A Novel Method to Measure the Tentorial Angle and the Implications on Surgeries of the Pineal Region

Pineal Tumor Surgery-The Choice of the Approach Related to Tumor Characteristics and Posterior Fossa Anatomy

OBJECTIVE

This research aimed to determine whether an adequate surgical approach can be chosen based on clearly defined values of anatomical landmarks (tentorial angle) and tumor size and extension.

METHODS

We conducted a retrospective analysis of patients operated on because of pineal tumors. The cohort was divided depending on the surgical approach. On preoperative magnetic resonance imaging, we measured maximal diameters, tumor volume, and tumor propagation. In the group of patients operated with the supracerebellar infratentorial approach, we also tested the correlation of tentorial angle with residual tumor. Differences among groups in resection, complications rate, and outcome were tested by the χ2 test. Finally, in both groups, the correlation of residual tumor with tumor volume, propagation, and diameters was tested using the receiver operating characteristic curve.

RESULTS

In the group operated with a supracerebellar approach, total resection was achieved in 78% of the patients. The critical value of cranio-caudal diameter correlated with tumor residue was 31 mm, for lateral-lateral diameter 25 mm, for the lateral extension 14 mm, and tumor volume 12 cm3. Tentorial angle did not influence the extent of the resection. In the group operated with an occipital transtentorial approach, the critical tumor volume related to tumor residue was 9 mm3, anterior-posterior diameter 29 mm, and cranio-caudal diameter 28 mm. The extent of the resection was significantly higher in the supracerebellar group.

CONCLUSIONS

In both approaches, tumors larger than 3 cm show an increased risk of subtotal resection. Except when most tumor volume is localized above the venous system, we advocate a supracerebellar corridor as an effective approach that is not limited by tentorial angle.

The Paramedian Supracerebellar Infratentorial Approach: 2-Dimensional Operative Video

INDICATIONS

The supracerebellar-infratentorial approach uses the plane between the tentorium and the superior surface of the cerebellum to expose the pineal region.

ANATOMIC ESSENTIALS

The bone opening is just underneath the level of the transverse sinus, and so its position must be noted preoperatively. The anatomy of the internal cerebral veins and the veins of Galen and Rosenthal should be examined as well.

ESSENTIALS STEPS OF THE PROCEDURE

The sitting position allows gravity-assisted expansion of the supracerebellar corridor, and a paramedian approach provides the biggest working space in the TIGER triangle, delineated by the tentorial surface of the cerebellum, the internal cerebral vein/Galen complex, and the vein of Rosenthal. The veil of arachnoid beyond the triangle must be carefully opened to expose the pineal region.

PITFALLS/AVOIDANCE OF COMPLICATIONS

For the sitting position, the operative team must be careful about air emboli. A patent foramen ovale is a contraindication for the position. The deep veins must be handled delicately to avoid complications.

VARIANTS AND INDICATIONS FOR THEIR USE

Several variations are shown in this video. For visualization, augmented reality is helpful, but since current augmented reality technology is microscope-based, its use can be ergonomically challenging if the tentorium is steep. 1 Our current preference is to use the exoscope for the major portion of the procedure until most of the tumor is out and then switch to hand-held endoscopes with various angles to finish the operation.The patients consented to the surgery, and all relevant participants consented to publication of their images.

The TIGR triangle of the pineal region: a virtual reality anatomic study

BACKGROUND

In this morphometric study, we describe the anatomy of the TIGR triangle, which is bordered by the tentorial surface of the cerebellum, the internal cerebral vein and vein of Galen complex, and the vein of Rosenthal. These structures define the window, or deep keyhole, to access the pineal region in non-midline supracerebellar infratentorial approaches.

METHODS

The posterior fossa anatomy of 16 patients was studied in virtual reality (VR), and the TIGR triangles were defined and measured with special attention on its angular orientation in the posterior fossa. The angular expanse of the posterior fossa was measured and recorded as the transverse-sigmoid junction (TSJ) angle. Because a perpendicular corridor through an anatomic aperture provides the best exposure, we studied the starting point along the TSJ angle that offers the best exposure of TIGR.

RESULTS

In the 31 posterior fossa sides included in the study, the perpendicular trajectory through the TIGR triangle was on average 27.13° CI 95% (range: 5.97°-48.53°) from the midline. When comparing the SCIT variants, both the paramedian and lateral approaches provided near-perpendicular trajectory through the TIGR triangle in a majority of specimens. However, the modified paramedian approach, with starting point defined as TSJ angle/3, provided the most perpendicular path through the TIGR triangle.

