Endoscopic transsphenoidal transclival approaches have been developed and their role is widely accepted for extradural pathologies. Their application to intradural pathologies is still debated but is undoubtedly increasing. Different authors have reported various extracranial, anterior transclival approaches for intradural pathologies. The aim of a review of Belotti et al. was to provide a historical overview of transclival approaches applied to intradural pathologies. PubMed was searched in October 2018 using the terms transcliv*, cliv* intradural, transsphenoidal transcliv*, transoral transcliv*, transcervical transcliv*, transsphenoidal brainstem, and transoral brainstem. Exclusion criteria included not reporting reconstruction techniques, anatomical studies, reviews without new data, and transcranial approaches. Ninety-one studies were included in the systematic review. Since 1966, transcervical, transoral, transsphenoidal microsurgical, and, recently, endoscopic routes have been used as a corridor for transclival approaches to treat intradural pathologies. Each approach presents a curve that follows Scott's parabola, with evident phases of enthusiasm that quickly faded, possibly due to high post-operative CSF leak rates and other complications. It is evident that the introduction of the endoscope has led to a significant increase in reports of transclival approaches for intradural pathologies. Various reconstruction techniques and materials have been used, although rates of CSF leak remain relatively high. Transclival approaches for intradural pathologies have a long history. We are now in a new era of interest, but achieving effective dural and skull-base reconstruction must still be definitively addressed, possibly with the use of newly available technologies 1).
Penetration of the clivus is required for surgical access of the brainstem. The endoscopic transclivus approach is a difficult procedure with high risk of injury to important neurovascular structures.
Cheng et al. undertook a novel anatomical and radiological investigation to understand the structure of the clivus and neurovascular structures relevant to the Extended endoscopic endonasal approach and determine a safe corridor for the penetration of the clivus.
They examined the clivus region in the Computed tomography angiography (CTA) images of 220 adults, magnetic resonance (MR) images of 50 adults, and dry skull specimens of 10 adults. Multiplanar reconstruction (MPR) of the CT images was performed, and the anatomical features of the clivus were studied in the coronal, sagittal, and axial planes. The data from the images were used to determine the anatomical parameters of the clivus and neurovascular structures, such as the internal carotid artery and inferior petrosal sinus.
The examination of the CTA and MR images of the enrolled subjects revealed that the thickness of the clivus helped determine the depth of the penetration, while the distance from the sagittal midline to the important neurovascular structures determined the width of the penetration. Further, data from the CTA and MR images were consistent with those retrieved from the examination of the cadaveric specimens.
The findings provided certain pointers that may be useful in guiding the surgery such that inadvertent injury to vital structures is avoided and also provided supportive information for the choice of the appropriate endoscopic equipment 2).
Lateral extension and previous treatment are factors that could make the surgery more difficult. Intradural extension did not limit the radicality of the removal 7).
For large tumors intraoperative MRI (IMRI) is of significant help. Dural reconstruction of large defects emerged as the greatest challenge of this technique even for experienced endoscopic surgeons 8).
An extended transnasal endoscopic access has to be performed according to a bilateral sphenoethmoidectomy with harvesting of a vascularized septomucosal flap for later skull base reconstruction. In such a way a broad access to the central skull base is gained under endoscopic view, thus allowing removal of the tumor in a four-hand technique with one surgeon holding the endoscope and a sucker while the second surgeon was able to use two instruments. The clivus is reduced by the use of a high-speed drill and Kerrison punches. Tumor removal is performed using curettes and an ultrasound aspirator 9).
The mucosal septectomy can compromise the integrity of the posterior septum and damage the vascularized pedicled nasoseptal flap (PNSF), a robust reconstructive option. With the possibility of an intraoperative cerebrospinal fluid (CSF) leak and the reported success of the PNSF for repair of these defects, preserving the integrity of the PNSF is beneficial during the endoscopic endonasal approach.
Eloy et al. present a new variation which preserves the mucosal integrity of the posterior nasal septum and PNSF. This mucosal-sparing variation of the traditional endoscopic endonasal transclival and transodontoid approaches allows for the preservation of posterior mucosal nasoseptal integrity, and salvages a reconstructive option for future usage. This is accomplished at no expense to visualization, surgical access, or maneuverability 10).
Two hundred twelve patients (mean age 47.9 years, 57.1% male) underwent transclival endoscopic endonasal approach (EEA) for lower clivus lesions. In addition to the lower clivus, resection involved the occipital condyle in 14.2% of patients, the foramen magnum in 16.5%, and the atlantooccipital joint (AO) in 1.4%. Quantification of condyle resection revealed complete resection in 3 cases, 75% resection in 8 cases, 50% resection in 6 cases, and 25% resection in 13 cases. Seven of these patients had EEA combined with an open, far lateral approach. In total, 7 patients required arthrodesis following EEA (3.3%), 4 of them after a combined approach. All patients who underwent arthrodesis had primary bone tumors such as chordoma, chondrosarcoma, or osteosarcoma (P = .022). Degree of condyle resection was a significant factor predisposing to occipitocervical instability (P = .001 and P < .001 for 75% and 100% condyle resection, respectively). Use of a combined approach was significantly associated with arthrodesis (P < .001).
EEA resection of the occipital condyles that results in greater than 75% condyle resection or EEA in combination with an open approach significantly increases the risk of AO instability and likely necessitates AO fixation 11).