veins

Intercostal Veins

1. Anterior Intercostal Veins:

   - Description: Nine pairs (two in each space), formed by venae comitantes of the internal thoracic artery.

   - Connections:

     - The 7th, 8th, and 9th anterior intercostal veins end in the musculophrenic vein.

     - The upper six anterior intercostal veins end in the internal thoracic vein.

   - Internal Thoracic Vein:

     - Formed by the union of the superior epigastric vein and the musculophrenic vein.

     - Drains into the brachiocephalic (innominate) vein.

2. Posterior Intercostal Veins:

   - Right Side:

     - The 1st right posterior intercostal vein ends in the right innominate vein.

     - The 2nd, 3rd, and 4th right posterior intercostal veins form the right superior intercostal vein, which ends in the arch of the azygos vein.

     - The 5th to 11th right posterior intercostal veins, along with the right subcostal vein, end in the azygos vein.

   - Left Side:

     - The 1st left posterior intercostal vein ends in the left innominate vein.

     - The 2nd, 3rd, and 4th left posterior intercostal veins form the left superior intercostal vein, which ends in the left innominate vein.

     - The 5th to 8th left posterior intercostal veins end in the superior hemiazygos (accessory hemiazygos) vein.

     - The 9th to 11th left posterior intercostal veins, along with the left subcostal vein, end in the inferior hemiazygos (hemiazygos vein).

   - Both hemiazygos veins cross the midline from left to right to end in the azygos vein.

Azygos Vein

- Location: Present only on the right side.

- Origin: Union of the right subcostal vein and the right ascending lumbar vein at the level of the T12 vertebra, or from the posterior aspect of the inferior vena cava.

- Course: Enters the thorax via the aortic opening of the diaphragm opposite the T12 vertebra on the right side of the aorta and thoracic duct, ascends in the posterior mediastinum in front of the vertebral column and behind the esophagus and root of the right lung, then ascends in the superior mediastinum and arches above the root of the right lung.

- Termination: Drains into the back of the superior vena cava at the level of the angle of Louis opposite the 2nd right costal cartilage.

- Tributaries:

  1. Right ascending lumbar vein

  2. Right subcostal vein

  3. Right posterior intercostal veins from the 5th to 11th

  4. Right superior intercostal vein (in the arch)

  5. Right bronchial veins (from the right lung)

  6. Hemiazygos veins

  7. Pericardial and esophageal veins

  8. Mediastinal veins

Hemiazygos Vein

- Superior Hemiazygos:

  - Course: Courses the posterior mediastinum on the left side, crossing the midline at the level of the T8 vertebra behind the aorta, esophagus, and thoracic duct, and terminates in the azygos vein at the level of T8.

  - Tributaries: 5th to 8th left posterior intercostal veins and left bronchial veins from the left lung.

- Inferior Hemiazygos:

  - Origin: Union of the left subcostal vein and left ascending lumbar vein.

  - Course: Enters the thorax by piercing the left crus of the diaphragm to ascend in the posterior mediastinum, crossing the midline at the level of the T12 vertebra behind the aorta, esophagus, and thoracic duct.

  - Termination: Terminates in the azygos vein at the level of T8.

  - Tributaries: 9th to 11th left posterior intercostal veins, mediastinal and esophageal veins.

Intercostal Nerves

- Location: Lies in the lower part of the costal groove (caudally to the intercostal vessels).

- Anterior (ventral) ramus of the 12 thoracic nerves.

  - The last one (T12) is known as the subcostal nerve.

  - The upper 11 are known as intercostal nerves.

- Classification:

  1. Typical (T3 to T6): Supply the thoracic wall only.

  2. Atypical:

     - T1: Supplies the upper limb.

     - Lower six thoracic nerves (T7 to T12): Supply the abdominal wall.

- Branches of Typical ICN:

  1. Communicating branches with the sympathetic trunk.

  2. Muscular branches to the intercostal muscles, divided into anterior and posterior branches.

  3. Lateral cutaneous branches: Supply the skin on the lateral thoracic wall.

  4. Anterior cutaneous branches: Supply the skin of the front.

  5. Collateral branches: Supply intercostal muscles, parietal pleura, and periosteum of the ribs.

- Branches of Atypical Nerves:

  - T1 Nerve (1st ICN):

    1. Large branch: Ascends in front of the neck of the first rib to join the brachial plexus.

    2. Small branch: Forms the 1st ICN which has no lateral and anterior cutaneous branches.

  - T2 Nerve (2nd ICN): The lateral cutaneous branch does not divide and supplies the floor of the axilla and the upper part of the medial side of the arm, known as the intercostobrachial nerve.

  - Lower 5 ICN (T7 to T11): Supply the intercostal muscles, muscles, and skin of the anterior abdominal wall.

  - T12 Nerve (subcostal Nerve): Passes below the last rib to supply the anterior abdominal wall only.

Clinical Notes:

- Stab wounds through the posterior parts of intercostal spaces are more dangerous than the lateral parts because the intercostal nerves in the posterior part run in the middle of the space but as they pass laterally and forwards, they become protected by the costal groove.

- The safe site for needle puncture is in the lateral parts of intercostal spaces to avoid injury to the posterior intercostal nerves and vessels.

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