Aggressive Resection with Reconstruction of the Superior

Tentorial Meningiomas

Case 9: Aggressive Resection with Reconstruction of the Superior

Sagittal Sinus (Fig. 9.11)

A 47-year-old woman who had twice undergone tumor resection and γ-knife treatment at a previous hospital showed recurrent tumor at the torcular Herophili. Preoperative CT venography demon-

strated occlusion of the straight sinus and left transverse sinus, but venous flow from the superior sagittal sinus to the right transverse sinus was preserved. Thus, an aggressive resection with reconstruction of the sinus using a saphenous vein graft was performed. Simpson G1 removal of the tumor was performed without any complications.

Fig. 9.11 Case 9. Preoperative axial (a) and sagittal (b) T1-weighted magnetic resonance images with gadolinium showing the posterior type of tentorial meningioma.

Preoperative CT venography shows occlusion of the straight sinus and left transverse sinus, although venous flow from the superior sagittal sinus to the right transvers sinus is preserved (c). Postoperative axial (d) and sagittal (e) T1-weighted magnetic resonance images with gadolinium show total resection of the tumor. After craniotomy, the tumor, superior sagittal sinus, and right transverse

sinus are exposed (f). The left transverse sinus and tentorial edge are cut at the lateral and anterior margins of the tumor (g, h). The cerebellar surface is peeled from the torcular Herophili (i). Most of the tumor is resected with no residual tumor around the torcular Herophili (j). After anastomosis between the right transverse sinus and superior sagittal sinus using a saphenous vein graft is performed (k, l), the tumor is totally removed (m)

Fig. 9.11 (continued)

Conclusions

• Surgical difficulty is related to tumor location.

• Incisural lesions require a skull base approach.

• Falcotentorial lesions are difficult but can be well controlled by meticulous strategy.

• Lateral lesions and posterior lesions that do not involve the major venous sinuses are rela- tively simple to treat.

• Surgical management of posterior lesions invading the sinus remains controversial.

• The normal deep venous system should be preserved to avoid any complications.

References

1. Samii M, Carvalho GA, Tatagiba M, Matthies C, Vorkapic P. Meningiomas of the tentorial notch:

surgical anatomy and management. J Neurosurg.

1996;84(3):375–81.

2. Sekhar LN, Jannetta PJ, Maroon JC. Tentorial meningiomas: surgical management and results.

Neurosurgery. 1984;14(3):268–75.

3. Goto T, Ohata K, Morino M, et al. Falcotentorial meningioma: surgical outcome in 14 patients.

J Neurosurg. 2006;104(1):47–53.

4. Mantovani A, Di Malio S, Ferreira MJ, Sekhar LN. Management of meningiomas invading the major dural venous sinuses: operative technique, results, and potential benefit for higher grade tumors. World Neurosurg. 2014;82(3–4):455–67.

5. Raza SM, Gallia GL, Berm H, Weingart JD, Long DM, Olivi A. Perioperative and long-term outcomes from the management of parasagittal meningiomas invading the superior sagittal sinus. Neurosurgery.

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2001;49(5):1029–37.

7. DiMeco F, Li KW, Casali C, et al. Meningiomas invading the superior sagittal sinus: surgical experience in 108 cases. Neurosurgery. 2004;55(6):1263–72.

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W.T. Couldwell (ed.), Skull Base Surgery of the Posterior Fossa, https://doi.org/10.1007/978-3-319-67038-6_10

Foramen Magnum Meningiomas

Angela M. Richardson, Karolyn Au, and Jacques Morcos

A.M. Richardson, MD, PhD • K. Au, MD, MSc J. Morcos, MD, FRCS(Eng), FRCS(Ed), FAANS (*) Department of Neurological Surgery, University of Miami/Jackson Memorial Hospital, Miami, FL, USA e-mail: [email protected]

10

Introduction

Foramen magnum meningiomas (FMMs) are a rare entity; they account for 2.5% of all intracra- nial meningiomas and 4% of posterior fossa meningiomas [22]. The pathologic entity of FMM was first described in 1872; the first publication describing surgical removal was in 1922 [10].

That same year Cushing described a nomenclature for these lesions and published his series. The location of these lesions at the craniocervical junction in proximity to, and possibly encasing, the lower cranial nerves or vertebral arteries makes successful removal particularly challenging [14, 20]. A meningioma is considered to arise from the foramen magnum if the insertion of the tumor is in the region bounded anteriorly by the lower third of the clivus and the upper edge of the body of C2, laterally by the jugular tubercles and the upper aspect of the C1 laminas, and posteriorly by the anterior edge of the squamous occipital bone and C2 spinous process [8]. The large majority (90%) of these tumors are located ventrally or ventrolat- erally requiring a lateral or anterior trajectory for successful surgical removal [8, 21, 23].

