Transoral Approaches to Midline Skull Base Tumors




Abstract


Transoral approaches have a significant advantage in providing the most direct route to ventral skull base pathology. Extended transoral approaches such as palatotomy, mandibular split, and mandibuloglossotomy can be used for increased rostrocaudal surgical access. Although these approaches give the easiest access to the lower craniocervical junction, the risks of postoperative infection and cerebrospinal fluid leak have to be considered. Preoperative management of dental disease, meticulous intraoperative reconstruction, and postoperative antibiotics assist in managing these complications. Combining endoscopic transoral and endonasal approaches provides improved surgical access and decreases the morbidity associated with the extended transoral approaches.




Keywords

Biopsy, Craniocervical junction, Endonasal approaches, Transoral approach, Velopharyngeal insufficiency, Ventral skull base

 





© 2018 Elsevier Inc. All rights reserved. Please note that the copyright for the original figures submitted by the contributors is owned by Contributors.




  • 1.

    Historical Background


    Ventral surgical approaches to the craniocervical junction have evolved over the past century. Historically, due to their deep-seated location and concerns for sterility, ventral craniocervical lesions were approached via posterior and lateral approaches, yielding unsatisfactory outcomes.


    In 1919, Kanavel described a transoral approach to remove a bullet lodged in the ventral skull base. In 1962, Fang and Ong published their series of 12 patients who underwent transoral and transthyrohyoid approaches for craniocervical decompression.


    Although the transoral route is the most direct route to the craniocervical area, poor outcomes initially resulted in lack of its acceptance. With the advent of advanced imaging techniques, antibiotics, and microscopic techniques and surgical instrumentation, the transoral approach was revisited and popularized by Crockard and Menezes.


    Over the years, multiple modifications were made to the transoral approach described earlier by Fang and Ong including extended transoral approaches, mandibular split, and mandibuloglossectomy, each of which provided further exposure in the rostral and caudal directions. Over the past two decades, advances in endoscopic and endoscopic-assisted techniques have helped circumvent some of the limitations of the microscopic techniques.


    Most of the published series of transoral approaches have focused on extradural craniocervical junction pathology. Patient series of transoral approaches for clival chordomas are limited by low incidence. In this chapter, we describe the transoral approach, extended transoral approaches, endoscopic-assisted approaches, and future trends.


  • 2.

    Preoperative/Perioperative Considerations


    Treatment of lesions in this area involves a multidisciplinary team approach that includes neurosurgeons, otolaryngologists/head and neck surgeons, neuroradiologist, neuroanesthesiologist, dentists, and pathologists.


    Lesions affecting the median craniocervical junction are rare, and their diagnosis and treatment are made difficult by their deep-seated anatomic location. Thorough clinical history, examination, and preoperative imaging are critical in establishing a diagnosis and for surgical planning. In this section, we will highlight critical issues that should be considered and discussed with the patient during the preoperative visit.



    • a.

      Imaging


      Preoperative imaging is paramount for the diagnosis and surgical planning. Because of the deep-seated location of the clivus, imaging is often used in lieu of surgical biopsy to establish the diagnosis of clival pathology. This usually includes thin-cut computed tomography (CT) and magnetic resonance imaging (MRI) with and without contrast. Magnetic resonance angiography is obtained if there is concern for close association of vascular structures to the lesion.


      Thin-cut CT scan and MRI are used for intraoperative image guidance (i.e., navigation). CT scan helps establish bony changes at the craniocervical junction including the clivus, spine, occipital condyles, and jugular foramina. MRI better defines the soft tissue extension including its laterolateral and rostrocaudal extent, as well as its relationship with neurovascular structures and their degree of compression. Therefore imaging is a key determinant when choosing the surgical approach to the lesion.


    • b.

      Physical examination



      • i.

        Mouth opening needs to be assessed and documented prior to surgery, as it will have a significant impact on the surgical approach and management of the perioperative airway. Usually between 2.5 and 3 cm are needed between the mandibular and maxillary incisors for adequate microscopic visualization and instrumentation.


      • ii.

        Dentition should be formally evaluated, and dental infections should be treated prior to surgery to decrease bacterial burden and the risk of infectious complications.


      • iii.

        Velopharyngeal insufficiency (VPI) and associated voice changes and swallowing difficulties should be discussed with the patient. This morbidity is commonly reported and is most common when the palate is split.



    • c.

      Biopsy


      Although biopsy can usually be performed easily via a transoral or transnasal route, frequently, imaging is sufficient to establish the diagnosis and biopsy is not needed. Most commonly, lesions are approached with the goal of complete surgical extirpation.


    • d.

      Airway management


      Patients are usually orally intubated. In select patients, the airway may need to be secured using awake fiber-optic intubation. Patients with significant trismus, patients who may undergo a mandibular split/glossotomy approach, or those who might have significant postoperative tongue swelling require a tracheostomy. This may be performed under local anesthesia if the risk for losing the airway during intubation is significant. This is especially true in patients with rheumatologic diseases resulting in ankyloses of the temporomandibular joint. Therefore, the need or potential need for a tracheostomy should be included in the informed consent discussion.


    • e.

      Perioperative antibiotics



      • i.

