Tentorial Meningiomas: Reappraisal of Surgical Approaches and Their Outcomes

Original Article

Tentorial Meningiomas: Reappraisal of Surgical Approaches and Their Outcomes Anil Nanda1, Devi Prasad Patra1, Amey Savardekar1, Tanmoy K. Maiti2, Subhas K. Konar3, Christina Notarianni1, Bharat Guthikonda1, Shyamal C. Bir1

BACKGROUND: Tentorial meningiomas are notorious for their critical location. Selection of a suitable approach that exposes the multicompartmental growth of tumor is important for a complete and safe resection. This paper discusses about various operative approaches and their overall surgical outcome.

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METHODS: We retrospectively reviewed our 41 patients with tentorial meningiomas. They were classified according to the modified Yasargil classification. The symptomatic improvement and progression-free survival (PFS) were analyzed at follow-up.

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RESULTS: Tumors were almost equally distributed in all location groups. Tumors along the lateral tentorial hiatus were operated on via a subtemporal or transsylvian approach. Tumors along the posterior tentorial hiatus, tentorial membrane, or torcula were operated on by an occipital interhemispheric transtentorial, infratentorial supracerebellar, or a combined approach. Tumors along the petrous attachment were operated on by a retromastoid suboccipital or a combined presigmoid-retrosigmoid approach. Seventy-six percent had total excision (Simpson grade 1 and 2). Group II tumors had the highest total resection rate (100%). Headache and diplopia were the symptoms that significantly improved postoperatively. Over a median follow-up of 65 months, 13 patients (31.7%) had recurrence. There was no significant difference in recurrence rates and PFS in tumors at different locations. Extent of excision and tumor grade were the significant factors

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Key words - Operative - Outcome - Skull base - Surgical approaches - Tentorial meningioma Abbreviations and Acronyms CSF: Cerebrospinal fluid GKRS: Gamma Knife radiosurgery GTR: Gross total resection PFS: Progression-free survival WHO: World Health Organization

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affecting PFS in both univariate and multivariate analysis (P [ 0.01 and 0.03, respectively). CONCLUSIONS: Similar to intracranial meningiomas at other locations, extent of resection and tumor grade significantly affect the PFS for tentorial meningiomas. Careful preoperative planning based on the location and extension of the tumor guides the optimal surgical approach that translates into maximal safe resection.

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INTRODUCTION

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entorial meningiomas comprise 3%e6% of all intracranial meningiomas.1,2 Because of their critical relation to the neurovascular structures around the tentorial hiatus, microsurgical resection is challenging. Extensive surgical resection is frequently limited because of their proximity to the neurovascular structures and cranial nerves.2-4 Surgical morbidity and mortality have declined as a result of advances in resection techniques, intraoperative neuroimaging, and neuroanesthesia with monitoring.2,5 Also, the emergence of targeted radiotherapy has quelled the appetite of most neurosurgeons for achieving gross total resection (GTR). Still, the best outcomes depend on the extent of resection at primary surgery. To optimize the extent of resection, choosing the right approach that gives adequate exposure of the tumor along with the surrounding neurovascular structures is of paramount importance. In this study, we discuss our experience with tentorial meningiomas with special reference to the different surgical approaches and the surgical outcomes.

From the 1Department of Neurosurgery, Louisiana State University Health-Shreveport, Shreveport, Louisiana, USA; 2Department of Neurosurgery, Cleveland Clinic, Cleveland, Ohio, USA; and 3Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, India To whom correspondence should be addressed: Anil Nanda, M.D., M.P.H. [E-mail: [email protected]] Citation: World Neurosurg. (2017). https://doi.org/10.1016/j.wneu.2017.10.115 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.

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METHODS We retrospectively analyzed our data on patients with tentorial meningiomas treated between January 1995 and June 2015 after approval from the institutional review board with informed patient consent.6 Tumors were classified according to location based on the modified Yasargil classification7,8 (Figure 1). The extent of microsurgical resection was graded using the Simpson grade. Simpson grade 1 and 2 resections were collectively termed GTR. The analysis was conducted using SPSS software, version 22.0 (IBM Corp., Armonk, New York, USA). Kaplan-Meier analysis was used to assess progression-free survival (PFS). The log-rank (Mantel-Cox) test was used to assess significance in recurrence rates. A Cox proportional hazards regression model was used to determine independent significant factors of PFS. c2 tests were also used where appropriate. A P value of <0.05 was considered significant. Surgical Approaches Surgical approaches to the tentorial meningiomas were broadly divided into 3 groups based on the location of the tumor and their extension (Table 2). Posterior Approaches. Tumors along the posterior margin of the tentorial hiatus, the tentorial membrane, and torcula are accessed via posterior approaches that involve an occipital or suboccipital route or their combinations. Important determinants in selecting the type of posterior approach are the supratentorial or infratentorial location of the tumor, course of the basal veins in the quadrigeminal cistern in relation to the tumor, and angulation of the tentorium, and so on. When the tumor pushes the basal veins

Figure 1. Location of tentorial meningiomas according to modified Yasargil classification. T1-T2, medial incisural meningioma; T3-T8, falcotentorial meningioma; T4, paramedian meningioma; T5, peritorcular meningioma; T6-T7, lateral tentorial meningioma.

