In 2004, de Divitiis et al. studied an endoscopic transoral-transclival intradural approach on 15 cadavers, without maxillotomy or mandibulotomy, and estimated a safe entry zone achieved endoscopically through the clivus [10].

In 2006, Balasingam et al. conducted a cadaveric anatomical study to assess the area of surgical exposure and the available liberty of action for instrument manipulation by four different surgical approaches to the extracranial periclival region: the traditional transoral route, transoral with a palate split, LeFort I osteotomy, and median labioglossomandibulotomy [4].

In 2009, Pillai et al. performed an odontoidectomy in nine specimens by a direct transoral approach; endoscope-assisted (five cases) or a combined endoscopic-microscopic procedure, evaluating the surgical working area and the surgical freedom; the authors concluded that the endoscope and image guidance allowed them to approach the ventral CVJ transorally with minimal tissue dissection, no palatal splitting, and no compromise of surgical freedom [31].

The main advantages of the endoscopic endonasal approach to the ventral CVJ are minimal invasiveness, unlimited surgical access to the rostral midline CVJ, avoidance of palatal split, and less operative morbidity overall compared with the transoral approach. Thanks to a relatively inclined surgical trajectory, in a rostral-to-caudal direction, the compressive pathology of basilar invagination, including the lower clivus and odontoid tip, may be removable without removing the C1 anterior arch, thus maintaining the stability of C1–C2 [2]. In 2009, Kassam’s team published the concept of the “nasopalatine line” (NPL) [12]. The NPL is a reliable predictor of the maximal length of inferior dissection, and odontoid surgery can be performed safely according to a preoperative radiological study of the potential anatomical limitations of the endonasal approach. In 2012 Aldana et al. proved that a line in the midsagittal plane, the nasoaxial line (NAxL), connecting the midpoint of the distance from the rhinion to the anterior nasal spine of the maxillary bone and the C2 vertebra, tangential to the posterior nasal spine of the palatine bone, accurately predicted the lowest limit of this approach on the cervical spine [1].

In 2011, Russo et al. [35] described the microsurgical anatomy and limits of exposure of the endoscopically assisted high anterior cervical, submandibular approach to the clivus and foramen magnum; the optimal route to access pathologies located ventral to the pontomedullary region. Two extensions of the approach were studied and described: an extended anterior far-lateral clivectomy and an inferior petrosectomy, thus extending the exposure to the anterior foramen magnum and the anterior cerebellopontine region.

In a study on nine cadaver heads, in 2009, Baird et al. assessed surgical access to the craniovertebral junction using three endoscopic approaches: endonasal, transoral, and transcervical. Data suggested that the surgical goals of lower clival and odontoid decompression were achieved using the endonasal and transoral approaches, and the distance to the target area was shorter in the first approach. The transcervical approach was unable to achieve more than 1 cm of lower clival resection, thus not allowing complete odontoid resection [5]. In 2010, Seker et al. reported that the transnasal endoscopic approach provided a shorter route to the CVJ, while the transoral approach achieved a wider opening [36].

However, the two approaches should be considered as complementary rather than as alternatives. When removing large lesions that extend from the upper clivus to below C2, the transnasal and transoral routes may be successfully combined. The transcervical approach has the clear clinical advantage of reducing the risk of meningitis and of cerebrospinal fluid leak; its advantages also include maintaining a sterile surgical field, a familiar approach, and an optimal surgical trajectory for pathological findings lower than C2.

In 2012, Dallan et al. [11] investigated a new robotic surgical setting, the DaVinci system, in two cadavers, comparing the traditional transoral and the combined transoral-transnasal approaches to the CVJ. They concluded that the lower the placement of the robotic arms, the easier was the dissection of the rhinopharynx, basisphenoid, and upper clivus.

Visocchi et al. [42] compared the surgical exposition angle and the working channel volume of both the transnasal and transoral approaches in a cadaver, by means of a comparative neuroradiological “real-time” study. They concluded that the transnasal approach, as widely discussed, is a viable strategy for reaching the CVJ, but that this approach has limited angular (nostrils, choanae) and linear (NPL) surgical exposure, which, in our view, makes it suitable only for certain types of diseases and prevents its systematic applicability in other conditions, such as lateral tumors and pathologies caudal to C2. However, an obvious advantage of this approach is that there is no need to cut the soft palate; this minimizes potential postoperative morbidities, such as swallowing disturbances and hypernasal speech, which have a major negative impact on the quality of life (if there is a palatine veil dysfunction). The transoral approach provides a better exposure of the CVJ, both on the sagittal plane and on the transverse plane. Finally, the combination of the two approaches must be considered as an option for accomplishing a particular surgical goal. From a purely anatomical point of view, the results of Visocchi et al. seem to suggest that, in normal anatomical conditions, the transnasal approach to the CVJ is an oblique approach, which allows only the piecemeal removal of CVJ pathology and is not recommended for large tumors and low and far laterally sited CVJ pathologies. The transnasal approach is limited in the caudal direction down to the NAxL, whereas the transoral approach is limited in the rostral direction in an anatomically normal specimen [42]. In a further study, Visocchi and colleagues have confirmed the NAxL to be a reliable preoperative predictor of the maximal extent of inferior dissection for the transnasal approach. Moreover, these authors identified the corresponding palatal line for evaluating the upper limit of the transoral approach (from the inferior dental arch up to the hard palate), which represents the maximal extent of superior dissection; they called it the surgical palate inferior arcade (SPIA), and, interestingly, it can be found by a simple lateral head X-ray examination with open mouth. The NAxL appears to vary more than the SPIA. Finally, the pros and cons of each approach have to be taken into account, as well as the choice of a combined transoral and transnasal approach [47].