Three-step anterolateral approaches to the skull base

Spatial convergence of distant cortical regions during folding explains why arteries do not cross the sylvian fissure

OBJECTIVE

Cortical folding places regions that are separated by a large distance along the cortical surface in close proximity. This process is not homogeneous; regions such as the insular opercula have a much higher cortical surface distance (CSD) to euclidean distance (ED) than others. Here the authors explore the hypothesis that in the folded brain the CSD, and not the ED, determines regions of common irrigation, because this measure corresponds more closely with the distance along the prefolded brain, where the subarachnoid arterial vascular network starts forming.

METHODS

The authors defined a convergence index that compared the ED to the CSD and applied it to the cortical surface reconstruction of an average brain. They then compared cortical convergence to the irrigation patterns of major sulci and fissures of the brain, by assessing whether these structures were crossed or not crossed by arterial vessels in 20 fixed hemispheres.

RESULTS

The regions of highest convergence (top 1%) were clustered around the sylvian fissure, which is the only brain depression with high convergence values along its edges. Arterial crossings were commonly observed in every major sulcus of the brain, with the exception of the sylvian fissure, constituting a highly significant difference (p < 10-4).

CONCLUSIONS

Arteries do not cross regions of high convergence. In the adult brain the CSD, rather than the ED, predicts the regional irrigation pattern. The distant origin of the frontal and temporal lobes creates a region of high cortical convergence, which explains why arteries do not cross the sylvian fissure.

Meningo-orbital band detachment: A key step for the extradural exposure of the cavernous sinus and anterior clinoid process

The meningo-orbital band (MOB) is the most superficial dural band that tethers the fronto-temporal dura to the periorbita. It is usually encountered when performing a pterional or fronto-temporo-sphenoidal approach, and it disrupts surgical access to deeper regions. Our objective was to perform a detailed anatomy study and a stepwise method to successfully detach the MOB using cadaveric specimens. We used six formalin-fixed, silicone-injected cadaveric heads. On each side, we performed a pterional approach plus mini-peeling of the anterior third of the middle fossa and/or extradural anterior clinoidectomy. We also applied this technique in three clinical cases to prove its safety and efficacy. The detachment of the MOB consists in four steps, 1) detachment of the temporal and frontal dura, 2) cutting of the MOB, 3) exposure and drilling of the anterior clinoid process, and 4) pealing of the lateral wall of the cavernous sinus. Using clinical cases, we explain how to adapt the technique depending on the localization of the lesion. The detachment of the MOB is the key to safely expose the cavernous sinus and the anterior clinoid process. The authors proposed a step-by-step method for the safe and effective detachment of the MOB. It is recommended, particularly to less experienced neurosurgeons that are starting with skull base surgery, and also to experts that want to expand their knowledge.

Craniopharyngiomas: experience and results

INTRODUCTION

Craniopharyngiomas are a big challenge in the neurosurgical field. Because these lesions involve important systems, surgeons must weigh the risks of aggressive resection against the long-term challenges of recurrence. We present the outcomes of our patients based on clinical results, degree of resection, recurrence and disease-free survival.

MATERIALS AND METHODS

We reviewed medical records in all patients who had undergone surgical resection for craniopharyngioma at (Hospital Italiano de Buenos Aires) between 2007 and 2019. We considered ophthalmological examinations, imaging studies, endocrinological studies and surgical complications. Radical resections were planned in all of the patients. To help choose the correct surgical approach, craniopharyngiomas were classified based on tumor location.

RESULTS

Thirty cases of craniopharyngioma were analysed. 12.5% were classified as intrasellar, 12.5% as prechiasmatic, 43.75% as retrochiasmatic, and 31.25% as intraventricular. Overall, 38 cases involved a transcranial surgery (15 orbitozygomatic approach; 19 pterional approach and 4 transcallosal approach), seven involved a transsphenoidal approach, two microscopic transnasal approach and one ventricular endoscopy for emptying the craniopharyngioma cyst. Gross-total resection was achieved in 43.7% and near-total resection (more than 90%) in 25%. The mean follow-up period after resection was 4.7 years. Tumor recurrence occurred in 48%, with an average of 42.7 disease-free months.