Clinical Presentation

FMMs are typically slow growing with an indo- lent course, but when they become symptomatic, they most commonly present with quadriparesis, sensory abnormalities, ataxia, and dysfunction of cranial nerves (CN) IX and X [22]. Patients often describe suboccipital headache or upper cervical pain, exacerbated by coughing or strain- ing [10]. The vague nature of symptoms often prevents early diagnosis with a mean of 31 months to diagnosis from symptom onset [7].

The classic presentation of weakness associated with a FMM is initial weakness in the ipsilateral arm. Progression then occurs to the ipsilateral leg, then the contralateral leg, and finally the contralateral arm [7]. With compression at the craniocervical junction, patients may also have downbeat nystagmus on physical exam. Other signs that may be present include wasting of the sternocleidomastoid, trapezius, or intrinsic mus- cles of the hands [10].

Evolution of Surgical Approach to FMM

A suboccipital craniotomy with drilling of the condyle/jugular tubercle was initially described for resection of craniospinal lesions in 1978 [22].

Heros then described the far-lateral approach

in 1986 for the treatment of lesions of the vertebrobasilar system [13]. A similar technique was then described in 1988 for the resection of anterior foramen magnum pathology [12]. Since those early descriptions, many variations on the far- lateral approach have been described with differing degrees of mastoidectomy, condylec- tomy, the extent of the cervical laminectomy, and mobilization of the vertebral artery depending on the specifics of the case [5, 21]. In 1991, six variations of the dorsolateral approach for meningioma resection were reported: transfacetal, retrocondylar, partial transcondylar, complete transcondylar, extreme-lateral transjugular, and transtubercular [17].

Classification

Foramen magnum meningiomas may be classi- fied based on their compartment of development (intradural or extradural), their relation to the vertebral artery (below, above, or on both sides), and the location of their dural attachments (posterior, lateral, or anterior) [8]. FMMs are considered anterior if the origin is bilateral with respect to the anterior midline (Fig. 10.1), lateral if the origin is between midline and the dentate ligament, and posterior if the origin is posterior to the dentate ligament. Extradural meningiomas at the foramen magnum are less common than intradural tumors, but complete resection is more challenging due to their invasive nature [8, 15]. In tumors that originate beneath the vertebral artery, the cranial nerves are displaced cranially and posteriorly. However, in tumors that originate above the vertebral artery, the location of the cranial nerves is variable, and great care must be taken to avoid injury during tumor resection [15].

Preoperative Assessment

Preoperative workup is aimed at determining the best surgical approach and proximity to nearby structures in order to accurately assess

surgical risks. CT is the best tool for assessing bony anatomy in regard to hyperostosis and cal- cifications, as well as allowing for preoperative determination of the surgical corridor and the degree of bony removal required. In the event of significant bony erosion by the tumor, the patient may require surgical fusion to prevent instability at the craniocervical junction. MRI remains the imaging modality of choice for assessing soft tissues, including the origin of the tumor and the involvement of the critical neurovascular structures located nearby [19].

Many advocate vascular imaging (CTA, MRA, or conventional angiography) preoperatively to evaluate arterial feeders, venous drainage, and the extent of vascular involvement. In particular, defining the V3 and V4 segments of the vertebral artery along with the origin of the PICA will aid in operative plan- ning and the avoidance of complications [8].

Identification and analysis of vessels that are encased in tumor are particularly important.

The presence of significant stenosis is sugges- tive of tumor invasion of the adventitia. In these cases, conventional angiography allows the surgeon to determine if vessel sacrifice is a feasible option based on the results of balloon occlusion test and the presence or absence of collaterals [4].

Surgical Considerations

Patients presenting with FMMs are usually considered for surgery if the lesion is symptomatic, has experienced growth, or is causing mass effect on the brainstem. In these patients, radiosurgery is considered difficult due to the absence of a plane between the tumor and the brainstem and the likelihood of ongoing compression of the brainstem.

As most foramen magnum meningiomas are located ventrally, surgical resection via a far- lateral or extreme-lateral approach may be uti- lized (see chapter on the far-lateral approach).

For midline posterior tumors that do not cross the

plane of the dentate ligament, a midline posterior approach is indicated. Midline anterior tumors without significant spinal extension may appear at first glance to be best approached via an endoscopic endonasal route (EEA), if the tumor is located on the anterior rim of the foramen magnum, the origin is medial to the hypoglossal canal and jugular foramen with posterior and lateral displacement of the lower cranial nerves.

