Transzygomatic approach to the tentorial incisura: surgical anatomy

Cranio-Orbito-Zygomatic Approach: Core Techniques for Tailoring Target Exposure and Surgical Freedom

Background: The cranio-orbito-zygomatic (COZ) approach is a workhorse of skull base surgery, and each of its steps has a precise effect on target exposure and surgical freedom. The present study overviews the key techniques for execution and tailoring of the COZ approach, focusing on the quantitative effects resulting from removal of the orbitozygomatic (OZ) bar, orbital rim, and zygomatic arch. Methods: A PRISMA-based literature review was performed on the PubMed/Medline and Web of Science databases using the main keywords associated with the COZ approach. Articles in English without temporal restriction were included. Eligibility was limited to neurosurgical relevance. Results: A total of 78 articles were selected. The range of variants of the COZ approach involves a one-piece, two-piece, and three-piece technique, with a decreasing level of complexity and risk of complications. The two-piece technique includes an OZ and orbitopterional variant. Superolateral orbitotomy expands the subfrontal and transsylvian corridors, increasing surgical freedom to the basal forebrain, hypothalamic region, interpeduncular fossa, and basilar apex. Zygomatic osteotomy shortens the working distance of the pretemporal and subtemporal routes. Conclusion: Subtraction of the OZ bar causes a tremendous increase in angular exposure of the subfrontal, transsylvian, pretemporal, and subtemporal perspectives avoiding brain retraction, allowing for multiangled trajectories, and shortening the working distance. The COZ approach can be tailored based on the location of the lesion, thus optimizing the target exposure and surgical freedom and decreasing the risk of complications.

Tentorial Incision vs. Retraction of the Tentorial Edge during the Subtemporal Approach: Anatomical Comparison in Cadaveric Dissections and Retrospective Clinical Case Series

Objective  The aim of this study was to compare tentorial incision (group A) versus retraction and tack up suture (group B) of the tentorial edge during the subtemporal approach for surgery in the high basilar region. Design  24 cadaveric dissections and 4 clinical cases of aneurysms of the high basilar region are presented. Assessment included visibility and operability afforded by either tentorial incision creating a dural flap (group A) or retraction of the tentorial edge and tethering with a suture (group B). Four patients, two with superior cerebellar artery aneurysms and two with proximal posterior cerebral artery aneurysms were treated with each approach. Results  In the quantitative evaluations, we found no significant difference in the exposure of the posterior cerebral, superior cerebellar, and perforant arteries as well as surgical working area provided by either approach. However, tentorial incision allowed a significantly greater exposure of the basilar artery and the fourth cranial nerve (both p  < 0.001). Concerning operability, tentorial incision provided no objective advantage for direct clipping of the high basilar region (groups A vs. B, p  > 0.05). Subjectively, clipping of the high basilar segment was feasible using tentorial tethering only. Conclusion  Retraction of the free edge of the tentorium downward by tethering with a suture is simple and fast method for exposure of aneurysms in the high basilar region when the pathology does not require a proximal control. In our data the rather more invasive and time consuming tentorial incision provided an additional objectified advantage only for placement of a proximal temporary clip.

Indications and Safety of the Zygomatic Osteotomy in Middle Cranial Fossa Surgery: A Retrospective Cohort Review

Background  Zygomatic osteotomy, an adjunct to middle cranial fossa (MCF) surgical approaches, improves the superior-inferior angle of approach and minimizes temporal lobe retraction. However, a decision-making algorithm for selective use of the zygomatic osteotomy and the impact of the zygomatic osteotomy on surgical complications have not been well documented. Objective  We described an algorithm for deciding whether to use a zygomatic osteotomy in MCF surgery and evaluated complications associated with a zygomatic osteotomy. Methods  A retrospective review of MCF cases over 11 years at our academic tertiary referral center was conducted. Demographic variables, tumor characteristics, surgical details, and postoperative complications were extracted. Results  Of the 87 patients included, 15 (17%) received a zygomatic osteotomy. Surgical trajectory oriented from anterior to posterior (A-P) was significantly correlated with the use of the zygomatic osteotomy. Among the cases approached from A-P, we found (receiver-operating characteristic curve) that the cut-off tumor size that predicted a zygomatic osteotomy was 30 mm. Of the 87 cases included, 15 patients had a complication. The multivariate logistic regression model failed to reveal any significant correlation between complications and zygomatic osteotomies. Conclusions  We found that the most important factor determining the use of a zygomatic osteotomy was anticipated trajectory. A-P approaches were most highly correlated with zygomatic osteotomy. Within those cases, a lesion size cut-off of 30 mm was the secondary predicting factor of zygomatic osteotomy use. The odds of suffering a surgical complication were not significantly increased by use of zygomatic osteotomy.