        Preoperatively the patient is screened with a nasal swab for methicillin-resistant Staphylococcus aureus ( MRSA ) to guide the choice of perioperative antibiotics.


      • ii.

        Mupirocin nasal ointment is used for 7 days prior to surgery in patients who are MRSA positive or for those from whom the culture could not be obtained.


      • iii.

        Chlorhexidine gluconate mouthwash is used for 2 days prior to the surgery.




  • 3.

    Surgical Approaches


    The ventral skull base was initially approached via a standard transoral/transpharyngeal route. This was subsequently modified to include palatotomy, mandibular split, and mandibuloglossotomy. These approaches, often described as extended transoral approaches, provide progressively greater rostrocaudal surgical access.


    Sloan et al. measured in cadavers the increase of exposure in the sagittal and axial planes by modifying the standard transoral approach with sequential mandibulotomy and mandibuloglossotomy, with and without palatotomy. The exposure from a standard transoral approach extended from the lower third of the clivus to the middle of the C2 vertebral body. As anticipated, the extended transoral approaches improved the sagittal and axial angles of exposure. Mandibulotomy increased exposure to the midclivus rostrally and to the C2-C3 vertebral interspace caudally. Mandibuloglossotomy further increased exposure to the upper third of the clivus and to the C4-C5 vertebral interspace. In each of these aforementioned approaches, addition of palatotomy further increased the rostral exposure.



    • A.

      Transoral/Transpalatal Approaches



      • I.

        Indications


        Median extradural and intradural pathologies involving the lower to middle third of the clivus and vertebral bodies of C1-C3.


        Irreducible craniocervical pathology.


        In combination with other ventral approaches, such as the endoscopic endonasal approach (EEA) for pathologies involving the upper clivus.


      • II.

        Procedure



        • a.

          The patient is orally intubated using a reinforced endotracheal tube.


        • b.

          A broad-spectrum antibiotic with cerebrospinal fluid (CSF) penetration is recommended; a third-generation cephalosporin, such as cefepime or ceftriaxone, is given 1 h prior to incision. Vancomycin is added if the patient is MRSA positive.


        • c.

          The oral cavity is prepped using chlorhexidine gluconate mouthwash.


        • d.

          The patient is laid supine with gentle cervical extension with the head in a three-point fixation system or on a horseshoe head holder.


        • e.

          Intraoperative image guidance navigation is set up.


        • f.

          A Dingman oral retractor or an equivalent mouth gag is used to expose the oropharynx ( Fig. 13.1 ). The mouth retractor is released every 20–30 min during the procedure to decrease compression injury to the lingual and hypoglossal nerves and the tongue. Perioperative IV corticosteroids are administered to diminish tongue swelling.




          Figure 13.1


          Standard transoral approach using the Dingman retractor to expose the oropharynx. The endotracheal tube has been secured in the midline with the retractor.


        • g.

          The soft palate may be retracted superiorly to allow for further rostral exposure by placing a red rubber catheter through the nose ( Fig. 13.2 ).




          Figure 13.2


          A red rubber catheter is used to retract the soft palate superiorly to increase rostral access.


        • h.

          The rostral and caudal extents of the lesion are then determined using navigation, and the approach can be further modified (see sections below) if further exposure is needed.


        • i.

          Relevant anatomy has been discussed in previous chapters; briefly, access to the arch of C1 requires sequential incision through the pharyngeal mucosa, pharyngeal constrictor muscles raphe, buccopharyngeal fascia, alar fascia, prevertebral fascia, longus colli/longus capitis, and anterior vertebral longitudinal ligament.


        • j.

          These can be approached in two ways.



          • i.

            A midline incision is made through the pharyngeal mucosa and superior constrictor muscle raphe to the level of the anterior vertebral longitudinal ligament, which is incised, dissected, and retracted laterally to expose the vertebral body and the clivus.


          • ii.

            Alternatively, an inferiorly based myofascial flap can be created by incising a rectangular flap starting just below the most caudal aspect of the lesion and extending just above its rostral aspect. The mucosa and pharyngeal constrictor muscle are incised to the level of the prevertebral fascia. This is then displaced inferiorly into the oropharynx/hypopharynx. The prevertebral fascia, longus colli muscles, and the vertebral ligaments are then dissected and retracted laterally.



        • k.

          The clivus, anterior arch of C1, and odontoid process are then drilled as needed to expose the lesion.


        • l.

          Drilling and dissection near the midline are safe. Bothersome bleeding may be encountered at the marginal sinus at the level of the foramen magnum; it is usually controlled with a paste of gelatin and thrombin, gelatin sponges, and bipolar cautery.


        • m.

          Superiorly, the lateral limits of dissection are the tori of the eustachian tubes and the paraclival carotid arteries and, more inferiorly, the vertebral artery and the hypoglossal canal. Ectatic parapharyngeal carotid arteries can be near midline and may need to be mobilized laterally. A general rule is to limit lateral dissection to the tori tubarius.




    • B.

      Extended Transoral Approaches


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Feb 21, 2019 | Posted by in NEUROSURGERY | Comments Off on Transoral Approaches to Midline Skull Base Tumors

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