CONCLUSION

We studied the size, spatial orientation, and morphology of the TIGR triangle. Our data indicated that the best exposure of TIGR is through a modified paramedian SCIT approach, in which the starting point one third of the way from midline to the TSJ.

Open Surgical Approaches for Meningiomas

Meningiomas are the most common intracranial extra-axial primary tumor. Although most are low grade and slow growing, resection can be technically challenging, particularly when located at the skull base. Appropriate craniotomy and approach selection are of paramount importance to minimize brain retraction, optimize exposure, and achieve complete resection. This article summarizes various craniotomies and their approaches to meningiomas, and illustrates some nuances in performing these techniques with cadaveric dissection and operative videos.

Occipital Interhemispheric Transtentorial Approach for Tumors of Posterior Third Ventricular Region: Review of Surgical Results

Background

Controversies exist regarding the ideal surgical approach for tumors in posterior third ventricular region (PTV).

Objective

To evaluate the results of occipital interhemispheric transtentorial (OITT) approach for tumors in PTV.

Materials And Methods

Thirty-three patients underwent surgery via OITT approach for PTV tumors at Sri Sathya Sai Institute of Higher Medical Sciences during the study period of 5 years (June 2011-May 2016). Ideal trajectory for OITT approach was determined by neuronavigation. Endoscope was used for removing any residual lesion at the blind spots.

Results

Postoperative magnetic resonance imaging (MRI) performed in all the patients revealed gross total or near-total (>95%) excision of tumor in 31 patients (93.9%). Preoperative neurological deficits improved either completely or significantly following excision of the tumor in 73.3% (11/15) of the patients. Outcome was good (modified Rankin scale ≤2) at discharge in 93.9% (31/33) and at a final follow-up of 3 months or more in 96.8% (30/31) of the patients. None of the patients died during the postoperative period. Complications included upgaze palsy (transient- 6.1% [2/33], persisting- 3% [1/33]), visual field defects (transient- 3% [1/33], persisting- 3% [1/33]), transient third nerve paresis (1/33-3%), transient hemiparesis (1/33-3%), operative site hematoma (1/33-3%), small posterior cerebral artery (PCA) territory infarct (1/33-3%), and small venous infarct (1/33-3%). At least one follow-up MRI could be performed in 23 patients. Final follow-up MRI revealed no recurrence or increase in the size of the residual lesion compared to postoperative images in 20 patients (20/23-87%) and large recurrence in 3 patients (3/23-13%) with high-grade lesions.

Conclusion

Gross total/near-total excision can be performed in majority of the PTV tumors through OITT approach with minimal morbidity and mortality.

Long term outcomes following surgery for pineal region tumors

PURPOSE

Pineal region tumors are surgically demanding tumors to resect. Long term neuro-oncologic outcomes following surgical excision of tumors from this region have been underreported. We sought to define the long term outcomes of patients undergoing resection of pineal region tumors.

METHODS

A retrospective analysis of a prospectively maintained database was performed on patients who underwent intended surgical excision of pineal region tumors. Overall survival (OS) and progression free survival (PFS) were the primary endpoints of this study. Factors associated with OS, PFS and the degree of resection were analyzed, along with 30-day complication rates and dependence on CSF diversion.

RESULTS

Sixty-eight patients with a mean age of 30.9 ± 15.3 years were analyzed. The median clinical and radiographic follow-up was 95.7 and 48.2 months, respectively. The supracerebellar infratentorial and the occipital transtentorial corridors were utilized in the majority of cases (80.9%). The gross total resection (GTR) rate was 52.9% (n=36). The 5-year OS and PFS rates were 70.2% and 58.5%, respectively. Achieving GTR was associated with improved OS (HR 0.39, p = 0.03) and PFS (HR 0.4, p = 0.006). The 30-day mortality rate was 5.9%. The need for CSF diversion was high with 77.9% of patients requiring a shunt or ETV by last follow-up.

CONCLUSIONS

This is the first modern surgical series providing long term follow-up for patients undergoing surgical resection of pineal region tumors. Obtaining a GTR of these challenging tumors is beneficial with regards to PFS/OS. Higher grade tumors have diminished PFS/OS and are treated with adjuvant chemotherapy and/or radiotherapy.

