Far lateral supracerebellar infratentorial approach for the treatment of upper brainstem gliomas: clinical experience with pediatric patients

Endoscopic-assisted paramedian supracerebellar infratentorial approach to the posterior portion of the third ventricle: anatomical study and surgical cases

BACKGROUND

To date, morphometrical data providing a systematic quantification of accessibility and operability parameters to the boundaries of the posterior portion of the third ventricle (PTV) when applying an endoscopic-assisted paramedian supracerebellar infratentorial approach (EPSIA) are lacking. We performed an anatomical study and complemented our findings with surgical cases.

METHODS

Eight EPSIAs towards the PTV were performed in cadaveric specimens. Optimal approach angles (OA), surgical freedom (SF) and operability indexes (Oi) to the PTV boundaries were assessed. Additionally, a 54-year-old man and 33-year-old woman were operated on PTV tumors applying the EPSIA.

RESULTS

Sagittal OA to ventricle's roof and floor was 36±1.4° and 25.5±3.5° respectively, axial OA to the ipsilateral and contralateral ventricle's wall were 9.5±1.3° and 28.5±1.6°. SF was maximal on the contralateral wall (121.2±19.3mm2), followed by the roof (112.7±18.8mm2), floor (106.6±19.2mm2) and ipsilateral wall (94.1±15.7mm2). SF was significantly lower along the ipsilateral compared the contralateral wall (P<0.01) and roof (P<0.05). Facilitated surgical maneuvers with multiangled exposure were possible up to 8.5±1.07mm anterior to ventricle's entrance, whereas surgical maneuvers were possible but difficult up to 15.25±3.7mm. Visualization of more anterior was possible up to a distance of 27±2.9mm, but surgical maneuvers were barely feasible. EPSIA enabled successful resection of both PTV tumors and postoperative course was uneventful.

CONCLUSIONS

EPSIA can be effective for approaching the PTV, enabling surgery along all boundaries, but especially on its roof and contralateral wall. In the not-enlarged ventricle, surgical maneuvers are feasible up to the level of the Monro foramen, becoming more limited anteriorly.

Supracerebellar Infratentorial Approach, Indications, and Technical Pitfalls

Posterior tentorial incisura not infrequently requires to be exposed for tumors of pineal gland, pulvinar, midbrain and cerebellum, aneurysms, arteriovenous malformations. Residing almost at the center of the brain, this area is almost equal distance to any point on the calvarium behind coronal sutures enabling alternative routes to encounter. Compared to supratentorial routes either subtemporal or suboccipital approach, infratentorial supracerebellar route has several advantages as providing shortest, most direct approach to the lesions of this area without encountering any important arteries and veins. Since its initial description at the early twentieth century, a wide range of complications arising from cerebellar infarction, air embolism, and neural tissue damage have been encountered. Working in a deep, narrow corridor without enough illumination and visibility under very limited anesthesiology support hindered popularization of this approach. In the contemporary era of neurosurgery, advanced diagnostic tools and surgical microscopes with state-of-the-art microsurgery techniques coupled with modern anesthesiology have eliminated almost all drawbacks of infratentorial supracerebellar approach.

Surgical considerations for maximal safe resection of exophytic brainstem glioma in the pediatric age group

Background:

Brainstem glioma is the leading cause of morbidity and mortality among all central nervous system tumors, especially in childhood as it represents about 20% of all pediatric brain tumors. Therefore, this study aimed to present our experience in a tertiary center in a developing country with limited resources for the surgical management of exophytic brainstem gliomas.

Methods:

This retrospective study included pediatric patients with brainstem (midbrain, pontine, or medullary) focal or diffuse gliomas whether low or high grade that had dorsal, ventral, or lateral exophytic component who were presented to our hospitals from January 2019 to January 2021. The patients’ data were collected, such as age, sex, preoperative and postoperative clinical condition, radiological data, surgical approach, extent of tumor removal, histopathology, follow-up period, and adjuvant therapy.

Results:

A total of 23 patients were included in this study. The telovelar approach was used in 17 patients, the supracerebellar infratentorial approach in three patients, and the retrosigmoid, transcerebellar, and occipital transtentorial approach once for each patient. Twenty patients underwent near-total excision, and three underwent subtotal excision. Two-thirds of our cases (17 patients) were low-grade gliomas, with the remaining one-third comprising entirely of either anaplastic astrocytoma (five patients) or glioblastoma multiforme (one patient). The follow-up period of the patients extended from 3 months to 24 months.

Conclusion:

Exophytic brainstem glioma surgery can result in good outcomes with minimal complications when near-total excision is attempted through a properly chosen approach and adherence to some surgical techniques and considerations.

