Anterior Approaches

Anterior approaches to the CTJ allow direct access to the vertebral bodies and intervertebral disks. These range from supraclavicular approaches that do not require any bony procedures to transmanubrial, transternal, and transclavicular approaches that include osteotomy of the manubrium, sternum, or clavicle, respectively, to allow better exposure of the upper thoracic vertebrae.

The thoracic inlet is the first structure encountered during the anterior approach. The superior mediastinum is defined anteriorly by the manubrium. The T2–T3 level is typically at the suprasternal notch, and T4–T5 is at the sternal angle ( Fig. 25-1 ). Sternohyoid muscle originates from the ventrocaudal hyoid bone and inserts on the dorsal surface of the manubrium ( Fig. 25-2 ). It also attaches to the sternoclavicular joint capsule. Sternothyroid muscle attaches along the dorsal midline of the manubrium, and sternocleidomastoid (SCM) muscle arises on the mastoid process and superior nuchal line and attaches to the manubrioclavicular joint, whose nervous supply is from the accessory nerve. Arterial supply branches come from the superior thyroid artery. Removal of the manubrium and medial third of the clavicle reveals the pleural apices, which are covered by an extension of the transthoracic fascia, called the Sibson fascia .

T2–T3 level at the suprasternal notch and T4–T5 level at the sternal angle.

Superficial muscles of anterior neck.

The superior mediastinum contains several vascular and visceral compartments. In terms of fascial layers, the visceral fascia circumscribes the trachea, esophagus, and thyroid gland, defining a visceral compartment. Carotid sheath circumscribes the carotid artery, internal jugular vein, and vagus nerve, defining a neurovascular compartment. These adjacent compartments create a potential space, the viscerocarotid space, which extends from the base of the skull to C7 to T4, depending on the location of the fusion between the visceral and alar fascia ( Fig. 25-3 ). Blunt dissection of the viscerocarotid space exposes the alar fascia and retropharyngeal space. The visceral compartment continues down to the bronchi, where the fascia fuses with the parietal and visceral pleurae. Carotid sheath extends down to the subclavian vessels, where it fuses into the axillary sheath. In the superior mediastinum, the vascular compartment is not circumscribed by its own well-defined fascial sheath but is defined secondarily by independent surrounding fascia. The prevertebral fascial extension, the transthoracic fascia, lies ventral, and the visceral fascia lies caudal. The parietal pleurae make up the lateral border, and the pericardium provides the inferior border.

Dissection through the viscerocarotid space leads to the proximal thoracic prevertebral space.

In terms of veins, brachiocephalic veins with their branches descend from the neck into the superior mediastinum just posterior to the thymus gland. The right brachiocephalic vein is formed just posterior to the medial end of the right clavicle and descends vertically into the superior mediastinum. In contrast, the left brachiocephalic vein is formed just posterior to the medial end of the left clavicle and descends diagonally to join the right brachiocephalic vein just posterior to the right first costal cartilage to form the superior vena cava. In the superior mediastinum, the left brachiocephalic vein courses obliquely from left inferior to right superior. Tributaries that drain into the brachiocephalic veins include the vertebral and first posterior intercostal veins in the neck; the internal thoracic, thymic, and inferior thyroid veins in the superior mediastinum; and the superior intercostal vein, which drains the second and third intercostal spaces.

The aortic arch initially ascends posteriorly to the superior vena cava but also turns diagonally posterior, then it turns inferior just anterior and to the left of the vertebral column. A second concave turn occurs as the arch curves around the anterolateral visceral compartment to reach the vertebral column. Brachiocephalic artery is the first branch off the aortic arch, and it ascends vertically and slightly rightward to divide into the right common carotid and subclavian arteries posterior to the right sternoclavicular joint. The left common carotid artery arises next off the arch and ascends essentially vertically into the carotid sheath without branching in the superior mediastinum. The left subclavian artery is the third branch; it ascends superiorly and leftward to curve around the thoracic inlet and into the axillary sheath without divisions in the superior mediastinum.

By incising the alar and mediastinal fascia, the median compartment of the retromediastinal space can be entered. The prevertebral fascia covers the vertebral bodies and envelops the longus colli. Autonomic branches to the cardiopulmonary plexi may be seen in this region and can be sacrificed if necessary. Structures that may potentially cross the retropharyngeal and retromediastinal spaces include the right recurrent laryngeal nerve, which can cross the retropharyngeal or retromediastinal space anywhere from C7 to T3; the left recurrent laryngeal nerve, which loops around the ligamentum arteriosum and ascends within the visceral fascia between the esophagus and trachea; and lymphatics that terminate in the thoracic duct on the left side, course dorsal and to the left of the esophagus between the visceral and alar fascia in the superior mediastinum, and ascend to the C7 level. The lymphatics lie laterally in a plane dorsal to the carotid sheath and then run caudally and ventrally to the branches of the thyrocervical trunk and phrenic nerve. They terminate at the junction of the left internal jugular and subclavian veins. A lymphatic trunk located on the right side follows a course similar to that of the thoracic duct.