Purely nasal floor mucosa-free graft for reconstruction after endoscopic endonasal transellar approach: an anatomical and clinical analysis.

BACKGROUND/OBJECTIVE: In this radioanatomical study with clinical correlate, we study a variation of the 'extended nasal floor mucosa' (ENFM) free-graft, the purely nasal floor mucosa (PuNFM) free-graft. The objectives of this study are to evaluate the coverage surface area provided by the PuNFM, study the adequacy of the PuNFM in the reconstruction of endoscopic endonasal approach (EEA) transsellar postoperative defects and compare and evaluate this reconstructive technique with current sellar region reconstruction practices. METHODS: Dissections were performed on five cadaveric specimens. PuNFM were harvested bilaterally and the area provided for reconstruction was calculated. Twenty-five consecutive cases of pituitary adenomas resected through an EEA were analyzed to estimate the sellar defect surface area (SDSA) after a transsellar EEA and calculate the area of PuNFM bilaterally. RESULTS: The median cadaveric SDSA was 4.77 cm2, with a median left and right side PuNFM area of 5.09 and 5.19 cm2, respectively. Clinically, the median SDSA was 5.36 cm2, and the total radiological PuNFM surface area was 5.46 cm2, with modified Knosp grade >2 tumors having larger SDSA than that of Knosp grade <2 tumors. The PuNFM graft proved to be most effective for covering modified Knosp <2 tumor defects. CONCLUSIONS: The PuNFM represents a variation of the ENFM free-graft sellar defect reconstruction technique that provides sufficient surface area to reconstruct the majority of the sellar defects related to transsellar EAA for pituitary adenomas. This technique may positively impact sinonasal function and quality of life. Future prospective clinical studies are needed to verify these findings.

Endoscopic endonasal pituitary gland hemi-transposition for resection of a dorsum sellae meningioma.

A 69-year-old female with incidental diagnosis of a dorsum sellae meningioma had shown significant tumor growth after initial conservative management. The procedure started with a microscopic sublabial transsphenoidal approach to the sella and the suprasellar space. Due to limitations to a safe dissection and removal of the retrosellar component, the surgery was converted to a purely endoscopic endonasal approach with left hemi-transposition of the pituitary gland, followed by drilling of the dorsum sellae and removal of the left posterior clinoid process. A complete tumor resection was achieved, and a multilayer skull base reconstruction was performed without complications. The video can be found here: https://youtu.be/BEolyK-To_A .

Exoscope-assisted temporal bone resection: operative videos of the lateral and total techniques.

Skull base malignancies arising from the parotid gland, skin, or external auditory canal (EAC) can potentially involve the temporal bone. Management of these invasive tumors represents a true challenge considering the critical neurovascular relationships. Exoscope-assisted temporal bone resection (TBR) plays a crucial role in addressing such malignancies. The extent of disease is evaluated using the Pittsburgh staging system, which then guides the boundaries of resection. Lateral TBR (LTBR) relies on removal of the EAC and lateral ossicles and is generally appropriate for stage T1 and T2 tumors. Total TBR (TTBR) is reserved for high-grade tumors involving the petrous apex. The video can be found here: https://stream.cadmore.media/r10.3171/2023.10.FOCVID23135.

The "Crista Ovale": A Reliable Anatomical Landmark in Transorbital Endoscopic Approaches to the Middle Cranial Fossa.

BACKGROUND: Transorbital endoscopic approaches (TOEAs) have emerged as adjunct and alternatives for accessing the middle cranial fossa (MCF). Nuances of the skull base anatomy from a ventral transorbital endoscopic viewpoint remain to be fully described. OBJECTIVE: To assess the anatomy of the "crista ovale" (COv), described transcranially as the midsubtemporal ridge (MSR), from a ventral transorbital perspective and evaluate its role as a landmark in TOEA to the MCF. METHODS: Lateral TOEAs to the MCF were performed in 20 adult cadaveric heads (40 sides). The presence of the COv/MSR was evaluated under endoscopic visualization. Anatomic relationships between COv/MSR and surrounding structures were assessed. The presence of COv/MSR was also examined in 30 cadaveric head computed tomography (CT) scans (60 sides). RESULTS: The COv/MSR was identified in 98% (39/40) of sides at the MCF, as 1 of 4 major configurations. The COv/MSR was found anterolateral to the foramen ovale and foramen spinosum (mean distance: 9.2 ± SD 2.4 mm and 12.3 ± SD 2.6 mm, respectively) directly anterior or anteromedial to the petrous apex (mean distance: 26.2 ± SD 2.6 mm) and at a mean 47.6 ± SD 4.7 mm from the approach's surgical portal. It was recognized in 95% (57/60) of CT scans. CONCLUSION: The COv/MSR can be readily identified during TOEA to the MCF and on CT. It serves as a reliable landmark to localize the foramen ovale, foramen spinosum, and petrous apex. Further studies may confirm its surgical significance in transorbital endoscopic procedures.