Extreme Lateral Supracerebellar Infratentorial Approach: Surgical Anatomy and Review of the Literature

OBJECTIVE

The extreme lateral supracerebellar infratentorial (ELSI) approach has the potential to access several distinct anatomical regions that are otherwise difficult to reach. We have illustrated the surgical anatomy through cadaveric dissections and provided an extensive review of the literature to highlight the versatility of this approach, its limits, and comparisons with alternative approaches.

METHODS

The surgical anatomy of the ELSI has been described using 1 adult-injected cadaveric head. Formalized noninjected brain specimens were also dissected to describe the brain parenchymal anatomy of the region. An extensive review of the literature was performed according to each targeted anatomical region. Illustrative cases are also presented.

RESULTS

The ELSI approach allows for wide exposure of the middle and posterolateral incisural spaces with direct access to centrally located intra-axial structures such as the splenium, pulvinar, brainstem, and mesial temporal lobe. In addition, for skull base extra-axial tumors such as petroclival meningiomas, the ELSI approach represents a rapid and adequate method of access without the use of extensive skull base approaches.

CONCLUSIONS

The ELSI approach represents one of the most versatile approaches with respect to its ability to address several anatomical regions centered at the posterior and middle incisural spaces. For intra-axial pathologies, the approach allows for access to the central core of the brain with several advantages compared with alternate approaches that frequently involve significant brain retraction and cortical incisions. In specific cases of skull base lesions, the ELSI approach is an elegant alternative to traditionally used skull base approaches, thereby avoiding approach-related morbidity.

Interpeduncular Sulcus Approach to the Posterolateral Pons

OBJECTIVE

In this article, we describe a new safe entry point for the posterolateral pons.

METHODS

To show the adjacent anatomy and measure the part of the interpeduncular sulcus that can be safely accessed, we first performed a review of the literature regarding the pons anatomy and its surgical approaches. Thereafter, 1 human cadaveric head and 15 (30 sides) human brainstems with attached cerebellums were bilaterally dissected with the fiber microdissection technique. A clinical correlation was made with an illustrative case of a dorsolateral pontine World Health Organization grade I astrocytoma.

RESULTS

The safe distance for accessing the interpeduncular sulcus was found to extend from the caudal end of the lateral mesencephalic sulcus to the point at which the intrapontine segment of the trigeminal nerve crosses the interpeduncular sulcus. The mean distance was 8.2 mm (range, 7.15-8.85 mm). Our interpeduncular sulcus safe entry zone can be exposed through a paramedian infratentorial supracerebellar approach. When additional exposure is required, the superior portion of the quadrangular lobule of the cerebellar hemispheric tentorial surface can be removed. In the presented case, surgical resection of the tumor was performed achieving a gross total resection, and the patient was discharged without neurologic deficit.

CONCLUSIONS

The interpeduncular sulcus safe entry zone provides an alternative direct route for treating intrinsic pathologic entities situated in the posterolateral tegmen of the pons between the superior and middle cerebellar peduncles. The surgical corridor provided by this entry point avoids most eloquent neural structures, thereby preventing surgical complications.

Extreme lateral supracerebellar infratentorial approach: how I do it

BACKGROUND

The extreme lateral supracerebellar infratentorial (ELSI) approach was initially proposed to treat lesions of the posterolateral surface of the pons principally cavernomas. The versatility of the approach allowed its use for other pathologies like gliomas, aneurysms, epidermoids, and meningiomas.

METHOD

We describe here the ELSI approach along with its advantages and limits in comparison with other surgical approaches for the treatment of meningiomas of the petroclival region.

CONCLUSION

ELSI is a versatile approach that allows access to the anterolateral brainstem surface including extensions to the midbrain diencephalic junction when needed. ELSI compares favorably to other surgical alternatives with respect to the approach-related morbidity, while allowing adequate access to treat the pathology.

Mapping the Internal Anatomy of the Lateral Brainstem: Anatomical Study with Application to Far Lateral Approaches to Intrinsic Brainstem Tumors

INTRODUCTION

Intramedullary brainstem tumors present a special challenge to the neurosurgeon. Unfortunately, there is no ideal part of the brainstem to incise for approaches to such pathology. Therefore, the present study was performed to identify what incisions on the lateral brainstem would result in the least amount of damage to eloquent tracts and nuclei. Case illustrations are also discussed.

MATERIALS AND METHODS

Eight human brainstems were evaluated. Based on dissections and the use of standard atlases of brainstem anatomy, the most important deeper brainstem structures were mapped to the surface of the lateral brainstem.

