1 Tentorial Meningiomas Francesco Signorelli

Transcription

1 Meta data Explanation Please review proofs carefully for typographical and factual errors only; mark corrections in the file using the discretion. Please read your chapter carefully to confirm that no errors have crept in. Please pay particular attention that figures and their legends and in-text callouts match appropriately. 1 Tentorial Meningiomas Francesco Signorelli Michel W. Bojanowski 1.1 Introduction and Backround Definition, Pathophysiology, and Epidemiology primary intracranial tumors. They are of mesodermal origin, thought to grow from the arachnoidal cap cells of the arachnoid villi and granulations. Meningiomas are classified as tentorial if they have their largest attachment to the tentorium even if there is some attachment to the dura of adjacent sites. In this chapter, the authors will not discuss meningiomas arising from the dura of the petrous bone or the clivus with secondary involvement of the tentorium. Tentorial meningiomas (TMs) are relatively rare, in most series malignant features in up to 10% of cases. They have a clear female predominance (up to 80%) and may occur at all ages. The tentorium cerebelli is a dural extension that separates the inferior portion of the occipital and temporal lobes from the cerebellum. A large opening at its anterior border, the tentorial incisura provides the communication between the supratentorial and infratentorial spaces. The lateral and posterior borders enclose the transverse sinus and the torcular; they are attached to the inner aspects of the occipital and parietal bones, enclosing the superior petrosal sinuses ( Fig. 1A). TMs may grow on the superior and/or inferior surface of the tentorium. They arise more frequently anteriorly, from the free tentorial edge: from its apex at the oculomotor triangle (tentorial fold meningiomas) to its most posterior part, at the confluence of the vein of Galen and the straight sinus (anterior falcotentorial meningiomas). They may also originate from the lateral tentorial aspect, in relation to the torcular or along the transverse sinus. Less frequently, they develop in an intermediate location, on the surface of the tentorium, away from its edge 1

2 and away from its outer aspect, where the major venous sinuses occur ( Fig. 1B). Fig. 1.1 (A) Axial superior view of the tentorium and surrounding structures demonstrating various locations of tentorial meningiomas (highlighted in red) with suggested approaches for resection based on location. (B) Midsagittal view of the tentorium and surrounding structures demonstrating various locations of tentorial meningiomas (TMs). Note the relation to surrounding venous channels. 1. Anteriorly located TM with supra and infratentorial extension; 2. posteriorly located TM, near the torcular, with supratentorial extension. (VG, vein of Galen; SSS, superior sagittal sinus; ISS, inferior sagittal sinus; St.S, straight sinus; SVV, superior vermian vein; Ce, cerebellum) 2

3 Clinical Presentation TMs can display a wide variety of symptoms, according to their site and size. Symptoms and signs of intracranial hypertension are the most common findings, followed by cerebellar ataxia, long tract signs, and cranial nerve dysfunction. 3