Transzygomatic Approach to Skull Base: History, Evolution, and Possibility of a Simple Modification

The surgical approaches to anterior, middle, and lateral skull base have evolved drastically, transcending from an era of oblivion to well-defined and systematically executed, state-of-the-art, refined surgery. The transzygomatic approach, which was developed to access the nasopharynx, has been applied to versatile locations of skull base pathology, with continuous evolution and modification of the osteotomies and skin flaps involved. A simple modification is proposed which could help reach a compromise between the wide exposure provided by the hemicoronal incision and the minimally invasive preauricular approach.

Lateral transzygomatic middle fossa approach and its extensions: surgical technique and 3D anatomy

BACKGROUND

Various approaches to lesions involving the middle fossa and cavernous sinus (CS), with and without posterior fossa extension have been described. In the present study, we describe the surgical technique for the extradural lateral tranzygomatic middle fossa approach and its extensions, highlight relevant 3D anatomy.

METHODS

Simulations of the lateral transzygomatic middle fossa approach and its extensions were performed in four silicon-injected formalin fixed cadaveric heads. The step-by-step description and relevant anatomy was documented with 3D photographs.

RESULT

The lateral transzygomatic middle fossa approach is particularly useful for lesions involving the middle fossa with and without CS invasion, extending to the posterior fossa and involving the clinoidal region. This approach incorporates direct lateral positioning of patient, frontotemporal craniotomy with zygomatic arch osteotomy, extradural elevation of the temporal lobe, and delamination of the outer layer of the lateral CS wall. Extradural drilling of the sphenoid wing and anterior clinoid process allows entry into the CS through the superior wall and exposure of the clinoidal segment of the ICA. Posteriorly, drilling the petrous apex allows exposure of the ventral brainstem from trigeminal to facial nerve and can be extended to the interpeduncular fossa by division of the superior petrosal sinus.

CONCLUSION

The present study illustrates 3D anatomical relationships of the lateral transzygomatic middle fossa approach with its extensions. This approach allows wide access to different topographic areas (clinoidal region and clinoidal ICA, the entire CS, and the posterior fossa from the interpeduncular fossa to the facial nerve) via a lateral trajectory. Precise knowledge of technique and anatomy is necessary to properly execute this approach.

[Transzygomatic pterional approach. Part 2: Surgical experience in the management of skull base pathology]

OBJECTIVES

To present our experience with the transzygomatic pterional approach in the treatment of neurosurgical pathology of the base of the skull located in the middle cranial fossa and surrounding areas.

METHOD

A retrospective study of pathological findings, surgical outcomes and complications in a series of 31 cases operated on between 2009 and 2011 using a transzygomatic pterional approach.

RESULTS

The lesions involved the sphenoid wing (25.9%), several regions due to invasive growth pattern (19.5%), the temporal lobe (16.1%) and cavernous sinus (12.9%). The others were located in the floor of the middle fossa, Meckel's cave, incisural space, cisterns and infratemporal region. The pathological nature of the lesions was: benign meningioma (42%), temporal lobe tumour (19.5%), vascular disease (12.9%), inflammatory lesions (6.4%), atypical meningioma (6.4%), epidermoid cyst (6.4%), neurinoma (3.2%) and poorly differentiated infratemporal carcinoma (3.2%). The approach was usually combined extra-intradural (58.1%) and, less frequently, just extradural (16.1%) or intradural (25.8%). Approach-related complications were minor: haematomas in the wound not requiring treatment (67.8%), superior transient facial paresis (9.7%), transient temporomandibular joint dysfunction (12.9%) and atrophy of the temporal muscle (16.2%). There were no hardware-related complications or cosmetic issues related to the osteotomy and posterior osteosynthesis of the zygomatic arch.

CONCLUSIONS

The pterional approach combined with osteotomy of the zygomatic arch allows mobilising the temporalis muscle away from the temporal fossa, consequently exposing its entire surface to complete the temporal craniotomy up to the middle fossa; it helps to access and treat pathology in this region or it can be used as a corridor to approach surrounding areas.

