16 Parasagittal Meningiomas
Introduction
Parasagittal meningiomas are complex lesions with a wide spectrum of clinical and surgical nuances. Retrospective single-center clinical series and technical case reports make up the majority of the literature to date, and lack of class I evidence has hindered consensus on clinical management, surgical treatment, and adjuvant therapeutics for these lesions. In 1938 Cushing and Eisenhardt1 first defined parasagittal meningiomas as those that fill the parasagittal angle, without brain tissue between the tumor and the superior sagittal sinus (SSS). These tumors may involve one, two, or all the SSS walls and may or may not completely occlude flow. Since that description, advances in diagnostic neuroradiology, larger clinical series, and novel surgical techniques have increased our ability to diagnose these lesions at earlier stages and have facilitated our ability to achieve more radical resections with preservation or restoration of vascular flow. Furthermore, development of interventional neuroradiology techniques has increased our understanding of cerebral venous hemodynamics, and stereotactic radiosurgery continues to improve our ability to treat residual or recurrent disease. The following chapter reviews our current understanding of the diagnostics and natural history of these challenging tumors and summarizes modern surgical and adjuvant treatment algorithms.
Epidemiology
Parasagittal meningiomas represent 21 to 31% of intracranial meningiomas. Cushing and Eisenhardt1 and Olivecrona2 proposed the first classification of these tumors according to their location along the SSS. The reported incidence of tumors located in the anterior third (between the crista galli and the coronal suture) has ranged from 14.8 to 33.9%, tumors located in the middle third (from the coronal to the lambdoid suture) range from 44.8 to 70.4%, and those located in the posterior third (from the lambdoid suture to the torcula) range from 9.2 to 29.6%.3 In a clinical series by Black and colleagues, tumors involved the anterior third of the SSS in 12.8% of the cases, the middle third in 69.2%, and the posterior third in 17.9%. Tumors in this series were preferentially located on the right side (59% vs 33.3%), and bilateral tumors presented in only 7.7% of cases.4
Pathological Findings
Parasagittal meningiomas tend to occur where arachnoid granulations are denser, with ~15% of tumors presenting with invasion of the SSS.5 A higher incidence of atypical and malignant meningiomas has been reported in the parasagittal region when compared with meningiomas in other locations.6 In some series, the percentage of malignant and atypical lesions is 3.7% and 14.8%, respectively.7 In a surgical series of 108 patients previously presented by the authors, benign, mostly transitional meningiomas (World Health Organization [WHO] grade I) were identified in 86 patients (79.6%); “atypical” meningiomas (WHO grade II) were diagnosed in 16 patients (14.8%), and malignant meningiomas (WHO grade III) were diagnosed in four patients (3.7%). Whereas grade I lesions were significantly more frequent among women, grade II and III lesions as well as hemangiopericytomas prevailed among men. Since publication of this series, 76 more patients have been acquired (total of 184). Of these, 151 patients (82%) were WHO grade I, 26 patients (14.1%) were WHO grade II, and five patients (2.7%) were WHO grade III. Table 16.1 illustrates the pathological characterization of tumors in this series.8
Histopathological Findings | |
Histological Type | No. of Cases |
Transitional (mixed) | 87 |
Fibrous (fibroblastic) | 28 |
Atypical | 26 |
Meningothelial | 21 |
Psammomatous | 6 |
Malignant | 5 |
Secretory | 4 |
Microcystic | 2 |
Hemangiopericytoma | 2 |
Angioblastic | 2 |
Chordoid | 1 |
Total | 184 |
From DiMeco et al.117 | |
Natural History
In 1957 Simpson9 described infiltration of the SSS as a major factor related to recurrence of parasagittal meningiomas. Since then it is known that the extent of surgical re-section and pathological grade correlates with the rates of recurrence, although residual parasagittal tumors may remain stable over time, and effective predictive factors are yet to be established.5 Among the subtypes of WHO grade I tumors, psammomatous tumors with a high density of calcification rarely recur,10 and angioblastic meningiomas appear to have markedly higher rates of recurrence.11–13
Clinical Presentation
Symptoms
Presenting symptomatology is largely related to the proximity of the lesion to the Rolandic fissure. As illustrated by Cushing’s description of General Leonard Wood’s case,1,14 these patients typically present with sensory or motor seizures involving the contralateral lower extremity. After seizures, contralateral hemiparesis constitutes the second most common presenting symptom, followed by paresthesias, papilledema, and dementia ( Table 16.2 ). Tumors arising from either the anterior or posterior third, however, can remain undetected for long periods of time until mass effect triggers noticeable symptoms. Lesions in the anterior third occasionally present with a long-standing history of headaches or a frontal lobe syndrome, whereas posterior third–based lesions may present with homonymous hemianopsia. The mass effect exerted by tumors arising in the middle third on the precentral and postcentral gyri, and on the paracentral lobule, triggers earlier symptomatology and facilitates faster diagnosis, resulting in smaller lesions upon presentation.3 Before the advent of magnetic resonance imaging (MRI), midline calvarial bossing was considered to be a cardinal sign of a large parasagittal meningioma ( Fig. 16.1 ). In a series of 154 parasagittal meningiomas, anterior third tumors most often presented with headaches (36%) or mental status changes (36%), whereas posterior third tumors presented with headaches (36%), visual symptoms (21%), focal seizures (21%), or mental status abnormalities (21%).15
