Simulation of the occipital transtentorial approach incorporating visualization of the cerebellar tentorium using three-dimensional computed tomography angiography and gadolinium-enhanced T1-weighted magnetic resonance imaging: Technical note

doi:10.21203/rs.3.rs-2717614/v1

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Simulation of the occipital transtentorial approach incorporating visualization of the cerebellar tentorium using three-dimensional computed tomography angiography and gadolinium-enhanced T1-weighted magnetic resonance imaging: Technical note

https://doi.org/10.21203/rs.3.rs-2717614/v1

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The occipital transtentorial approach (OTA) is one of the most useful approaches to the lesions of the pineal region, dorsal brainstem, and supracerebellar region. However, a wide operative field is sometimes difficult to obtain due to the large tentorial sinus and bridging veins. This study evaluated the usefulness of preoperative simulation of OTA, specifically including the cerebellar tentorium in 9 patients. All patients underwent computed tomography angiography and venography and gadolinium-enhanced three-dimensional T1-weighted magnetic resonance images (Gd-3D-T1WI). The images were fused and the cerebellar tentorium and tumor manually extracted from Gd-3D-T1WI to obtain the preoperative simulation images. Visualization of the cerebellar tentorium could discriminate between bridging veins from the occipital lobe and cerebellum, and recognize the site of bridging to the tentorial sinus and variants which may interfere with the tentorial incision. Simulation of the tentorial incision was also possible based on the relationships between the tumor, tentorial sinus, bridging vein, and cerebellar tentorium. The simulation suggested that safe tentorial incision was difficult in two sides because of the crossed tentorial sinus draining the left basal vein and draining veins from the glioblastoma. The OTA was performed in eight cases and no difficulty was experienced in the tentorial incision in all cases. The simulation findings of the bridging vein and tentorial sinus were consistent with the intraoperative findings. Preoperative simulation including the cerebellar tentorium is useful for determining the optimum and safe side and required extent of the tentorial incision necessary for tumor resection with the OTA.

Occipital transtentorial approach

Preoperative simulation

Cerebellar tentorium

Bridging veins

Tentorial sinus

The occipital transtentorial approach (OTA) is commonly used to access the pineal region, splenium, dorsal brainstem, and supracerebellar region [1–8]. Appropriate incision of the cerebellar tentorium is essential to achieve safe and wide exposure of the lesion [9]. Therefore, determination of the optimum side and required extent of incision of the cerebellar tentorium requires preoperative understanding of the anatomical relationships between the cerebellar tentorium, tumor, and bridging veins from the occipital lobe or cerebellum and draining into the tentorial sinus.

Simulation based on three-dimensional (3D) computed tomography (CT) angiography (CTA), CT venography (CTV), and gadolinium-enhanced 3D T1-weighted magnetic resonance (MR) imaging (Gd-3D-T1WI) is considered to be a powerful tool for the preoperative evaluation of the anatomical structures in this region [2, 6, 10–12]. However, the relationships between the tumor, cerebellar tentorium, bridging veins from the cerebellar or occipital lobe to the tentorial sinus, and the presence of normal variants of vascular structures are sometimes difficult to understand because simulation of the cerebellar tentorium has never been investigated.

Here, we report our experience with simulation of the OTA using images of the cerebellar tentorium based on Gd-3D-T1WI with CTA and CTV, and discuss the usefulness for preoperative planning.

Patients

Nine consecutive patients with tumors in the pineal region, supracerebellar region, or dorsal brainstem were treated in our department between 2019 and 2021.

Simulation Images

All patients underwent preoperative 3D plain CT, CTA, CTV, and Gd-3D-T1WI of the head. Subtraction processing of the CTA and CTV used an image processing workstation (Ziostation2, Ziosoft, Tokyo, Japan) to obtain the subtraction CTA and subtraction CTV. The plain CT, subtraction CTA, subtraction CTV, and Gd-3D-T1WI were then fused on the workstation, and the cerebellar tentorium and tumor manually extracted from the Gd-3D-T1WI for fusion with the subtraction CTV to obtain the final simulation images. All CT scanning was performed with an ultra-high resolution CT scanner (Aquilion Precision CT, Canon Medical Systems Corporation, Otawara, Tochigi, Japan) and MR imaging with an MR system (Ingenia 3.0T CX, Philips Healthcare, Andover, MA).

Determination Of Surgical Approach And Operative Procedure

The approach route was determined based on the findings of the anatomical relationship between the tumor location and the distribution of the tentorial sinus and bridging veins from the occipital lobe and cerebellum.

The OTA was performed via unilateral occipital craniotomy. Before incision of cerebellar tentorium, the tentorial and straight sinuses and bridging vein from the occipital lobe were evaluated using the surgical microscope (OPMI PENTERO or KINEVO 900, Carl Zeiss Meditec Japan, Tokyo, Japan) and indocyanine green (ICG) video-angiography.

The suboccipital approach was performed via suboccipital craniotomy. During and after tumor resection, the bridging veins draining into the cerebellar tentorium were preserved to prevent damage to the drainers of the tumor and cerebellum.

