Topography of chest wall (draw scheme of intercostal space)

Introduction

The chest wall forms the protective outer boundary of the thoracic cavity and plays a critical role in respiration and protection of vital thoracic organs such as the heart and lungs. Understanding its layered structure and neurovascular components—especially within the intercostal spaces—is essential for safe and effective clinical procedures, including thoracentesis, chest tube insertion, and regional anesthesia.

1. General Topography of the Chest Wall

Boundaries of the Chest Wall

• Anteriorly: Sternum (manubrium, body, xiphoid process) and costal cartilages
• Posteriorly: Thoracic vertebrae (T1–T12)
• Laterally: Ribs and intercostal muscles
• Superiorly: Thoracic inlet
• Inferiorly: Diaphragm (separates thoracic cavity from abdominal cavity)

Bony Framework

• 12 thoracic vertebrae
• 12 pairs of ribs
  • Ribs 1–7: True ribs (directly attach to sternum via costal cartilage)
  • Ribs 8–10: False ribs (attach indirectly via the cartilage of rib 7)
  • Ribs 11–12: Floating ribs (do not attach to sternum)

2. Intercostal Spaces

Intercostal spaces are the anatomical intervals between adjacent ribs. There are 11 intercostal spaces on each side.

Contents of Each Intercostal Space

1. Muscular layers
2. Neurovascular bundle
3. Connective tissue and fat

Muscular Layers (External to Internal)

1. External intercostal muscles
   • Fiber direction: downward and forward (“hands in pockets”)
   • Function: elevate ribs during inspiration
3. Internal intercostal muscles
   • Fiber direction: downward and backward
   • Function: depress ribs during forced expiration
5. Innermost intercostal muscles
   • Separated from internal intercostals by intercostal vessels and nerve

3. Intercostal Neurovascular Bundle

Each intercostal space contains a neurovascular bundle that runs in the costal groove located on the inferior border of the rib above. The components of this bundle, arranged from superior to inferior, follow the order: Vein, Artery, Nerve (commonly remembered as VAN).

• Intercostal vein: This is the most superior component within the bundle. It is responsible for venous drainage of the intercostal space and typically drains into the azygos or hemiazygos system (posteriorly) or into the internal thoracic vein (anteriorly).
• Intercostal artery: Found just below the vein, the artery supplies the intercostal muscles, overlying skin, and parietal pleura. Each intercostal space usually contains a posterior intercostal artery, which arises from the thoracic aorta, and anterior intercostal branches, which come from the internal thoracic artery (a branch of the subclavian artery).
• Intercostal nerve: This is the most inferior element of the neurovascular bundle and is the anterior ramus of a thoracic spinal nerve (T1–T11). It provides motor innervation to the intercostal muscles and sensory innervation to the skin and parietal pleura.

Additionally, collateral branches of the nerve and vessels may run near the superior border of the rib below. This is clinically significant because during procedures like thoracentesis, the needle is inserted just above the upper edge of the lower rib to avoid damaging the main neurovascular bundle that lies in the costal groove of the upper rib.

4. Clinical Relevance

Thoracentesis

• Performed to remove pleural fluid
• Needle inserted above the superior border of the rib below (to avoid main neurovascular bundle)
• Usually done in 7th–9th intercostal space, posterior axillary line

Intercostal Nerve Block

• Local anesthetic is injected around the intercostal nerve
• Needle must pass through skin, subcutaneous tissue, external, internal, and possibly innermost intercostal muscles

Chest Tube Insertion

• Done in mid-axillary line, usually at the 5th intercostal space
• Tube passed above the rib to avoid damaging VAN

5. Diagram – Cross-section of Intercostal Space

Skin

↓

Superficial fascia

↓

External intercostal muscle

↓

Internal intercostal muscle

↓

--> VAN (Vein - Artery - Nerve) in costal groove

↓

Innermost intercostal muscle

↓

Endothoracic fascia

↓

Parietal pleura

↓

Pleural cavity

↓

Visceral pleura

↓

Lung

Note: Neurovascular bundle is located between internal and innermost intercostal muscles.

References

1. Paulsen, F., Waschke, J. Sobotta Atlas of Human Anatomy, Vol. 2, 16th ed. Elsevier.
2. Drake, R.L., Vogl, A.W., Mitchell, A.W.M. Gray’s Anatomy for Students, 4th ed. Elsevier.
3. Moore, K.L., Dalley, A.F., Agur, A.M.R. Clinically Oriented Anatomy, 8th ed. Wolters Kluwer.