Endoscopic Approaches to the Paramedian Skull Base: An Anatomic Comparison of Contralateral Endonasal and Transmaxillary Strategies.

BACKGROUND: The expanded endoscopic endonasal approach (EEA) is limited laterally by the internal carotid artery (ICA). The EEA to the paramedian skull base often requires complex maneuvers such as dissection of the Eustachian tube (ET) and foramen lacerum (FL), and ICA manipulation. An endoscopic contralateral transmaxillary approach (CTMA) has the potential to provide adequate exposure of the paramedian skull base while bypassing manipulation of the aforementioned anatomic structures. OBJECTIVE: To quantify and compare the surgical nuances of a CTMA and a contralateral EEA when approaching the paramedian skull base in cadaveric specimens. METHODS: Five adult cadaveric heads were dissected bilaterally (10 sides) using a contralateral EEA and a CTMA to expose targets of interest at the paramedian skull base. For each target in both approaches, the surgical freedom, angle of attack, the corridor's "perspective angle," and "turning angle" to circumvent the ICA, ET, and FL were obtained. RESULTS: The CTMA achieved superior surgical freedom at all targets ( P < .05) except at the root entry point of cranial nerve XII. The CTMA provided superior vertical and horizontal angles of " attack " to the majority of targets of interest. Except when approaching the root entry point of cranial nerve XII, the CTMA " turning angle " around the ICA, ET, and FL were wider with CTMA for all targets. CONCLUSION: A CTMA complements the EEA to access the paramedian skull base. A CTMA may limit the need for complex maneuvers such as ICA mobilization and dissection of the ET and FL when approaching the paramedian skull base.

Therapeutic response to pazopanib: case report and literature review on molecular abnormalities of aggressive prolactinomas.

Introduction: Aggressive prolactinomas (APRLs) pose a significant clinical challenge due to their high rate of regrowth and potentially life-threatening complications. In this study, we present a case of a patient with an APRL who had a trial of multiple therapeutic modalities with the aim to provide a review of molecular abnormalities and management of APRLs by corroborating our experience with previous literature. Methods: A total of 268 articles were reviewed and 46 were included. Case reports and series, and studies that investigated the molecular and/or genetic analysis of APRLs were included. Special care was taken to include studies describing prolactinomas that would fall under the APRL subtype according to the European Society of Endocrinology guidelines; however, the author did not label the tumor as "aggressive" or "atypical". Addiontionally, we present a case report of a 56-year-old man presented with an invasive APRL that was resistant to multiple treatment modalities. Results: Literature review revealed multiple molecular abnormalities of APRLs including mutations in and/or deregulation of ADAMTS6, MMP-9, PITX1, VEGF, POU6F2, CDKN2A, and Rb genes. Mismatch repair genes, downregulation of microRNAs, and hypermethylation of specific genes including RASSF1A, p27, and MGMT were found to be directly associated with the aggressiveness of prolactinomas. APRL receptor analysis showed that low levels of estrogen receptor (ER) and an increase in somatostatin receptors (SSTR5) and epidermal growth factor receptors (EGFR) were associated with increased invasiveness and higher proliferation activity. Our patient had positive immunohistochemistry staining for PD-L1, MSH2, and MSH6, while microarray analysis revealed mutations in the CDKN2A and POU6F2 genes. Despite undergoing two surgical resections, radiotherapy, and taking dopamine agonists, the tumor continued to progress. The patient was administered pazopanib, which resulted in a positive response and the patient remained progression-free for six months. However, subsequent observations revealed tumor progression. The patient was started on PD-L1 inhibitor pembrolizumab, yet the tumor continued to progress. Conclusion: APRLs are complex tumors that require a multidisciplinary management approach. Knowledge of the molecular underpinnings of these tumors is critical for understanding their pathogenesis and identifying potential targets for precision medical therapy.