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upward, an infratentorial approach is preferred, and when the veins are pushed downward, a supratentorial approach is used. Occipital Interhemispheric Transtentorial Approach (n ¼ 16). Tumors with a large component in the midline supratentorial location are approached through this corridor (Figures 2 and 3, illustrative case 1). The patient is placed in a lateral position with the ipsilateral side down. A lumbar drain can be placed to aid cerebrospinal fluid (CSF) drainage. A horseshoe incision is used crossing the sagittal sinus and ipsilateral transverse sinus. Burr holes are placed across the sinuses, and the craniotomy exposes the sagittal sinus and transverse sinus. The dura is opened based on the sagittal sinus. The CSF is drained via a lumbar drain, which makes the ipsilateral occipital lobe fall as a result of gravity, thereby greatly reducing the need for retraction. The occipital lobe is retracted downward and outward to expose the interhemispheric fissure. It is important to reduce the retraction of the occipital lobe to prevent postoperative visual field defects. Extra exposure can be gained by retracting the falx upward. The small bridging veins from the occipital lobe to the falx are divided. Sometimes a precerebellar vein is encountered on the capsule of the tumor, which can safely be coagulated if necessary. However, it is important to identify the deep basal veins through the arachnoid at the deeper aspect of the tumor that are splayed over the capsule. The basal vein of Rosenthal needs special mention, because it sometimes mimics the darkcolored mesencephalic cistern and should not be inadvertently opened. After removal of the supratentorial component, the tentorium is divided 1 cm parallel to the straight sinus to access tumors in the infratentorial location. In the deeper aspect, the relation of the fourth nerve to the tentorium should be identified before division of the tentorium. Infratentorial Supracerebellar Approach (n ¼ 6). This approach is used for tumors of infratentorial location (Figures 4 and 5, illustrative case 2). The patient is placed in a sitting position with the head flexed to keep the tentorium in a horizontal plane. A midline or paramedian suboccipital craniotomy is made based on the location of the tumor. For tumors straddling the midline, a large suboccipital craniotomy exposes the torcula and both the transverse sinuses. The dura is divided in a Y-shaped fashion and is reflected upward. The infratentorial supracerebellar space is entered while dividing the bridging arachnoid adhesions and occasional bridging veins. The tumor is encountered and is devascularized by coagulating and dividing its attachment to the tentorium. It is important to identify the midline and the falcotentorial junction that contains the straight sinus. The most difficult and challenging part is the tumor dissection at the deeper aspect. The basal veins are identified at the superior aspect, underneath the arachnoid membrane, and the brainstem is identified at the inferior aspect, immediately behind the capsule. A conservative approach is recommended in this region, preferably leaving behind any adherent component. For the tumors in the paramedian location, the classic retromastoid craniotomy can be extended medially and the tumor can be devascularized working in the plane below the tentorium (Figure 5, illustrative case 2). A rim of tentorium can be removed in tumors in the lateral locations to achieve a Simpson grade 1 excision. While the tentorium is removed, the arachnoid overlying the occipital lobe needs to be preserved.

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Figure 2. Occipital interhemispheric approach. (A) Outline of skin incision (red) and craniotomy (dotted white line). (B) The skin flap has been reflected and craniotomy has been performed. The sagittal and transverse

Combined Supratentorial and Infratentorial Approach (n ¼ 1). This approach is most commonly used for torcular meningioma extending to either side (Figure 6, illustrative case 3). The patient is placed in a sitting or semisitting position, and a midline vertical incision extending across the torcula is used. A craniotomy exposes the torcula, sagittal sinus, and both the transverse sinuses and the dural flaps are reflected based on the sinuses. Initially, an interhemispheric approach is used along both the sides to remove tumor from the supratentorial component. Then, a supracerebellar approach is used for the infratentorial component. For tumors invading the sinuses, we prefer to coagulate the sinus attachment without division of the sinus.

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sinuses are visible. (C) The occipital lobe has been retracted to expose the tumor along the tentorium. (D) The tentorium has been divided to expose the infratentorial portion of the tumor.

However, division and excision of the sinus followed by reconstruction can be an option. Posterolateral Approaches. Posterolateral approaches are mainly designed for tumors along the anteromedial edge of the tentorium and along the attachment of the petrous bone. For tumors with an infratentorial location, a simple retromastoid suboccipital approach is used. In tumors with significant supratentorial extension, a combined transmastoid approach that exposes the tumor above and below the transverse sinus. Retromastoid Suboccipital Approach (n ¼ 8). This approach exposes tumors along the petrous bone (Figures 7 and 8, illustrative case 4).

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Figure 3. Illustrative case 1. A 58-year old woman presented with headache and visual field defect for a duration of 2 months. Magnetic resonance imaging showed (AeC) a meningioma at the falcotentorial junction (T8, group II tentorial meningioma) in the supratentorial location.

