Endoscopic skull base surgery

Skull base dural reflection models: tool for teaching neuroanatomy at resource-scarce centers

Skull base dural reflections are complex, and along with various ligaments joining sutures of the skull base, are related to most important vessels like internal carotid arteries (ICA), vertebral arteries, jugular veins, cavernous sinus, and cranial nerves which make surgical approaches difficult and need thorough knowledge and anatomy for a safe dissection and satisfactory patient outcomes. Cadaver dissection is much more important for the training of skull base anatomy in comparison to any other subspecialty of neurosurgery; however, such facilities are not available at most of the training institutes, more so in low- and middle-income countries (LMICs). A glue gun (100-Watt glue gun, ApTech Deals, Delhi, India) was used to spread glue over the superior surface of the bone of the skull base over desired area (anterior, middle, or lateral skull base). Once glue was spread over the desired surface uniformly, it was cooled under running tap water and the glue layer was separated from the skull base. Various neurovascular impressions were colored for ease of depiction and teaching. Visual neuroanatomy of the inferior surface of dural reflections of the skull base is important for understanding neurovascular orientations of various structures entering or exiting the skull base. It was readily available, reproducible, and simple for teaching neuroanatomy to the trainees of neurosurgery. Skull base dural reflections made up of glue are an inexpensive, reproducible item that may be used for teaching neuroanatomy. It may be useful for trainees and young neurosurgeons, especially at resource-scarce healthcare facilities.

Three-Dimensional Endoscopic Endonasal Surgery: A Systematic Review

OBJECTIVES

To compare participant performance and preference in the use of three-dimensional (3D) endoscopy compared to traditional two-dimensional (2D) endoscopy.

METHODS

PubMed, Embase, Medline, ClinicalKey, BMJ Case Reports, and the Cochrane library were systematically searched for English-language articles published between 2005 and 2020. Studies reporting comparisons of outcomes between 3D and 2D endoscopes were identified. Data relating to performance-related outcomes, as well as the participants' preferred endoscope were extracted, and pooled using meta-analysis models.

RESULTS

Ten studies were included in the qualitative synthesis. Six studies reported results of participants completing simulated tasks with endoscopes, while four reported full procedures. Peg transfer tasks (n = 4 cohorts) were found to be completed significantly faster with the 3D versus 2D endoscope (pooled mean difference 6.8 seconds, 95% confidence interval [CI]: 2.3-11.3), while no significant difference in times taken was observed for touch tasks (n = 4; pooled mean difference 3.7 seconds, 95% CI: -1.9 to 9.2). The secondary outcome of participant preference was reported by five studies, in which a significant preference for the 3D endoscope was observed (P = .010), with a pooled total of 72% (95% CI: 59-83) of participants preferring this to the 2D endoscope.

CONCLUSIONS

There is a growing body of evidence in support of 3D visualization in endoscopy. We have demonstrated 3D endoscopy to be associated with a significantly shorter time to performing simulated, reproducible and controlled tasks, and to be the preference of participants. This study provides grounds for further evaluation of the technology, and the potential for a greater widespread use. Laryngoscope, 2021.

The historical perspective in approaches to the spheno-petro-clival meningiomas

The current literature regarding surgical treatment for tumors in the sphenopetroclival (SPC) region is merely scarce. Through a comprehensive literature review, we investigated the indications, outcomes, and complications of different surgical approaches to the SPC meningiomas. Given its complicated relationship between these slow-progression tumors and some critical neurovascular structures in the SPC region, surgical treatment of these tumors faces the challenge of achieving a maximal grade of resection, while preserving patient functionality. The development of new surgical techniques and approaches in recent years have permitted the advancement in the treatment of these tumors, with acceptable rates of morbidity and mortality. The choice of a surgical approach as a treatment for the lesion depends mainly on the type of tumor extension, surgeon's preferences, and the displacement of neurovascular structures. Rather than focusing on one single strategy of treatment, the skull-base surgeon should tailor the approach based on the origin and features of the lesion; as well as the peculiarities of the surgical anatomy. This strategy aims to decrease morbidity and to optimize tumor resection and patient quality of life.

