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Inter costal nerve

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Intercostal Nerves

Origin

The intercostal nerves are the anterior rami of thoracic spinal nerves T1 to T11. They lie in the intercostal spaces between adjacent ribs. The anterior ramus of T12 (the subcostal nerve) runs inferior to rib XII and is not technically an intercostal nerve, though it is closely related.
  • Gray's Anatomy for Students, p. 193-195

Course and Position in the Intercostal Space

Each nerve runs in the subcostal groove on the inferior (inner) surface of its corresponding rib, between the internal intercostal muscle and the innermost intercostal muscle. The neurovascular bundle arrangement from top to bottom is:
V - A - N (Vein, Artery, Nerve)
The nerve is the most inferior structure in the groove.
Intercostal Nerves - Branches and Course
Fig. 3.33 Intercostal Nerves - Gray's Anatomy for Students

Fiber Types Carried

Each intercostal nerve carries three types of fibers:
  1. Somatic motor - to muscles of the thoracic wall (intercostal, subcostal, and transversus thoracis)
  2. Somatic sensory - from skin and parietal pleura
  3. Postganglionic sympathetic fibers - to the periphery

Branches of a Typical Intercostal Nerve

BranchOriginDistribution
Lateral cutaneous branchMid-axillary lineDivides into anterior and posterior branches; supplies overlying skin of the trunk
Anterior cutaneous branchTerminal branchEmerges parasternally (or anteriorly on abdominal wall); supplies anterior chest/abdominal skin
Small collateral branchWithin intercostal spaceRuns along the superior border of the lower rib

Segmental Landmarks (Dermatomes)

LevelSurface landmark
T4Nipple line
T6Xiphoid process
T10Umbilicus
T12Suprapubic/inguinal
Innervation of the Anterior Abdominal Wall by Intercostal Nerves (T6-T12)
Innervation of the anterior abdominal wall - Gray's Anatomy for Students

Special/Atypical Intercostal Nerves

  • T1 - Most of the anterior ramus contributes to the brachial plexus (C5-T1). Only a small branch enters the first intercostal space.
  • T2 (intercostobrachial nerve) - The lateral cutaneous branch of T2 crosses the axilla and supplies the medial surface of the upper arm. This is important in breast/axillary surgery as it is often sacrificed, causing sensory loss in the axilla and inner arm.
  • T7-T11 - Follow the inferior slope of the lateral ribs and cross the costal margin to enter the abdominal wall, supplying muscles and skin there.
  • T12 (subcostal nerve) - Travels below rib XII to supply the abdominal wall and iliac skin.

Neurovascular Bundle - Ultrasound View

The intercostal neurovascular bundle lies deep to the external and internal intercostal muscle layers, and superficial to the innermost intercostal muscle:
Ultrasound of Intercostal Neurovascular Bundle
Ultrasound-guided intercostal nerve block - Morgan & Mikhail's Clinical Anesthesiology, 7e

Clinical Applications

1. Chest Tube Insertion

Always insert at the upper margin of a rib to avoid the neurovascular bundle (vein, artery, nerve) that runs in the subcostal groove. The recommended site is the 7th-8th intercostal space, posterior axillary line, for pleural effusion.
  • THIEME Atlas of General Anatomy, p. 228

2. Intercostal Nerve Block

Used for analgesia in:
  • Rib fractures
  • Post-thoracotomy pain
  • Tube thoracostomy
  • Mastectomy/upper abdominal surgery
  • Herpes zoster (shingles) affecting the chest wall
Technique: Needle inserted at the rib angle (~6 cm lateral to midline), advancing to the subcostal groove with the needle angled cephalad at 10-15 degrees. Deposit 2-5 mL of local anesthetic. Blocking posterior to the mid-axillary line ensures coverage of both the lateral cutaneous and anterior branches.
Intercostal Nerve Block - Area of Anesthesia (T3-T12)
Area of anesthesia with intercostal nerve blocks (anterior and posterior views) - Roberts & Hedges' Clinical Procedures in Emergency Medicine
Duration: 8-18 hours with long-acting local anesthetic (e.g., bupivacaine)
Complications:
  • Pneumothorax (~8-9% cumulative, ~1.4% per individual block)
  • Intravascular injection (arterial or venous puncture)
  • Parietal pleural puncture

3. Lateral Thoracotomy

Division of thoracic wall muscles causes significant postoperative pain; intercostal nerves (particularly lateral cutaneous branches) are at risk during thoracotomy incisions.

4. Breast Innervation

The nipple is innervated by the 4th intercostal nerve (T4). Innervation of the breast overall is via anterior and lateral cutaneous branches of T2-T6.

5. Intercostobrachial Nerve (T2)

Commonly divided during axillary lymph node dissection for breast cancer, resulting in numbness/dysesthesia of the axilla and medial arm. Surgeons attempt to preserve it when possible.
Sources:
  • Gray's Anatomy for Students, pp. 193-197
  • Morgan & Mikhail's Clinical Anesthesiology, 7e
  • Tintinalli's Emergency Medicine, p. 287
  • Roberts & Hedges' Clinical Procedures in Emergency Medicine
  • THIEME Atlas of General Anatomy and Musculoskeletal System, p. 228
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