The patients are put in a modified lateral or three-quarter prone position. This position allows a more vertical orientation of the petrous ridge that brings the petrous apex more into the operative field. After a standard retromastoid craniotomy, the cerebellum is retracted, and the tumor is exposed along the petrous bone. At this point, it is important to realize the location of the tumor in relation to the VII-VII cranial nerve complex. Tumors lying posterior to the nerves are identified early in the course and should be carefully decompressed, especially along the posterior capsule, where the nerve complex is usually stretched. After initial intratumoral decompression, the lateral capsule is dissected, and the nerves are identified at the internal acoustic meatus and are followed medially. Tumors lying anterior to the VII-VIII nerve complex need a unique technical approach. From a retromastoid perspective, 3 nerve groups are identified, which divides the operative view broadly into 3 corridors. The upper corridor lies between the lower border of the tentorium and the trigeminal nerve, the middle

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An occipital interhemispheric approach was used and a gross total excision was achieved (postoperative magnetic resonance imaging, DeF). Postoperatively, the visual field deficit improved.

corridor between the trigeminal and the VII-VIII nerve complex, and the lower corridor between the VII-VIII complex and the lower cranial nerve fibers. In most cases, the tumor lies in the upper and middle corridor; however, the tumor is initially approached through the most expanded corridor. The nerves are stretched over the tumor with an intervening arachnoid layer. The initial goal is intratumoral decompression, which makes the stretched arachnoid layer easily separate from the tumor. This strategy helps to develop a good dissection plane between the capsule and the arachnoid. Again, during the dissection of the capsule, the nerves are identified at their anterolateral dural exit and followed medially toward the brainstem. Tumors extending above and anterior to the petrous ridge can be approached by a limited petrosectomy at the apex above the auditory meatus, which is facilitated by medial mobilization of the trigeminal nerve after opening the Meckel cave. For safe drilling, it is important to understand the anatomy of the petrous apex in relation to the petrous segment of the internal carotid artery, semicircular canals, and the jugular

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Figure 4. Illustrations for Infratentorial supracerebellar approach. (A) Outline of skin incision (red) and craniotomy (dotted white line). (B) Skin flap has been retracted and craniotomy performed to expose the transverse sinus superiorly. (C) The dura has been

bulb. Tumors with a supratentorial component can be removed by division of the tentorium. At this step, the fourth nerve is identified and preserved below the tentorium. Combined Presigmoid and Retrosigmoid Transmastoid Approach (n ¼ 2). This approach is used in tumors along the lateral margin of the tentorium with both infratentorial and supratentorial components (Figures 9 and 10, illustrative case 5). The patient is positioned similar to the retromastoid approach except that the head is placed more horizontally. A single large curvilinear incision is used starting from above the ear, extending posteriorly and inferiorly traversing the base of mastoid. An initial retrosigmoid craniotomy is made, exposing the transverse sinus and sigmoid sinus completely. Then, the mastoid and posterior temporal base

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reflected up based on the sinus and the tumor exposed along the inferior surface of the tentorium. (D) The tentorium has been divided to expose the small supratentorial component.

are drilled flat to the upper edge of the petrous bone protecting the fallopian canal and the labyrinth. The bony labyrinth of the lateral and posterior semicircular canals serves as the end point of bone drilling. This process exposes the presigmoid dura posteriorly and the temporal dura superiorly. They are opened in a C-shaped manner. The tentorium is divided up to the hiatus, which gives ample space for dissection. Again, the fourth cranial nerve needs to be identified below the tentorium during the division. A wide exposure of the space between the trigeminal nerve and the VII-VIII complex is thus achieved from a superior perspective. After initial tumor decompression from the retrosigmoid corridor, both the compartments can be combined behind the transverse sinus to achieve a total excision of the tumor. In cases

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with anterior tumor extension to the middle fossa, the temporal lobe can be retracted, and tumor can be removed along the tentorial edge. Lateral and Anterolateral Approach. Subtemporal Approach (n ¼ 6). This route is usually favored for tumors along the free edge of the tentorium lying in the middle incisural space anterolateral to the brainstem (Figure 11). The patient is positioned lateral with the head placed horizontal to the floor. A horseshoe incision around the ear is used. Sometimes, a question-mark incision is used behind the hairline extending along the superior temporal line up to the back of the ear that curves anteriorly up to the tragus. A temporal craniotomy is made and the base is drilled flush to the petrous. The dura is opened in a C-shaped manner based inferiorly. One important step at this point is to identify the vein of Labbé and its mobilization by dividing its arachnoidal adhesions, which gives some extra space for temporal lobe retraction. The temporal lobe is retracted superiorly with great caution to avoid injuring the vein of Labbé. The small basal veins connecting the inferior surface of the temporal lobe to the dura are coagulated and divided. The tentorium and the tumor are visualized along the depth. The tentorium is divided to visualize the infratentorial component of the tumor and to safeguard the major neurovascular structures in the underlying cistern. It is worth emphasizing the position of the trochlear nerve because it is easily damaged in unprepared hands, especially in this approach, because the nerve lies directly below the tentorium. The nerve needs to be identified at its entry point to the tentorium. The limiting factor in this approach is the need for temporal lobe retraction and subsequent postoperative deficits and therefore should not be used for large tumors with multicompartmental extension. Orbitozygomatic Transylvian Approach (n ¼ 2). This route is sometimes preferred to reduce the temporal lobe retraction, especially in tumors extending to the anterior tentorial hiatus (Figures 12 and 13, illustrative case 6). Addition of an orbitozygomatic osteotomy gives a direct basal view of the region from the anterolateral direction. The patient is placed supine, with the head tilted and rotated to the opposite side. A curved hairline incision is used extending below the tragus. The craniotomy is made in 1 or 2 pieces and the temporal bone is drilled flat to the base. The dura is opened in a C-shaped manner and the sylvian fissure is opened wide. This procedure helps in minimizing the retraction of the temporal lobe. The medial temporal lobe structures are retracted and the tentorial hiatus and the tumor at the medial margin are identified. It is important to preserve the arachnoid layer in the cistern, which contains important neurovascular structures. Sometimes, an interdural approach is used after craniotomy to mobilize the trigeminal nerve for access to the cavernous sinus region.