Validation Of Simulation Images Comparing Intraoperative Findings

Simulation images and intraoperative findings were reviewed to evaluate the usefulness of simulation images in planning tumor resection. First, the usefulness of the simulation of the cerebellar tentorium in determining the optimum route and required extent of incision of the cerebellar tentorium was assessed. Second, the agreement of the simulation images with the observed anatomical relationship between the tentorial sinus and bridging veins, and the courses of tentorial and straight sinuses were examined. Anatomical relationships between the tentorial sinus and bridging veins were classified into four groups as previously reported [13]. Groups I, II, and III included the sinuses draining the occipital lobe, cerebellar hemisphere, and cerebellar tentorium, respectively. Group IV included tentorial sinuses originating from a vein bridging to the tentorial free edge.

Patient characteristics

Patient characteristics are shown in Table 1. The six male and three female patients were aged from 7 to 71 years. Histological diagnosis was germ cell tumor in 5 cases, pilocytic astrocytoma in 2, glioblastoma in 1, and pineoblastoma in 1. Tumors were located in the pineal lesion in 6 cases, cerebellum in 2, and tectum in 1.

Determination Of Approach Route Based On Simulation Images

The simulation images including the cerebellar tentorium clearly demonstrated the tentorial sinus and the bridging veins draining into the tentorial sinus, compared to the simulation images without the cerebellar tentorium (Supplementary Figs. 1–3). The preoperative findings of the tentorial sinus and its bridging veins, and the presence of normal variants are summarized in Table 1. Based on these findings, the approach route and the side and range of tentorial incision were determined for the OTA. Findings that indicated the risk of postoperative complications were found in two of nine cases. A case of pineal choriocarcinoma indicated that tentorial incision might lead to injury of the basal vein or the tentorial sinus (Fig. 1). A case of cerebellar glioblastoma suggested that tentorial incision and retraction of the cerebellar tentorium might damage the draining veins of the glioblastoma (dashed arrow in Fig. 2) and those of the cerebellum draining into the tentorial sinus (arrow and arrowhead in Fig. 2). Therefore, right suboccipital craniotomy and tumor resection was selected instead of the OTA. Tumor resection were performed through the OTA in eight patients and the suboccipital approach in one. The lesions were successfully exposed without complications caused by selection of an inappropriate approach route in all cases.

Estimation Of Preoperative Simulation Based On Intraoperative Findings

The preoperative simulation images identified all tentorial sinuses around the tentorial incision observed during surgery with the surgical microscope and ICG video-angiography in all eight sides examined (Figs. 3 and 4). However, the course of the straight sinus could not be recognized with the surgical microscope and ICG video-angiography in two sides because of the thickened dura mater (Cases 1 and 7) (Fig. 4). Therefore, simulation imaging of the cerebellar tentorium is a useful complementary method for preoperative understanding of the anatomy of the tentorial and straight sinuses.

The relationships between the bridging veins and tentorial sinuses on the simulation images were classified as type I (Fig. 3) in four sides, type II (Supplementary Figs. 1 and 2) in nine sides, type III in three sides, types I and II in one side, and type IV in one side (Fig. 1) (Table 1), and the patterns in the side of craniotomy were type I (Fig. 3) in two sides, type II in six sides (Fig. 2), and type III in one side. Intraoperative findings showed the bridging vein from the occipital lobe was observed in both cases with type I (Cases 2 and 7). In contrast, no bridging veins from the cerebellum were observed during OTA in the cases with type II because any potentially interfering bridging veins from the cerebellum were distant from the tentorial incision (Cases 2, 4, 5, 6, and 8). Exceptionally, the bridging vein from the cerebellum was observed in the case with type II treated by suboccipital craniotomy (Case 9) (Fig. 2). No bridging veins either from the cerebellum or occipital lobe were found in the case with type III.

These findings suggest that the simulation method provides accurate preoperative imaging of the relationships between the bridging vein and the tentorium, and no difficulty or complication was experienced during tentorial incision in the eight cases treated through the OTA.

The present study demonstrated that preoperative simulation imaging including the cerebellar tentorium based on Gd-3D-T1WI combined with routine vascular structure and tumor imaging obtained from CTA, CTV, and Gd-3D-T1WI could demonstrate the anatomical relationships between the tentorial sinus, bridging veins from the occipital lobe or cerebellum, deep veins, and tumor. This method can provide preoperative information about the optimum side and required extent of the tentorial incision.

Reported anatomical studies of the tentorial sinuses have suggested that injury to the tentorial sinus itself does not lead to adverse consequences in most cases because of the collateral pathways [13, 14]. However, understanding the course of the basal veins and bridging veins draining into the tentorial sinus is very important [5, 13, 15] as the primitive tentorial sinus, which drains the superficial middle cerebral vein [5, 16], and multiple venous channels may interfere with the tentorial incision [17]. Venous infarction in the occipital lobe and cerebellum, caused by direct injury or retraction of the occipital lobe or cerebellar tentorium, is one of the major complications of tumor resection in this region [3, 4, 9, 13, 14, 18–20]. Therefore, clear understanding the complex anatomical structures around the cerebellar tentorium is important to avoid this complication [4, 10, 13, 16, 17, 21].