Breadth and Depth: Three-Dimensional Endoscopic Field of View: Two-Dimensional Versus Three-Dimensional Endoscopic Field of View

BACKGROUND

Three-dimensional (3D) endoscopy is an emerging tool in ear-nose-throat (ENT) and skull base surgery with the benefit of providing real-time depth perception. Several investigators have reported that the field of view (FOV) is reduced in 3D endoscopes compared with regular 2-dimensional (2D) endoscopes. Thus, we objectively compared the FOV of 2D and 3D endoscopes.

METHODS

Using a standard 2D and 2 different 3D ENT endoscopes, images were captured of 1-mm graph paper from a set distance of 6 cm. The FOV was calculated from these images and compared among the endoscopes.

RESULTS

The VisionSense 3D endoscope had a slightly smaller FOV (9.1 cm vs. 10.1 cm; -9.9%), and the Karl Storz 3D endoscope showed a slightly larger FOV (10.4 cm vs. 10.1 cm; +3.0%). However, the results were complicated by the different-shaped images produced by the 3D endoscopes.

CONCLUSION

The differences in the FOV between the 2D and 3D endoscopes used in ENT surgery were not clinically significant. Thus, the FOV should not be considered a limitation of 3D technology.

Three-dimensional endoscopy: The future of nasoendoscopic training

OBJECTIVES/HYPOTHESIS

Three-dimensional (3D) endoscopy is an emerging tool in surgery that provides real-time depth perception. Its benefits have been investigated in surgical training, but the current literature lacks significant objective outcome data. We aimed to objectively compare the efficacy of two-dimensional (2D) versus 3D high-definition endoscopes in novice users.

STUDY DESIGN

Prospective, randomized crossover study.

METHODS

Ninety-two novice medical students who used both 2D and 3D endoscopes to complete two validated tasks in a box trainer participated in the study. Time taken and error rates were measured, and subjective data were collected.

RESULTS

Wilcoxon tests showed 3D technology was significantly faster than 2D (78 vs. 95 seconds, P = .004), and errors per task were significantly lower (3 vs. 5, P < .001). Sixty-nine percent of participants preferred the 3D endoscope.

CONCLUSIONS

3D high-definition endoscopy could be instrumental in training the next generation of endoscopic surgeons. Further research is required in a clinical setting.

LEVEL OF EVIDENCE

2b Laryngoscope, 129:1280-1285, 2019.

The pterygoclival ligament: a novel landmark for localization of the internal carotid artery during the endoscopic endonasal approach

OBJECTIVE

The transpterygoid extension of the endoscopic endonasal approach provides exposure of the petrous apex, Meckel's cave, paraclival area, and the infratemporal fossa. Safe and efficient localization of the lacerum segment of the internal carotid artery (ICA) is a crucial part of such exposure. The aim of this study is to introduce a novel landmark for localization of the lacerum ICA.

METHODS

Ten cadaveric heads were prepared for transnasal endoscopic dissection. The floor of the sphenoid sinus was drilled to expose an extension of the pharyngobasilar fascia between the sphenoid floor and the pterygoid process (the pterygoclival ligament). Several features of the pterygoclival ligament were assessed. In addition, 31 dry skulls were studied to assess features of the bony groove harboring the pterygoclival ligament.

RESULTS

The pterygoclival ligament was identified bilaterally during drilling of the sphenoid floor in all specimens. The ligament started a few millimeters posterior to the posterior end of the vomer alae and invariably extended posterolaterally and superiorly to blend into the fibrous tissue around the lacerum ICA. The mean length of the ligament was 10.5 ± 1.7 mm. The mean distance between the anterior end of the ligament and midline was 5.2 ± 1.2 mm. The mean distance between the posterior end of the ligament and midline was 12.3 ± 1.4 mm. The bony pterygoclival groove was identified at the confluence of the vomer, pterygoid process of the sphenoid, and basilar part of the occipital bone, running from posterolateral to anteromedial. The mean length of the groove was 7.7 ± 1.8 mm. Its posterolateral end faced the anteromedial aspect of the foramen lacerum medial to the posterior end of the vidian canal. A clinical case illustration is also provided.

