Prevertebral and Paravertebral Regions

INTRODUCTION

• The prevertebral region extends from the base of the skull to approximately the T2 vertebral level.
• The paravertebral region lies on either side of the prevertebral region and extends from the transverse process of C1 to the first rib.

Prevertebral Region

It contains the following structures:

1. Prevertebral muscles:
   • Rectus capitis anterior.
   • Rectus capitis lateralis.
   • Longus colli (longus cervicis).
   • Longus capitis.
2. Vertebral arteries: First and second parts.
3. Joints: Cervical vertebral joints and adjoining craniovertebral joints.

Paravertebral Region

It contains the following structures:

1. Scalene muscles: Scalenus anterior, scalenus medius, and scalenus posterior.
2. Cervical plexus: Its roots and branches.
3. Phrenic nerve: It descends over the anterior surface of scalenus anterior.
4. Cervical pleura: It covers the apex of the lung at the root of the neck.

PREVERTEBRAL (ANTERIOR VERTEBRAL) MUSCLES

• The prevertebral muscles lie anterior to the cervical vertebral column.
• They include four muscles:
  • Rectus capitis anterior.
  • Rectus capitis lateralis.
  • Longus colli (longus cervicis).
  • Longus capitis.

General Features

• Fascial covering: These muscles are covered by the prevertebral layer of deep cervical fascia.
• Actions: They mainly flex and stabilise the head and cervical vertebral column. Rectus capitis lateralis assists in lateral flexion and stabilisation of the atlanto-occipital joint.
• Nerve supply: They receive motor fibres from the anterior (ventral) rami of cervical spinal nerves.

PARAVERTEBRAL MUSCLES

– The paravertebral region contains three scalene muscles:

1. Scalenus anterior.
2. Scalenus medius.
3. Scalenus posterior.

General Features

• Attachments: The scalene muscles extend from the cervical transverse processes to the upper two ribs. Scalenus anterior and medius attach to the first rib, whereas scalenus posterior attaches to the second rib.
• Actions: They produce lateral flexion of the cervical spine and elevate the upper ribs during forced inspiration.
• Fascial covering: They are covered anteriorly by the prevertebral fascia.
• Nerve supply: They receive branches from the anterior (ventral) rami of cervical spinal nerves, mainly C3–C8, with variations among individual muscles.
• Size: Scalenus medius is the largest, whereas scalenus posterior is the smallest of the three muscles.

SCALENUS MINIMUS

• Scalenus minimus is a small, rudimentary muscle that is occasionally present in the lower neck.
• Origin: It arises from the anterior aspect of the transverse process of C7.
• Insertion: It attaches to the inner border of the first rib, behind the groove for the subclavian artery, and blends with the cervical pleura or its fascial covering.
• Suprapleural membrane: Also called Sibson’s fascia, it is a thickening of the prevertebral fascia covering the apex of the lung. It may blend with fibres of scalenus minimus.

SCALENE TRIANGLE

– The scalene (interscalene) triangle is a narrow triangular space between scalenus anterior and scalenus medius.

Boundaries

• Anteriorly: Scalenus anterior.
• Posteriorly: Scalenus medius.
• Inferiorly (base): First rib.

Contents

1. Subclavian artery (second part).
2. Three trunks of the brachial plexus.

Note: The subclavian vein passes anterior to scalenus anterior and does not traverse the interscalene triangle.

SCALENOVERTEBRAL TRIANGLE

– The scalenovertebral triangle, also called the triangle of the vertebral artery, is a paired triangular space situated at the root of the neck.

Boundaries

• Medially: Lower oblique part of longus colli.
• Laterally: Scalenus anterior.
• Apex: Transverse process of C6.
• Base: First part of the subclavian artery.

Floor (Posterior Wall)

1. Transverse process of C7.
2. Ventral ramus of C8 spinal nerve.
3. Neck of the first rib.
4. Cervical pleura covering the apex of the lung.

Roof (Anterior Wall)

– Carotid sheath and its contents.

Contents

1. First part of the vertebral artery and accompanying vertebral vein.
2. Thyrocervical trunk.
3. Inferior thyroid artery.
4. Cervical sympathetic trunk and stellate ganglion.
5. Thoracic duct on the left side.
6. Ansa subclavia.

Important Anatomical Relations

• Vertebral artery: Its first part ascends vertically from the subclavian artery towards the transverse foramen of C6.
• Sympathetic trunk: It lies posterior to the carotid sheath and in close relation to the vertebral artery.
• Ansa subclavia: It is a sympathetic nerve loop connecting the middle and inferior cervical sympathetic ganglia. Its fibres pass around the subclavian artery.
• Thoracic duct: Its terminal portion arches through the root of the neck on the left side before draining near the left venous angle.

CERVICAL PLEXUS

– The cervical plexus is a network of nerves formed by the anterior rami of the upper four cervical spinal nerves (C1–C4).

Formation

• The anterior rami of C1–C4 are interconnected by three nerve loops.
• The first loop curves forwards near the transverse process of the atlas, while the second and third loops are directed backwards.

Position and relations

• Anteriorly: Prevertebral fascia, internal jugular vein, and sternocleidomastoid.
• Posteriorly: Levator scapulae and scalenus medius.

Branches

The cervical plexus gives superficial (cutaneous) and deep branches.

A. Superficial Branches

These branches provide cutaneous sensation to the head, neck, and shoulder region.

