Anatomy

Anatomy

1. The thoracic spinal nerves exit from the intervertebral foramina and divide into dorsal and ventral rami. The ventral rami become the intercostal nerves, which travel within the intercostal spaces below the inferior border of the superior rib and innervate the thoracic and abdominal walls. All intercostal nerves except for T1 give off a lateral cutaneous branch, which innervates the lateral chest. The anterior cutaneous branches of intercostal nerves T2-5 provide sensory innervation to the medial breast, and the lateral cutaneous branches innervate the lateral breast, while the supraclavicular nerve innervates the superior pole of the breast. Other nerves that contribute to breast innervation are lateral and medial pectoral, long thoracic, intercostobrachial (which innervates the axilla and axillary tail of the breast), and thoracodorsal nerves (Figure 21.3).
   

   Figure 21.16 Thoracic paravertebral block with transverse approach using ultrasound guidance.

   A, The two-sided arrow shows the placement of the US probe. B, The PVS is located ventral to the superior costotransverse ligament (yellow arrows) and posterior to the TP. The blue arrows show the needle approaching the PVS, and the white arrows designate the pleura. ESM, erector spinae muscle; PVS, paravertebral space; TP, transverse process.

2. The thoracic paravertebral space (TPVS) is a wedge-shaped space that exists on both sides of the thoracic vertebra and is limited anterolaterally by the pleura, medially by vertebra, and posteriorly by the superior costotransverse ligament (SCTL). It contains the ventral and dorsal rami, sympathetic chain, and intercostal vessels.
3. The intercostal nerves arising from T6-11 ultimately terminate in the anterolateral abdominal wall and are known as the thoracoabdominal nerves. The ventral ramus of T12 is known as the subcostal nerve and travels entirely in the abdominal wall. The anterior abdominal wall receives sensory innervation from the ventral rami of the T6-L1 spinal nerves. The terminal branches of these nerves travel through the lateral abdominal wall within the transversus abdominis plane (TAP), the fascial plane between the internal oblique muscle (IOM) and the transversus abdominis muscle (TAM), and generate a plexus. The upper T6-9 segmental nerves exit the intercostal space and enter the TAP lateral to the linea alba. The anterior cutaneous branches of the thoracoabdominal nerves enter the rectus muscle and sheath lateral to the linea semilunaris and form a plexus with each other. The presence of both TAP and rectus sheath plexuses explains why the precise dermatomal map may not be accurate. The L1 nerve divides into iliohypogastric and ilioinguinal nerves (see Section VIII.A.1).