CONCLUSIONS

The pterygoclival ligament is a consistent landmark for localization of the lacerum ICA. It may be used as an adjunct or alternative to the vidian nerve to localize the ICA during endoscopic endonasal surgery.

Trigeminocardiac reflex during endoscopic juvenile nasopharyngeal angiofibroma surgery: an appraisal

Juvenile nasopharyngeal angiofibroma is a locally aggressive benign tumour which has propensity to erode the skull base. The tumour spreads along the pathways of least resistance and is in close proximity to the extracranial part of trigeminal nerve. Advancements in expanded approaches for endoscopic excision of tumours in infratemporal fossa and pterygopalatine fossa increase the vulnerability for the trigeminocardiac reflex. The manipulation of nerve and its branches during tumour dissection can lead to sensory stimulation and thus inciting the reflex. The aim of our study is to report the occurrence of trigeminocardiac reflex in endoscopic excision of juvenile nasopharyngeal angiofibroma. To describe the occurence of trigeminocardiac reflex during endoscopic endonasal excision of juvenile nasopharyngeal angiofibroma. We studied the occurrence of TCR in 15 patients (out of 242 primary cases and 52 revision cases) operated for endoscopic endonasal excision of JNA. The drop in mean arterial blood pressure and heart rate were observed and measured. To the best of our knowledge of English literature, this is the first case series reporting TCR as complication in endoscopic excision of JNA. occurence of this reflex has been mentioned in various occular, maxillofacial surgeries but its occurence during endoscopic excision of JNA has never been reported before. Manifestation of trigeminocardiac reflex during surgery can alter the course of the surgery and is a potential threat to life. It is essential for the anesthetist and surgeons to be familiar with the presentations, preventive measures and management protocols.

Updates in anterior skull base reconstruction

PURPOSE OF REVIEW

This article summarizes the indications and surgical techniques for the reconstructions of anterior skull base defects.

RECENT FINDINGS

There is increasing popularity of the vascularized pedicled flaps in endoscopic skull base surgery for the successful reconstruction of anterior skull base defects, compared with the use of free-tissue grafts. The location and size of the defect as well as the rate of cerebrospinal fluid (CSF) flow are important considerations for selection of the most appropriate reconstructive approach. Recent literature provides evidence suggesting that pedicled flaps may be more effective for clival defects and high-flow CSF leaks, potentially reducing the incidence of postoperative CSF leaks. Although the nasoseptal flap (NSF) continues to be the mainstay of endoscopic skull base reconstruction, alternative vascularized flaps exist when the NSF is impractical or unavailable, and new surgical approaches continue to evolve.

SUMMARY

Vascularized pedicled flaps, and especially the NSF, have greatly reduced complications associated with endoscopic skull base surgery. Multiple considerations should be taken into account during closure of skull base defects, and several options are available to accommodate different needs.

Modeling alterations in sinonasal physiology after skull base surgery

BACKGROUND

Endonasal endoscopic skull base surgery (EESBS) often requires significant alterations in intranasal anatomy. For example, posterior septectomy (PS) with middle turbinate resection (MTR) is frequently performed to provide access to large sellar and clival tumors. However, little is known about the alterations that occur in sinonasal physiology. This study was designed to assess changes in sinonasal physiology after virtually performed endoscopic skull base surgery.

