Thorax Systems Anatomy

Thorax Overview

Systems Anatomy

  • We will explore different headings of each structure or area in systems anatomy:
    • Surface anatomy
    • Osteology
    • Relationships to other structures and areas
    • Arterial blood supply and venous drainage
    • Nerve innervation
    • Specialized tissue or structures
    • Histology
    • Function

Surface Anatomy

Key Landmarks

  • Supra-sternal/Jugular Notch:
  • Manubrio-sternal angle: Located at vertebral level T4
    • Forms the thoracic plane by connecting posteriorly with the base of the 4th thoracic vertebra
  • Nipple position:
    • Located in the 4th intercostal space in men
    • Corresponding dermatome is T4

Anterior Thoracic Wall

  • Clavicle
  • Xiphoid Process:
    • Corresponds with T9 vertebral level
  • Sternal Angle:
    • Corresponds with T4 vertebral level
  • Jugular Notch:
    • Corresponds with T2 vertebral level

Mediastinum

Mediastinum Overview

  • Right pleural cavity: Contains right lung
  • Inferior mediastinum: Houses the heart
  • Superior mediastinum: Contains great vessels
  • Left pleural cavity: Contains left lung
  • Diaphragm:
Superior Mediastinum
  • Extends from thoracic inlet to sternal angle (inferior border T4)
  • Contains:
    • Thymus
    • Great vessels
    • Esophagus
    • Trachea
Inferior Mediastinum (T4-T12)
  • Divided into three regions:
    • Anterior: Between pericardium and sternum; contains thymus
    • Middle: Contains the heart, vessels, phrenic nerve, and lung roots
    • Posterior: Between pericardium and vertebrae; contains esophagus, thoracic aorta

Anatomical Features

  • Right pleural cavity
  • Ribs
  • Diaphragm
  • Vertebral column
  • Superior thoracic aperture
  • Left pleural cavity
  • Rib I
  • Inferior thoracic aperture
  • Manubrium of sternum
  • Sternal angle
  • Body of sternum
  • Xiphoid process
  • Inferior thoracic aperture

Surface Anatomy (Detailed)

  • Apex Position:
    • Approximately 2 cm above medial 1/3 of clavicle
  • Fissures:
    • Horizontal Fissure:
    • From the 4th costal cartilage horizontally
    • Oblique Fissure:
    • From T3 spinous process to 6th costal cartilage anteriorly
  • Costodiaphragmatic recess:
    • Region between lung and pleural reflection
  • Tracheal Bifurcation:
    • Located at the sternal plane or just below T4/T5
  • Lung Characteristics:
    • Soft and compliant, will fill empty spaces in thorax

Osteology

Thoracic Cage

  • Components:
    • 12 pairs of ribs
    • 12 thoracic vertebrae and intervertebral disks
    • Sternum
  • Functions of Thoracic Skeleton:
    • Protects organs and structures of the thorax
    • Provides stable support for the upper extremity and head
    • Flexible; can change dimensions during ventilation

Ribs

  • Classification:
    • True Ribs (1-7):
    • Attach directly to the sternum
    • False Ribs (8-10):
    • Attach to the 7th costal cartilage
    • Floating Ribs (11-12):
    • No anterior attachment
  • Typical Ribs (3-9):
    • Have two articular verbra facets
    • Composed of head, neck, and body along with tubercle and subcostal groove
  • Atypical Ribs:
    • 1st Rib: Wide and short with one articular facet
    • 2nd Rib: Short with area for serratus anterior
    • 10-12 Ribs: Only one articular facet

Intercostal Space

  • Definition: Area between two ribs; 1st intercostal space is between rib 1 and 2.

Muscles

  • Three muscle layers include:
    • External Intercostal Muscle
    • Internal Intercostal Muscle
    • Innermost Intercostal Muscle
    • Transversus Thoracis

Myotome & Dermatome

  • Branches of Intercostal Nerve Include:
    • Rami communicantes (connect each intercostal nerve to sympathetic trunk)
    • Lateral and anterior cutaneous branches
    • Muscular branch (innervates intercostals, transversus thoracis)

Thoracic Wall Muscles

  • Muscles of the thoracic wall include:
    • Serratus posterior
    • Serratus anterior
    • Levatores costarum
    • Intercostal muscles (including external, internal, and intimate)

Diaphragm Anatomy

Parts of the Diaphragm

  1. Sternal Part:
    • Two muscular slips attached to xiphoid process
  2. Costal Part:
    • Wide muscular slips attached to inferior six costal cartilages and their ribs
  3. Lumbar Part:
    • Composed of two aponeurotic arches:
      • Medial and lateral arcuate ligaments
      • Crura ascend to central tendon (left and right crura)
      • Attached to anterior aspect of upper three lumbar vertebrae

