[Endoscopic transnasal resection of clival meningiomas]. / Endoskopicheskoe transnazal'noe udalenie meningiom skata.

Treatment of clival meningiomas is still one of the unresolved issues in modern neurosurgery. There are several treatment strategies. These ones include various combinations of follow-up, surgical CSF drainage, tumor resection and radiotherapy. OBJECTIVE: To assess postoperative outcomes in patients with clival meningiomas. MATERIAL AND METHODS: We analyzed 18 patients with large or giant clival meningiomas. RESULTS: We assessed extent of resection using the scale by G. Frank and E. Pasquini (2002): total resection - 95-100%, subtotal - 80-95%, partial - 50-80%, extended biopsy - <50% of tumor. Total resection was achieved in 1 patient (5.5%), subtotal - 5 (27.8%), partial - 12 (66.7%). At the same time, brainstem decompression and regression of hydrocephalus were observed in all cases. Fourteen patients were followed-up. Median follow-up was 8.5 months. Seventeen patients underwent radiotherapy due to predominant partial and subtotal resection. Total focal dose ranged from 50 to 57 Gy in standard fractionation mode. None patient had residual tumor enlargement throughout the follow-up period. There were no lethal outcomes. CONCLUSION: Endoscopic transnasal access to clival meningiomas in appropriate anatomical features of tumor and surrounding structures is a full-fledged alternative to transcranial treatment in these patients. This approach provides total resection and brainstem decompression. These facts increase life expectancy without deterioration of the quality of life.

[Surgical and combined treatment of patients with craniovertebral junction meningioma: a single-center retrospective study of 196 cases]. / Analiz rezul'tatov khirurgicheskogo i kombinirovannogo lecheniya patsientov s meningiomami oblasti kraniovertebral'nogo perekhoda: odnotsentrovoe retrospektivnoe issledovanie 196 sluchaev.

Treatment of craniovertebral junction meningioma is a difficult task. Surgical treatment is the gold standard for these patients. However, it is associated with high risk of neurological impairment, while combined treatment (surgery + radiotherapy) provides more favorable outcomes. OBJECTIVE: To present the results of surgical and combined treatment of patients with craniovertebral junction meningioma. MATERIAL AND METHODS: There were 196 patients with craniovertebral junction meningioma who underwent surgical or combined (surgery + radiotherapy) treatment at the Burdenko Neurosurgery Center between January 2005 and June 2022. The sample included 151 women and 45 men (3.4:1). Resection of tumor was performed in 97.4% of patients, craniovertebral junction decompression with dural defect closure - 2%, ventriculoperitoneostomy - 0.5%. As the second stage, 40 patients (20.4%) underwent radiotherapy. RESULTS: Total resection was achieved in 106 patients (55.2%), subtotal - 63 (32.8%), partial - 20 (10.4%), tumor biopsy was performed in 3 (1.6%) cases. Intraoperative complications occurred in 8 patients (4%), postoperative complications - in 19 (9.7%) cases. Radiosurgery was carried out in 6 (15%) patients, hypofractionated irradiation - 15 (37.5%), standard fractionation - 19 (47.5%) patients. Tumor growth control after combined treatment made up 84%. CONCLUSION: Clinical outcomes in patients with craniovertebral junction meningioma depend on tumor dimensions, topographic and anatomical localization of tumor, resection quality and relationship with surrounding structures. Combined treatment of anterior and anterolateral meningiomas of the craniovertebral junction is preferable compared to total resection.

[The DNA methylation profiling in the study and treatment of patients with meningiomas of the craniovertebral junction]. / Znachenie analiza metilirovaniya DNK v issledovanii i lechenii patsientov s meningiomami oblasti kraniovertebral'nogo perekhoda.

The paper presents the experience of using DNA methylation status in patients with meningiomas of the craniovertebral junction area in a neurosurgical clinic. A clinical case of combined treatment of a patient with meningioma of the craniovertebral junction and the choice of tactics based on the result of DNA methylation analysis of meningioma are described.

[Rosai-Dorfman intracranial histiocytosis: case report and literature review]. / Intrakranial'nyi gistiotsitoz Rozai­Dorfmana: sluchai iz praktiki i obzor literatury.

