Isidro Mateo Veterinary Hospital, Universidad Alfonso, Villanueva de la Cañada, Spain Several common pathological conditions affect the cervicothoracic spine including disk herniations (either extrusions or protrusions), cervical spondylomyelopathy, and vertebral fractures and luxations (Figure 17.1) [1–6]. Some of them can be managed with a conventional dorsal or lateral approach for laminectomy or hemilaminectomy (particularly when lateralized) [1–3, 6, 7]. However, if the lesion is midline located in the ventral spinal canal or implant placement in the vertebral bodies is desirable, an approach to the ventral aspect of C6–T2 vertebral bodies and corresponding intervertebral disk spaces is required [4, 5,8–10]. The exposition of these structures is limited using the conventional ventral approach to the cervical spine as they are hindered by the manubrium and the depth of the access (Figure 17.1b). Resection of the manubrium and median manubriotomy are surgical techniques that can be performed to improve exposure of the ventral aspect of C6–T2 vertebral bodies and intervertebral disks [8, 10]. Most neurosurgeons are familiar with the ventral anatomy of the neck but the complex anatomy and delicate neurovascular structures near the thoracic inlet and mediastinum may dissuade them from a deep cervicothoracic approach. A precise knowledge of the anatomy will allow a safe access to this region. After a superficial midline skin incision is made from the mid‐cervical region to the cranial margin of the second sternebra, the sternocephalicus and superficial pectoral muscles are exposed (Figure 17.2A). Superficial pectoral muscles originate paramedially on the cranial end of the sternum and run laterally and distally covering the biceps brachii muscle to the humerus. The sternocephalicus muscle is a flat muscle arising on the manubrium and has two components: the mastoid and occipital part. The mastoid part is cranially directed to the mastoid part of the temporal bone, whereas the occipital part attaches to the dorsal nuchal line of the occipital bone. At their origin the muscles of the two sides are intimately joined, but they separate at the middle of the neck and each crosses under the external jugular vein of its own side. Because of this divergence, there is a space ventral to the trachea in which the bilateral sternohyoideus and sternohyoideus muscles appear. The sternohyoideus muscle arises from the deep surface of the manubrium and the cranial edge of the first costal cartilage and extends cranially as flat longitudinal fibers to be inserted on the basihyoid bone covering the ventral surface of the trachea. The sternothyroideus muscle lies deep to the sternohyoideus muscle and arises from the first costal cartilage to be inserted on the lateral surface of the thyroid lamina, adjacent to the lateral surface of the trachea on its course. Dorsal to the trachea, the deep fascia of the neck can be visualized covering the longus coli muscle, which is a long muscle composed of separate bundles that lies in the ventral aspect of the bodies of cervical and six first thoracic vertebrae. Bundles in the cervical portion arise on the ventral border of the transverse process of the sixth to the third cervical vertebrae and end on the ventral spine of the next preceding vertebra, making a V shaped pattern running cranially (Figure 17.2B). The thoracic portion of the muscle arises on the ventral surface of the first six thoracic vertebrae to be inserted on the ventral border of the wing of the sixth cervical vertebra and on the transverse process of the seventh cervical vertebra. Figure 17.1 Sagittal CT myelogram (a) and CT (b) reconstruction and transverse CT myelogram at C7–T1 intervertebral disk space (c) showing C7–T1 vertebral subluxation associated with discospondylitis (a) and disk extrusions (b and c) causing severe spinal cord compression (arrows). Note the position of the manubrium relative to caudal cervical vertebrae (dashed lines in B) hindering its access. Figure 17.2 The cranial is to the left and caudal to the right in all of the images. (A) A ventral midline skin incision made from the mid–cervical area to the second sternebra exposes the sternohyoid (a), sternocephalicus (b), and pectoral muscles (c). (B) Deep ventral cervical spine with median manubriotomy. The trachea and esophagus have been retracted to the left (top of the image). The fingers pinpoint the transverse processes of C6, and the tip of the scissors pinpoints the C6–C7 intervertebral disk space. Note the V–shaped disposition of the longus coli muscle (asterisk). The vagosympathetic trunk (arrowheads), right common carotid artery (acc), right brachiocephalic trunk (bt), and internal thoracic vein (itv) are also depicted in the image. Figure 17.3 The cranial is to the left and caudal to the right in all of the images. (A) Vascular anatomy of the thoracic inlet. The right sternocephalicus muscle and the first right rib have been removed to allow visualization of deep vascular structures: (a) right common carotid artery; (b) right subclavian artery and ramifications; (c) internal thoracic artery; (d) external jugular vein; (e) right and left brachiocephalic veins; (f) internal thoracic vein; (g) internal jugular vein (not filled with colored latex); and (h) right subclavian vein. (B) Retraction of the internal thoracic vein allows visualization of cranial vena cava (i). In the midline between the sternohyoideus muscles, the unpaired caudal thyroid vein can be observed with bilateral branches. This vein arises primarily from the deep surfaces of the sternothyrohyoideus muscles, but on one or both sides its most cranial tributary may arise in the thyroid lobe or lobes. It terminates in the cranial angle formed by the merging brachiocephalic veins which, cranial to the thoracic inlet, form the cranial vena cava (Figure 17.3). Brachiocephalic veins of both sides are formed by the confluence of caudally coursing external jugular and the medially coursing subclavian vein of each side (Figure 17.3). The external jugular vein receives the venous blood from the head. It crosses the lateral surface of the brachiocephalic muscle obliquely superficially under the skin. The internal jugular vein usually terminates in the caudal portion of the external jugular vein, but rarely terminates in the brachiocephalic vein (Figure 17.3). The brachiocephalic trunk, the first branch of the aortic arch, passes obliquely to the right across the ventral surface of the trachea and gives rise to the left common carotid artery and terminates at the right common carotid artery and the right subclavian artery (Figure 17.3). Common carotid arteries are included in their respective carotid sheaths with the vasosympathetic trunk and internal jugular vein, which lie in the angle formed by the longus coli or longus capitis dorsally, the trachea ventromedially, and the brachiocephalicus and sternocephalicus muscles laterally (Figure 17.2B). The right recurrent laryngeal nerve, a branch that leaves the right vagus nerve at the level of the caudal side of the subclavian artery, is intimately associated with the lateral surface of the trachea until its end in the larynx. The left recurrent laryngeal nerve, a branch of the left vagus nerve, has similar disposition to the left but arches caudally around the aorta. Although care should be taken during manipulation, laryngeal dysfunction due to surgical trauma is extremely rare. Sympathetic innervation of the head is transmitted via the sympathetic trunk, which runs with the internal jugular vein, common carotid artery, and vagus nerve in the carotid sheath (Figure 17.2B). The vagus nerve contains parasympathetic preganglionic axons that course caudally down the neck to thoracic and abdominal organs. The trachea is immediately dorsal to the sternohyoideus muscle. It occupies a midline position under the longus coli muscle from the larynx to its bifurcation at the level of the fourth or fifth thoracic vertebra dorsal to the cranial part of the base of the heart.
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Ventral Approach to the Cervicothoracic Spine
Introduction
Surgical Anatomy [10–12]
Muscles
Vessels
Nerves
Viscera
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