METHODS

Three-dimensional models of the sinonasal passage were created from computed tomography scans in three subjects with varying anatomy: no SD (SD), right anterior SD, and left anterior SD, respectively. Four additional surgery types were performed virtually on each model: endoscopic transsphenoidal approach (ETSA) with small (1 cm) PS (smPS), ETSA with complete (2 cm) PS, ETSA with smPS and right MTR, and ETSA with complete PS and right MTR. Computational fluid dynamics (CFD) simulations were performed on the 3 presurgery and 12 virtual surgery models to assess changes from surgery types.

RESULTS

Increased nasal airflow corresponded to amount of tissue removed. Effects of MTR on unilateral airflow allocation were unchanged in subject with no SD, worsened in leftward SD, and reversed in rightward SD. Severity of airflow and mucosal wall interactions trended with amount of tissue removed. MTR hindered flow interactions with the olfactory mucosa in subjects with SD.

CONCLUSION

CFD simulations on virtual surgery models are able to reasonably detect changes in airflow patterns in the computer-generated nasal models. In addition, each patient's unique anatomy influences the magnitude and direction of these changes after virtual EESBS. Once future studies can reliably correlate CFD parameters with patient symptoms, CFD will be a useful clinical tool in surgical planning and maximizing patient outcomes.

Three-Dimensional Hand-to-Gland Combat: The Future of Endoscopic Surgery?

Objective To compare two dimensional (2D), three-dimensional (3D) non-high-definition (HD), and 3D HD endoscopic surgical techniques. Methods We describe our initial operative experience with a novel 3D HD endoscopic endonasal approach involving a pituitary adenoma resection, provide a case series, and review the current literature. This is the first case in Europe using the new 3D HD endoscope. Results Although research evidence remains limited, there are no significant negative perioperative or postoperative outcomes when compared with 2D endoscopic techniques. In our experience the narrow operating corridors of endoscopic surgery cannot be addressed with 3D endoscopic techniques. The new 3D HD endoscope creates imaging quality similar to conventional 2D HD systems. Conclusion Three-dimensional endoscopic endonasal techniques provide an exciting new avenue, effectively addressing potential depth perception difficulties with current 2D systems.

An advanced navigation protocol for endoscopic transsphenoidal surgery

OBJECTIVE

To report our clinical experience with an advanced navigation protocol that provides seamless integration into the operating workflow of endoscopic transsphenoidal surgery.

PATIENTS AND METHODS

From 32 consecutive cases of endoscopic transsphenoidal surgery, an optimal setup of continuous electromagnetic instrument navigation was created. Additionally, our standard multimodality image navigation of T1-weighted magnetic resonance (MR) images for soft tissue, MR angiogram for vascular structures, and computed tomography (CT) for solid bone was advanced by the addition of a CT surface rendering for fine paranasal sinus structures. The anatomic structures visualized and their clinical impacts were compared between standard and advanced visualization protocol. Bone-windowed CT images served as reference. The accuracy of the navigation setup was assessed by intraoperative landmark tests. Potential tissue shift was calculated by comparing pre- and postoperative MR angiograms of 20 macroadenomas.

RESULTS

After a learning curve of 2 cases (1 ferromagnetic interference and 1 dislocation of the patient reference tracker), the advanced navigation protocol was feasible in 30 cases. Advanced multimodality imaging was able to visualize significantly finer paranasal sinus structures than multimodality image navigation without CT surface rendering, equal to bone-windowed CT images (P < 0.001, McNemar test). This was found helpful for orientation in cases of complex sphenoid sinus anatomy. The accuracy of the advanced navigation setup corresponded to standard optic navigation with skull fixation. A tissue shift of median 2 mm (range 0-9 mm) was observed in the posterior genu of the internal carotid arteries after tumor resection.

CONCLUSIONS

The advanced navigation protocol permits continuous suction-tracked navigation guidance during endoscopic transsphenoidal surgery and optimal visualization of solid bone, fine paranasal sinus structures, soft-tissue and vascular structures. This may add to the safety of the procedure especially in cases of anatomical variations and in cases of recurrent adenomas with distorted anatomy.