Occipital transtentorial approach for pineal region lesions: Addressing the controversies in conventional teaching

BACKGROUND

The occipital transtentorial (OT) approach is well-established approach for pineal region tumors and can be of choice for the lesions located around the suboccipital part of tentorium such as the quadrigeminal plate, posterior part of thalamus, tentorial surface of cerebellum, splenial region, posterior falx, and lesions around the tentorial incisura. However, it is not very much extensively used in the above-mentioned locations other than the pineal region.

METHODS

Thirty-one patients of pineal region lesions were operated by OT approach, the role of conventional preoperative evaluation of the anatomy of the venous sinuses, deep venous system, and tentorial angle was investigated.

RESULTS

A variety of lesions were operated using this approach achieving gross and near total resection in majority of the cases (76.6%), with acceptable postoperative mean modified Rankin scales (1.8).

CONCLUSION

The OT is a preferable approach for pineal region lesions for patients of all ages and can be tailored for achieving high resectability rates irrespective of the status of the deep venous system and tentorial angle, with reasonable postoperative surgical outcome.

Surface reconstruction from routine CT-scan shows large anatomical variations of falx cerebri and tentorium cerebelli

BACKGROUND

Finite element modeling of the human head offers an alternative to experimental methods in understanding the biomechanical response of the head in trauma brain injuries. Falx, tentorium, and their notches are important structures surrounding the brain, and data about their anatomical variations are sparse.

OBJECTIVE

To describe and quantify anatomical variations of falx cerebri, tentorium cerebelli, and their notches.

METHODS

3D reconstruction of falx and tentorium was performed by points identification on 40 brain CT-scans in a tailored Matlab program. A scatter plot was obtained for each subject, and 8 anatomical landmarks were selected. A reference frame was defined to determine the coordinates of landmarks. Segments and areas were computed. A reproducibility study was done.

RESULTS

The height of falx was 34.9 ± 3.9 mm and its surface area 56.5 ± 7.7 cm². The width of tentorium was 99.64 ± 4.79 mm and its surface area 57.6 ± 5.8 cm². The mean length, height, and surface area of falx notch were respectively 96.9 ± 8 mm, 41.8 ± 5.9 mm, and 28.8 ± 5.8 cm² (range 15.8-40.5 cm²). The anterior and maximal widths of tentorial notch were 25.5 ± 3.5 mm and 30.9 ± 2.5 mm; its length 54.9 ± 5.2 mm and its surface area 13.26 ± 1.6 cm². The length of falx notch correlated with the length of tentorial notch (r = 0.62, P < 0.05).

CONCLUSION

We observe large anatomical variations of falx, tentorium, and notches, crucial to better understand the biomechanics of brain injury, in personalized finite element models.

Neuraxial dysraphism in EPAS1-associated syndrome due to improper mesenchymal transition

Objective

To investigate the effect of somatic, postzygotic, gain-of-function mutation of Endothelial Per-Arnt-Sim (PAS) domain protein 1 (EPAS1) encoding hypoxia-inducible factor-2α (HIF-2α) on posterior fossa development and spinal dysraphism in EPAS1 gain-of-function syndrome, which consists of multiple paragangliomas, somatostatinoma, and polycythemia.

Methods

Patients referred to our institution for evaluation of new, recurrent, and/or metastatic paragangliomas/pheochromocytoma were confirmed for EPAS1 gain-of-function syndrome by identification of the EPAS1 gain-of-function mutation in resected tumors and/or circulating leukocytes. The posterior fossa, its contents, and the spine were evaluated retrospectively on available MRI and CT images of the head and neck performed for tumor staging and restaging. The transgenic mouse model underwent Microfil vascular perfusion and subsequent intact ex vivo 14T MRI and micro-CT as well as gross dissection, histology, and immunohistochemistry to assess the role of EPAS1 in identified malformations.

Results

All 8 patients with EPAS1 gain-of-function syndrome demonstrated incidental posterior fossa malformations—one Dandy-Walker variant and 7 Chiari malformations without syringomyelia. These findings were not associated with a small posterior fossa; rather, the posterior fossa volume exceeded that of its neural contents. Seven of 8 patients demonstrated spinal dysraphism; 4 of 8 demonstrated abnormal vertebral segmentation. The mouse model similarly demonstrated features of neuraxial dysraphism, including cervical myelomeningocele and spinal dysraphism, and cerebellar tonsil displacement through the foramen magnum. Histology and immunohistochemistry demonstrated incomplete mesenchymal transition in the mutant but not the control mouse.