Histiocytosis is a group of idiopathic diseases accompanied by metabolic disorders and accumulation of metabolic products in histiocytes. Isolated Rosai-Dorfman histiocytosis of central nervous system is observed in less than 5% of cases. The authors report treatment and follow-up of a patient with intracranial Rosai-Dorfman disease. There were symptoms of lesion of the left cerebellopontine angle and epileptic seizures. Preoperative MRI identified two tumors (posterior cranial fossa on the left and right-sided parasagittal neoplasm). The authors carried out total resection of supratentorial tumor, after 3 weeks - subtotal resection of tumor in posterior cranial fossa. No recurrence after total resection was observed. Irradiation of infratentorial tumor with a total focal dose of 50 Gy after 6 months resulted tumor shrinkage throughout 12 months. Radiotherapy with the same dose was repeated throughout subsequent 12-month follow-up period due to progression of this focus. This treatment had a positive effect, but new skull base foci occurred. The authors emphasize the effectiveness of total resection and lower efficiency of subtotal excision combined with radiotherapy.

[Endoscopic fenestration of arachnoid cyst of posterior cranial fossa through third ventriculostomy]. / Endoskopicheskaya fenestratsiya arakhnoidal'noi kisty zadnei cherepnoi yamki cherez triventrikulostomu.

Arachnoid cysts (AC) are spaces with cerebrospinal fluid covered with arachnoid membrane. Most cysts are supratentorial and only 10-12% of ACs are found in posterior cranial fossa. This disease is usually diagnosed in childhood. In adults, ACs make up 1.4% of all focal lesions. ACs of posterior cranial fossa are often localized behind the cerebellum or in cerebellopontine angle. Most patients with cysts do not have permanent symptoms and should be followed-up. Surgery is indicated for cysts complicated by focal and hydrocephalic-hypertension symptoms. Microsurgical or endoscopic procedures are used. Surgical approach is determined by the closest location of cyst to brain surface. The authors report non-standard surgical approach for giant AC of posterior cranial fossa complicated by obstructive hydrocephalus, intracranial hypertension and visual function impairment. Endoscopic third ventriculostomy was followed by AC fenestration through ventriculostomy. Symptoms disappeared within 6 months after surgery.

[Surgical treatment of a patient with a traumatic arterial aneurysm of the M4 segment of the left middle cerebral artery. Case report and literature review]. / Khirurgicheskoe lechenie patsienta s travmaticheskoi anevrizmoi M4 segmenta levoi srednei mozgovoi arterii. Opisanie klinicheskogo sluchaia i obzor literatury.

OBJECTIVE: The purpose of the study is to present the results of successful treatment of a patient with traumatic arterial aneurysm of the middle cerebral artery (MCA). MATERIAL AND METHODS: A clinical case of traumatic arterial aneurysm of the M4 segment of MCA was studied. A patient with a ruptured traumatic aneurysm was transferred to Krasnogorsk City Hospital #1 for further examination and emergency surgery. RESULTS: On the sixth day after surgery, the patient was discharged in a satisfactory condition with almost complete regression of neurological symptoms. CONCLUSION: Treatment of traumatic arterial aneurysms requires an individual approach taking into account the past medical history, the clinical presentation, aneurysm location and anatomy, as well as the mechanism of injury. It is extremely difficult to suspect an arterial aneurysm after a patient had a traumatic brain injury as the incidence of this condition is very low. An angiographic study of cerebral vessels is needed for reliable diagnosis, not just solely performing standard computed tomography of the brain. Patients with this pathology require surgical intervention.

[Treatment of petroclival meningiomas: current state of the problem]. / Lechenie petroklival'nykh meningiom: sovremennoe sostoianie problemy.

Petroclival meningiomas (PCMs) are benign, slowly growing tumors. Surgery still remains the main treatment option for them. The desire for total resection of large extended PCMs often leads to the development or worsening of persistent neurological deficits. This paper presents a review of the world literature devoted to petroclival meningiomas. We discuss the issues of PCM classification, biology, diagnosis, and selection of the optimal algorithm for their treatment.

[Facial nerve injury in neurosurgery: a rehabilitation potential of botulinum therapy]. / Porazhenie litsevogo nerva pri neirokhirurgicheskikh operatsiiakh: reabilitatsionnyi potentsial botulinoterapii.