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RESULTS A total of 41 patients were operated on for tentorial meningioma in the study period (Table 1). The median age of presentation was 51 years, with a clear female preponderance (male/female ratio, 1:3.5). There was a comparable distribution of tumor in different location groups; however, most tumors were around the torcula (group 4). Different surgical approaches used for tumors based on tumor location and relation to tentorium are shown in Table 2. Outcome Analysis Surgical Outcomes. The extent of resection achieved in different locations is shown in Table 3. Overall, the rates of Simpson grade 1, 2, 3, and 4 resection were 20%, 56%, 14%, and 10%, respectively. Patients with tumors in group II (T3 and T8) were candidates for GTR in all cases. However, GTR was not possible with meningiomas at all other locations. The most common reason for subtotal resection was involvement of neurovascular structures. Patients with group 4 tumors had a higher rate of subtotal resection because of the involvement of torcula and nearby venous sinuses. We do not perform venous sinus resections for sinus involvement in meningiomas. The other common reason for subtotal resection was multicompartmental growth, which needs separate approaches for complete removal of the tumor. This was the most common reason for tumors in the group 1 and group 2 locations. Our practice is to remove the largest or symptomatic component of the tumor using a single approach and subsequent close follow-up. Recurrences were managed with Gamma Knife radiosurgery (GKRS) (Elekta, Stockholm, Sweden) or redo surgery. Two patients (one from group 4 and the other from group 1) who had a significant residual tumor (Simpson grade IV resection) received upfront GKRS 2 months after the surgery, one of whom subsequently required redo surgery. Two patients (4.8%) developed postsurgical infection, 1 patient (2.4%) developed CSF leak (after a retromastoid approach for group V tumor), 3 patients (7.3%) experienced postoperative hydrocephalus, and 6 patients (15%) developed new cranial nerve palsies. The most common cranial nerve involved was the trochlear nerve, which was injured during surgery for group 1 tumors using a subtemporal approach, which occurred in 3 patients, and a transsylvian approach in 1 patient. Similarly, there were instances of transient trigeminal and facial paresis in 1 patient each after a retromastoid approach for group V tumors. In 4 patients, diplopia improved in the follow-up period. Patients with hydrocephalus were managed with the placement of a ventriculoperitoneal shunt. Two patients developed postoperative confusion, which had improved at the time of discharge. Four patients developed transient visual field defects after surgery. There was no mortality in this series. On histopathologic

Figure 5. Illustrative case 2. A 42-year old woman presented with nonspecific headache and imbalance and magnetic resonance imaging showed (AeC) a meningioma arising from the left tentorial membrane in the infratentorial location (T4, group III tentorial meningioma). A paramedian suboccipital craniotomy was performed and tumor was accessed through a infratentorial supracerebellar approach. Gross total excision was achieved (DeF) and the tumor attachment to the transverse sinus was coagulated. There was a recurrence of tumor along the left transverse sinus after 7 years (GeI), which was subsequently treated with Gamma Knife radiosurgery (JeL).

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Figure 6. Illustrative case 3. A 38-year old woman presented with headache and visual field defect and magnetic resonance imaging showed (AeC) a transtentorial meningioma involving the torcula and right transverse sinus and straight sinus (T5, group IV meningioma). The patient was operated on through a combined supratentorial and infratentorial approach and the

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tumor was excised completely with coagulation of dura along the sinuses (DeF). After 1 year, the patient developed a small recurrence along the straight sinus (GeI), which was subsequently managed with Gamma Knife radiosurgery.

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Figure 7. Retromastoid suboccipital approach. (A) The position for retromastoid craniotomy and the outline for a curvilinear skin incision. (B) The outline of craniotomy at the junction of the sigmoid and transverse sinus just below the asterion. (C) The neurovascular corridors (between the V, VII-VIII complex and lower cranial

examination, 32 (78) were World Health Organization [WHO] grade 1 meningioma, and others were WHO grade 2. Symptomatic Improvement. The most common presenting symptom was nonspecific headache (75.6% of patients). Apart from headache, 13 patients (31.7%) were symptomatic preoperatively with cranial neuropathy or features of brainstem compression. Postoperatively, headache improved in 26 patients (P ¼ 0.0001) and diplopia improved in 6 patients (P ¼ 0.0004). However, there was no significant improvement with respect to ataxia, seizure, or confusion after resection. Recurrence and Further Treatment. The median follow-up period was 65 months (range, 6e250 months). Thirteen patients (31.7%) had recurrence of tumor in the follow-up period. The recurrence rate varied with Simpson grade of excision and the tumor location. Tumor recurrence occurred earlier and at a higher rate (75%) in Simpson grade IV excision, followed by grade III (50%), grade II (26%), and grade I (12.5%). Almost all patients with recurrences were managed with GKRS unless the tumor size precluded this modality of treatment. Two patients required redo

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nerves marked by dotted lines). (D) Tumor exposed along the inferior surface of the tentorium above the trigeminal nerve. V, trigeminal nerve; VII-VIII, facial and vestibulocochlear nerve complex; LCN, lower cranial nerves (cranial nerve 9e11); T, tumor; Tent, tentorium.

surgery because of the large size of the tumor. Of 11 patients (26.8%) who were managed with GKRS, 10 had stable tumors at follow-up. One patient who did not respond to GKRS required redo surgery.