In a recent series of combined convexity and para-sagittal meningiomas by Black et al, most patients who received surgical treatment were symptomatic at the time of surgery, with headache constituting the most prevalent symptom (35.9%), followed by motor findings (38.4%), and seizures (30.1%). The number of asymptomatic patients constituted 28.2% in that surgical series.4
Anatomical Considerations
Cross-sectional analysis of the SSS reveals a basic triangular shape that gradually increases in size as it extends distally toward the posterior third.16 The SSS communicates laterally with irregular interdural venous lacunae, which lie on either side of the dura mater and are occasionally accompanied by arachnoid granulations. These structures often appear as a filling defect or an intrasinusal mass on MRI. Eight to 12 external medial cortical veins and a similar number of internal cortical veins carry out most cortical venous drainage on each hemisphere.3
Angiographic analysis of 100 patients by Apuzzo et al showed that most parasagittal veins (70%) join the SSS in a segment of the sinus located between the coronal suture and 2 cm behind it.17 Furthermore, 53 of 100 SSS studied angiographically by Yamamoto and colleagues18 had venous tributaries that entered the sinus within 2 cm of the coronal suture, with 76% of these entering within 2 cm behind the coronal suture.
The anterior half of the SSS is narrower and has fewer associated venous lacunae, fewer pacchionian bodies, and smaller numbers of adjoining cortical veins entering the sinus than the posterior half, which facilitates surgical exploration.
Collateral venous blood flow was studied in 242 cases of parasagittal meningiomas by Tigliev et al.19 This study showed that, whereas in anterior third tumors 52.1% of cases had collateral blood flow through cortical veins, in middle or posterior third tumors, collateral drainage occurred through cortical veins in 67% of cases. Collateral blood flow through the extracerebral veins occurred in 56% of patients regardless of the location along the sinus.
Furthermore, in a study by Oka et al, collateral blood flow was also identified through meningeal veins and end-to-end anastomoses of superficial cerebral veins.20 These superficial cerebral veins are classified into four groups depending on the cortical area drained by them: with a superior sagittal group that drains the superior part of the medial and lateral surfaces of the frontal, parietal, and occipital lobes and the anterior part of the basal surface of the frontal lobe and empties into the SSS; a sphenoidal group that drains into the sphenoparietal and cavernous sinuses; a tentorial group that converges on the tentorial sinuses; and a falcine group that empties into the inferior sagittal or straight sinus.20 Andrews et al also presented an anatomical classification based on cadaveric analysis of 10 human brains,21 in which the para-sagittal veins were divided into anterior frontal, posterior frontal, parietal, and occipital. In that study the anterior frontal parasagittal region had an average of 6.5 veins on each hemisphere, the posterior frontal region had three veins, the parietal region had four veins, and the occipital region had one vein.
The results of these studies suggest that resection of the anterior third of the sinus has limited impact on the overall hemispheric venous drainage in most cases, and that sacrifice of the middle third of the SSS significantly affects venous return. Disruption of venous structures in the posterior third results in less restrictive venous drainage than sacrifice of middle third structures, but the true effect of these changes is directly related to the caliber of the sacrificed vessel and the cortical region draining through it.16,22,23
Classifications
Bonnal and Brotchi first provided a surgical classification of parasagittal meningiomas in 1978 that included eight tumor subtypes.24 Since then this classification has been modified and now describes five tumor subtypes developed to facilitate resection strategies.5 In this classification system type I lesions are those that only attach to the outer surface of the sinus wall. Type II lesions enter the lateral recess of the SSS. Type III lesions are those that invade one wall of the SSS. Type IV tumors have already invaded two sinus walls but have not compromised patency, and type V tumors are those that spread over the midline and invade all the walls of the sinus, resulting in complete occlusion ( Table 16.3 ).
