Intercostal nerves

Nervi intercostales

Also known as: thoracic ventral rami, T1–T11, subcostal nerve, thoracoabdominal nerves, intercostobrachial nerve

The ventral rami of T1–T11, which run in the intercostal spaces and supply the intercostal muscles, the skin of the chest wall and, through the lower nerves (T7–T11), the anterior abdominal wall. T12, below the 12th rib, is the subcostal nerve. Unlike other ventral rami, they do not form plexuses.

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Overview

Number11 pairs intercostal + 1 subcostal

Order in costal grooveVein–Artery–Nerve (VAN), superior to inferior

Key dermatomesT4 nipple; T10 umbilicus; T12/L1 inguinal ligament

Thoracoabdominal nervesT7–T11

Each intercostal nerve is the ventral ramus of a thoracic spinal nerve. It passes from the intervertebral foramen into its intercostal space and runs in the costal groove on the inferior border of the rib above. It lies between the internal and innermost intercostal muscles, at the bottom of the neurovascular bundle, below the intercostal vein and artery (VAN, from superior to inferior). Its branches are:
• a collateral branch, which runs along the upper border of the rib below;
• muscular branches;
• a lateral cutaneous branch at about the mid-axillary line;
• an anterior cutaneous branch near the sternum, or near the midline of the abdomen for the lower nerves.

The typical intercostal nerves (T3–T6) stay within the thorax. The atypical nerves are:
• T1: most of it joins the brachial plexus.
• T2: its lateral cutaneous branch forms the intercostobrachial nerve to the medial upper arm.
• T7–T11: the thoracoabdominal nerves, which leave the intercostal spaces and run between internal oblique and transversus abdominis to supply the abdominal wall muscles, rectus abdominis and the overlying skin and parietal peritoneum.

The subcostal nerve (T12) runs below the 12th rib. Each nerve receives a grey ramus communicans from the sympathetic trunk, which carries sympathetic fibres to the sweat glands and vessels of its dermatome.

Location: Intercostal spaces, in the costal groove between the internal and innermost intercostal muscles; T7–T11 continue into the anterolateral abdominal wall.

Anatomy

Innervation: - Motor: intercostal muscles, subcostales, transversus thoracis, serratus posterior, and (T7–T12) the anterolateral abdominal muscles (external and internal oblique, transversus abdominis, rectus abdominis).
• Sensory: the skin of the thoracic and abdominal walls in a dermatomal pattern, the parietal pleura, the peripheral diaphragm (T6/7–T11) and the parietal peritoneum.
Nerve roots: Ventral rami of T1–T11 (intercostal) and T12 (subcostal).
Course: Intervertebral foramen → posterior intercostal space (between the pleura and the internal intercostal membrane) → costal groove between the internal and innermost intercostals (lowest of the VAN bundle) → lateral cutaneous branch at the mid-axillary line → anterior cutaneous branch at the parasternal line. T7–T11 pass deep to the costal cartilages into the abdominal wall between internal oblique and transversus abdominis → pierce the rectus sheath.
Branches: Rami communicantes (to and from the sympathetic trunk), collateral branch, muscular branches, lateral cutaneous branch (the intercostobrachial nerve from T2), anterior cutaneous branch, and branches to the parietal pleura and, for T7–T11, the parietal peritoneum.
Relations: Each nerve lies below the posterior intercostal artery and vein in the costal groove, between the internal and innermost intercostal muscles, superficial to the parietal pleura (endothoracic fascia).

Function

Motor control of the intercostal muscles for breathing (elevation and depression of the ribs, stiffening of the chest wall)
Motor supply of the anterior abdominal wall (forced expiration, coughing, abdominal pressure)
Segmental sensation of the trunk (dermatomes T1–T12)
Sensation of the parietal pleura and peritoneum (sharp, well-localised pain)

Clinical significance

Thoracocentesis and chest drains

Because the neurovascular bundle lies in the costal groove under the rib above, needles and drains are inserted just above the upper border of the rib below. Chest drains go in the "triangle of safety", usually the 5th intercostal space in the mid-axillary line. An intercostal nerve block is placed at the angle of the rib, proximal to the lateral cutaneous branch, to anaesthetise the whole space, for example for rib fractures.

Herpes zoster (shingles)

Varicella-zoster virus reactivates in a dorsal root ganglion and spreads along one nerve. It produces a painful vesicular rash in a single thoracic dermatome that does not cross the midline. Thoracic dermatomes are the most commonly affected. Post-herpetic neuralgia is a common sequel in older patients.

Referred pain and the intercostobrachial nerve

Landmarks: T4 is the nipple and T10 the umbilicus. Cardiac pain can be referred to the medial arm through T1–T2, the intercostobrachial nerve. Lower intercostal irritation (pleurisy, rib fracture) can mimic abdominal pain. The intercostobrachial nerve is often injured in axillary node clearance, causing numbness of the medial upper arm.

Mnemonics

Neurovascular bundle

"VAN", from top to bottom: Vein, Artery, Nerve. The nerve is the least protected by the costal groove.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.