Analysis of the petrous portion of the internal carotid artery: landmarks for an endoscopic endonasal approach

OBJECTIVES/HYPOTHESIS

While there are many benefits to the endoscopic endonasal approach to the infratemporal fossa, involvement of the petrous portion of the internal carotid artery (ICA) poses a unique challenge. The endoscopic endonasal approach requires establishing the relationship of the petrous ICA to anatomical landmarks to guide the surgeon. This study evaluates the relationship of petrous ICA to specific anatomic landmarks, both radiographically and through cadaveric dissections.

STUDY DESIGN

Cadaveric and radiographic study.

METHODS

An endoscopic endonasal approach was used to access the petrous carotid and infratemporal fossa. Dissections exposed the petrous portion of the carotid artery and identified the foramen rotundum, ovale, and spinosum. Both anatomical and radiographic representations of these landmarks were then evaluated and compared relative to the petrous carotid.

RESULTS

The endoscopic endonasal approach to the infratemporal fossa with exposure of the petrous ICA afforded complete visualization of the entire segment of this portion of the ICA with limited anatomical obstruction. The foramen rotundum, ovale, and spinosum were successfully identified and dissected with preservation of their neuro/vascular contents. Computed tomography analysis calculated a mean distance to the petrous ICA of 16.34 mm from the foramen rotundum, 4.88 mm from the ovale, and 5.11 mm from the spinosum in males. For females, the values were 16.40 mm from the rotundum and 4.36 mm each from the ovale and spinosum.

CONCLUSION

An endonasal endoscopic approach to the infratemporal fossa with exposure of the petrous ICA is feasible. The anatomical landmarks can serve as both radiographic and surgical landmarks in this approach.

Endoscopic and Three-Dimensional Radiographic Imaging of the Pterygopalatine and Infratemporal Fossae

Objectives:

We sought to define the surgical endoscopic anatomy of the pterygopalatine fossa (PPF) and infratemporal fossa (ITF) through endoscopic cadaver dissections and radiographic imaging analysis.

Methods:

Eleven fresh cadavers were submitted to computed tomography (CT) and endoscopic dissection. We used 3-dimensional (3-D) CT reconstruction and endoscopic video imaging for analysis of the bony and soft tissue landmarks. One fixed cadaver head was grossly dissected to confirm the endoscopic anatomic findings.

Results:

The CT and 3-D CT reconstruction measurements between the pterygoid canal and the foramen rotundum averaged 4.36 mm and 5.09 mm, respectively. An osseous ridge (pterygoid ridge) was identified on the anterior face of the pterygoid process as a novel identifiable anatomic landmark in all of the specimens. The average length of the pterygoid ridge on 3-D CT reconstruction was 7.84 mm. The internal maxillary artery entered the PPF posteromedial to the temporalis tendon and anterolateral to the lateral pterygoid muscle. The average distance from the anterior edge of the lateral pterygoid plate to the foramen ovale was 17.1 mm.

Conclusions:

The pterygoid ridge is a novel and reliable osseous landmark that could assist surgeons during endoscopic surgery on the PPF and ITF. The neurovascular and muscular anatomic relationships were characterized for both the PPF and the ITF.

Anatomical and computed tomographic analysis of the transcochlear and endoscopic transclival approaches to the petroclival region

OBJECTIVES/HYPOTHESIS

Advances in the field of skull base surgery aim to maximize anatomical exposure while minimizing patient morbidity. The petroclival region of the skull base presents numerous challenges for surgical access due to the complex anatomy. The transcochlear approach to the region provides adequate access; however, the resection involved sacrifices hearing and results in at least a grade 3 facial palsy. An endoscopic endonasal approach could potentially avoid negative patient outcomes while providing a desirable surgical window in a select patient population.

STUDY DESIGN

Cadaveric study.

METHODS

Endoscopic access to the petroclival region was achieved through an endonasal approach. For comparison, a transcochlear approach to the clivus was performed. Different facets of the dissections, such as bone removal volume and exposed surface area, were computed using computed tomography analysis.