Surgical treatment of posterior cranial fossa and cerebellopontine angle tumors is associated with a risk of facial nerve dysfunction. The causes for facial muscle paresis include nerve compression by the tumor, destruction of the nerve structure by the tumor growing from nerve fibers, nerve injury during surgical removal of the tumor, etc. The first 3 months after facial nerve injury are a potential therapeutic window for the use of botulinum toxin type A (BTA). During this period, the drug is introduced both in the healthy side to improve the facial symmetry at rest and during mimetic movements and in the affected side to induce drug-induced ptosis. Post-paralytic syndrome develops 4-6 months after facial nerve injury. At this stage, administration of BTA is also an effective procedure; in this case, drug injections are performed on the affected side at small doses and symmetrically on the healthy side at doses doubling those for the affected side. BTA injections are mandatory in complex treatment of facial muscle paralysis.

[A technique of manufacturing anatomical preparations of the human brain based on injecting vessels with colored silicone (a technical note)]. / Sposob izgotovleniia anatomicheskikh preparatov golovnogo mozga cheloveka s in''ektsiei sosudov tsvetnym silikonom (tekhnicheskoe opisanie).

OBJECTIVE: The objective was to produce anatomical preparations by injecting vessels with colored silicone to study the brain and skull base anatomy. MATERIAL AND METHODS: Fresh, undissected, and unfixed cadavers were used. The internal carotid arteries and internal jugular veins were identified on both sides of the neck. The vessels were washed with running water. Then, a complex solution consisting of white silicone rubber, silicone oil (solvent), and a coloring pigment (red and blue pigments) at a ratio of 1:(0.9-1.1):(0.04-0.06), respectively, was prepared. About 30-60 s before injecting the complex solution into the vessels, a catalyst-hardener was added to the solution at a ratio of 1:(0.05-0.07). The complex solution was first introduced into the internal carotid artery until the solution came out from the contralateral internal carotid artery; then, the solution was injected into the internal jugular vein until the solution emerged from the contralateral internal jugular vein. RESULTS: The technique enables quick and high-quality visualization of both large and very small vessels of the brain and skull base. CONCLUSION: The proposed simple and inexpensive technique of manufacturing anatomical preparations improves the quality of training and mastering of microsurgical skills in residents and practicing neurosurgeons.

[Surgical approach to resection of vestibular schwannomas following stereotactic radiological treatment. Surgical outcomes and morphological changes in tumors after radiotherapy]. / Khirurgicheskaia taktika pri udalenii vestibuliarnykh shvannom posle stereotaksicheskogo radiologicheskogo lecheniia. Rezul'taty operatsii i morfologicheskie izmeneniia v opukholiakh posle oblucheniia.

INTRODUCTION: Radiation therapy of small vestibular schwannomas is quite often used as an effective alternative to surgical treatment. At the same time, 2-10% of patients are detected with radioresistant tumors progressing to varying degrees, which is associated with continued tumor growth. In these cases, a decision on surgical resection or re-irradiation of the tumor is made depending on the neurological symptoms, patient's somatic status, and neuroimaging data. Surgical outcomes and intraoperative findings in pre-irradiated patients have been poorly represented in the literature, for which reason we decided to conduct this study. The paper presents a series of patients with vestibular schwannomas who underwent surgical removal of the tumor after radiotherapy. MATERIAL AND METHODS: A total of 39 patients with vestibular schwannomas after radiotherapy underwent surgery at the Burdenko Neurosurgical Institute in 2007-2017. Of these, 22 patients had a tumor removed after a previously performed combined surgical and radiotherapy treatment (group I), and 17 patients underwent tumor resection after previous radiological treatment (group II). The surgical outcomes were studied depending on various factors, and an analysis of the morphological changes in vestibular schwannomas after radiological treatment was carried out. RESULTS: In group I, the tumor was resected totally in 18% of patients, almost totally in 5% of patients, subtotally in 68% of patients, and partially in 9% of patients. In group II, the tumor was resected totally in 6% of patients, almost totally in 12% of patients, subtotally in 76% of patients, and partially in 6% of patients. We found that post-radiation changes in patients undergoing surgery led to an increase in the response of neurovascular structures to surgical intervention, development of pronounced fibrosis around tumors, and changes in the structure of tumors that became more solid. As a result, surgical morbidity increased, and the patient's quality of life after surgery deteriorated.