PFS. The median PFS period in all cases was 149 months (Table 4). PFS at 3, 5, and 10 years after resection were 90%, 70% and 60%, respectively. The median PFS for groups I, II, III, IV, and V tumor locations were 53, 96, 247, 149, and 89 months, respectively. The median PFS for Simpson grades I, II, III, and IV was 247, 149, 60, and 33 months, respectively. There was a significant difference in PFS in patients undergoing GTR compared with patients undergoing subtotal excision (P ¼ 0.003) (Figure 14A). WHO grade 1 tumors had higher median PFS compared with grade 2 tumors (P ¼ 0.01) (Figure 14B). Other factors such as age, gender, ethnicity, or preoperative performance index did not have a significant effect on PFS. Multivariate analysis was conducted using all significant factors of the univariate analysis as covariates. The Simpson grade of excision (GTR vs. subtotal resection) and the grade of the tumor

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Figure 8. Illustrative case 4. An 80-year old female patient presented with headache and magnetic resonance imaging (AeC) showed a meningioma along the posterior petrous margin and attached to the inferior surface of the tentorium (T6, group V tentorial meningioma). She was operated on via

(WHO grade I vs. grade II) were the significant factors affecting the PFS (P ¼ 0.01 and P ¼ 0.03, respectively). DISCUSSION Tentorial meningiomas are considered a neurosurgical challenge because of their critical location adjacent to vital neurovascular structures. To approach these tumors and successfully extirpate them is an arduous task. These lesions necessitate the surgeon to use a multitude of surgical approaches from their armamentarium to achieve the desired goal of complete microsurgical resection. GTR is the desired goal because, regardless of the tumor location, the extent of resection has been shown to affect recurrence and overall patient outcome. As expected, surgical approaches are guided by the location of the tumor in relation to the tentorium and nearby neurovascular structures and need for brain retraction. As mentioned earlier, tentorial meningiomas require the surgeon

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a retromastoid suboccipital approach. The tumor was posterior to the seventh and eighth nerve complex and was removed completely without any complications (DeF).

to be adept at various surgical approaches to tackle them and hence, our endeavor to give a succinct review of these approaches depending on their location. For a better understanding of the suitable surgical approach for a particular tumor, we have divided the tumors broadly in 3 groups according to their relation to the tentorium (Figure 15). Choosing the Right Approach Tumors Along the Free Tentorial Margin. The tentorial notch or the tentorial incisura is the part of the tentorium that is not attached to any bony structures. It is a precarious region of the tentorium, because it encircles the perimesencephalic cistern that contains important neurovascular structures. Meningiomas arising at the free tentorial margin can be divided into 2 groups. Tumors Along Lateral Incisural Space (Anterolateral Group). The lateral incisural space contains the trochlear and trigeminal nerves and the anterior and posterior choroidal arteries. The relation of the

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Figure 9. Combined retrosigmoid and presigmoid approach. (A) The presigmoid and retrosigmoid area have been exposed through an extended retromastoid incision. (B) The transverse-sigmoid junction after craniotomy showing the presigmoid and retrosigmoid

trochlear nerve to the tentorium deserves special mention, because it is the most important nerve that a surgeon encounters and sometimes damages while approaching these tumors. In our series, 4 patients developed transient paresis of the nerve, and in 2 patients, the damage was permanent. The trochlear nerve can be broadly divided into 2 segments in relation to the tentorium. The first segment is the free segment that lies from the first contact of the nerve to the tentorium to its point of entry. The second segment is truly the tentorial segment and lies between the points of its entry into the tentorium and to the cavernous sinus. The point of entry is the most important landmark while incising the tentorium. It lies 1 cm behind the point of entry of the oculomotor nerve and, hence, division of the tentorium 1.5 cm behind the oculomotor nerve avoids risk of damage to the trochlear nerve.9 However, this distance can vary and hence there is a need to identify the trochlear nerve and visualize its entry into the tentorium before making the tentorial incision. Tumors in the lateral incisural space are most frequently accessed by a subtemporal approach, because it provides the shortest and most direct route. However, the complications from the retraction of the temporal lobe jeopardize its overall

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dura. (C) Opening of the dura along both the corridors. (D) The presigmoid corridor after division of the temporal dura, posterior fossa dura, and the tentorium. SPV, superior petrosal vein; SS, sigmoid sinus; Tent, tentorium; TS, transverse sinus; VOL, vein of Labbe´.

benefit. In our series, 6 patients were operated on by a subtemporal route and among them 2 developed postoperative confusion possibly because of temporal lobe retraction. The preservation of the vein of Labbé is important,10 so a preoperative venogram is sometimes suggested to obtain a better picture of the anatomy.11,12 A zygomatic osteotomy gives a flatter angle of attack and may need less retraction of the temporal lobe.13,14 Similarly, a transsylvian approach after a frontotemporo-orbitozygomatic craniotomy gives adequate exposure of the area and is useful for tumors extending to the cavernous sinus and parasellar area.15 Tumors Along Posterior (Medial) Incisural Space. The posterior incisural space mainly comprises the deep venous system. Tumors in this region tend to displace veins in one or the other direction and this is the key determinant for choosing the suitable approach. In our series, the posterior incisural space was the most favorable location for a gross total excision. The preferred approach in this area is the occipital interhemispheric transtentorial approach.5,8,16,17 This approach gives the shortest and most direct route to the posterior tentorial notch, which is helpful especially in patients with a steeply slanting tentorium. Small infratentorial extensions