Trans-Sulcal Parafascicular Port-Based Resection of a Subcortical Occipital High-Grade Glioma: 2-Dimensional Operative Video.

Minimally invasive trans-sulcal parafascicular port-based approaches can provide safe access to a wide variety of deep brain lesions.1,2 This surgical video illustrates the use of a minimally invasive port-based approach for resection of a subcortical right medial occipital lobe lesion in a 63-year-old woman who presented with seizures and bilateral left homonymous hemianopia. MRI showed a 2.5-cm contrast enhancing lesion with a necrotic center and significant T2 and fluid-attenuated inversion recovery signal consistent with vasogenic edema. Diffusion tensor imaging revealed compromise of the right optic radiations and edema extending through the right corticospinal tract. A minimally invasive trans-sulcal parafascicular port-based approach to the deep occipital lobe and periatrial region was performed under full exoscopic visualization. A gross total tumor resection was achieved, and histopathology revealed an IDH1-mutant, MGMT-methylated-positive glioblastoma. The patient's presentation, rationale, key surgical steps, and outcomes are discussed, and informed consent for surgery was obtained. The participants and any identifiable individuals consented to the publication of their image. Images at 3:50 used with permission from Nico Corporation. All rights reserved.

Microsurgical Gross Total Resection of an Intracanalicular-Cisternal (Koos-4) Vestibular Schwannoma via a Retrosigmoid Approach with Intraoperative Endoscopic Assistance.

We present the case of a 23-year-old female with a history of progressive hearing loss in the left ear, dizziness, and vertigo. Magnetic resonance imaging demonstrated a left mass extending from the internal auditory canal into the cerebellopontine angle (Koos-4).1 A retrosigmoid approach assisted with a microinspection tool was chosen.2-5 Microsurgical near total resection was achieved. The patient presented a postoperative facial deficit (House-Brackman grade 2 postoperative), with complete resolution after 2 months. Video 1 highlights the critical steps of the retrosigmoid approach and the benefit of using the microinspection tool for vestibular schwannoma resection.

Circulating Tumor DNA in Adults With Glioma: A Systematic Review and Meta-Analysis of Biomarker Performance.

BACKGROUND: Circulating tumor DNA (ctDNA) has emerged as a promising noninvasive biomarker to capture tumor genetics in patients with brain tumors. Research into its clinical utility, however, has not been standardized because the sensitivity and specificity of ctDNA remain undefined. OBJECTIVE: To (1) review the primary literature about ctDNA in adults with glioma to compare the sensitivity and specificity of ctDNA in the cerebrospinal fluid vs the plasma and (2) to evaluate the effect of tumor grade on detection of ctDNA. METHODS: PRISMA-guided systematic review and meta-analysis was performed using published studies that assessed ctDNA in either plasma or cerebrospinal fluid among adult patients with confirmed glioma. Summary receiver operating characteristic curves were generated using the Rücker-Schumacher method, and area under the curve (AUC) was calculated. RESULTS: Meta-analysis revealed improved biomarker performance for CSF (AUC = 0.947) vs plasma (AUC = 0.741) ctDNA, although this did not reach statistical significance ( P = .141). Qualitative analysis revealed greater sensitivities among single-allele PCR and small, targeted next-generation sequencing panels compared with broader panels. It additionally demonstrated higher sensitivity of ctDNA detection in high-grade vs low-grade gliomas, although these analyses were limited by a lack of specificity reporting in many studies. CONCLUSION: ctDNA seems to be a highly sensitive and specific noninvasive biomarker among adults with gliomas. To maximize its performance, CSF should be studied with targeted genetic analysis platforms, particularly in high-grade gliomas. Further studies on ctDNA are needed to define its clinical utility in diagnosis, prognostication, glioblastoma pseudoprogression, and other scenarios wherein neoadjuvant therapies may be considered.

Keyhole Supraorbital-Eyebrow Approach for Resection of an Olfactory Groove Meningioma with Intraoperative Endoscopic Assistance.