Conclusions

This study characterized posterior fossa and spinal malformations seen in EPAS1 gain-of-function syndrome and suggests that gain-of-function mutation in HIF-2α results in improper mesenchymal transition.

The Anatomy of the Sigmoid-Transverse Junction According to the Tentorial Angle

Dural sinuses have critical importance during intracranial approaches. Detailed anatomical knowledge of the dural sinuses is crucial for surgeons to reduce unexpected venous bleeding. The aim of this study was to investigate anatomical relation of sigmoid sinus and tentorium cerebelli according to clinically palpable landmarks and cranial morphometry. The authors evaluated 222 individuals' (94 women, 128 men) 3-dimensional computed tomography angiograms, retrospectively. The authors also studied on 12 mid-sagittal cut dried hemiskulls and 8 formalin fixed cadaver heads hemisected midsagitally. All measurements were completed using Osirix-Lite version 9 software. Craniometrical values were measured to define cranium morphology. Furthermore, level of the sigmoid sinus according to asterion and tentorial angle were evaluated in detail. Our results demonstrated that there were significant differences between parameters and genders, except vertical angle of the tentorium cerebelli. Distance between asterion and sigmoid sinus was statistically different between right and left sides in favor of the left side. This also varied depending on the position of the sigmoid sinus, as well. Only transverse angle between the upper point of external acoustic meatus and asterion demonstrated a significant correlation with age. This study evaluated the detailed 3D anatomy of sigmoid sinus and tentorium cerebelli related with the cranium morphology. Determining to sigmoid sinus anatomy according to clinically palpable landmarks has advantages for setting surgical protocols and reducing to unexpected injuries while surgery to these structures.

Surgical treatment of falcotentorial meningiomas: a retrospective review of a single-institution experience

OBJECTIVE

Meningiomas at the falcotentorial junction represent a rare subgroup of complex meningiomas. Debate remains regarding the appropriate treatment strategy for and optimal surgical approach to these tumors, and surgical outcomes have not been well described in the literature. The authors reviewed their single-institution experience in the management, approach selection, and outcomes for patients with falcotentorial meningiomas.

METHODS

From the medical records, the authors identified all patients with falcotentorial meningiomas treated with resection at the Barrow Neurological Institute between January 2007 and October 2017. Perioperative clinical, surgical, and radiographic data were retrospectively collected. For patients who underwent the supracerebellar infratentorial approach, the tentorial angle was defined as the angle between the line joining the nasion with the tuberculum sellae and the tentorium in the midsagittal plane.

RESULTS

Falcotentorial meningiomas occurred in 0.97% (14/1441) of the patients with meningiomas. Most of the patients (13/14) were female, and the mean patient age was 59.8 ± 11.3 years. Of 17 total surgeries (20 procedures), 11 were single-stage primary surgeries, 3 were two-stage primary surgeries (6 procedures), 2 were reoperations for recurrence, and 1 was a reoperation after surgery had been aborted because of brain edema. Hydrocephalus was present in 5 of 17 cases, 4 of which required additional treatment. Various approaches were used, including the supracerebellar infratentorial (4/17), occipital transtentorial/transfalcine (4/17), anterior interhemispheric transsplenial (3/17), parietal transventricular (1/17), torcular (2/17), and staged supracerebellar infratentorial and occipital transtentorial/transfalcine (3/17) approaches. Of the 17 surgeries, 9 resulted in Simpson grade IV resection, and 3, 1, and 4 surgeries resulted in Simpson grades III, II, and I resection, respectively. The tentorial angle in cases with Simpson grade I resection was significantly smaller than in those with an unfavorable resection grade (43.3° ± 4.67° vs 54.0° ± 3.67°, p = 0.04). Complications occurred in 10 of 22 approaches (17 surgeries) and included visual field defects (6 cases, 2 permanent and 4 transient), hemiparesis (2 cases), hemidysesthesia (1 case), and cerebellar hematoma (1 case).

CONCLUSIONS

Falcotentorial meningiomas are challenging lesions. A steep tentorial angle is an unfavorable preoperative radiographic factor for achieving maximal resection with the supracerebellar infratentorial approach. Collectively, the study findings show that versatility is required to treat patients with falcotentorial meningiomas and that treatment goals and surgical approach must be individualized to obtain optimal surgical results.