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Ventral foramen magnum meningiomas: the transcondylar approach

O. Al-Mefty, S. Ayoubi, AN Taha

27

Chapitre

Table of contents

Anatomy ........................................................................ 405Incidence ........................................................................ 407Classification ................................................................. 407Clinical presentation ..................................................... 407Surgical challenge .......................................................... 408Surgical approaches ...................................................... 408Perioperative protocol ................................................... 409Intraoperative neurophysiological monitoring ........... 409Operative management ................................................. 409 Patient position ....................................................... 411 Skin incision ............................................................ 411 Exposing the vertebral artery ................................. 412 Transposing the vertebral artery, drilling the bone and opening the dura .............................. 413 Exposing tumors located laterally .......................... 413 Exposing ventrally located tumors ......................... 413 Devascularizing and debulking the tumor ............ 413 Tumor dissection ..................................................... 414 Extent of resection .................................................. 414Surgery-related complications ...................................... 415Clinical outcomes .......................................................... 415Histological examination .............................................. 415Radiosurgery ................................................................. 415References ...................................................................... 415

Arising out of the arachnoid granulation at the cranio-cervical junction, foramen magnum meningiomas are located in a zone that extends anteriorly to the area between the lower third of the clivus and the upper edge of the axis, laterally from the jugular tubercle to the upper aspect of the C2 lamina and posteriorly from the anterior edge of the squamous occipital bone to the C2 spinous process (1–3). Ventral foramen magnum menin-giomas arise anterior to the ascending coronal plane between the first dentate ligament and the cranial nerve (CN) IX–CN XII on both sides. They occur in 68–98% of all cases of foramen magnum meningiomas (1, 3–5) (Fig. 1). Ventral meningiomas should be distinguished from dorsal (posterior) foramen magnum meningiomas

that are accessible and easier to treat and are different in presenting symptoms, neurological findings, opera-tive approach, postoperative results, complications, and mortality rates.

Anatomy

Understanding the anatomy of the suboccipital region is vital to approaching and removing ventral foramen magnum meningiomas. This is described in detail in the literature (6–8). A short description is provided here. The foramen magnum contains several critical neuro-anatomical and vascular structures. The neural struc-tures included the cerebellar tonsils, inferior vermis, fourth ventricle, caudal aspect of the medulla, lower cranial nerves (9–12), rostral aspect of the spinal cord, and upper cervical nerves (C1 and C2). Major arterial structures located within the foramen magnum include the vertebral arteries (VAs), PICAs, anterior and poste-rior spinal arteries. The VA courses through the foramen tranversalis until reaching the C1 where it curves above the lateral aspect of the posterior arch and proceeds rostral to pierce the dura mater just inferior to the lateral edge of the foramen magnum adjacent to the occipital condyle. Its intradural portion typically gives rise to the posterior spinal artery and PICA. Several anatomical structures are particularly relevant to surgery for ventral foramen magnum meningiomas: 1) the muscular layers: there are two muscular triangles as shown in Figure 2. The superior suboccipital triangle is formed by the obli-quus superior and the inferior muscles and the rectus capitis. The horizontal V3 with its muscular and poste-rior meningeal branches are found here. The inferior suboccipital triangle is formed by the obliquus capitis inferior, the semispinalis and the splenius cervicis muscles, housing the vertical V3, the periarterial auto-nomic neural plexus, the muscular and radiculomus-cular arteries of the vertical V3, the VA venous plexus,

B. George et al., Pathology and surgery around the vertebral artery© Springer-Verlag France, Paris 2011

406 Pathology and surgery around the vertebral artery

and the C2 nerve. 2) The posterior atlanto-occipital membrane: this is located ventral to the deep muscular layer covering the horizontal V3 courses at the foramen magnum between the inferior border and the posterior surface of the occipital bone and the posterior arch of the atlas. The venous compartment in the suboccipital

Fig. 1 – The position of ventral foramen meningiomas as seen on (A) axial MRI; (B) skull model; (C) sagittal MRI; (D) Skull model highlighting the obstruction of the tumor access by the occipital condyle.