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Figure 10. Illustrative case 5. A 45-year old female patient presented with headache and magnetic resonance imaging (AeD) showed a transtentorial meningioma along the petrous attachment with equal supratentorial and infratentorial component (T6, group V tentorial meningioma). A combined presigmoid and retrosigmoid approach was used. After initial tumor

can be easily removed with tentorial division 1 cm lateral and parallel to the falcotentorial junction.18 One significant disadvantage of this approach is the limited accessibility of the contralateral side; however, division of the falx 1 cm above the straight sinus along with the division of the contralateral tentorium, as suggested by Kawashima et al.,19 can provide a reasonable exposure to the contralateral side. One important limiting factor of the occipital approach is the need for occipital lobe retraction, which gives rise to postoperative visual field deficits, which can sometimes become permanent. Of our 16 patients who required occipital lobe retraction, 4 had visual field defects postoperatively, although the condition subsequently resolved. Sami et al.20 proposed the supracerebellar-infratentorial approach as an alternative approach with distinct advantages. First, the cerebellum tends to fall down with gravity and needs less retraction in the sitting position. Second, should the cerebellum require any retraction, it is well tolerated compared with the striate cortex of the occipital lobe. However, a supratentorial extension poses a significant problem, because it is difficult to remove transtentorially from below because of the steep angle of the tentorium to the horizontal plane. Moreover, it is less easy to locate the straight sinus from below.

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removal from below, the tentorium was exposed in the presigmoid corridor and was divided. The tumor was exposed with slight retraction of the temporal lobe and was completely excised with a good view from both compartments (EeH).

Tumors Along the Posterior Tentorial Margin and the Tentorial Membrane. These tumors are probably the easiest lesions amenable for complete surgical excision. Approaches for the tumors attached to the tentorial membrane are straightforward. Supratentorial tumors are approached through a supratentorialsuboccipital approach, infratentorial tumors via an infratentorial supracerebellar approach, and transtentorial tumors via either approach depending on the location of the maximum tumor mass. Tumors in the lateral aspect of the tentorium can be removed by a retromastoid suboccipital approach or a paramedian-infratentorial approach. The relatively difficult tumors are the falcotentorial and torcular meningiomas. A large torcular meningioma with both supratentorial and infratentorial components can best be resected by a combined 4-quadrant approach involving bilateral occipital and suboccipital craniotomy exposing the whole of the confluence of the venous sinuses. There may be less controversy in selecting the right approach, because the need of a supra, infra, or combined approach is mainly dictated by the location of the tumor. However, there have been major issues related to the need for resection of dural venous sinuses to achieve a gross total excision. Few studies have reported safe excision of the sinus in meningiomas with a completely occluded sinus1,5,10,17,21;

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Figure 11. Subtemporal approach. (A) The outline for skin incision. (B) The skin flap has been reflected inferiorly to expose the temporal bone. (C) The tentorium has been reflected to show the entry of the

however, other series have suggested preservation of infiltrated sinuses.1,8,20 Bassioni et al.2 in their series reviewed the venous sinus resection and tumor recurrence rate and concluded that infiltrated but patent sinuses need not be resected to decrease recurrence. None of the patients in our series underwent resection of the sinuses. The strategy of leaving behind the tumor invading venous sinuses comes at the cost of increased recurrence rates and, hence, patients should be carefully followed over time with regular magnetic resonance imaging. In our series, 1 patient with a possible small residual along the straight sinus developed recurrence after 1 year, which was subsequently managed with radiosurgery. Similarly, another patient developed recurrence along the transverse-sigmoid sinus 7 years after surgery and was treated with radiosurgery. Tumors Along Petrous Margin. These tumors can be separated into 2 groups: one group of tumors lying posterior to the seventh and eighth cranial nerve complex and the second lying anterior to it. Tumors in the first group are easier to approach through a simple retromastoid suboccipital approach; however, it is not uncommon to damage the hidden and posteriorly splayed nerve complexes if proper care is not

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IVth cranial nerve. (D) The tentorium has been divided to expose the IVth and Vth cranial nerve. IV, trochlear nerve; V, trigeminal nerve; PCA, posterior cerebral artery; Tent, tentorium.

taken during dissection of the deep tumor capsule. It is wiser to get hold of the exit of the nerves at the internal acoustic meatus early in the course and then follow it throughout the course of dissection. This is not a problem for tumors in the second group because the nerves are seen above and in front of the tumor capsule when viewed from a posterior aspect.20 The challenging task in these tumors is working in the corridors between the cranial nerves. The tumor extension toward the brainstem is the most difficult and crucial component to remove unless a clear arachnoid plane exists and has been identified. Tumor extension toward the middle fossa above the petrous apex can be removed though a premeatal drilling of the petrous apex with or without mobilization of the trigeminal nerve in the Meckel cave.22,23 In tumors with large supratentorial component or in transtentorial tumors, a combined approach using the presigmoid and retrosigmoid corridor can be used that can attack the tumor both from above and below. This approach is particularly helpful for transtentorial tumors extending deep down to the cerebellopontine angle. In a presigmoid approach, division of the tentorium and posterior temporal dura provides wide exposure of the trigeminal nerve and seventh-eighth nerve complex, which helps removal of transtentorial tumors

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Figure 12. Fronto-orbitozygomatic transsylvian approach. (A) The outline of frontotemporal craniotomy and orbitozygotomy. (B) The dura has been exposed along with the temporal base after craniotomy and temporal base drilling. (C) The sylvian fissure has been opened wide to expose the neurovascular structures

in this region.10,24-27 Two patients in our series were operated on via a combined presigmoid and retrosigmoid approach, and a gross total excision was achieved without recurrence in the follow-up.