[The efficacy of botulinum therapy in treatment of delayed facial palsy after resection of vestibular schwannoma]. / Éffektivnost' botulinoterapii v lechenii otsrochennoi neiropatii litsevogo nerva posle udaleniia nevrinomy slukhovogo nerva.

Delayed facial palsy is a complication developing 3 or more days after surgery. The etiology and pathogenesis of this condition has not been fully explored, and there are no treatment standards for it. As in the case of Bell's paralysis, glucocorticosteroids (GCSs) are currently used to treat delayed facial palsy. However, patients with contraindications to GCSs need new therapy modalities. AIM: We aimed to evaluate the efficacy and safety of botulinum therapy in patients with delayed facial palsy after neurosurgical interventions. MATERIAL AND METHODS: We examined 33 patients with delayed facial palsy developed 3 or more days after resection of vestibular schwannoma. The main group included 18 patients with contraindications to GCSs who received injections of botulinum toxin A (BTA) into the facial muscles of the healthy side for muscle relaxation. The comparison group consisted of 15 patients who received a course of prednisolone (1 mg/kg/day) for 5-7 days. The efficacy of treatment was assessed using the House-Brackmann scale and Clinical Global Impression Scale. The follow-up period after therapy was 3 months. RESULTS: Delayed facial palsy was more common in the following cases: the facial nerve was located near the antero-inferior tumor pole; the tumor was adherent to the facial nerve; the tumor extended in the oral direction; the tumor had with unclear borders and was 11 to 30 mm in size. In most patients of both groups, facial muscle palsy developed more than 11 days after surgery. Treatment both in the main and control groups resulted in a significant improvement: complete regression of the facial asymmetry in patients of the main group and comparison groups 3 months after treatment onset was 83.3 and 93.3% (House-Brackmann scale), respectively. CONCLUSION: Botulinum therapy may be recommended for patients with delayed facial palsy developed after vestibular schwannoma resection, who have contraindications to GCSs.

[Extended endoscopic endonasal posterior (transclival) approach to tumors of the clival region and ventral posterior cranial fossa. Part 2. Topographic and anatomical aspects and surgical technique]. / Éndoskopicheskii éndonazal'nyi zadnii rasshirennyi (transklival'nyi) dostup k opukholiam oblasti skata cherepa i ventral'nykh otdelov zadnei cherepnoi iamki. Chast' 2. Topografo-anatomicheskie aspekty i operativnaia tekhnika.

PURPOSE: to present the main topographic and anatomical features of the clivus and adjacent structures for improving and optimizing the extended endoscopic transnasal posterior (transclival) approach in removal of clival and ventral posterior cranial fossa lesions. MATERIAL AND METHODS: We performed a topographic and anatomical study of 25 cadaver heads, the vascular bed of which was filled with colored silicone using the original technique for visualizing the bed features and individual variability. RESULTS: We present the main anatomical landmarks necessary for performing the extended endoscopic endonasal posterior approach. Superior, medial, and inferior transclival approaches provide access to the anterior surface of the upper, middle, and lower neurovascular complexes of the posterior cranial fossa. CONCLUSION: The endoscopic transclival approach can be used to reach ventral posterior cranial fossa lesions. The endoscopic transnasal transclival approach is an alternative to transcranial approaches to clival lesions.

[Intracranial neurenteric cysts: experience of the Burdenko Neurosurgical Institute in the XXIth century]. / Intrakranial'naia neiroéntericheskaia kista: opyt Instituta neirokhirurgii im. akad. N.N. Burdenko, v XXI veke.

We present a series of cases of a rare pathology, intracranial neuroenteric cysts, a review of the international literature, and the experience in treating this pathology. MATERIAL AND METHODS: Seven patients with intracranial neuroenteric cysts underwent surgery at the Neurosurgical Institute in the period between 2000 and 2015. CONCLUSION: The main and only technique for treatment of intracranial neurenteric cysts is their resection.

[Endoscopic transnasal surgery for giant fibrous dysplasia of the skull base, spreading to the right orbital cavity and nasopharynx (a case report and literature review)]. / Endoskopicheskaya transnazal'naya khirurgiya gigantskoi fibroznoi displazii osnovaniya cherepa, rasprostranyayushcheisya v polost' pravoi orbity i nosoglotku (opisanie nablyudeniya i obzor literatury).

