What are intercostal spaces and what do they contain?

Intercostal spaces are the gaps between adjacent ribs and their costal cartilages, with 11 on each side. In a typical space (like the 3rd–6th), they contain three muscle layers (external, internal, and innermost intercostals), a neurovascular bundle (vein, artery, nerve in VAN order), and lymphatic vessels and nodes.

What are the functions of the intercostal muscles?

The intercostal muscles support the thoracic wall and aid in respiration. External intercostals elevate ribs during inspiration, internal intercostals act during expiration, and innermost intercostals have a similar function and lie deepest. All are supplied by the intercostal nerve of the corresponding space.

What is the neurovascular bundle in intercostal spaces, and where is it located?

The neurovascular bundle consists of the intercostal vein, artery, and nerve arranged in VAN order from top to bottom. It is located between the internal and innermost intercostal muscle layers, running along the costal groove of the rib.

How are intercostal nerves classified, and what are their atypical features?

Intercostal nerves are anterior primary rami of thoracic spinal nerves T1–T11 (T12 is the subcostal nerve). Typical nerves (T3–T6) stay in the intercostal space, while atypical ones include T1 (mostly to brachial plexus), T2 (gives intercostobrachial nerve), and T7–T11 (extend as thoracoabdominal nerves into the abdomen).

What are the sources of intercostal arteries?

Intercostal arteries come from two main sources. Posterior intercostal arteries: 1st and 2nd from the superior intercostal artery, 3rd–11th from the descending thoracic aorta. Anterior intercostal arteries: in the first 9 spaces, from the internal thoracic artery (1st–6th) and musculophrenic artery (7th–9th). They anastomose at costochondral junctions.

How do intercostal veins drain, and why is this important?

Intercostal veins drain differently based on location. Anterior intercostal veins: two in each of the first 9 spaces, draining into the internal thoracic vein (1st–6th) or musculophrenic vein (7th–9th). Posterior intercostal veins: one per space, draining into the azygos vein (right side), accessory hemiazygos (left upper spaces), or hemiazygos vein (left lower spaces). This is important for venous return in the thorax.

What is the clinical significance of the posterior intercostal artery?

The posterior intercostal artery crosses ribs obliquely, so it must be avoided during procedures like paracentesis thoracis (thoracentesis) to prevent injury and bleeding. This artery is a branch of the descending thoracic aorta for spaces 3–11.

Intercostal Spaces – Muscles, VAN Bundle & Clinical

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