Path to the Interpeduncular Fossa: Anatomical Comparison of Endoscopic-Assisted versus Standard Subtemporal Approach

Objective The aim of this study was to assess the assumed advantage of endoscopic assistance to the standard subtemporal approach. The idea was to measure qualitatively and quantitatively visibility versus operability. Design We performed eight subtemporal dissections on four cadaver heads. Our dissections integrated an operating microscope, endoscope, and neuronavigation. Comparison was made between visibility and operability afforded by the microscope alone or by the microscope-endoscope combination. Visibility was recorded as complete or incomplete and was quantified for key structures using linear measurements taken by the navigation system. Operability was determined by whichever maneuvers could be safely and comfortably accomplished in the space afforded. Results From our survey, the structures whose visibility most benefitted from the addition of the endoscope include: contralateral third nerve, posterior perforated substance, mammillary bodies, and contralateral superior cerebellar artery. With regard to quantitative evaluation, we found increased visibility of both basilar artery and posterior cerebral artery. With regard to the operability, no objective advantage was afforded by the addition of the endoscope. Subjectively, the maneuvers were easier to perform while using the endoscope. Conclusion Using the endoscope as an assistance tool during conducting classical subtemporal approach can help in overcome a lot of the classical subtemporal approach limitations.

Extradural endoscope-assisted subtemporal posterior clinoidectomy: a cadaver investigation study

BACKGROUND

Surgical treatment of distal basilar artery aneurysms is challenging because of the narrow surgical corridor, presence of vital perforating vessels, deep location, and difficulty in obtaining proximal control.

OBJECTIVE

To investigate using a cadaver model the feasibility of performing a transcranial extradural posterior clinoidectomy via a subtemporal route between V2 and V3 using an endoscope-microscope combination.

METHODS

Fourteen dissections were performed in 14 fresh cadaver heads. A standard pterional approach with removal of the zygomatic arch was followed by a 2-stage dissection to remove the posterior clinoid process. In stage 1 (microscopic stage), the area between the second and third trigeminal divisions (V2 and V3) was exposed and the anterior half of the bone between them was drilled to the sphenoid sinus cavity inferior to the carotid sulcus. In stage 2 (endoscopic stage), the drilling was continued to the carotid sulcus. Next, the endosteal layer of the dura lining the carotid sulcus was dissected from the bone that was then removed. At the end of this stage, the dura reflection that forms the posterior part of the pituitary capsule was exposed and the base of the posterior clinoid process was removed using a high-speed drill and curet. Finally, the dura was opened to confirm the removal of the posterior clinoid process.

RESULTS

It was possible to remove the posterior clinoid process in every specimen without any obvious anatomic injury to the surrounding structures.

CONCLUSION

This study demonstrated the feasibility of the resection of the posterior clinoid process extradurally. This maneuver could be incorporated in multiple cranial base approaches to the retrosellar area and interpeduncular cistern region.

The relationship between the zygomatic arch and the floor of the middle cranial fossa: a radiographic study

OBJECTIVE

Access to the floor of the middle cranial fossa (MCF) is often required for approaches to cranial base lesions. This study measures the craniocaudal distance between the zygomatic arch (ZA) and the floor of the MCF from a random sample of high-resolution computed tomography scans of the cranial base.

METHODS

Forty computed tomography scans were imported into an OsiriX station and reconstructed in multiple planes. The most caudal point of the MCF was determined in each computed tomography scan. The distances between that point and the root of the zygoma and the middle point of the ZA were calculated. The thickness of the temporalis muscle and the vertical height of the zygoma were also calculated. A 2-tailed, paired Student t test was used to compare right and left measurements with a 95% confidence interval and P value <.05 as statistically significant.

RESULTS

The foramen ovale was consistently the lowest point of the MCF. The average root-to-floor measurement was 5.05 +/- 0.42 mm above the floor of the MCF and distance of the mid-zygoma to the floor was 1.94 +/- 0.61 mm above the floor of MCF. The average temporalis muscle thickness and vertical height of the ZA were 22.22 +/- 0.36 mm and 8.10 +/- 0.13 mm, respectively. The muscle-to-floor measurement (muscle thickness + mid-zygoma-to-floor measurement) was 24.16 +/- 0.74 mm.