CONCLUSION

Total tumor resection is the best treatment for craniopharyngioma. Due to its high morbidity and mortality, a multidisciplinary team is necessary for the management of these tumors.

The Anterolateral Triangle: Implications for a Transnasal Prelacrimal Approach to the Floor of the Middle Cranial Fossa

Background

The anterolateral triangle enclosed by the foramen rotundum and foramen ovale constitutes part of the floor of the middle cranial fossa (MCF).

Objective

To assess the feasibility of a transnasal prelacrimal approach for accessing the floor of MCF via an anterolateral triangle corridor and to determine the extent of maximal exposure while safeguarding neurovascular structures.

Methods

A transnasal prelacrimal approach was performed in 5 cadaveric specimens (10 sides). Following the identification of foramen rotundum and foramen ovale, the bony ridge between 2 was drilled to expose the MCF. The temporal lobe dura was then elevated laterally, and the distances from foramen ovale to the respective borders of the area of the MCF window were measured using a surgical navigation device.

Results

The MCF was exposed with a 0° scope in all specimens also exposing significant landmarks including the middle meningeal artery, greater superficial petrosal nerve, superior petrous sinus, and arcuate eminence. Average distances from foramen ovale to the anterior, posterior, and lateral exposed borders were 22.86 ± 1.87 mm, 27.24 ± 0.94 mm, and 24.23 ± 1.61 mm, respectively. The average area of exposed MCF window was 554.12 ± 60.22 mm2. Preservation of vidian nerve, greater palatine nerve, lateral nasal wall, and nasolacrimal duct was possible in all 10 sides.

Conclusion

It is feasible to access the floor of MCF via an endoscopic transnasal prelacrimal approach with seemingly low risk.

Analysis of Temporobasal Vein with Short Subdural Segment for Anterior Transpetrosal Approach

BACKGROUND

The anterior transpetrosal approach (ATPA) is applied to petroclival and brainstem lesions. Although neurosurgeons need to minimize the risk of neurologic complications, brain retraction is necessary for procedures of ATPA. Bridging veins (BVs) limit mobility of the temporal lobe. In the present study, BVs around the petrous bone were analyzed, focusing on the dural entrance and termination points.

METHODS

The relationship between subdural and meningeal segments of temporobasal veins (TBVs) was analyzed by preoperative computed tomography venography in 102 patients who underwent ATPA. TBVs were classified by the dural entrance and termination points.

RESULTS

TBVs mainly entered the transverse sinus and rarely entered transverse-sigmoid sinus (T-S) junction and superior petrosal sinus (SPS). TBVs entered a dural sinus either directly or indirectly through a meningeal vein. The changes in vascular diameter of the lumen, shape, and course were identified between the subdural and meningeal segments. Generally, BVs with long subdural segment do not limit mobility of the temporal lobe. TBVs draining into the T-S junction and SPS tended to be shorter than those draining into the transverse sinus. Furthermore, a few TBVs indirectly entered the dural sinuses through the meningeal vein (early dural entrance). The subdural segment of these TBVs was much shorter.

CONCLUSIONS

TBVs entering the T-S junction or SPS with short subdural segment may limit the mobility of the temporal lobe. Changes in vascular diameter, shape, and course were detected by computed tomography venography, which was helpful to detect the subdural-meningeal transition.

[The orbitozygomatic approach. History, technique, and modifications]

The orbitozygomatic approach (OZA) has been used in neurosurgical practice since the 1980s. Many approach modifications have been proposed; anatomical and clinical developments have been conducted in many clinics. However, there is no algorithm for choosing an approach option, depending on the type and topographo-anatomical features of pathology.

MATERIAL AND METHODS

We searched for publications in the PubMed and Medscape databases using the keywords 'orbitozygomatic'.