The authors present the case of a 52-year-old male with a history of new-onset seizures who presented in status epilepticus. Computed tomography and magnetic resonance imaging demonstrated an olfactory groove mass. A keyhole supraorbital-eyebrow approach assisted with a microinspection tool was performed for tumor resection.1-5 A Simpson grade 2 tumor resection was achieved, and histopathology revealed a World Health Organization grade I olfactory groove meningioma. Postoperative and follow-up course has been unremarkable, with early postoperative imaging demonstrating no residual tumoral mass. The operative video highlights the advantages of using the microinspection tool for the visualization of deep lesions.

Exoscopic En Bloc Carotid-Sparing Total Temporal Bone Resection: Feasibility Study and Operative Technique.

OBJECTIVE: To delineate the steps of exoscopic en bloc carotid artery-sparing total temporal bone resection for malignancies involving the temporal bone in a cadaveric model. METHODS: Dissections were performed on 3 right-sided (3 sides) formalin-fixed, latex-injected cadaveric specimens. An exoscopic en bloc carotid artery-sparing total temporal bone resection was performed on each cadaver. In the past 4 years, 8 patients have undergone exoscope-assisted internal carotid artery-sparing total temporal bone resection with the technique described in this report. As an example, we present a representative case of a patient in whom this technique was used. RESULTS: Exoscope-assisted en bloc total temporal bone resections were performed on 3 right-sided cadaveric specimens. The following steps were described to circumferentially expose the petrous temporal bone: infratemporal fossa exposure, temporal craniotomy for subtemporal middle fossa approach to the petrous bone, retrosigmoid craniotomy, and transjugular approach. Finally, 3 skull base osteotomies were performed to liberate anterior, medial, posterior attachments of the petrous bone for en bloc removal. Possible extensions of these dissections as indicated by tumor pathology were described. A case illustration and operative video utilizing these techniques is presented. CONCLUSIONS: Exoscope-assisted en bloc carotid artery-sparing total temporal bone resection is a feasible technique for management of malignancies with temporal bone invasion.

Revascularization Is Associated With a Reduced Stroke Risk in Patients With Sickle Cell-Associated Moyamoya Syndrome.

BACKGROUND: Moyamoya syndrome refers to a progressive stenosis of the internal carotid arteries and can be associated with sickle cell disease. These codiagnoses result in severe risk for stroke, even in patients on optimal medical management. Surgical revascularization has been shown to be safe in small case series. OBJECTIVE: To evaluate the efficacy of revascularization with direct comparison to a medically managed control group within a single institution. METHODS: A retrospective cohort study of medically managed vs surgically revascularized patients with moyamoya syndrome and sickle cell disease was conducted. Demographic data and outcomes including the number of prediagnosis, postdiagnosis, and postrevascularization strokes were collected. Risk factors for stroke were identified using a binary logistic regression model, and stroke rates and mortality between groups were compared. RESULTS: Of the 29 identified patients, 66% were medically managed and 34% underwent surgical revascularization (50% direct and 50% indirect). Calculated stroke rates were 1 per 5.37 (medical management), 1 per 3.43 (presurgical revascularization), and 1 per 23.14 patient-years (postsurgical revascularization). There was 1 surgical complication with no associated permanent deficits. No risk factors for stroke after time of diagnosis were found to be significant. CONCLUSION: The results of this study demonstrate that revascularization is associated with a significant reduction in stroke risk, both relative to prerevascularization rates and compared with medical management. According to these findings, surgical revascularization offers a safe and durable preventative therapy for stroke and should be pursued aggressively in this patient population.

The Transorbital Pericranial Flap.

OBJECTIVE: The objective of the present study was to describe and evaluate the feasibility, mobility, and surface area provided by the simple and extended transorbital pericranial flap (TOPF). Furthermore, we compared this novel technique with the current practice of pericranial flap harvesting and insetting techniques. We also studied the adequacy of the TOPF in the reconstruction of postoperative anterior cranial fossa (ACF) defects. METHODS: The TOPF was performed bilaterally in 5 alcohol-preserved, latex-injected human cadaveric specimens. The TOPF was harvested in 2 stages: the orbitonasal stage and the cranial stage. For the orbitonasal stage, a transorbital superior eyelid approach was used. We have described 2 harvesting techniques for creating 2 distinct TOPF types (simple and extended) according to the main vascular pedicle. The superficial flap areas offered by the simple and extended TOPF and the traditional bicoronal pericranial flap were calculated and compared. The distances from the supratrochlear and supraorbital arteries to specified anatomical landmarks were also measured. Additionally, the ACF defect area of relevant surgical cases performed using endoscopic transcribriform approaches were measured on immediate postoperative computed tomography head scans using radiological imaging software. RESULTS: The harvest of both the simple and the extended TOPFs was efficient. As expected, the areas offered by simple and extended TOPFs were smaller than that offered by the traditional bicoronal flap. However, the surface area offered by either the simple or extended TOPF provides sufficient coverage for most ACF defects. A high spatial distribution was observed between the vascular pedicles and their respective foramen or notch. CONCLUSIONS: The TOPF represents a novel harvesting, tunneling, and insetting technique that offers a large, versatile, pedicled flap for coverage of most standard ACF defects after endoscopic surgery.