RESULTS

With these data, we defined superior acute and inferior obtuse corridors for surgical entrance into the lateral brainstem that would minimize injury to deeper tracts and nuclei, the damage to which would result in significant morbidity.

CONCLUSIONS

To our knowledge, a superficial map of the lateral brainstem for identifying deeper lying and clinically significant nuclei and tracts has not previously been available. Such data might decrease patient morbidity following biopsy or tumor removal or aspiration of brainstem hemorrhage. Additionally, this information can be coupled with the previous literature on approaches into the fourth ventricular floor for more complex, multidimensional lesions.

[3D anatomy of cerebellar peduncles based on fibre microdissection and a demonstration with tractography]

OBJECTIVE

To perform an anatomical and radiological study, using fibre microdissection and diffusion tensor tractography (DTT), to demonstrate the three-dimensionality of the superior, middle and inferior cerebellar peduncles.

MATERIAL AND METHODS

A total of 15 brain-stem, 15 cerebellar hemispheres, and 5 brain hemispheres were dissected in the laboratory under the operating microscope with microsurgical instruments between July 2014 and July 2015. Brain magnetic resonance imaging was obtained from 15 healthy subjects between July and December of 2015, using diffusion-weighted images, in order to reproduce the cerebellar peduncles on DTT.

RESULTS

The main bundles of the cerebellar peduncles were demonstrated and delineated along most of their trajectory in the cerebellum and brain-stem, noticing their overall anatomical relationship to one another and with other white matter tracts and the grey matter nuclei the surround them, with their corresponding representations on DTT.

CONCLUSIONS

The arrangement, architecture, and general topography of the cerebellar peduncles were able to be distinguished using the fibre microdissection technique. This knowledge has given a unique and profound anatomical perspective, supporting the correct representation and interpretation of DTT images. This information should be incorporated in the clinical scenario in order to assist surgeons in the detailed and critical analysis of lesions that may be located near these main bundles in the cerebellum and/or brain-stem, and therefore, improve the surgical planning and achieve a safer and more precise microsurgical technique.

Midline and off-midline infratentorial supracerebellar approaches to the pineal gland

OBJECTIVE

A common approach to lesions of the pineal region is along the midline below the torcula. However, reports of how shifting the approach off midline affects the surgical exposure and relationships between the tributaries of the vein of Galen are limited. The purpose of this study is to examine the microsurgical and endoscopic anatomy of the pineal region as seen through the supracerebellar infratentorial approaches, including midline, paramedian, lateral, and far-lateral routes.

METHODS

The quadrigeminal cisterns of 8 formalin-fixed adult cadaveric heads were dissected and examined with the aid of a surgical microscope and straight endoscope. Twenty CT angiograms were examined to measure the depth of the pineal gland, slope of the tentorial surface of the cerebellum, and angle of approach to the pineal gland in each approach.

RESULTS

The midline supracerebellar route is the shortest and provides direct exposure of the pineal gland, although the culmen and inferior and superior vermian tributaries of the vein of Galen frequently block this exposure. The off-midline routes provide a surgical exposure that, although slightly deeper, may reduce the need for venous sacrifice at both the level of the veins from the superior cerebellar surface entering the tentorial sinuses and at the level of the tributaries of the vein of Galen in the quadrigeminal cistern, and require less cerebellar retraction. Shifting from midline to off-midline exposure also provides a better view of the cerebellomesencephalic fissure, collicular plate, and trochlear nerve than the midline approaches. Endoscopic assistance may aid exposure of the pineal gland while preserving the bridging veins.

CONCLUSIONS

Understanding the characteristics of different infratentorial routes to the pineal gland will aid in gaining a better view of the pineal gland and cerebellomesencephalic fissure and may reduce the need for venous sacrifice at the level of the tentorial sinuses draining the upper cerebellar surface and the tributaries of the vein of Galen.

Anatomy and approaches along the cerebellar-brainstem fissures

OBJECT Fissure dissection is routinely used in the supratentorial region to access deeply situated pathology while minimizing division of neural tissue. Use of fissure dissection is also practical in the posterior fossa. In this study, the microsurgical anatomy of the 3 cerebellar-brainstem fissures (cerebellomesencephalic, cerebellopontine, and cerebellomedullary) and the various procedures exposing these fissures in brainstem surgery were examined. METHODS Seven cadaveric heads were examined with a microsurgical technique and 3 with fiber dissection to clarify the anatomy of the cerebellar-brainstem and adjacent cerebellar fissures, in which the major vessels and neural structures are located. Several approaches directed along the cerebellar surfaces and fissures, including the supracerebellar infratentorial, occipital transtentorial, retrosigmoid, and midline suboccipital approaches, were examined. The 3 heads examined using fiber dissection defined the anatomy of the cerebellar peduncles coursing in the depths of these fissures. RESULTS Dissections directed along the cerebellar-brainstem and cerebellar fissures provided access to the posterior and posterolateral midbrain and upper pons, lateral pons, floor and lateral wall of the fourth ventricle, and dorsal and lateral medulla. CONCLUSIONS Opening the cerebellar-brainstem and adjacent cerebellar fissures provided access to the brainstem surface hidden by the cerebellum, while minimizing division of neural tissue. Most of the major cerebellar arteries, veins, and vital neural structures are located in or near these fissures and can be accessed through them.