4 Up to one third of patients may present with chronic hydrocephalus with Hakim-Adam triad (dementia, memory loss, bradyphrenia), gait ataxia (mimicking Parkinson disease), and urinary incontinence. Hypoacousia is also a common finding, up to 30% of cases, even in cases of tumors remote from the cerebellopontine angle. In these cases, interference with auditory cortical pathways seems to be the most likely cause. Unusual presentations have been reported, such as facial pain, hemifacial spasm, and symptoms related to syringomyelia due to tonsillar herniation. Diagnosis and Imaging Computed tomography (CT) is often the first imaging study obtained showing an isodense lesion, which occasionally can be hyperdense or slightly hypodense compared with the nervous tissue. It has the characteristics of an extraaxial lesion, and may be surrounded by a variable amount of vasogenic edema. Contrast enhancement is usually homogeneous, except for areas of calcification, fat deposits, or tumor necrosis. CT provides a better view of bone invasion by the meningioma than does magnetic resonance imaging (MRI). Hyperostosis is characteristic of these tumors, and bone erosion may suggest a more aggressive behavior. CT may also reveal secondary obstructive hydrocephalus. MRI shows meningiomas to be isodense or slightly hypointense compared with the cortex on histologic subtypes. There is strong contrast enhancement after gadolinium injection. Dural enhancement is often seen beyond the lesion (dural tail). MRI best reveals the delineation of the tumor, the arachnoidal plane between the tumor and neural tissue, and its relationship with cranial nerves. On magnetic resonance angiography, one may appreciate displacement of the large intracranial vessels by the tumor. Magnetic resonance venography explores the involvement of the major venous sinus that can be invaded by the lesion. Discordant results have been published regarding diffusion weighted imaging as a method to predict the grading of a meningioma. Perfusion techniques may detect the pial-cortical supply of a meningioma, which is often associated with a more aggressive behavior and risk of recurrence. Meningiomas may be difficult to distinguish from a hemangiopericytoma. The latter, unlike a meningioma, shows an increased uptake of 11 C-methionine and 15 O-H 2 O, but a low uptake on 18 F-FDG (fludeoxyglucose) PET (positron emission tomography). Cerebral conventional angiography is not routinely performed and may reveal the dural vascular supply as well as perfusion by the pial vessels. The venous phase demonstrates the extent, if present, of involvement on the sinuses by the tumor. Embolization of the lesion by interventional angiography may facilitate the surgical treatment. Treatment Options and Alternatives Observation with serial imaging and clinical examinations 4

5 Radiosurgery/stereotactic radiotherapy Surgical resection Due to complex relationships with neurovascular structures, microsurgical resection of these tumors may be a challenge, especially for anteromedially (free tentorial edge) located lesions. Complete resection is sometimes inadvisable. Goals and Advantages of Selected Surgical Approach The primary therapeutic goal is complete surgical resection with preservation of surrounding neurovascular structures. There is a correlation between the extent of resection, as evaluated by the Simpson grade classification, and recurrence. Surgical approaches depend on the site of the attachment of the TM and whether its extension is supra- or infratentorial. Its relationship with cranial nerves, nervous tissue, major intracranial arteries, important draining veins (e.g., the vein of Labbé, the Galenic system) and venous sinuses may influence the surgical strategies. TMs involving the tentorial incisura are usually the most challenging. Depending on their location, the surgical approaches for these meningiomas vary. Anterior incisura: Pterional approach and its variants with orbital (if extension is toward the cavernous sinus) and zygomatic osteotomies (if extension is toward the middle fossa and interpeduncular cistern). Middle incisura: Subtemporal approach for supratentorial TMs if their anterior margin is at the level or behind the anterior aspect of the cerebral peduncles. The addition of a zygomatic osteotomy reduces the need for temporal retraction. Posterior incisura (meningiomas of the anteromedial portion of the tentorium): The occipital interhemispheric approach for lesions extending in the supratentorial space; the occipital interhemispheric transtentorial or the infratentorial supracerebellar approach for lesions extending inferiorly The surgical approaches for TMs not involving the tentorial incisura also vary according to location ( Fig. 1). Indications Paramedian and lateral meningiomas: When the extension is mainly infratentorial, the supracerebellar infratentorial (paramedian TMs) and retrosigmoid (lateral TMs) are the preferred approaches. In cases of prominent supratentorial extension, the suboccipital approach is used. A posterior subtemporal approach can alternatively be used for more laterally located TMs, but it may put at risk the vein of Labbé, especially if its confluence into the transverse sinus is located near the transverse-sigmoid junction. A posterior petrosectomy with a presigmoid approach may be considered in this situation. Torcular meningiomas and Falco-tentorial meningiomas are approached via a supracerebellar/suboccipital transtentorial route with, when necessary, exposure of all four quadrants formed by the confluence of the transverse sinuses with the superior sagittal and the inconstant occipital sinuses. 5