Diaphragm Apertures

  1. Caval Aperture:
    • Allows passage of inferior vena cava (T8)
  2. Esophageal Hiatus:
    • Passage of esophagus (T10)
  3. Aortic Hiatus:
    • Passage for aorta (T12)
  4. Other Openings:
    • Ascending lumbar veins, splanchnic nerves (greater, lesser, least), left/right phrenic nerves, sympathetic trunk

Arterial Supply of the Thoracic Region

Posterior Thoracic Arterial Supply

  • Posterior Intercostal Arteries:
    • Supplied by:
    • Intercostal spaces 1-3 from superior intercostal artery (from costocervical trunk, subclavian artery)
    • Intercostal spaces 3-11 from descending thoracic aorta
    • Includes 9 pairs of posterior intercostal arteries and 1 pair of subcostal arteries

Anterior Thoracic Arterial Supply

  • Anterior Intercostal Arteries:
    • Supplied by:
    • Subclavian artery
    • Internal thoracic artery

Venous Drainage

  • Venous Drainage Includes:
    • Intercostal veins, which accompany intercostal arteries and nerves
  • Types of Veins:
    • 11 posterior intercostal veins
    • 1 subcostal vein
    • Right: Supplies blood to superior intercostal vein leading to the superior vena cava (SVC)
    • Rest on the right: Lead into the azygos vein leading to SVC
    • Left: Utilizes accessory hemiazygos and hemiazygos veins, which lead to the azygos vein

Clinical Anatomy

Chest Pain Overview

  • Definition: Pain or discomfort in the chest, typically at the front.
  • Classification: Broadly classified into cardiac, possible cardiac, or non-cardiac.
  • Description of Pain:
    • Can be sharp, dull, pressure-like, heavy, or squeezing.
  • Associated Symptoms:
    • Pain in the shoulder, arm, upper abdomen, or jaw; nausea, sweating, shortness of breath.

Causes of Chest Pain

  • Life-Threatening Causes:

    • Pulmonary Embolus
    • Tension Pneumothorax
    • Aortic Dissection
    • Acute Myocardial Infarction / Angina
    • Oesophageal Rupture

  • Other Causes:

    • Shingles, Oesophageal spasm, Cervical spondylosis, Rib fracture, Pericarditis, Pneumonia, Cholecystitis, Bone metastasis, Costochondritis, Pleurisy, Empyema, Gastroesophageal Reflux Disease (GERD), Ulcers, Sickle cell crisis, Pancreatitis.

Spinal Nerves

  • Structure: Spinal grey matter shaped like a fluted column; appears butterfly-shaped in cross-section.
  • Components include:
    • Somatic Afferent
    • Splanchnic Afferent (GVA)
    • Splanchnic (Visceral) Efferent Fibres
    • Somatic Efferent
    • Postganglionic Fibre
    • Preganglionic Fibre

Ascending and Descending Tracts

  • Ascending Tracts:

    • Include the Dorsal Fasciculus Gracilis, Fasciculus Cuneatus, Posterior Spinocerebellar Tract, Anterior Spinocerebellar Tract, Lateral Spinothalamic Tract, Anterior Spinothalamic Tract.

  • Descending Tracts:

    • Include Lateral Reticulospinal Tract, Lateral Corticospinal Tract, Rubrospinal Tract, Medial Reticulospinal Tract, Anterior Corticospinal Tract, Vestibulospinal Tract, Tectospinal Tract.

Angina Pectoris

  • Symptoms involve visceral sympathetic pathway activation, with pain fibres stimulating sensory fibres following sympathetic fibres towards the spinal cord (T1-T4/5).
  • Pain can radiate as far as C8-T9, shared with somatic afferents, complicating diagnosis.
  • Density of visceral innervation is less compared to somatic innervation, leading to less precise pain differentiation.

Differential Diagnosis for Chest Pain

  • Cardiac: Myocardial infarction, Angina pectoris, Pericarditis
  • Vascular: Aortic dissection, Pulmonary embolus
  • Respiratory: Pneumonia, Pneumothorax
  • Gastrointestinal: Esophagitis, Peptic ulcer, Biliary disease
  • Musculoskeletal: Costochondritis, Rib fractures
  • Neurological: Herpes zoster

Myocarditis Criteria

  • Diagnosed based on symptoms and imaging evidence. Confirmed by histopathological evidence.

Chest Drain (Intercostal Drainage) Overview

  • Definition: A chest tube, or thoracostomy tube, is a flexible tube inserted through the chest wall into the pleural space.
  • Indications: Used to create negative pressure in the chest cavity, allowing lung re-expansion, and for removing air, blood, fluid, chyle, or purulence from the pleural space – particularly in a tension pneumothorax situation, a life-threatening emergency.
  • Chest Tube Placement: Requires knowledge of the “Safe Triangle” to avoid complications and must consider patient comfort due to pain associated with placement.