RESULTS

The endoscopic endonasal approach provided a sufficient corridor to the petroclival region with significantly less bone removal and nearly equivalent exposure of the surgical target, thus facilitating the identification of the relevant anatomy. The lateral approach allowed for better exposure from a posterolateral direction until the inferior petrosal sinus; however, the endonasal approach avoided labyrinthine/cochlear destruction and facial nerve manipulation while providing an anteromedial viewpoint. The endonasal approach also avoided external incisions and cosmetic deficits. The endonasal approach required significant sinonasal resection.

CONCLUSIONS

Endoscopic access to the petroclival region is a feasible approach. It potentially avoids hearing loss, facial nerve manipulation, and cosmetic damage.

[Transnasal endoscopic approaches to the cranial base]

Recent advances in surgical endoscopy have made it possible to reach nearly the whole cranial base through a transnasal approach. These 'expanded approaches' lead to the frontal sinuses, the cribriform plate and planum sphenoidale, the suprasellar space, the clivus, odontoid and atlas. By pointing the endoscope laterally, the surgeon can explore structures in the coronal plane such as the cavernous sinuses, the pyramid and Meckel cave, the sphenopalatine and subtemporal fossae, and even the middle fossa and the orbit. The authors of this contribution use most of these approaches in their endoscopic skull base surgery. The purpose of this contribution is to review the hitherto established endoscopic approaches to the skull base and to illustrate them with photographs obtained during self-performed procedures and/or cadaver studies.

Management of sinonasal chondrosarcoma: a systematic review of 161 patients

BACKGROUND

This study reviews the published literature related to management of sinonasal chondrosarcoma. Clinical presentation, demographics, radiographic diagnosis, treatment, and management outcomes of this uncommon disease are reported.

METHODS

A systematic review of studies for sinonasal chondrosarcoma from 1950 to 2012 was conducted. A PubMed search for articles related to this condition, along with bibliographies of the selected articles was performed. Articles were examined for patient data that reported survivability. Demographic data, disease site, treatment strategies, follow-up, outcome, and survival were analyzed.

RESULTS

A total of 63 journal articles were included, comprising a total of 161 cases of sinonasal chondrosarcoma. The average follow-up was 77.4 months (range, 1 to 325.2 months). Surgical resection was the most common treatment modality, used in 72.0% of cases. A combination of surgery and radiation therapy was the second most commonly used treatment modality, used in 21.7% of cases.

CONCLUSION

This review contains the largest pool of sinonasal chondrosarcoma patients to date and suggests aggressive surgical resection is the most common treatment modality for this condition. The use of adjuvant radiotherapy for prevention of local recurrence after subtotal or total resection has not been proven effective. However, the use of radiotherapy in addition to surgical resection has shown benefit in some studies in terms of survival.

Craniofacial resection and its role in the management of sinonasal malignancies

Sinonasal malignancy is rare, and its presentation is commonly late. There is a wide variety of pathologies with varying natural histories and survival rates. Anatomy of the skull base is extremely complex and tumors are closely related to orbits, frontal lobes and cavernous sinus. Anatomical detail and the late presentation render surgical management a challenging task. A thorough understanding of anatomy and pathology combined with modern neuroimaging and reliable reconstruction within a multidisciplinary team is imperative to carry out skull base surgery effectively. While endoscopic approaches are gaining credibility, clearly, it will be some time before meaningful comparisons with craniofacial resection can be made. Until then, craniofacial resection will remain the gold standard for managing the sinonasal malignancies of the anterior skull base, as it has proved to be safe and effective.