Sindou and Alvernia have proposed a similar classification that attempts to guide surgical decision making and preoperative planning based on six categories. Type I lesions present with attachment to the outer surface of the sinus wall but without disruption of the wall or intrasinusal invasion. Type II lesions are those with tumor invading the lateral recess but without invading the lateral wall. Type III lesions show invasion of the ipsilateral sinus wall. Type IV lesions are those with invasion of both the lateral wall and the roof of the SSS. Types V and VI reflect a complete sinus occlusion, with or without one free wall, respectively3,7 ( Table 16.4 ).
Differential Diagnosis
A myriad of lesions can affect the parasagittal region, ranging from meningiomas of all histopathological grades, to hemangiopericytomas, lymphomas, meta-static disease, and extramedullary hematopoiesis, among others.13 The consistency of findings on imaging studies, however, greatly facilitates diagnosis. Similarly, intraoperative appearance of these lesions and frozen-section analysis are characteristic, can quickly confirm the diagnosis and contribute to intraoperative decision making.
Diagnostic Evaluation
Computed Tomography
Computed tomography (CT) is particularly beneficial in cases in which either hyperostotic or lytic calvarial changes are expected because it can aid in planning of the craniotomy flap. In addition, in cases in which bone flap replacement is hindered by marked tumor invasion, CT data can be used to fashion precise prosthetic implants for cranioplasty.5
MRI/MRA/MRV
MRI with and without contrast remains the imaging study of choice for evaluation of parasagittal meningiomas. MRI provides specific information on the size and consistency of the lesion and on its relationship with the falx, the meninges, the surrounding cerebral cortex, and the vascular structures involved ( Fig. 16.2 ). Magnetic resonance angiography (MRA) in combination with contrast-enhanced MRI is now considered the gold standard in most centers.5 MRA provides accurate, noninvasive visualization of the arterial and venous anatomy, which facilitates analysis of sinus patency and invasion, and visualization of collateral venous drainage patterns that develop following sinus occlusion. MRA exhibits some advantages over DSA due to its noninvasive nature and its ability to detect multidirectional flow. Although a comprehensive overview of the major dural sinuses and their patency can be obtained with two-dimensional (2-D) phase contrast imaging, more specific details on cortical venous anatomy can be seen with 3-D phase contrast sequences.5 Magnetic resonance venography (MRV) can provide preoperative insight on venous infiltration and visualize collateral venous anastomoses; in one study, up to 87% of the collateral venous anastomoses secondary to parasagittal meningiomas were visualized.25
Furthermore, through additional image reconstruction from 2-D and 3-D sequences, information regarding direction of flow in a given vascular structure can also be obtained. The MRA data obtained is in some cases, however, limited when compared with digital subtraction angiography (DSA), particularly in visualization of the arterial supply to the tumor and in confirming sinus patency in cases with high degrees of obstruction where sinus flow is scarce and slow. Therefore, both techniques are used in a complementary fashion in cases requiring clarification, and in those in which embolization is considered.5
The use of functional MRI and fiber tractography has been reported and could be beneficial in patients with parasagittal tumors that invade beyond the pial surface.4
Digital Subtraction Angiography
Before surgery, visualization of venous anatomy is fundamental in operative planning. Details on patency of the sinus, arterial tributaries to the tumor and its relationship with cortical structures, and location of cortical draining veins and their point and angle of entry into the SSS are carefully considered.
Depression of the internal cerebral veins is frequently seen in parasagittal tumors, and the shape of the vessel was used to guide angiographically assisted localization before CT and MRI imaging. Marc and Schechter described multiple angiographic findings related to venous flow rerouting secondary to partial or complete SSS occlusion, including nonvisualization of the occluded segment, failure of cortical veins to reach the SSS, delayed emptying of veins at the site of obstruction, and reversal of normal venous flow with collateral venous channels connecting the SSS with other venous structures, such as the lateral sinus and the middle cerebral vein.26 The thalamostriate vein can also be depressed in the more anteriorly located lesions; this finding was often referred to as “closing of the venous angle.”
