Intercostal nerve

Intercostal nerves are branches of the anterior rami of the thoracic spinal nerves which arise from T1 to T11 (first to eleventh) thoracic spinal segments. Please note that the twelfth thoracic spinal nerve (T12) it not a pure intercostal nerve, as it runs underneath the twelfth rib and enters the abdominal wall. It is therefore, referred to as the subcostal nerve.

Each intercostal nerve is part of a neurovascular bundle, which comprises of an intercostal vein, artery and nerve. The neurovascular bundle runs inside the subcostal groove situated along the lower margin of each rib. Hence, when performing a pleural tap, one needs to ensure that the chest tube is inserted into the intercostal space, along the upper border of the lower rib, and NOT along the lower border of the upper rib. This is to minimize the risk of injury to the intercostal nerve, or intercostal vessels during the pleural tap.

While coursing through the subcostal groove the intercostal nerve and vessels are bounded by internal intercostal muscle on the outside and innermost intercostal muscle on the inside.

The intercostal nerves are divided into typical and atypical categories. Typical intercostal nerves range from third to sixth and remain confined to their respective intercostal spaces within the thoracic wall. A typical intercostal nerve gives off several branches, including:

• Gay and white rami communicantes (connecting with the sympathetic trunk),

• Muscular branches (innervating intercostal muscles and thoracic wall muscles),

• Collateral branch (running along the superior border of the lower rib, innervating intercostal muscles, parietal pleura and periosteum of the rib),

• Lateral and anterior cutaneous branches (providing sensory innervation to skin of lateral and anterior thoracic walls, respectively),

On the contrary, the atypicals include the first two intercostal nerves and the seventh to eleventh intercostal nerves. Unlike the typical intercostal nerves, these innervate other body regions as well. For instance, the first intercostal nerve contributes to the brachial plexus. It lacks anterior and lateral cutaneous branches. The second intercostal nerve gives off an additional intercostobrachial branch that provides cutaneous innervation to the floor of axilla. It is responsible for the referred ischemic cardiac pain in the axilla and upper proximal arm region. The seventh to eleventh atypical intercostal nerves also innervate anterior abdominal wall muscles and are called thoracoabdominal nerves.