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along the posterior clinoid and medial tentorial margin. ACA, anterior cerebral artery; ACP, anterior clinoid process; BA, basilar artery; ICA, internal carotid artery; ON, optic nerve; Pcom, posterior communicating artery; Tent, tentorium.

Surgical Outcome Degree of Tumor Resection. Complete excision of the tentorial meningioma remains the only safeguard against recurrence; however, the extent of resection is a function of the location of

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Figure 13. Illustrative case 6. A 41-year old male patient presented with headache and gait ataxia and magnetic resonance imaging (AeC) showed a meningioma along the free margin of the tentorium at the lateral tentorial hiatus with compression over the medial temporal lobe and the brainstem (T1, group I tentorial meningioma). The tumor was approached via a frontotemporo-orbitozygomatic craniotomy transsylvian approach. After

the tumor in the tentorium and its invasion of surrounding neurovascular structures. The quest for total resection is often linked with increased neurologic morbidity and should be tempered on a casewise basis depending on the skills and experience of the neurosurgeon. Our experience has been molded on similar lines, with patient safety as our topmost priority. Complete resection (grades I and II) and subtotal resection (grades III and IV) were performed in 76% and 24% of patients in this series, respectively. This percentage of complete resection was comparable with the percentage (77%e91.3%) in the published literature.7,28 The resection rate varied in different tumor locations. It was possible to perform GTR in all cases of tumors in the T3 and T8/group II location; however, it

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removal of the tumor along the medial tentorial margin, a partial anterior petrosectomy was performed to expose the tumor along the crural cistern. A subtotal excision of the tumor was achieved (DeF) with residual tumor along the crural cistern. The patient received Gamma Knife radiosurgery for the residual tumor.

was not possible in cases at other locations because of involvement of tumors with dural sinuses or cranial nerves. Similar experiences of difficulty in resection of tumors in different locations were observed by Bassiouni et al.2 Tumor Recurrence Rate. Among posterior fossa meningiomas, tentorial meningiomas are often considered to have a higher rate of recurrence and worse prognosis in terms of recurrence-free survival after extensive resection.29 The recurrence rate of tentorial meningioma reported in the existing literature is 8.6%e26%.2 In this series, the overall recurrence rate was slightly higher at 31.7%. This difference may be explained by the higher rate of subtotal resection in our series as a result of

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Table 1. Patient Demographics and Tumor Characteristics

Table 2. Tumor Locations and Surgical Approaches

Patient Demographics

Tumor Location Modified Yasargil Classification

Total number of patients Age, years median (range)

41 51 (30e88)

Group I (T1, T2) (n ¼ 9)

Relation to Tentorium (n) Supratentorial (6)

Gender Male Female

Transtentorial (0)

32 (78)

Infratentorial (3)

Retromastoid (2) Subtemporal (1)

Supratentorial (2)

Occipital interhemispheric supratentorial (2)

34 (82.9)

African Americans

Group II (T3, T8) (n ¼ 4)

7 (17.1)

Transtentorial (0)

Clinical presentation Headache

31 (75.6)

Confusion

1 (2.4)

Diplopia

7 (17.1)

Visual field defect

5 (12.2)

Seizure

1 (2.4)

Gait disturbance

2 (4.9)

Facial numbness

2 (4.9)

Hydrocephalus

2 (4.9)

Group III (T4) (n ¼ 9)

Group IV (T5) (n ¼ 10)

Tumor characteristics

Infratentorial (2)

Occipital interhemispheric transtentorial (2)

Supratentorial (3)

Occipital supratentorial (3)

Transtentorial (2)

Occipital supratentorial (2)

Infratentorial (4)

Suboccipital infratentorial (3) Retromastoid (1)

Supratentorial (5)

Occipital interhemispheric supratentorial (5)

Transtentorial (1)

Combined supra and infratentorial approach (1)

Infratentorial (4)

Occipital interhemispheric transtentorial (2) Suboccipital infratentorial (2)

Supratentorial (1)

Subtemporal presigmoid (1)

Transtentorial (3)

Combined pre and retrosigmoid (2) Retrosigmoid (1)

Infratentorial (5)

Retromastoid (4) Suboccipital infratentorial (1)

Location in relation to tentorium Supratentorial

17 (41.4)

Transtentorial

6 (14.6)

Infratentorial

18 (44)

Group V (T6, T7) (n ¼ 9)

Location (modified Yasargil classification) Group I (T1, T2)

9 (22)

Group II (T3, T8)

4 (9.8)

Group III (T4)

9 (22)

Group IV (T5)

10 (24.4)

Group V (T6, T7)

9 (22)

Values are number (%) except where indicated otherwise.