For large meningiomas (> 5 cm), determination of arterial feeding branches to the tumor, which may arise from the anterior or middle cerebral arteries, can facilitate preemptive intraoperative devascularization by selective embolization4 ( Fig. 16.3 ). DSA is an invasive diagnostic procedure with variable morbidity risks that can vary significantly among operators and between centers; for this reason some authors do not advocate its use in a routine manner unless preoperative embolization is being considered.5
Surgical Indications
The slow-growing nature of most parasagittal meningiomas, combined with our ability to conduct close radiological follow-up with serial MRI/MRA imaging and to treat residual or recurrent disease with radiosurgery,27 has significantly changed the surgical indications for these lesions and modified the goals of surgery.5 Tumors involving critical cortical veins or partially patent sinuses can be subtotally resected, and the remnants can be followed radiographically or treated with adjuvant radio-surgery. If the lesion recurs, a conservative approach to allow for proper collateral circulation to be established and for progressive sinus thrombosis to occur can significantly decrease morbidity.5,20 The long-term recurrence seen by some high-volume centers despite gross total re-section (GTR) of sinus-invading tumors followed by graft repairs has also raised questions about the benefits of radical resection and grafting, and the frequency of sinus reconstruction procedures appears to be decreasing. Black and colleagues recommend yearly MRI follow-up for patients older than age 65 who are asymptomatic or have tumors less than 3 cm in diameter.4
Hancq and colleagues now propose conservative extrasinusal tumor resection of lesions invading a partially patent sinus, leaving residual intrasinusal tumor and conducting yearly MRI/MRA follow-up with adjuvant radio-surgery if tumor progression is observed.5 They reserve intrasinusal tumor removal for lesions with completely obliterated sinuses, in which robust collateral flow has reestablished venous drainage over time. This treatment algorithm is shared by the authors and continues to be followed by several centers.28,29
Preoperative Considerations
Endovascular Interventions
Embolization
Preoperative embolization has been used as an adjuvant therapy to reduce intraoperative blood loss and decrease surgical time in meningioma surgery.30–33 The role of palliative embolization, however, remains controversial. Tumor edema or hemorrhage has been reported after embolization of meningiomas with polyvinyl alcohol (PVA) particles, and the safety and efficacy of stand-alone embolization of meningiomas have been questioned.34 The potential complications of embolization for these lesions, however, can be devastating.35,36
After a diagnostic arteriogram is obtained, blood supply to the tumor is identified, and the safety and feasibility of embolization are determined. Using real-time digital-subtraction fluoroscopy or “road-mapping” technology, a microcatheter is navigated through the larger diagnostic angiography catheter and directed over a microguidewire to the artery supplying the meningioma. Superselective angiography is performed through the microcatheter to verify the location and identify any normal branches, which would preclude safe embolization.37,38 The embolic material is injected under continuous real-time digital-subtraction fluoroscopy to allow penetration into the tumor bed, which will result in devascularization and subsequent necrosis.
The use of new embolization materials such Onyx (ev3 Neurovascular, Irvine, CA), in combination with superselective catheterization, has increased our ability to perform these procedures safely.34 Nonetheless, larger series and randomized trials are needed to determine specific safety and efficacy for parasagittal meningiomas.
Stenting
In most cases, venous collateralization typically prevents the onset of intracranial hypertension as a result of sinus occlusion from invading tumor. If intracranial hypertension presents, surgical decompression and tumor resection are attempted. In some cases, additional comorbidities, poor functional status, or advanced age may prevent surgical treatment. Similarly, partially resected lesions can also exhibit significant recurrence and associated intracranial hypertension. An alternative palliative method for intracranial hypertension therapy is ventriculoperitoneal shunt (VPS) placement, which can decrease intracranial pressure until further venous collateralization develops or additional aggressive surgical treatment is performed.39 If intracranial hypertension were to occur despite VPS placement, venous outflow obstruction can be relieved by endoluminal stent placement.39,40 Higgins et al39 reported the case of a patient with a recurrent falcine meningioma that developed persistent intracranial hypertension from occlusion of the straight sinus and of the sinus confluence point in the posterior third of the SSS. This patient was treated with transvenous stenting of the SSS into the right transverse sinus via a left jugular puncture. The patient required full anticoagulation for 2 months thereafter and remained on low-dose aspirin after that. Intracranial hypertension symptoms had significantly improved at 3 months, and the patient continued to do well on the 9-month follow-up evaluation. Ganesan et al40 also described their experience with a posterior third parasagittal meningioma with sinus invasion and intracranial hypertension. The patient responded to transvenous stenting with an Omnilink balloon-mounted stent (Guidant Corp., Indianapolis, IN), with significant improvement at 3 months postprocedure. In this case the patient was able to receive stereotactic radiosurgery after stenting without the risk of additional postradiation edema. Despite the inherent risk of poststenting thrombosis and the need for anticoagulation followed by antiplatelet therapy, venous sinus stenting constitutes a viable salvage therapy for flow restoration.
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