BACKGROUND: An extended endoscopic endonasal approach is increasingly used in surgical treatment of space-occupying skull base lesions. The international literature reports only 20 cases of surgical treatment for fibrous dysplasia (PD) of the skull base using the endoscopic endonasal approach. We present our experience with the endoscopic endonasal approach in surgical treatment for giant fibrous dysplasia of the skull base, spreading to the right orbital cavity and nasopharynx. CLINICAL CASE: A 26-year-old male patient presented with cranial pain, Vth nerve dysfunction on the right, right keratopathy. OD=0.2 (near acuity - 0.3), OS=1.0, OD - incomplete eyelid closure of 2 mm, conjunctival injection, mucous discharge, corneal opacity in the lower pole and paracentrally, OS - normal appearance. Severe right-sided exophthalmos (more than 15 mm), impaired nasal breathing on the right, nasal (hemorrhagic) discharge. Magnetic resonance imaging and spiral computed tomography scans revealed a bone density lesion located in the area of the orbit, nasal cavity, maxillary sinus on the right, and labyrinth of the ethmoid bone. The patient underwent endonasal endoscopic resection of the lesion. RESULTS: The lesion was resected totally, which was confirmed by control SCT. Right-sided exophthalmos partially regressed (on the right: exophthalmos of 8 mm; protrusion: OD=23 mm, OS=15 mm; the eyeball was displaced downward and outward). The visual and oculomotor functions did not change. The neurological status remained at the preoperative level. CONCLUSION: Fibrous dysplasia of the skull base is an extremely rare disease. Modern techniques expand the indications for surgery of giant tumors of the skull base using minimally invasive approaches, in particular the endoscopic endonasal approach.

[Extended endoscopic endonasal posterior (transclival) approach to tumors of the clival region and ventral posterior cranial fossa. Part 1. Topographic and anatomical features of the clivus and adjacent structures]. / Éndoskopicheskii éndonazal'nyi zadnii rasshirennyi (transklival'nyi) dostup k opukholiam oblasti skata i ventral'nykh otdelov zadnei cherepnoi iamki. Chast' 1. Topografo-anatomicheskie osobennosti skata i pogranichnykh s nim obrazovanii.

OBJECTIVE: to describe the main topographic and anatomical features of the clival region and its adjacent structures for improvement and optimization of the extended endoscopic endonasal posterior (transclival) approach for resection of tumors of the clival region and ventral posterior cranial fossa. MATERIAL AND METHODS: We performed a craniometric study of 125 human skulls and a topographic anatomical study of heads of 25 cadavers, the arterial and venous bed of which was stained with colored silicone (the staining technique was developed by the authors) to visualize bed features and individual variability. Currently, we have clinical material from more than 120 surgical patients with various skull base tumors of the clival region and ventral posterior cranial fossa (chordomas, pituitary adenomas, meningiomas, cholesteatomas, etc.) who were operated on using the endoscopic transclival approach. RESULTS: We present the main anatomical landmarks and parameters of some anatomical structures that are required for performing the endoscopic endonasal posterior approach. The anatomical landmarks, such as the intradural openings of the abducens and glossopharyngeal nerves, may be used to arbitrarily divide the clival region into the superior, middle, and inferior thirds. The anatomical landmarks important for the surgeon, which are detected during a topographic anatomical study of the skull base, facilitate identification of the boundaries between the different clival portions and the C1 segments of the internal carotid arteries. The superior, middle, and inferior transclival approaches provide an access to the ventral surface of the upper, middle, and lower neurovascular complexes in the posterior cranial fossa. CONCLUSION: The endoscopic transclival approach may be used to access midline tumors of the posterior cranial fossa. The approach is an alternative to transcranial approaches in surgical treatment of clival region lesions. This approach provides results comparable (and sometimes better) to those of the transcranial and transfacial approaches.

[Neurosurgery in a patient on dual antiplatelet therapy. Case report and the review of the literature]. / Neirokhirurgicheskoe vmeshatel'stvo u patsienta, nakhodiashchegosia na dvoinoi dezagregantnoi terapii. Opisanie sluchaia i obzor literatury.