tumor involvement of surrounding neurovascular structures. In addition, the recurrence rate varied according to the Simpson grade of resection.10,30 PFS was better (149 months) in patients undergoing total excision compared with those with subtotal excision (53 months). A similar trend was observed in other series too.10,28,31 Recurrence rate was higher in group V (55%) and group IV (50%) locations, which is because of the lower rate of GTR in these groups (Table 3). Predictors of Recurrence. The results from the existing literature showed that predictors for tentorial recurrence may be unique part because of their location and propensity to invade the

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FOZ transylvian (2) Subtemporal (4)

9 (22)

Ethnicity White

Surgical Approaches (n)

neurovascular structures and bone. Since the original report by Simpson,32 extent of resection has been proved to be one of the important factors predicting recurrence in meningiomas. Likewise, the finding of this study also showed that extent of resection is an isolated predictor of recurrence for tentorial meningioma. After Simpson’s era, research-based evidence suggested that some of the other factors had a significant role in recurrence of meningioma, which includes the location and WHO grade of tumor, and so on.33-37 A higher grade of tumor is associated with a higher recurrence rate and is an independent factor affecting recurrence. The negative impact of older age on PFS, surgical mortality, and morbidity is well known. Therefore, extensive resection is not encouraged in elderly patients.38,39 However, the results of the present study comparing age difference (65 years and older compared with younger than 65 years) did not reach statistical significance in PFS. Similarly, other patient factors such as gender, ethnicity, or preoperative performance status did not have any significant influence on PFS.

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Table 3. Extent of Resection, Pathologic Grade, and Recurrence Rate in Different Tumor Locations Tumor Site T1-T2/ Group I

T3-T8/ Group II

T4/ Group III

T5/ Group IV

T6-T7/ Group V

I

3

0

3

1

1

II

3

4

5

5

6

III

2

0

1

2

2

IV

1

0

0

2

0

1

7 (78)

4 (100)

8 (89)

6 (60)

7 (78)

2

2 (22)

0 (0)

1 (11)

4 (40)

2 (22)

44

25

22

30

33

Simpson grade

World Health Organization grade, n (%)

Recurrence rate (%)

Table 4. Cox Regression Univariate and Multivariate Analysis of Factors Affecting Recurrence-Free Survival Univariate Analysis

Multivariate Analysis

Median Recurrence-Free Survival (months)

Hazard Ratio (95% Confidence Interval)

>65 years

139

1.6 (0.48e5.69)

0.42

—

—

65 years

90

0.38 (0.11e1.35)

0.13

—

—

0.14 (0.71e10.22)

0.14

—

—

0.16

—

—

0.17 (0.04e0.65)

0.009*

0.18 (0.05e0.7)

0.01*

3.7 (1.16e12.0)

0.02*

3.4 (1.07e11.17)

0.03*

0.37 (0.11e1.27)

0.11

—

—

Variables

P Value

Hazard Ratio (95% Confidence Interval)

P Value

Age

Gender Male Female

61 149

Ethnicity White African American

149 36

Tumor location Group 1

53

Group 2

96

Group 3

247

Group 4

149

Group 5

89

Simpson grade of excision Total (I and II) Subtotal (III and IV)

149 53

World Health Organization tumor grade I

247

II

38

Karnofsky Performance Status score >70

149

70

60

Bold values with an asterisk denotes statistically significant values.

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Figure 14. Kaplan-Meir curves showing progression-free survival in different group of patients. (A) Among different Simpson grade of excision.

Limitations The present study has several limitations because of its retrospective nature. The resections were performed by multiple surgeons with different levels of surgical expertise, although most of the surgeries were performed by the principal author. The impact of the learning curve on the overall resection rate and complication rate should not

(B) Among different grades of tumor. GTR, gross total resection; STR, subtotal resection; WHO, World Health Organization.

be underestimated. There have been slight modifications in the surgical techniques practiced by individual surgeons; however, all surgical approaches have been described in a standardized manner. The most important limitation is the low number of meningiomas in each group, which meant that statistical significance was difficult to reach in our study.

Figure 15. Schematic diagram summarizing the location of the tumor and preferred surgical approach. FTOZ, fronto-temporal-orbito-zygomatic.

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CONCLUSIONS Tentorial meningiomas deserve special attention because of their relation to important neurovascular structures. A multitude of approaches are possible for operating on tumors at a particular location; however, relation of tumor to cranial nerves, need of brain retraction, and location of the tumor in relation to tentorium are important factors to determine the most suitable approach. Careful preoperative planning is necessary, and in

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system and recurrence-free survival after surgery for World Health Organization Grade I meningioma. J Neurosurg. 2017;126:201-211. 38. Bateman BT, Pile-Spellman J, Gutin PH, Berman MF. Meningioma resection in the elderly: nationwide inpatient sample, 1998-2002. Neurosurgery. 2005;57:866-872 [discussion: 866-872]. 39. Scheitzach J, Schebesch KM, Brawanski A, Proescholdt MA. Skull base meningiomas:

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neurological outcome after microsurgical resection. J Neurooncol. 2014;116:381-386.

was published as an abstract of oral presentations in Journal of Neurological Surgery: Skull Base 2017 (78: S01). Received 29 July 2017; accepted 23 October 2017

Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Part of the research work was presented at the Annual Meeting of the North American Skull Base Society 2017 and

Citation: World Neurosurg. (2017). https://doi.org/10.1016/j.wneu.2017.10.115 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.

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