[Shifting paradigm in skull base surgery: Roots, current state of the art and future trends of endonasal endoscopic approaches]

During the last two decades, endoscopic endonasal approach has completed the minimally invasive skull base surgery armamentarium. Endoscopic endonasal skull base surgery (EESBS) was initially developed in the field of pituitary adenomas, and gained an increasing place for the treatment of a wide variety of skull base pathologies, extending on the midline from crista galli process to the occipitocervical junction and laterally to the parasellar areas and petroclival apex. Until now, most studies are retrospective and lack sufficient methodological quality to confirm whether the endoscopic endonasal pituitary surgery has better results than the microsurgical trans-sphenoidal classical approach. The impressions of the expert teams show a trend toward better results for some pituitary adenomas with the endoscopic endonasal route, in terms of gross total resection rate and probably more comfortable postoperative course for the patient. Excepting intra- and suprasellar pituitary adenomas, EESBS seems useful for selected lesions extending onto the cavernous sinus and Meckel's cave but also for clival pathologies. Nevertheless, this infatuation toward endoscopic endonasal approaches has to be balanced with the critical issue of cerebrospinal fluid leaks, which constitutes actually the main limit of this approach. Through their experience and a review of the literature, the authors aim to present the state of the art of this approach as well as its limits.

Olfactory groove meningioma: discussion of clinical presentation and surgical outcomes following excision via the subcranial approach

OBJECTIVES/HYPOTHESIS

To describe surgical outcomes and radiographic features of olfactory groove meningiomas treated by excision through the subcranial approach. Special emphasis is placed on paranasal sinus and orbit involvement.

STUDY DESIGN

Retrospective review of a series of patients.

METHODS

Nineteen patients underwent excision of olfactory groove meningioma (OGM) via the transglabellar/subcranial approach between December 1995 and November 2009. Nine patients had previously undergone prior resection at outside institutions, and four had prior radiotherapy in addition to a prior excision. Transglabellar/subcranial surgical approach to the anterior skull base was performed.

RESULTS

Tumor histology included three World Health Organization (WHO) grade III lesions, one WHO grade II lesion, and 15 WHO grade I lesions. Fourteen patients had evidence of extension into the paranasal sinuses, with the ethmoid sinus being most commonly involved. Kaplan-Meier estimates of mean overall and disease-free survival were 121.45 months and 93.03 months, respectively. The mean follow-up interval was 41.0 months, and at the time of data analysis three patients had recurrent tumors. Seven (36.8%) patients experienced a major complication in the perioperative period; there were no perioperative mortalities. Orbit invasion was observed in four patients, with optic nerve impingement in 11 patients. Of these, three patients had long-term diplopia. No patients experienced worsening of preoperative visual acuity.

CONCLUSIONS

Olfactory groove meningiomas demonstrate a propensity to spread into the paranasal sinuses, particularly in recurrent cases. Given a tendency for infiltrative recurrence along the skull base, this disease represents an important area of collaboration between neurosurgery and otolaryngology. The subcranial approach offers excellent surgical access for excision, particularly for recurrences that involve the paranasal sinuses and optic apparatus.

Cholesterol granuloma of the petrous apex

The traditional approaches to symptomatic cholesterol granuloma (CG), the most common benign pathologic lesion of the petrous apex, have historically been transotic, including middle fossa, translabyrinthine, retrocochlear, or infra- or retrolabyrinthine approaches. These approaches were often fraught with risk to the vestibular or cochlear apparatus, the need for brain retraction, or lack of a natural drainage pathway after marsupialization of the granuloma. This article reviews the literature on the transnasal approach to petrous apex CGs, including medial, medial with carotid medialization, and transpterygoid approaches. Of the 19 reported CGs treated with endoscopic drainage, only one recurrence was noted.

[Modern skull base surgery from the perspective of neurosurgeons]

At present, modern skull base surgery is a highly sophisticated interdisciplinary collaboration of various diagnostic and therapeutic disciplines. The overall goal is the treatment of complex tumorous, traumatic, vascular and inflammatory processes or developmental disorders of the skull base with preservation of function. The paper presents modern concepts, procedures and minimally invasive strategies in skull base surgery and also critically discusses the current trend to endoscopic and robot-assisted surgical techniques.