Preoperative investigation has adopted angiography, CT, and MR imaging. Angiography can reveal real time blood flow and is useful to detect any large feeding arteries of the tumor and the draining route. Recently, 3D CT and 3D MR imaging have become useful for preoperative assessment of the OTA through image processing to show the tumor localization, surrounding structures, and associated blood vessels [4, 11, 12]. 3D CTA demonstrated variations of the galenic system in 150 patients, and identified the variations requiring care at incision of the cerebellar tentorium as the basal vein draining into the persistent primitive tentorial sinus, and drainage of the internal occipital vein to the transverse sinus through the cerebellar tentorium [4]. 3D CT demonstrated the persistent primitive tentorial sinus in 10% of adult patients with unruptured aneurysm [5]. Furthermore, high-resolution 3D multifusion imaging combining with MR imaging, MR angiography, CT, and 3D rotational angiography was useful for preoperative simulation of hemangioblastoma, especially of the vascular structures [12].

In this study, the cerebellar tentorium was included in the preoperative simulation of OTA. This technique had four advantages for the preoperative simulation of tentorial incision, comparing to that without the cerebellar tentorium. First, visualization of the cerebellar tentorium enabled identification of the bridging veins to the tentorial sinus, most commonly from the cerebellum, followed by the occipital lobe [13]. Preoperative evaluation of the presence and location of any cerebellar bridging veins behind the cerebellar tentorium is especially important because these veins are not visible before tentorial incision. Cerebellar bridging veins are most frequently located in the intermediate third of the hemisphere and between the medial and intermediate borders [16], but are rarely located anterior to the cerebellar tentorium [14, 16]. These distributions of cerebellar bridging veins imply that the extensive posterior tentorial incision necessary for cerebellar tumor requires extreme care. Second, the basal vein sometimes drains into the tentorial sinus [4, 13] as in our Case 4. The present simulation method allows individual determination of the feasibility of tentorial incision by showing the required range of incision and courses of the basal vein and tentorial sinus. Third, this simulation method provides clear information on the course of the straight sinus which could not be observed by the surgical microscope and ICG video-angiography due to thickening of the dura mater in two cases. This advantage will also potentially useful for the resection of extra-axial tumor with invasion to the straight sinus and confluence, but this study did not investigate this aspect. Fourth, the appropriate range of tentorial incision could be simulated, which was especially useful in cases of large tumor. These advantages suggest that preoperative simulation including the cerebellar tentorium is useful for determining the optimum side and required extent of the tentorial incision in the OTA.

There are some limitations of this study. This simulation method provides accurate anatomical information about the bridging vein and tentorial sinus around cerebellar tentorium. However, these structures incorporate complex and individualized collateral pathways [16]. Therefore, this method has limits to predict venous infarction due to the preoperative work-up based on CT and MR imaging [18]. Until imaging of the venous systems is improved, we agree with the strategy that focuses on preservation of the venous structure as much as possible based on the preoperative simulation and careful surgical strategies. Second, extraction of the cerebellar tentorium was performed manually and so the simulation images took a long time to reconstruct. Development of automatic segmentation [22] of the cerebellar tentorium is a promising strategy for improving the preoperative simulation.

In conclusion, preoperative simulation including the cerebellar tentorium is very useful for determining the optimum and safe side and required extent of the tentorial incision necessary for tumor resection with the OTA.

Author contributions

YS: Original draft, Data curation, Review and editing

MK: Original draft, Data curation, Conceptualization, Review and editing

YS: Data curation, Review and editing

SK: Image processing, Data curation, Review and editing

HN: Image processing, Data curation, Review and editing

SM: Conceptualization, Data curation, Review and editing

RS: Data curation, Conceptualization, Review and editing

TT: Conceptualization, Supervision, Review and editing

Statements and declarations

Ethical approval This study was approved by the ethical board of Tohoku University hospital.

Consent to participate: . Informed consent was obtained from all patients.

Funding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Competing interests: The authors have no relevant financial or non-financial interests to disclose.

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Table 1 is available in the Supplementary Files section.

No competing interests reported.

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Version 1

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Simulation of the occipital transtentorial approach incorporating visualization of the cerebellar tentorium using three-dimensional computed tomography angiography and gadolinium-enhanced T1-weighted magnetic resonance imaging: Technical note

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Version 1

Abstract

Figures

Introduction

Methods And Materials

Patients

Simulation Images

Determination Of Surgical Approach And Operative Procedure

Validation Of Simulation Images Comparing Intraoperative Findings

Results

Patient characteristics

Determination Of Approach Route Based On Simulation Images

Estimation Of Preoperative Simulation Based On Intraoperative Findings

Discussion

Declarations

References

Tables

Additional Declarations

Supplementary Files

Status:

Version 1