Transoral–Translabiomandibular Approach to the Craniovertebral Junction

10.1055/b-0034-84454

Transoral–Translabiomandibular Approach to the Craniovertebral Junction

Ivo P. Janecka

The clivus and upper cervical vertebral bodies constitute the craniovertebral junction (CVJ). These anatomical structures at the cranial base are located anterior to the neural axis ( Fig. 23.1 ). In general, surgical treatment of lesions located anterior to the neural axis should be accessed through an anterior approach. To do so requires selection of a transfacial approach because of the anteroinferior anatomical relationship of the facial viscerocranium to the cranial base ( Fig. 23.2 ).

The advantages of transfacial approaches include the following:

Facial anatomy has developed through the embryonic fusion of nasofrontal, maxillary, and mandibular processes. Normally, the fusion takes place in the midline or in the paramedian region, thus logically presenting optimal lines of “separation” of facial units for a surgical approach, permitting the least traumatic displacement.
The primary blood supply to the “facial units” is through the external carotid system, which also has a lateral-to-medial direction of flow, thus ensuring viability of displaced surgical units.
The midface contains multiple “hollow” anatomical spaces (oronasal cavity, nasopharynx, paranasal sinuses) that facilitate the relative ease of surgical access to the central skull base.
Displacement of facial units for an approach to the central cranial base offers much greater tolerance to postoperative surgical swelling, as opposed to similar displacement of the content of the neurocranium.
Reestablishment of the normal anatomy, following repositioning of the facial units during the reconstructive phase of surgery, has a high degree of functional as well as aesthetic achievement.

However, transfacial approaches also have certain disadvantages, such as the following:

The surgical wound can be contaminated with oropharyngeal bacterial flora.
Facial incisions can cause visible scars to develop.
The patient may have emotional considerations related to “surgical facial disassembly.”
Supplementary airway management (postoperative endotracheal intubation, temporary tracheostomy) may be needed.

Three-dimensional reconstruction of platybasia with odontoid invagination.

Human skull demonstrating potential skeletal units, which can be displaced for surgical exposure to the skull base.

Patient Selection

To be considered for transfacial/transoral surgery to the CVJ, the patient must have a pathological entity located at the central cranial base that is judged to be best treated with surgery. Such entities would include benign and malignant tumors, as well as congenital and posttraumatic deformities.

Adequate imaging is necessary to define the extent of the pathological process, as well as to show the key neighboring anatomical structures and the potential for their preservation. Appropriate modalities include computed tomography (CT), magnetic resonance imaging (MRI; static and dynamic), and sometimes four vessel angiography. Numerous questions need to be answered by the imaging studies: the true extent of the lesion, its relationship to the key anatomical structures (e.g., vessels, dura, brainstem, cranial nerves), and the potential expendability of such structures during surgical resection. A patient would not be considered for this type of surgery if the lesion (e.g., lymphoma, most metastatic lesions) is best treated by nonsurgical modalities, or if the oronasopharynx is actively infected.

The timing of surgery is guided by the nature of the pathological process and the urgency for treatment as well as by the patient′s overall medical status. In general, malignant processes or impending brainstem compressions are treated expeditiously. Benign tumors and congenital deformities are treated electively.

A biopsy for tissue diagnosis will differentiate the neoplasms into surgical and nonsurgical categories. Patients with malignant tumors for whom transfacial/transoral surgery is not recommended are usually offered radiotherapy and/or chemotherapy. External beam radiotherapy may be supplemented with brachytherapy. Some benign lesions may be followed with scans to assess their growth potential if the surgical treatment has a high likelihood of worsening the patient′s deficit.

Transoral approaches create potential risk to the function and aesthetics of the following structures: skin, dentition, facial skeleton, mucosal lining of the upper airway, paranasal sinuses, eustachian tubes, superior constrictor muscles, soft and hard palate, and tongue. From the neurovascular point of view, the locations of the upper cervical and petrous segments of the internal carotid arteries, as well as cranial nerves V3 (especially the lingual nerve) and XII, must be recognized. Furthermore, the vertebral arteries are at potential risk, especially in congenital anomalies of the CVJ with an associated asymmetry. If the vertebral arteries are exposed during surgery, these vessels must be covered with vascularized tissue to prevent the likelihood of subsequent vessel rupture.