A young and booming approach: the extreme lateral supracerebellar infratentorial approach

Surgical accesses to lesions of the posterolateral pontomesencephalic junction (PMJ) region and the posterolateral tentorial gap remain a challenge in the field of neurosurgery. Since the first report of application of the extreme lateral supracerebellar infratentorial (ELSI) approach in resecting the PMJ lesions in 2000, a few articles concerning the ELSI approach have been published. The present review mainly provided an intimate introduction of the ELSI approach, and evaluated it in facets of patient position, skin incision, craniectomy, draining veins, retraction against the cerebellum, exposure limits, patient healing, as well as advantages and limitations compared with other approaches. The ELSI approach is proposed to be a very young and promising approach to access the lesions of posterolateral PMJ region and the posterolateral tentorial gap. Besides, it has several advantages such as having a shorter surgical pathway, causing less surgical complications, labor-saving, etc. Still, more studies are needed to improve this approach.

Supracerebellar Infratentorial Approach to Cavernous Malformations of the Brainstem

OBJECTIVE

The supracerebellar infratentorial (SCIT) approach can be performed at the midline (median variant), lateral to the midline (paramedian variant), or at the level of the angle formed by the transverse and sigmoid sinuses (extreme lateral variant). We analyzed our experience with SCIT approaches for the surgical treatment of cavernous malformations of the brainstem (CMBs).

METHODS

Demographic, clinical, radiologic, and surgical data from 45 patients (20 males and 25 females; mean age, 36.2 years) with CMBs surgically removed through SCIT approaches were reviewed retrospectively. Anatomic information was explored using cadaver head dissection.

RESULTS

Twenty-three lesions were in the midbrain, 3 were at the midbrain and extended to the thalamus, 9 were at the pontomesencephalic junction, and 10 were in the upper pons. All patients presented with hemorrhage. The median variant was used in 13 patients, the paramedian variant in 9, and the extreme lateral variant in 23. Intraoperatively, all CMBs were associated with a developmental venous anomaly. At last follow-up, 88% of the patients were the same or better. After a mean follow-up of 20 months, their mean Glasgow Outcome Scale score was 4.1.

CONCLUSION

SCIT approaches provide excellent exposure to CMBs located at the posterior incisural space, not only in the midline but also in the posterolateral surface of the upper pons and midbrain. Careful preoperative planning and neuronavigational assistance are needed to determine the best angle of attack and trajectory for SCIT approaches. Refined microsurgical techniques are paramount to achieve safe surgical removal of CMBs with good outcomes.

Auditory midbrain implant: a review

The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in deaf patients who cannot sufficiently benefit from cochlear implants. The authors have begun clinical trials in which five patients have been implanted with a single shank AMI array (20 electrodes). The goal of this review is to summarize the development and research that has led to the translation of the AMI from a concept into the first patients. This study presents the rationale and design concept for the AMI as well a summary of the animal safety and feasibility studies that were required for clinical approval. The authors also present the initial surgical, psychophysical, and speech results from the first three implanted patients. Overall, the results have been encouraging in terms of the safety and functionality of the implant. All patients obtain improvements in hearing capabilities on a daily basis. However, performance varies dramatically across patients depending on the implant location within the midbrain with the best performer still not able to achieve open set speech perception without lip-reading cues. Stimulation of the auditory midbrain provides a wide range of level, spectral, and temporal cues, all of which are important for speech understanding, but they do not appear to sufficiently fuse together to enable open set speech perception with the currently used stimulation strategies. Finally, several issues and hypotheses for why current patients obtain limited speech perception along with several feasible solutions for improving AMI implementation are presented.

Transanterior Perforating Substance Approach to the Thalamomesencephalic Junction

Objective:

Lesions in the thalamomesencephalic junction can be reached via an anterolateral approach, interhemispheric approach, transcortical (parieto-occipital lobule) approach, subtemporal approach, supracerebellar approaches, or transsylvian-insular approach. We now describe a new approach, a transanterior perforating substance approach, to this territory.