6 Surgical removal is indicated if the meningioma is symptomatic by mass effect, unless the symptoms are mild in elderly patients or in patients with advanced life-threatening diseases. Large asymptomatic tumors may be removed in otherwise healthy younger patients. In cases of small asymptomatic lesions, simple observation is appropriate even for young patients, especially if there is no brain edema. This is also the case for those presenting with seizures that are medically well controlled. When symptoms are related to infiltration of neurovascular structures as in the case of the cavernous sinus with limited tumor size, surgery is unlikely to achieve a clinical improvement. In these cases, radiation therapy (stereotactic radiosurgery) is preferred. When surgery is indicated, complete removal of the meningioma is the goal, although it is preferable to leave residual tumor in some circumstances to avoid significant neurologic deficit. Radiation therapy has proven its efficacy in the treatment of residual or recurrent TMs. Contraindications Asymptomatic lesions in elderly patients Patients with advanced life-threatening diseases or other medical comorbidities prohibiting surgery. 1.2 Operative Details and Preparation Preoperative Planning and Special Equipment Preoperative imaging must be carefully reviewed, with particular attention to Arterial supply and venous drainage of the meningioma Extent of involvement of the related dural sinuses Relationships with normal intracranial arteries and veins, including the vein of Labbé Relationship with the surrounding brain tissue and cranial nerves Categorization of the TM according to its location and extension ( Fig. 1) Preoperative embolization in selected cases facilitates the surgical resection of these lesions by reducing their vascularization. Neuronavigation is a good tool to plan the craniotomy and the trajectory of approach. It also allows one to assess the exact intraoperative location at the tentorium and at the base of the skull with its surrounding neurovascular structures. The ultrasonic aspirator is essential for tumor debulking prior to dissection of the tumor capsule. Intraoperative electrophysiologic monitoring of cranial nerves and brainstem evoked potentials helps in identifying the course of the nerves and may alert the neurosurgeon before any irreversible damage occurs to these structures. Expert Suggestions / Comments In cases where the tumor is well vascularized and bleeding is expected, preoperative embolization is recommended. 6

7 The neurosurgeon must have comprehensive knowledge of the surgical anatomy of the skull base and the tentorial incisura. Using preoperative studies, the neurosurgeon must have a thorough understanding of the particular tumor and its relationships with normal, but possibly displaced neurovascular structures. One should avoid blunt dissection as traction injuries may occur if the tumor is adherent to cranial nerves or other important surrounding structures. Intraoperative electrophysiologic monitoring helps improve the outcome. Key Steps of the Procedure The various approaches according to location and extension already mentioned ( Fig. 1) must allow not only good exposure of the tumor, but also early exposure of its blood supply. It is paramount to work with a relaxed brain to minimize brain manipulation and retraction. This can be achieved with appropriate positioning, proper exposure, osmotic diuretics, early cisternal opening for cerebrospinal fluid (CSF) drainage, and ventriculostomy in cases of hydrocephalus. Early devascularization of the tumor from its dural feeders must be achieved without significant brain retraction. Partial debulking of the tumor may sometimes be necessary to reach the feeders. Removal consists of alternately debulking the tumor and dissecting its outer border from the surrounding normal tissue. Sharp dissection must be used and blunt dissection avoided whenever possible. It is important to recognize and preserve the arachnoidal plane, which is the surgical route of dissection, to protect the brain tissue. The plane of dissection must be exposed by retracting the performed sharply and always under direct vision to avoid injury to the brain, cranial nerves, and blood vessels. Particular attention must be paid when the tumor takes its blood supply from pial arachnoidal plane. In eloquent areas, this may present a limiting factor for complete tumor resection. Intraoperative electrophysiologic monitoring of cranial nerves and brainstem evoked potentials help in identifying the course of the nerves and may alert the neurosurgeon before any irreversible damage occurs to these structures. In cases of venous sinus involvement, it is important to preserve the patent venous sinus and the potential venous collaterals to avoid a venous infarction. It is reasonable in these circumstances to leave a small residual tumor and coagulate its attachment to the venous sinus while preserving the sinus wall. Although it is recommended to remove extensively the enhancing dura, this is often not possible and coagulation of the tumor attachment and the surrounding dura is usually associated with a long recurrence-free interval. The dura is closed in a watertight manner. Duraplasty may be necessary in certain cases. A standard multilayered closure then ensues based on the approach used, with care taken to prevent the possibility of a CSF fistula. Avoidances / Hazards / Risks Majors risks include injury to adjacent cranial nerves, injury to the brainstem, brain swelling, and hemorrhage due to unwarranted retraction or to the occlusion of normal parenchyma venous 7