However, significant inferior extension would necessitate removal of the anterior arch of C1, the C2 odontoid process, and the ligamentous complex that provides stability at the craniocervical junction. Therefore these tumors are usually managed via a posterolateral approach [4]. The

proponents of the EEA would state that it allows for tumor resection without retraction of brain tissue and does not necessitate crossing the plane of the cranial nerves. In anteriorly based tumors, this approach allows for early access to the dural blood supply with improved visualization during tumor resection and decreased intraoperative blood loss. Also, involved bone and dura may be resected more easily as compared to a more lateral trajectory. Our objection to utilizing the EEA to intradural meningiomas is based on five cate- gories of pitfalls. First, the bony removal in this approach necessitates reconstruction of the skull base and is accompanied by a significant risk of CSF leak [11]. Second, lower rates of complete

Fig. 10.1 MRI of a 38-year-old female presenting with headaches and dysphagia. (a–c) Preoperative imaging. (a, b) T1-weighted image with gadolinium demonstrating an anteriorly located FMM eccentric to the right. (c)

T2-weighted image. (d–f) Postoperative imaging T1 weighted with gadolinium demonstrating successful resection of the tumor

resection are achieved. Similar to the case with tuberculum sella meningiomas, the dural tails, not well appreciated on preoperative MRIs, often extend lateral to the “presumed” margins of the tumor and are missed or not seen properly during an endoscopic approach. Third, the current, even state-of-the-art instrumentation available for endoscopic skull base surgery lags behind the more mature microscopic arsenal available to microsurgeons. Fourth, the nasal/nasopharyngeal mucosa postoperative morbidity is not trivial and often mischaracterized. Lastly, if a transoral approach is combined with a transnasal route, there is the risk of velo-palatine insufficiency [9].

Additionally, this approach requires a multi- disciplinary team and not all surgeons are famil- iar or adept with it.

The vertebral artery is identified early in lateral surgical approaches, and the decision must be made to work around the artery or mobilize it.

We agree with those surgeons who argue against mobilization of the vertebral artery in most cases [6, 14, 15, 23], although, others routinely employ this tactic [16, 20]. Encasement of the vertebral artery by tumor can be seen, and if identified preoperatively, the consequences of vessel sacrifice can be anticipated with balloon occlusion testing.

Both extradural encasement and repeat surgery are associated with increased risk of vessel rup- ture as well as incomplete removal (41% and 51%, respectively) [20, 23].

Monitoring

Many surgeons recommend the use of somatosen- sory evoked potentials, brainstem auditory evoked potentials, and electromyographic monitoring of the lower cranial nerves (CN X, XI, XII), and this is good practice for this type of surgery [8].

Approaching via a transnasal route mandates monitoring CN VI motor and sensory evoked potentials as this cranial nerve will be encoun- tered early during the approach to the tumor [4].

The senior author has experienced cases where the radicular artery traveling with the C1 nerve root would have been sacrificed (with devastating consequences) to improve exposure for a foramen

magnum meningioma during a far-lateral approach, had it not been for a change in evoked potentials when a temporary clip was placed on the artery to test its contribution to the vascular supply of the upper cervical cord.

Specific Microsurgical Considerations

A detailed discussion of the far-lateral approach is described in the chapter dedicated to that sub- ject. Patient positioning, location of the incision, and drilling of the foramen magnum are addressed there. Once the approach to a foramen magnum meningioma has been completed, be it a far lateral or unilateral suboccipital, there are some general principles to be respected.

The dura is opened in a linear or C-shaped manner based laterally. The dentate ligament should be divided, with particular attention to not confuse it with a portion of the spinal accessory nerve (located posterior to the dentate). The other relational anatomy of relevance is that the V4 segment of the vertebral artery is anterior to the 12th nerve rootlets, which in turn are anterior to the 9/10/11th nerve complex, while the PICA originates at variable heights along the V4 and also courses in a variable direction between the nerves (Fig. 10.2). Once the dentate ligament is divided, the rostrocaudal extent of the tumor needs to be defined. A good practice is to lyse all arachnoidal fibers above and below the tumor, then posterior and medial to the tumor, to allow the cerebellum and other structures to “fall away”

from the tumor with gravity. This helps define the

“boundaries” of the resection and focuses the surgery. Self-retaining retractors are almost never used. We favor the use of nonstick Telfa strips to create the surgical boundaries.