Methods:

A 33-year-old man with progressive right arm tremors, mild hemiparesis, and a cavernous malformation of the thalamomesencephalic junction was followed for 5 years. Because of clinical progression, he underwent a left orbitozygomatic approach to the cavernous malformation, which could not be accessed because of a high-riding basilar artery. Hence, a new transsylvian corridor of exposure was developed using frameless neuronavigation. The trajectory, which was dorsal to M1, led through the perforating branches of M1. Care was taken to avoid violating any arterial perforators. To reach the lesion, a small opening into the brain was created near the optic tract.

Results:

The cavernous malformation was resected totally. Postoperatively, the patient's tremors were cured. No visual deficits were encountered. Imaging showed a small ischemic stroke in the basal ganglia likely related to manipulation of a perforator. Initially, his hemiparesis worsened, but it improved significantly within 10 months with only a moderate decrease in strength.

Conclusion:

The transanterior perforating substance approach effectively allowed access to the thalamomesencephalic junction and was associated with significant morbidity. However, the safety of the approach needs further validation. Neuronavigation is indicated to choose the most direct trajectory through the M1 perforators. Tractography may help protect the optic tract.

Comparative Analysis of the Retrosigmoid and Lateral Supracerebellar Infratentorial Approaches along the Lateral Surface of the Pontomesencephalic Junction: A Different Perspective

Objective:

To quantitatively assess the working distance and angle of attack among the retrosigmoid (RS), lateral supracerebellar (LS), and extreme lateral supracerebellar (EL) views on the lateral surface of the pontomesencephalic junction.

Methods:

Eight sides of silicone-injected fixed cadaveric heads were dissected using the three approaches. All predetermined anatomic points were collected by use of a frameless stereotactic device. The length of exposure and the angle of attack were calculated and compared. Predissection imaging was obtained for illustration.

Results:

The LS and EL approaches created a horizontal working space as compared with the vertical working space created by the RS approach. The RS view gained less posterior exposure margin than the LS and EL views (posterosuperior margin values: RS, 4.3 ± 1.7 mm; LS, 6.4 ± 2.0 mm; EL, 7.3 ± 2.0 mm; P &lt; 0.001; posteroinferior margin: RS, 2.7 ± 2.7 mm; LS, 4.9 ± 2.8 mm; EL, 8.3 ± 2.5 mm; P &lt; 0.001). When the tentorium is intact, transverse sinus retraction significantly accentuates the field of view by the EL approach compared with the LS approach at both the anteroinferior (P &lt; 0.05) and posteroinferior (P &lt; 0.001) margins. Between the supracerebellar types, the vertical angle of attack was significantly improved and the horizontal angle was significantly decreased when complete venous retraction was performed.

Conclusion:

The supracerebellar views offer greater advantage over the RS view when the surgeon is working more posteriorly on the pontomesencephalic junction. Between the supracerebellar views, venous retraction creates a significantly wider vertical angle and also improves the exposure when the surgeon is working more inferiorly.

Auditory Midbrain Implant

HYPOTHESIS

The lateral suboccipital approach is a well-established route for safe removal of vestibular schwannomas in neurofibromatosis Type 2 (NF2) patients. The goal of this study was to assess if this approach can be extended to a lateral supracerebellar infratentorial approach to enable insertion of an auditory midbrain implant (AMI) penetrating array along the tonotopic gradient of the inferior colliculus central nucleus (ICC).

BACKGROUND

The AMI is a new auditory prosthesis designed for penetrating stimulation of the ICC in patients with neural deafness. The initial candidates are NF2 patients who, because of the growth and/or surgical removal of bilateral acoustic neuromas, develop neural deafness and are unable to benefit from cochlear implants. The ideal surgical approach in NF2 patients must first enable safe removal of vestibular schwannomas and then provide sufficient exposure of the midbrain for AMI implantation.

METHODS

This study was performed on formalin-fixed and fresh cadaver specimens. Computed tomography scan and magnetic resonance imaging were used to study the heads of the specimens and for surgical navigation.

RESULTS

The lateral suboccipital craniotomy enabled sufficient exposure of the cerebellopontine angle and internal auditory canal for tumor removal. It could then be extended to a lateral supracerebellar infratentorial approach that provided good exposure of the dorsolateral aspect of the tentorial hiatus and mesencephalon for implantation of the AMI along the tonotopic gradient of the ICC. This approach did not endanger the trochlear nerve or any major midline venous structures in the quadrigeminal cistern.

CONCLUSION

This modified lateral suboccipital approach ensures safe removal of large vestibular schwannomas and provides sufficient exposure of the inferior colliculus for ideal AMI implantation.