Nuances of Microsurgical and Endoscope Assisted Surgical Techniques to the Cranio-Vertebral Junction: Review of the Literature

Purpose: An update of the technical nuances of microsurgical endoscopic assisted approaches to the craniocervical junction (transnasal, transoral and transcervical) if provided from the literature in order to better contribute to identify the best strategy. Methods: A non-systematic update of the review and reporting on the anatomical and clinical results of endoscopic assisted and microsurgical approaches to the craniocervical junction (CVJ) is performed. Results: Pure endonasal and cervical endoscopic approaches still have some disadvantages, including the learning curve and the deeper surgical fi eld. Endoscopically assisted transoral surgery with 30° endoscopes represents an emerging option to standard microsurgical techniques for transoral approaches to the anterior CVJ. This approach should be considered as complementary rather than an alternative to the traditional transoral-transpharyngeal approach. Conclusions: Transoral (microsurgical or video-assisted) approach with sparing of the soft palate still remains the gold standard compared to the ‘‘pure’’ transnasal and transcervical approaches due to the wider working channel provided by the former technique. Transnasal endoscopic approach alone appears to be superior when the CVJ lesion exceeds the upper limit of the inferior third of the clivus. Of particular interest the evidence that advancement in reduction techniques can avoid ventral approach. Review Article Nuances of Microsurgical and Endoscope Assisted Surgical Techniques to the Cranio-Vertebral Junction: Review of the Literature Visocchi Massimiliano1*, Signorelli Francesco1, Iacopino Gerardo2 and Barbagallo Giuseppe3 1Institute of Neurosurgery, Catjholic University of Rome, Italy 2Department of Experimental Biomedicine and Clinical Neurosciences, School of Medicine, Neurosurgical Clinic, University of Palermo, Italy 3Division of Neurosurgery, Department of Neurosciences, Policlinico “G. Rodolico” University Hospital, Catania, Italy Dates: Received: 02 December, 2016; Accepted: 03 February, 2017; Published: 06 February, 2017 *Corresponding author: Visocchi Massimiliano, MD, Institute of Neurosurgery, Catjholic University of Rome, Italy, Tel: + 39 360807781; E-mail:


Introduction
Endoscopic endonasal, transoral and transcervical approaches have recently been developed as promising options to the traditional transoral microsurgery to the CVJ, and may become more mainstream as experience with these approaches increases (cons: learning curve, loss of 3-dimensional visualization) [1,2].
The transoral-transpharyngeal approach historically remains the ''gold standard'' for anterior approaches to the upper cervical spine when indicated according to the Menezes algorithm (Figure 1) [3]. However, there are still technical diffi culties with the operating microscope, such as the need to see and work through a narrow opening in a deep cavity; to improve visualization; soft palate splitting and even hard palate resection along with extended maxillotomy are occasionally required. To overcome such complications, endoscopic assisted procedures for CVJ decompression have been developed. The endoscopic approaches to the CVJ include endoscopic endonasal approach, endoscopic transoral approach, robot-assisted endoscopic transoral approach, combined endoscopic transnasal and transoral approach, and endoscopic transcervical approach [4,5]. The aim of the current review is to give an update on the anatomic fundamentals of endoscopic assisted surgery to the CVJ and to report on the available clinical results.
In 2009, Pillai et al., performed an odontoidectomy in 9 specimens by a direct transoral approach; endoscope assisted (5 cases) or combined endoscopic--microscopic aid, evaluating the surgical working area and the surgical freedom; the authors Table 1: major fi ndings in anatomical studies of endoscopic assisted approaches to the cranio cervical junction.