Combined microsurgical-endoscopic paramedian supracerebellar-infratentorial approach for resection of a pineal low-grade glioma.

The authors present the case of a 20-year-old male with a history of headaches and blurred vision found to have a pineal mass and chronic hydrocephalus. The patient initially underwent an endoscopic third ventriculostomy and pineal mass biopsy that revealed a low-grade neuroepithelial neoplasm. A microsurgery-endoscope-assisted paramedian supracerebellar-infratentorial approach was chosen and a gross-total resection was achieved. The patient's postoperative and follow-up course has been unremarkable, with early postoperative imaging demonstrating no residual tumoral mass. The operative video highlights the advantages of endoscopic visualization for deep lesions in the pineal region and posterior third ventricle. The video can be found here: https://stream.cadmore.media/r10.3171/2021.4.FOCVID2119.

Sellar Cholesterol Granuloma Mimicking Cystic Sellar Lesions: A Report of Three Cases and Literature Review.

BACKGROUND: Cystic lesions in the sellar region include a variety of entities, such as craniopharyngioma, Rathke cleft cyst (RCC), intrasellar arachnoid cyst, cystic pituitary adenomas, cholesterol granulomas (CGs), and xanthogranulomas (XGs). The distinction among them remains a preoperative challenge due to similarities in their clinical and radiologic findings. CASE DESCRIPTION: We describe 3 cases with cystic sellar lesions. The first patient is a woman who presented with headache and hormonal disturbances, including high levels of prolactin, with a sellar and suprasellar cystic lesion discovered on magnetic resonance imaging. She was initially treated with dopamine agonists with normalization of prolactin levels but no changes on the size of the lesion. She underwent an endoscopic endonasal resection and the histology resulted in a CG/XG. The second patient is a woman who consulted for an incidentally discovered sellar cyst. During the follow-up, the lesion demonstrated enlargement with compression of the optic chiasm. With a preoperative diagnosis of RCC, the lesion was removed through an endoscopic endonasal transsellar approach. Final pathologic diagnosis was consistent with CG/XG. The third case was that of a man who presented with refractory headaches and vision loss, with a sellar/suprasellar cystic lesion on magnetic resonance imaging. He underwent endoscopic endonasal transsellar surgery for resection of what preoperatively was thought to be a giant RCC; final pathology again was consistent with CG/XG. CONCLUSIONS: CG/XG is an uncommon pathology with unspecific clinical and radiologic features. However, this pathology should be considered in the differential diagnosis of mixed cystic/solid lesions in the sellar region.

Surgical anatomy of the orbit. A systematic and clear study of a complex structure. / Anatomía quirúrgica de la órbita. Un estudio sistematizado y claro de una estructura compleja.

BACKGROUND AND OBJECTIVE: The orbit is a structure of interest for many medical specialties. Surgical approaches to the orbit present significant difficulties for the general neurosurgeon. Whoever decides to practice orbital surgery must have vast anatomical knowledge of this structure. However, although many of the existing publications about orbital anatomy show the complexity of this structure in detail, they fail to facilitate their understanding. The purpose of this study was to systematise and simplify the anatomical study of the orbit from a surgical perspective, to facilitate its understanding. MATERIALS AND METHODS: A review of the international literature on the subject was carried out, and the principle of the rule of 7was followed for its ordering. For illustration purposes, photographs of cadaveric preparations and digital drawings were used. RESULTS: The orbits are 2cavities located symmetrically on both sides of the nose. They have a pyramidal shape, with 4sides, a posterior vertex, an anterior base and their axis established from the sagittal plane at a 20-degree angle. A distinctive feature of the orbit is that its elements are organised into groups of seven: 7bones, 7intraorbital extraocular muscles and 7nerves. CONCLUSION: A systematisation of the orbital anatomy was performed with clear illustrations to simplify its study. The understanding of the anatomy of the orbit is vital to classify lesions and provides a solid basis when choosing the most appropriate approach for their treatment.

