High Cervical Retropharyngeal Approach to the Craniocervical Junction

Overview

Retropharyngeal approaches to the upper cervical spine are anterior approaches directed through the fascial planes of the neck. The main advantage of anterior approaches is the direct route to the lesion, avoiding the potential need to work around or manipulate neural structures. The transcervical approach can provide access to the C2 body and odontoid process, the anterior arch of C1, and the lower clivus. The major targets of these approaches are anterior or anterolateral lesions of the craniovertebral junction (CVJ), such as anterior midline extradural tumor of the first, second, and third cervical vertebrae or hangman’s fracture. The retropharyngeal approach is an option to reach high cervical targets or those of the CVJ, and it can obviate the need to open the oropharynx and avoids potential risks associated with the transoral approach.

Because full occlusion of the teeth is essential for optimum exposure of this approach, nasotracheal intubation or tracheostomy is recommended, and no other access is given between the teeth. Retropharyngeal approaches require dissection of fascial planes in the submandibular and carotid triangle rostral to the hyoid bone and adjacent to the superior pharyngeal constrictor muscle, ultimately accessing the space between the upper cervical vertebral bodies and the prevertebral fascia.

Two types of retropharyngeal approaches are well established: one route is medial to the carotid sheath, the other is lateral to it. The former is the medial retropharyngeal approach, and it may cause complications that include injury to the glossopharyngeal, hypoglossal, and superior laryngeal nerves, but it holds the advantages of a more anterior approach angle. The latter is a lateral retropharyngeal approach, and it has the advantage of a low incidence of nerve palsy and fewer anatomic structures for dissection; the disadvantage is a slightly lateral approach.

Medial Retropharyngeal Approach (Anterior Retropharyngeal Approach)

The patient is positioned with the head slightly extended to raise the mandible up and away from the surgeon’s line of view, and the head is rotated 30 degrees contralateral to the surgical approach. The four methods of skin incisions are 1) transverse, 2) oblique vertical, 3) hockey stick, and 4) T-shaped. A submandibular transverse skin incision is enough for exposure of the atlas and axis, but for the additional exposure of any cervical level below C2, a vertical skin incision should be added with a transverse T-shaped skin incision. Regardless of the kind of incision, the important point is wide dissection of the cervical fascia planes. A transverse incision is made from the midline of the neck to the mastoid tip with one finger width (~2 cm) below the mandible’s lower margin. A vertical skin incision is extended inferiorly as far as necessary for better exposure and to avoid stretch injury to the surrounding structures.

The side of approach is decided by the laterality of the lesion and the surgeon’s preference. If lower cranial nerve impairment is already present, the approach should be performed from the side of impairment.

After the skin incision, a wide subcutaneous flap should be prepared on each side of the incision superficial to the platysma muscle. The medial edge of the platysma muscle is grasped in the midline. Vertical incision of the platysma is made from the mental symphysis to the superior notch of the thyroid cartilage, and the platysma muscle is undermined and freed; the platysma can then be transected across its fibers parallel to the direction of the primary incision for the full length of the exposure ( Fig. 4-1 ).

The fascial plane between the pharynx and the prevertebral muscles is reached through an exposure directed along the anterior border of the sternocleidomastoid muscle (SCM) and between the carotid sheath laterally and the esophagus and trachea medially. By performing the initial exposure inferiorly, the approach can be considered an extension of the familiar anterior cervical approach. To expose the CVJ, additional superior exposure is needed. Structures that may be divided from below to above to increase the exposure include the ascending pharyngeal and superior thyroid arteries, external laryngeal nerve, ansa hypoglossi, internal laryngeal nerve, lingual artery, stylohyoid muscle, anterior belly of the digastric muscle, stylohyoid ligament, and the stylopharyngeus and styloglossus muscles.

The superficial cervical fascia and platysma muscle are mobilized superiorly, and subsequently the submandibular gland and facial artery and vein are visualized ( Fig. 4-2 ). At that time, the marginal mandibular branch of the facial nerve is identified with the aid of a nerve stimulator; inadvertent injury to this nerve will result in drooping at the corner of the mouth as a result of orbicularis muscle paresis. This nerve usually runs anteriorly below the angle of the mandible and lies in the upper part of the submandibular gland in the subplatysmal plane of the superficial cervical fascia. The superficial fascia should be incised below this nerve and lifted over the submandibular gland, keeping the dissection deep and inferior to the submandibular gland as the exposure is extended and retracted superiorly to reduce the risk of injury to the marginal mandibular branch of the facial nerve.

For more comfortable retraction of the submandibular gland, the facial vein is transected, and the facial artery is dissected until fully retracted. The facial artery runs posterior to the submandibular gland, and the facial vein is medial to it in the mandibular notch.

Following retraction of the submandibular gland, the next fascial plane, including the digastric muscle, is exposed and transected. The digastric muscle and tendon, fascial sling, and stylohyoid muscle are then exposed ( Fig. 4-3 ). The digastric tendon is attached to the hyoid bone by the fascial sling, which is transected; the digastric muscle and stylohyoid muscle are retracted superiorly, and the next fascial plane is exposed.