1. Lesser occipital nerve (C2): It supplies the skin behind the auricle and over the lateral occipital region.
2. Great auricular nerve (C2–C3): It supplies the skin over the parotid region, angle of mandible, and lower part of the auricle.
3. Transverse cervical nerve (C2–C3): It supplies the skin over the anterior region of the neck.
4. Supraclavicular nerves (C3–C4): They supply the skin over the clavicle, shoulder, and upper anterior chest wall.

B. Deep Branches

1. Communicating Branches

• Sympathetic communications: Grey rami communicantes connect the cervical plexus with the cervical sympathetic trunk.
• Hypoglossal nerve: C1 fibres accompany the hypoglossal nerve and contribute to the supply of geniohyoid, thyrohyoid, and infrahyoid muscles.
• Accessory nerve: Fibres from C2–C3 communicate with the nerve supplying sternocleidomastoid, whereas C3–C4 fibres communicate with the nerve supplying trapezius.

2. Muscular Branches

• Rectus capitis anterior: C1–C2.
• Rectus capitis lateralis: C1–C2.
• Longus capitis: C1–C3.
• Longus colli: Anterior rami of cervical spinal nerves.

3. Indirect Muscular Branches

• Ansa cervicalis (C1–C3): It supplies sternohyoid, sternothyroid, and omohyoid.
• Accessory nerve communications (C2–C4): They contribute mainly proprioceptive fibres to sternocleidomastoid and trapezius.
• Phrenic nerve (C3–C5): It provides motor innervation to the diaphragm.

Note: The dorsal scapular nerve (mainly C5) arises from the brachial plexus and supplies levator scapulae and rhomboid muscles. It is not a branch of the cervical plexus.

PHRENIC NERVE

• The phrenic nerves are paired mixed peripheral nerves supplying the diaphragm.
• Root value: C3, C4, and C5, with C4 providing the major contribution.
• They provide the principal motor supply to the diaphragm and sensory innervation to adjoining serous membranes.

Functional components

1. Motor Fibres

– They supply the corresponding halves of the diaphragm.

2. Sensory Fibres

• Proprioceptive fibres: They convey information from the diaphragm.
• General sensory fibres: They supply the fibrous and parietal serous pericardium, mediastinal pleura, central diaphragmatic pleura, and central diaphragmatic peritoneum.

3. Sympathetic Fibres

– They accompany the nerve and contribute to vasomotor regulation.

Formation

– Each phrenic nerve arises mainly from the anterior ramus of C4, with contributions from C3 and C5.

Course

• The nerve emerges near the lateral border of scalenus anterior and descends obliquely across its anterior surface.
• At the root of the neck, it passes posterior to the subclavian vein and anterior to the subclavian artery.
• It enters the thorax and descends through the superior and middle mediastina, between the mediastinal pleura and fibrous pericardium.
• Both phrenic nerves pass anterior to the roots of the lungs and reach the diaphragm.

Right Phrenic Nerve

• It descends along the right side of the superior vena cava and fibrous pericardium.
• It reaches the diaphragm near the inferior vena cava and usually passes through or adjacent to the caval opening at T8.
• It supplies mainly the right half of the diaphragm.

Left Phrenic Nerve

• It crosses the arch of aorta and descends along the left surface of the fibrous pericardium.
• It pierces the muscular part of the left dome of the diaphragm.
• It supplies mainly the left half of the diaphragm.

Relations in the neck

Anteriorly

1. Skin, superficial fascia, and platysma.
2. Investing layer of deep cervical fascia.
3. Sternocleidomastoid.
4. Inferior belly of omohyoid.
5. Internal jugular vein.
6. Subclavian vein.
7. Thoracic duct on the left side, near the root of the neck.

Posteriorly

– Scalenus anterior muscle.

Branches and Distribution

• Each phrenic nerve divides near the diaphragm into anterior and posterior branches, with further medial and lateral subdivisions.
• These branches enter the diaphragm mainly from its inferior surface.
• Right phrenic nerve: It supplies the right hemidiaphragm and part of the right crus.
• Left phrenic nerve: It supplies the left hemidiaphragm and may contribute to the crural musculature.
• Sensory branches supply the pericardium, mediastinal pleura, central diaphragmatic pleura, and central diaphragmatic peritoneum.

ROOT OF THE NECK

• The root of the neck is the region immediately superior to the thoracic inlet.
• It forms a passage between the neck, thorax, and upper limbs.

Thoracic inlet

The thoracic inlet, also called the superior thoracic aperture, has the following boundaries:

• Posteriorly: Body of the first thoracic vertebra.
• Laterally: First ribs and their costal cartilages.
• Anteriorly: Superior border of the manubrium sterni.

Structures Passing Through the Root of the Neck

1. Common carotid and subclavian arteries.
2. Internal jugular and subclavian veins.
3. Trachea.
4. Oesophagus.
5. Cervical pleura and apices of the lungs.
6. Thoracic duct on the left side.
7. Vagus, phrenic, and sympathetic nerves.
8. Brachial plexus.

Cervical Pleura

• The cervical pleura is the upward extension of parietal pleura covering the apex of the lung.
• It extends into the root of the neck, approximately 2–3 cm above the medial third of the clavicle, although its position varies.

Suprapleural Membrane (Sibson’s Fascia)

• It is a thickened extension of the prevertebral fascia covering the cervical pleura.
• It extends from the transverse process of C7 to the inner border of the first rib.
• It reinforces the cervical pleura and helps prevent excessive upward displacement of the lung apex during respiration.