Ideally, the next step should then be an exposure to the dural base of the tumor for early bipolar devascularization (Fig. 10.3). This step is always straightforward in the case of a lateral origin of the tumor, but may be more problem- atic in the case of a large midline base covered by a large bulk of tumor, particularly when the vertebral artery and its perforators may be

Fig. 10.2 Intraoperative photograph during resection of a FMM (patient shown in Fig. 10.1) from the right side. At the superior aspect of the field, the dura can be appreciated lying flat due to complete drilling of the foramen magnum. This allows optimal visualization of the surgical

field. The tumor can be seen displacing the medulla and CN XI posteriorly, creating a working corridor. Distortions of the normal anatomy are common with these tumors, and care must be taken to identify the key neural and vascular structures

Fig. 10.3 The inferior aspect of the tumor has been identified, and early coagulation of the base using the bipolar devascularizes the mass, simplifying piecemeal removal as resection progresses

engulfed in the tumor. Here, a “test” resection of an accessible piece of tumor is done first to see how vascular it might be. Piecemeal resection can continue if the tumor is not too bloody, without further consideration given to reaching the base first (Figs. 10.4, 10.5). If on the other hand the vascularity is significant, then a tai- lored corridor to the dural base should be cre- ated through a careful and systematic partial debulking of the most accessible part of the tumor. Once part of the base is reached, the tumor can be devascularized, leading to incre-

mental exposure of more of the base, more debulking, and so on with sequential steps of increasing returns. The tumor shell most adher- ent to neurovascular structures is naturally left for the end of the resection, when more space is available to tease it out safely. It has been our observation that no matter how large or fibrous or invasive a foramen magnum meningioma is, it never transgresses the pia of the medulla, which, for unclear reasons, is not the case for large petroclival meningiomas that unfortu- nately often invade the pons subpially.

Fig. 10.4 With this same exposure, the jugular foramen can be seen. Inspection of the superior portion of the tumor allows

visualization of the CN IX, X complex with an appreciation for the distortion of normal anatomic relationships caused by the tumor. CN XII can be seen displaced posteriorly (in comparison to the CN IX and X) as it is draped over the tumor surface

Fig. 10.5 Depending on the particular anatomy of the tumor and locations of the neural and vascular structures, the surgeon may work through one or more surgical corridors that are offered. Debulking continues through these various approaches

As in most meningioma surgeries, the principles of using sharp dissection and measured countertraction cannot be overemphasized.

Ultrasonic aspirators must be used with caution, as they will not respect perforators or buried arteries and nerves (Fig. 10.6).

Once the bulk of visible tumor is removed, one can then address the dural base (Figs. 10.7, 10.8). It is not at all uncommon for a segment of meningioma to extend in the interdural space, which is why the dural base has to be resected as completely as possible. The depth of the resection rarely needs to go through and through to the bone, as FMM rarely invades that deeply.

Outcomes and Complications

Over the past 20 years, the overall reported mor- tality for FMM resection is 6.2% with a lower rate of permanent morbidity in the far-lateral approach as compared to the extreme-lateral approach (0–17% vs. 21–56%) [8]. In Yasargil’s review of 114 FMMs, a good outcome was achieved in 69% of patients, fair in 8%, and poor in 10% [24]. In larger series (>10 patients), neurological improvement was seen in 70–100% of patients [8]. Cerebellar and long tract signs tend to improve postoperatively; however, only a minority of patients experience recovery of pre-

the tumor can be performed using sharp dissection. An ultrasonic aspirator may also be used, but this must be done with caution to avoid damage to the surrounding structures

Fig. 10.7 With progressive debulking, portions of the tumor can be pushed away from the surrounding structures and removed

Fig. 10.8 Adequate visualization provided by the exposure allows bipolaring of the dural base following tumor resection, yielding a Simpson Grade 2

existing cranial nerve deficits [22]. Lower cranial nerve palsies are the most commonly observed postoperative deficit, although these deficits (unlike those present preoperatively) have a ten- dency to recover with time [1–3]. Dysphagia with an attendant risk of aspiration pneumonia may be seen in up to 10% of patients. Multiple regression analysis identified tumor recurrence, arachnoid scarring, prevalent cranial extension, and absence of preoperative lower CN dysfunction as signifi- cantly associated with aspiration pneumonia [18]. Vigilance is required postoperatively to minimize these risks.

Conclusions

Foramen magnum meningiomas are a rare entity with the potential for significant symptoms preoperatively and significant complications postoperatively. Thorough preoperative imaging and evaluation aids in determining the extent of neurovascular involvement and in detailing the bony anatomy in the region of the tumor. With adequate surgeon experience and selection of the optimal surgical approach, successful extirpation of the tumor may be achieved.

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Dalam dokumen Skull Base Surgery of the Posterior Fossa (Halaman 132-145)