RESULTS

A total of 447 publications matching the search terms were found. In most of them, the approach was either not actually orbitozygomatic or was mentioned in the description of a clinical case. One hundred and nineteen full text Russian or English papers were available for detailed analysis. Of these, we selected 72 most relevant publications.

DISCUSSION

There were no studies demonstrating disadvantages of the OZA compared to traditional craniotomies. Orbitozygomatic approaches are widely used in routine neurosurgical practice. Existing approaches are not without disadvantages. The publications are based on small material. The recommendations on choosing the optimal OZA option are based on the authors' opinion, i.e. they satisfy the minimum level of evidence. There are no studies comparing the efficacy of OZA options in different types and topographo-anatomical variants of neurosurgical pathology of the anterior and middle skull base.

CONCLUSION

The reasonability of using the orbitozygomatic approach in neurosurgical practice is obvious. There are a large number of orbitozygomatic approaches and their modifications. The modern literature lacks an algorithm for choosing the optimal OZA option for specific types and topographo-anatomical variants of the pathological process.

Microsurgical Anatomy of the Interfascial Vein. Its Significance in the Interfascial Dissection of the Pterional Approach

BACKGROUND: The pterional approach (PA), together with its variants, is still one of the most common methods used by surgeons to reach the anterior and middle cranial base. A highly important technical detail during a PA is the preservation of the frontotemporal branch of the facial nerve, which can be achieved through an interfascial dissection.

OBJECTIVE: To describe the anatomy of the interfascial vein (IFV), highlighting its recognition as a significant anatomic reference to perform an interfascial dissection (IFD).

METHODS: Eight adult cadaveric heads, fixed with formaldehyde and injected with colored silicone, were studied. In 6 heads, an IFD was performed, simulating a PA. In the 2 remaining heads, the IFV was dissected. In addition, an IFD was performed in 10 patients, studying the IFV anatomy.

RESULTS: In the 6 cadaveric heads in which the PA with an IFD was performed, and in the 10 patients who underwent a PA with an IFD, the IFV was found. If the interfascial space is divided into thirds, in all cases, the IFV was located within the middle third of the interfascial fat pad. On the 2 cadaveric heads in which the IFV was anatomically dissected, the IFV was also located within the middle third of the interfascial space.

CONCLUSION: Recognizing the IFV in the interfascial space is of great help as an anatomic landmark to confirm that one is actually between both layers of the superficial temporal fascia.

Minimum Transpetrosal Retrolabyrinthine Approach for Revascularization of Posterior Cerebral Artery: Operative Nuance

BACKGROUND

Revascularization of the posterior cerebral artery (PCA) can be essential for treating complex cerebral aneurysms in the posterior circulation, and it is considered technically challenging. To help decrease the difficulty of this technique, we developed the minimum transpetrosal approach (MTPA).

OBJECTIVE

The technical nuances of the MTPA were innovated by cadaver head dissections and an actual clinical case.

METHODS

Four sides of the formalin-fixed cadaver heads were used to investigate if the posterior cerebral artery could be exposed with this minimum retraction of the temporal lobe in the subtemporal approach and the MTPA. By using the MTPA, 1 patient harboring a ruptured PCA aneurysm underwent superficial temporal artery-PCA anastomosis followed by isolation of the aneurysm.

RESULTS

In the cadaver head dissections, we noticed that the PCAs were difficult to expose with gentle retraction of the temporal lobe in the subtemporal approach. By performing an additional retrolabyrinthine mastoidectomy, performed as the MTPA, all 4 PCAs were easily exposed in the 4 wide surgical fields. The maximum widths of the surgical fields above and below the PCA could be successfully measured in 2 cases, which were 13.3 mm and 11.2 mm, respectively (mean, 12.3 mm). Additionally, in the actual live surgery using MTPA, the PCAs were relative easy to expose with a surgical field wide enough to perform PCA bypass, which was performed without complication.

CONCLUSION

The MTPA may be the most favorable approach for PCA bypass that can be performed easily with minimal temporal lobe retraction.