CONCLUSION

The routine use of a zygomatic osteotomy in approaches to the MCF does not provide very much increased exposure. However, in patients with exceptionally thick temporalis muscles or a high ZA, a zygomatic osteotomy may be helpful in providing exposure of the floor of the MCF.

Trans-zygomatic middle cranial fossa approach to access lesions around the cavernous sinus and anterior parahippocampus: a minimally invasive skull base approach

PURPOSE

Exposure of the cavernous sinus or anterior parahippocampus often involves a wide exposure of the temporal lobe and mobilization of the temporalis muscle associated with temporal lobe retraction. The authors present a cadaveric study to illustrate the feasibility, advantages and landmarks necessary to perform a trans-zygomatic middle fossa approach to lesions around the cavernous sinus and anterior parahippocampus.

METHODS

The authors performed bilateral trans-zygomatic middle fossae exposures to reach the cavernous sinus and parahippocampus in five cadavers (10 sides). We assessed the morbidity associated with this procedure and compared the indications, advantages, and disadvantages of this method versus more extensive skull base approaches. A vertical linear incision along the middle portion of the zygomatic arch was extended one finger breadth inferior to the inferior edge of the zygomatic arch. Careful dissection inferior to the arch allowed preservation of facial nerve branches. A zygomatic osteotomy was followed via a linear incision through the temporalis muscle and exposure of the middle cranial fossa floor.

RESULTS

A craniotomy along the inferolateral temporal bone and middle fossa floor allowed extradural dissection along the middle fossa floor and exposure of the cavernous sinus including all three divisions of the trigeminal nerve. Intradural inspection demonstrated adequate exposure of the parahippocampus. Exposure of the latter required minimal or no retraction of the temporal lobe.

CONCLUSIONS

The trans-zygomatic middle fossa approach is a simplified skull base exposure using a linear incision, which may avoid the invasivity of more extensive skull base approaches while providing an adequate corridor for resection of cavernous sinus and parahippocampus lesions. The advantages of this approach include its efficiency, ease, minimalism, preservation of the temporalis muscle, and minimal retraction of the temporal lobe.

Modifications to the orbitozygomatic approach. Technical note

The orbitozygomatic craniotomy is one of the workhorse approaches of skull base surgery, providing wide, multidirectional access to the anterior and middle cranial fossae as well as the basilar apex. Complete removal of the orbitozygomatic bar increases the angles of exposure, decreases the working depth of the surgical field, and minimizes brain retraction. In many cases, however, only a portion of the exposure provided by the full orbitozygomatic approach is needed. Tailoring the extent of the bone resection to the specific lesion being treated can help lower approach-related morbidity while maintaining its advantages. The authors describe the technical details of the supraorbital and subtemporal modified orbitozygomatic approaches and discuss the surgical indications for their use. Modifications to the orbitozygomatic approach are an example of the ongoing adaptation of skull base procedures to general neurosurgical practice.

Preservation of the temporal branch of the facial nerve in pterional-transzygomatic craniotomy

The temporal branch of the facial nerve may be saved in a pterional-transzygomatic craniotomy if the dissection is carried beneath the superficial temporal fascia. The anatomical and technical aspects of this exposure are described in this report.

An anatomicosurgical study of the temporal branch of the facial nerve

The surgical anatomy of the temporal branch of the facial nerve was studied bilaterally in 10 embalmed cadaveric heads. Particular attention was paid to the relationships between the temporal branch, the galeal-fascial layers, and the fat pads of the temporal-zygomatic region. The temporal branch of the facial nerve pierces the parotidomasseteric fascia below the zygomatic arch. This branch travels first in the subcutaneous tissue and then, above the zygomatic arch, in the subgaleal space. The temporal branch divides into an anterior, a middle (frontal), and a posterior ramus soon after it pierces the parotid fascia. The course of the terminal twigs of the temporal branch of the facial nerve in the subgaleal space is extremely variable, with their location being at times posterior to the anterior one-fourth of the temporalis muscle. Occasionally, a twig for the frontalis muscle may run in between the two layers of the superficial temporal fascia. Because of these findings (anteroposterior variability of temporal branch twigs and recurrent intrafascial twig), Yasargil's interfascial dissection may at times fail. A combined frontotemporal scalp/superficial temporal fascia dissection is anatomically suited to preserve the temporal branch of the facial nerve.