INTRODUCTION: A neurosurgical intervention in a patient on dual antiplatelet therapy is a serious challenge for both the neurosurgeon and anesthesiologist.. MATERIAL AND METHODS: The article describes a clinical case of a successful urgent neurosurgical intervention (ventriculoperitoneostomy for obstructive hydrocephalus caused by a large meningioma of the posterior surface of the petrous pyramid) in a patient on dual antiplatelet therapy (DAT) due to a recently placed coronary stent.. CONCLUSION: Given a high risk of coronary stent thrombosis, the surgery was performed in the presence of ongoing DAT. There were no intracranial hemorrhagic complications, but subcutaneous hemorrhagic complications developed. The article discusses the features of managing similar patients whose number is growing.

[Use of surgical approaches to the posterior cranial fossa in patients in a lying position]. / Primenenie khirurgicheskikh dostupov k zadnei cherepnoi yamke v polozhenii lezha.

BACKGROUND: Various suboccipital approaches are extensively used in modern neurosurgery for treatment of posterior cranial fossa disease. The main patient's positions on the operating table during surgery are half-sitting and lying ones. MATERIAL AND METHODS: The article provides a detailed description and methodology of retrosigmoid suboccipital and median suboccipital approaches in a lying position. CONCLUSION: The retrosigmoid suboccipital and median suboccipital approaches in a lying position, when used correctly, provide a good view of the operating field with the minimal risk of complications associated with the patient's position on the operating table.

[The algorithm for surgical treatment of skull base tumors invading the craniovertebral junction].

UNLABELLED: Surgical treatment of skull base tumors invading the craniovertebral junction is a complex medical problem due to a high rate of adverse postoperative outcomes in these patients. AIM: The study aim was to optimize surgical treatment in patients with skull base tumors invading the craniovertebral junction. MATERIAL AND METHODS: A comparative analysis of 2 groups of patients was performed. The study group included 28 patients with skull base and craniovertebral junction chordomas who underwent single-stage surgery, including posterior occipitospondylodesis and tumour resection using the transoral and combined transoral and transnasal approaches, in the period between 2000 and 2015. The control group included 21 patients with the same pathology who underwent microsurgery using the transoral approach without occipitospondylodesis in the period between 1990 and 2009. RESULTS: Most of the patients in both groups were operated on at late disease stages when they presented with gross clinical signs. The use of single-stage occipitospondylodesis and transoral skull base tumor removal significantly (compared to the control group) extends indications for surgical treatment of skull base tumors, which were previously considered unresectable, and provides better results. CONCLUSION: New surgical techniques significantly increase the completeness of tumor resection, decrease the rate of postoperative complications, accelerate the rehabilitation process, and improve the patient's quality of life.

[The successful treatment of a patient with Lhermitte--Duclos disease (A case report and literature rewiew)].

INTRODUCTION: Lhermitte--Duclos disease is a rare autosomal dominant inherited disorder characterized by the loss of the normal cerebellar cortex architecture and hamartoma formation in the cerebellar hemispheres. Most commonly, this disease manifests in the third and fourth decades of life. Approximately 220 cases of Lhermitte--Duclos disease have been reported in medical literature to date. MATERIAL AND METHODS: The authors describe successful two-stage surgical treatment of a young female patient with Lhermitte--Ducos disease. CONCLUSION: This case report familiarizes practitioners with the clinical manifestations and neuroimaging features of Lhermitte--Duclos disease that facilitates timely diagnosis and proper treatment of the condition.

[Endoscopic endonasal surgical treatment of large pituitary adenoma, spreading into the posterior fossa].

AIM: The objective of the study was to develop the tactics of surgical treatment of large and giant pituitary adenomas, spreading into the posterior cranial fossa. MATERIAL AND METHODS: Patients with large hormonally inactive pituitary adenoma, extending to the right cavernous sinus and posterior cranial fossa. RESULTS: The endoscopic endonasal removal a large endo-supra-latero(D)-retrosellar pituitary tumor was conducted. Control MRI shows that the tumor was removed radically. Oculomotor disturbances were observed in the early postoperative period, which significantly regressed within 6 months. The article provides detailed analysis of the world literature on the issue under discussion. Illustrative pre-, intra-, and post-operative photographs, as well as histological preparations are shown. CONCLUSION: Modern minimally invasive techniques make it possible to remove large pituitary adenomas (and other tumors) of the posterior cranial fossa using endoscopic endonasal approach. Such operations must be carried out at highly specialized institutions by the surgeons who have extensive experience in endoscopic transnasal surgery of skull base tumors.