Author
Year Approach

Major Findings
Ammirati and Bernardo [6] 1998 Endoscopic transoral approach Median mandibulotomy/glossotomy or the LeFort I approach with hard palate splitting if atlantooccipital and C1-C2 joints access is not necessary.
de Divitiis et al. [7] 2004 A limited clival and dural opening (20x15mm) allows full view of the anterolateral brainstem and cisternal spaces around it, from the spinomedullary junction to the interpeduncolar cistern.
Balasingam et al. [8] 2006 Both median labioglossomandibulotomy as the classic transoral provide a good exposure of the CVJ but limiting exposure of the clivus, which was instead well visualized in its inferior third by the transoral route by a palate split. Maximal exposure of the extracranial clivus was gained by LeFort I approach.
Youssef [9] 2008 Mandibulotomy and mandibuloglossotomy decreased operative distance while increasing exposure in the axial and sagittal planes. Palatotomy increased rostral exposure without changing the caudal or axial exposure or the operative distance.
Pillai et al. [10] 2009 The use of an endoscope coupled with image guidance offers several advantages for providing access to the lower clivus and C1-C2 region Dallan et al. [11] 2012 The combined transoral transnasal approach is the best answer to gain adequate space and optimal visualization in the rhinopharyngeal and upper clival region.
Alfi eri et al. [12] 2002 Endoscopic transnasal approach First description, in an anatomic study, of the endonasal route to the cranio-cervical junction, providing access from the anterior cranial fossa to the whole clivus, the upper cervical spine up to the body of C2.
Messina et al. [13] 2007 Data suggest as the binostril technique provides, without any additional surgical trauma, a better manoeuvrability of the surgical tools and the possibility to work with "three hands".
Ciporen et al. [14] 2010 The combination of supraorbital or transorbital endoscopic pathways with transnasal approaches appear to improve anatomic target visualization in the central corridor of the anterior cranial fossa.
Aldana et al. [15] 2012 A line in the midsagittal plane, the NAxL, accurately predicted the lowest limit of the craniovertebral junction.
Little [16] 2013 Signifi cant increase in angular range of motion during fl exion-extension and axial rotation at C0-C1 joint after the inferior third clivectomy and intradural exposure of the foramen magnum, suggesting posterior surgical fusion.
Perez-Orribo [17] 2013 Increase of range of motion mostly in fl exion/extension and less in axial rotation at the C0-C1 joint after removal of the lower third of the clivus and progressive occipital condylectomy.
Russo et al. [18] 2011 Endoscopic transcervical approach The study described the microsurgical anatomy and the limits of exposure of the high anterior cervical, submandibular, approach to the clivus and foramen magnum, endoscopic assisted.
Baird et al. [19] 2009 Compared Approaches Surgical goals of lower clival and odontoid decompression were achieved using the endonasal and transoral approach. The transcervical approach was unable to achieve more than 1 cm of lower clival resection, not allowing complete odontoid resection.
Seker et al. [20] 2010 Both transoral and transnasal approaches provide direct access to the CVJ avoiding neural and brain retraction but with a difference in level and extention of exposure. The transnasal endoscopic approach provides the shorter route to the CVJ while the transoral exposure gains a wider opening.

Visocchi et al. [2] 2014
The endoscope assisted transoral approach allows a better surgical control of the CVJ, in sagittal and transverse planes, providing a larger working channel and an easier manoeuvrability. The transnasal approach is limited in caudal direction down to the NPL; the transoral approach is limited in the rostral direction Van Abel KM [21] 2015 According to a recent anatomical study, the lower incidence of post-operative dysphagia with the endonasal approach is likely related to the lower density of neuronal elements from the pharyngeal plexus above the palatal plane.

Surgical studies (
In small children an endonasal approach may be limited by the small nares. If reduction cannot be achieved, a 540° procedure may be necessary in some cases (depending on the pathology), whereby the posterior approach and incision is temporarily closed and the patient is repositioned supine for a ventral decompres-sion followed by reopening of the posterior incision and the patient is repositioned supine for a ventral decompression followed by reopening of the posterior incision and posterior fi xation. All patients undergo neck fl exion\ extesion MRI of the CVJ. The patient is positioned supine with crown halo with traction; an intraoperative 3D CT is obtained in traction. The patient is then placed prone and another 3D CT is obtained. The algorithm is updated Figure 1 Velopharyngeal insuffi ciency 1,8% pharyngeal wound deiscence 0,7% Terry C. Burns [45]  Menezes at al., [3] underlines the importance of the intraoperative reduction strategies. If reduction cannot be achieved, a 360° procedure may be necessary in some cases Pure endonasal and cervical endoscopic approach deserves consideration but still has some disadvantages: (1)  Transnasal endoscopic approach alone appears to be superior when the CVJ lesion exceeds the upper limit of the inferior third of the clivus. Furthermore, combined transnasal and transoral procedures can be tailored according to the specifi c pathological and radiological fi ndings. Finally, experience is required with greater numbers of patients and long-term follow-up to further validate all the endoscopic techniques.
In our opinion and in agreement with other authors, the endoscopic endonasal approach, rather than an alternative, should be considered a complementary approach to the standard transoral-transpharyngeal route [42].
According to a recent anatomical study, the lower incidence of post-operative dysphagia with the endonasal approach is likely related to the lower density of neuronal elements from the pharyngeal plexus above the palatal plane [21].
However, the time to extubation and oral feeding was signifi cantly shorter in the endonasal group. Similarly Ponce-Gó mez and colleagues reported their own series of patients treated using both approaches and found comparable rates of neurological improvement after odontoidectomy, with less time to extubation and oral feeding, as well as shorter hospital stay in the endonasal group [35].