The potential postoperative risks are related to the quality of wound healing, involving the dura as well as the wall of the oropharynx. Cerebrospinal fluid (CSF) leakage and/or breakdown of the wound closure are highly undesirable and require intensive treatment.

Preoperative Planning

All patients are given a broad spectrum antibiotic with Gram positive and Gram negative coverage. It is started within 1 hour prior to surgery and continued for ~48 hours postoperatively or until the spinal drain (if used) is removed. Preoperative oral irrigation with a clindamycin solution may be used to reduce microbial flora.

Surgical Technique

Anesthetic Technique

Anesthesia is usually induced with pentobarbital and maintained with enflurane. Oral endotracheal intubation is usually satisfactory (a contoured Raey tube is preferred). In some cases, preliminary tracheostomy is performed. Neurophysiological monitoring includes monitoring of cranial nerve XII (by tongue electromyography) as well as monitoring of brainstem evoked potentials in transdural cases. All patients have arterial as well as central venous pressure lines. Elective hypotension is not used. A precordial stethoscope is used to alert the anesthesiology team to venous air embolism. When dural transgression is anticipated, a spinal drain is inserted.

Patient Positioning

Most patients are positioned supine on the operating table with the head rigidly fixed. An alternative position is a right lateral position (for right handed surgeons) for a limited midline lesion. The advantage of this position is gravity-dependent drainage away from the immediate surgical field.

Draping

A complete preparation of the face and neck is performed with Betadine, and the oropharynx is irrigated with diluted Betadine solution. This area is then draped. In addition, the lateral thigh is prepared and draped as a fascia lata donor site.

Skin Incisions

Depending on which approach is used, the extent of the incisions varies considerably. For the basic transoral approach, no skin incisions are made. Only the soft palate is retracted with transnasal rubber catheters. This palatal elevation exposes the palpable arch of C1. If significant platybasia is present or the lower one third of the clivus must be reached, a midline soft palate split is added. An extended transoral approach includes lateral incisions of the palate, the floor of the mouth, and a mandibular osteotomy. In addition, when very wide exposure of the central and paracentral skull base is required, bilateral maxillary osteotomies are performed through additional facial incisions. For the harvesting of the vascularized muscle flap used in reconstruction, a hemicoronal scalp incision is performed to reach the temporalis muscle. When a mandibular split is performed, the lower lip is incised in a paramedian position, and the incision is extended horizontally into the soft tissues of the upper neck.

Splitting of the Soft Palate

The midline of the soft palate and the posterior pharyngeal wall is infiltrated with 0.5% lidocaine viscous with 1:200,000 epinephrine for hemostasis. The soft palate is incised in the midline with a no. 11 scalpel blade, as is the uvula. Care must be taken to avoid injuring the posterior pharyngeal wall with the tip of the no. 11 blade. It is possible to release the levator palati muscle submucosally from its attachment to the hard palate. This maneuver permits more lateral retraction of the bisected soft palate, further increasing the surgical exposure at the CVJ. The soft palate halves are gently retracted laterally with 4–0 Dexon sutures (Covidien, Norwalk, CT) affixed to the perioral frame of the Dingman′s mouth gag ( Fig. 23.3 ).

Mandibular Split

The lower lip incision is performed in a zigzag fashion to conform to the tension lines of the paracentral lip skin with possible extension horizontally into the upper neck. Mandibular osteotomy is performed just medial to the mental foramen, preserving lower lip sensation. Usually an interdental space is found that is wide enough to permit placement of a reciprocating saw for the osteotomy. This cut is also performed in a step fashion, which then permits more stable reconstructive reapproximation of the bone. Prior to the osteotomy, it is wise to select an appropriate miniplate for ventral fixation, contour it to the mandible, and create drill holes. This strategy assists in the postoperative reestablishment of a normal occlusion ( Fig. 23.4 ).