, tingling, or weakness in upper limb

    • Ischemic muscle pain, weak pulse in affected arm

  • Adson Test: Weak or absent radial pulse indicates TOS

Cervical Rib

  • Developmental elongation of C7 transverse process that can compress lower trunk of brachial plexus, presenting pain and muscle atrophy in the hand

Sternal Puncture

  • Procedure for bone marrow aspiration/biopsy from the manubrium

    • Risk of injuring brachiocephalic vein or arch of aorta

Ribs Overview

  • 12 pairs of long, curved bones from vertebrae to sternum, classified into:

    • True ribs (1-7): Attach directly to the sternum

    • False ribs (8-10): Attach indirectly through the 7th costal cartilage

    • Floating ribs (11-12): No anterior attachment, free at the front

Intercostal Muscles & Nerves

  • Intercostal Spaces: 11 pairs occupying spaces between ribs, containing:

    • Intercostal muscles: external, internal, and innermost

    • Vessels and nerves in neurovascular plane along costal groove

  • Intercostal Nerves (T1-T12): Facilitating motor and sensory innervation of thoracic wall

Herpes Zoster (Shingles)

  • Viral disease affecting spinal ganglion causing burning pain in dermatome area and vesicular eruptions on skin

Intercostal Nerve Block

  • Anesthetic injected at paravertebral line in an intercostal space to block sensation

Thoracocentesis

  • Procedure to aspirate fluid from pleural cavity through intercostal space to avoid vessel injury

Arterial Supply of Thoracic Wall

  • Includes anterior intercostal arteries from the internal thoracic artery and posterior intercostal arteries from descending aorta

    • Notably, collateral circulation develops in aortic coarctation leading to rib notching due to eroded ribs

Venous Drainage of Thoracic Wall

  • Anterior intercostal veins drain into internal thoracic vein; posterior intercostal veins drain into azygos/hemiazygos veins

Movements of the Thoracic Wall

  • Inspiration:

    • Active process increasing thoracic volume by contracting external intercostals and diaphragm

  • Expiration:

    • Passive process involving relaxation of intercostal muscles and diaphragm; elastic recoil of lungs decreases thoracic volume

Flail Chest

  • Occurs with multiple rib fractures, leading to paradoxical movement of segments; severely impacts ventilation and oxygenation

Diaphragm

  • Main respiratory muscle with central tendon and muscular parts; innervated by phrenic nerve (C3, 4, 5)

  • Major openings for aorta (T12), esophagus (T10), and inferior vena cava (T8)

  • Develops from multiple embryonic structures and can present congenital defects using Bochdalek hernia

Phrenic Nerve

  • Affected by injury leading to paralysis of diaphragm causing characteristic radiographic findings (e.g., elevation during inspiration)