Pituitary Adenoma Concomitant with Chiari I Malformation: Case Report and Literature Review.

BACKGROUND: Pituitary adenomas (PA) are usually benign neoplasms. Chiari I malformation (CIM) is an uncommon finding. Isolated cases associating functional PA and CIM have been reported. The concomitant presence of a nonfunctional PA and a CIM has not yet been described in the literature. CASE DESCRIPTION: We present the case of a 35-year-old patient whose symptoms were compatible with CIM. Magnetic resonance imaging of the brain, with and without contrast material, confirmed the CIM and incidentally encountered a PA. The patient was treated initially for her PA through an endoscopic endonasal approach with complete tumor resection, confirming a nonfunctional PA. Posterior fossa decompression was successfully accomplished 3 months later. The patient has been followed up for 5 years and has been free of symptoms, with no recurrence of her PA. This represents the first reported case of a nonfunctional PA with a concomitant CIM. CONCLUSION: This is the first reported case of a concomitant CIM and a nonfunctional PA. We discuss our successful management and conduct a systematic review of the literature to provide the most up-to-date guidance on managing these singular cases with concomitant pathologic conditions.

Endoscopic Endonasal Focal Transclival-Medial Condylectomy Approach for Resection of a Foramen Magnum Meningioma: 2-Dimensional Operative Video.

The endoscopic endonasal approach (EEA) provides direct access to foramen magnum meningiomas; however, it often requires extensive exposure including septal flap elevation with septum removal, complete sphenoidotomy, and panclivectomy.We present a case of a 54-yr-old-female with an incidental foramen magnum lesion followed up with serial imaging who presented 10 mo later with progressive neck discomfort and episodes of dizziness, with confirmed tumor progression and further brainstem compression. A focal transclival EEA with medial condylectomy was performed preserving the upper two-thirds of the clivus, the nasal septum, and the sphenoid sinus. Gross total removal of a meningioma WHO Grade-1 was achieved with dura resection on the majority of the tumor (Simpson 2). Closure was achieved with a random pedicled inverted V nasaopharyngeal flap. There were no complications, all symptoms improved, and no recurrence was seen in 12 mo of follow-up.IRB approval was neither required nor saught for this single case report. The patient gave informed consent.

The Eustachian Tube as a Landmark for Early Identification of the Abducens Nerve During Endonasal Transclival Approaches.

BACKGROUND: Expanded endonasal approaches have the potential to injure the abducens nerve (cranial nerve [CN] VI). The nerve's root entry zone (REZ) and cisternal segment (CS) are particularly prone to injury during the clivus resection and dural incision of transclival approaches. OBJECTIVE: To investigate the role of the eustachian tube (ET) as a surgical landmark for the REZ and CS of CN VI. METHODS: Transclival expanded endonasal approaches were performed bilaterally in 6 fresh-frozen cadaveric specimens (12 sides). Anatomic relationships between ET and CN VI were documented with neuronavigation. RESULTS: The mean vertical distance from the inferior brainstem point to the horizontal projection of CN VI REZ, CS midpoint, and interdural segment (ID) were 26.38 mm (95% confidence interval [CI] 17.36-35.4), 38.61 mm (95% CI 25.61-51.61), and 42.68 mm (95% CI 30.14-55.22), respectively. The relative vertical distance from the ET to the horizontal projections of the REZ, CS midpoint, and its ID were 6.43 mm (95% CI 3.25-9.61), 18.66 mm (95% CI 11.52-25.8), and 22.72 mm (95% CI 16.02-29.42), respectively. In the axial plane the angles between the ET and (1) the REZ and its midline horizontal projection point, (2) the midpoint and its midline horizontal projection point, and (3) ID and its midline horizontal projection point were 9.81 ± SD 5.20°, 18.50 ± SD 4.87°, and 24.71 ± SD 6.21°, respectively. CONCLUSION: The ET may serve as a constant landmark to reliably predict the position of the REZ and CS of CN VI.