8 drainage or major venous sinuses. Salvage and Rescue Neurovascular structures must be preserved even when the absence of an interface between the tumor and the cranial nerves, the brainstem, and blood vessels prevents its complete resection. Intraoperative electrophysiologic monitoring may reduce the risk of injuring these delicate structures. The venous sinuses must also be preserved because sinus reconstruction is hazardous and associated with a high risk of thrombosis. Residual tumor can be followed or treated by adjuvant radiation therapy. 1.3 Outcomes and Postoperative Course Postoperative Considerations Emergence from anesthesia should be controlled avoiding straining, coughing, and arterial hypertension. Close monitoring in the intensive care unit is necessary for prompt recognition of mental status changes or the appearance of new neurologic deficits. Whenever possible, an MRI performed within 24 hours after surgery allows evaluation of the extent of tumor resection. Studies suggest that radiation therapy (stereotactic radiosurgery) may be beneficial in partially resected meningiomas. Whether radiation therapy should be administered early after surgery or at recurrence is not firmly established. Complications Complications are related to site and size of the meningioma, occurring more frequently in medially located tumors. Complications include brain swelling and hemorrhage due to excessive brain retraction or dural sinus or venous occlusion, injury to cranial nerves and brainstem, stroke secondary to occlusion of normal parenchyma artery, CSF leak. Outcomes and Prognosis In a recent series the mortality was shown to be less than 10% and morbidity around 25%; however, these series include complex petroclival and cerebellopontine meningiomas originating from the petrous bone. Medially located TMs are associated with a higher rate of complications compared with those located more laterally. Meningiomas are slow growing, usually benign tumors. Subtotal resection for tumors in close relationship to critical neurovascular structures is usually associated with a long recurrence-free term. Radiation therapy (stereotactic radiosurgery) in selected patients may increase the mean time 8

9 of recurrence. Radiation therapy is indicated for both recurrent and malignant TMs. 2 References 1. Bassiouni H, Hunold A, Asgari S, Stolke D, Tentorial meningiomas: clinical results in 81 patients treated microsurgically. Neurosurgery 2004; 55: (1) 108 (pub-id: ) 2. Bret P, Guyotat J, Madarassy G, Ricci AC, Signorelli F, Tentorial meningiomas. Report on twenty-seven cases. Acta Neurochir (Wien) 2000; 142: (5) (pub-id: ) 3. Hashemi M, Schick U, Hassler W, Hefti M, Tentorial meningiomas with special aspect to the tentorial fold: management, surgical technique, and outcome. Acta Neurochir (Wien) 2010; 152: ( 5) (pub-id: ) 4. Aguiar PH, Tahara A, de Almeida AN, Kurisu K. Microsurgical treatment of tentorial meningiomas: Report of 30 patients. Surg Neurol Int (1): pii, Rhoton AL, JrTentorial incisura. Neurosurgery 2000; 47: (3) SupplS131 S153 (pub-id: ) 6. Rostomily RC, Eskridge JM, Winn HR, Tentorial meningiomas. Neurosurg Clin N Am 1994; 5: (2 ) (pub-id: ) 7. Shukla D, Behari S, Jaiswal AK, Banerji D, Tyagi I, Jain VK, Tentorial meningiomas: operative nuances and perioperative management dilemmas. Acta Neurochir (Wien) 2009; 151: (9) (pub-id: ) 8. Yasargil MG. Meningiomas. In: Yasargil MG, ed. Microneurosurgery of CNS tumors IVB. 9