Fig. 2 – Anatomical dissection of the suboccipital deep muscle triangle (from old draft).

region, bordered proximally by the lateral (periosteal) ring, distally by the distal (dural) ring, inferiorly by the posterior arch of the atlas, ventrally by the dura and the capsule of the atlanto-occipital condylar joint, and dorsally by the posterior atlantooccipital membrane, is a structure strikingly similar to the parasellar cavernous

C

A B

D

Ventral foramen magnum meningiomas: the transcondylar approach 407

Age in different reports ranged from 17–77 years (mean 39–58 years) (7, 9, 14, 15). Percentage of male patients was (0–35%) and of women patients (64–100%) (7, 9, 14–16).

Classification

Boulton et al. (7) classified foramen magnum menin-giomas as originating primarily or invading secondarily the foramen magnum; anteroposterior and laterome-dial; and to small (one-third the transverse dimension of the foramen magnum), medium (one-third to half its dimension) and large (half). Bruneau and George (8) classified the lesions according to compartment of development (intradural, intraextradural, and extra-dural); dural insertion for intradural tumors (posterior treated with midline approach, and lateral and medial treated with posterolateral approach); and relation to the VA for the lateral tumors (below, above, and one both sides) (Fig. 4).

Clinical presentation

The clinical presentation of foramen magnum menin-giomas is protean. Even in the era of MR imaging, diagnoses might be delayed or incidental (7, 17). The mean duration of symptoms is 8–10 months (7, 18). Early features of foramen magnum meningiomas include occipital headaches and upper cervical pain, which is often exacerbated by neck flexion or valsalva maneuvers. Classic foramen magnum syndrome is defined by deve-lopment of unilateral arm sensory and motor deficits that progress to the ipsilateral leg, then the contralateral leg, and finally contralateral upper extremity (7). Long tract findings characteristic of upper motor lesions are found paradoxically in the presence of atrophy in the intrinsic muscles of the hands. Later findings include spastic quadriparesis and lower cranial nerve palsies (7). Other symptoms include pain/sensory changes, facial numbness/pain, hemihypesthesia, decreased hearing, swallowing, diplopia, shoulder weakness, tongue weakness, spasms, uncoordination/loss of dexterity, ataxic incoordination/gait difficulties, dysarthria, and hydrocephalus.

Differential diagnosis includes other neoplasms in areas as well as diseases that cause similar symptoms, such as multiple sclerosis, amyotrophic lateral sclerosis, syringomyelia, and cervical spondylosis (12, 19).

Fig. 3 – Illustration depicting the venous network in the suboccipital area so called “the suboccipital cavernous sinus.” Abbreviations: acv: anterior condylar vein, pcv: posterior condylar vein, lcv: lateral condylar vein, jb: jugular bulb, scs: suboccipital cavernous sinus, lr: lateral ring, ms: marginal sinus, jv: internal jugular vein, av: anastomotic vein, vvp: vertebral venous plexus, vavp: vertebral artery venous plexus. Reproduced with permission from Arnautovic KI, Al-Mefty O, Pait TG, et al. (1997) The suboc-cipital cavernous sinus. J Neurosurg 86:256.

sinus, and hence named the suboccipital cavernous sinus (6) (Fig. 3). Aside from anatomical and likely physio-logical consideration, this intrinsic venous network dictates operative consideration for the transcondylar approach particularly if the VA is to be mobilized.

Incidence

These lesions represent 0.3–3.2% of all meningiomas, 4.2–20% of all posterior fossa meningiomas, and 60–77% of all benign extramedullary tumors at the craniospinal junction (1, 4, 9–13). Their rare inci-dence limits experience in their treatment. Yasargil et al. (12) have reviewed 114 patients who were surgically treated for foramen magnum meningiomas whose cases were reported between 1924 and 1976. They found an overall mortality rate of approximately 13%, an over good outcome of 69%, a fair outcome of 8%, and poor outcome of 10%.


Surgical challenge

Owing to their location, ventral foramen meningiomas remain some of the most challenging meningiomas to treat. Often, they are not discovered until they are large, and the patient may be asymptomatic during a relatively long period (7, 9). Difficulty in treating ventral foramen magnum meningiomas comes from the large number of vital neurovascular structures crowded into a deeply hidden central area. The close relation to neurovascular elements raises the potential risk associated with radical removal of these lesions. However, treatment of ventral foramen magnum meningiomas has advanced with deve-lopment of modern diagnostic modalities, refinement of microsurgical techniques, publication of microsurgical anatomical studies, development of skull base approaches, and advancements in neuroanesthesia, intraoperative neurophysiological monitoring, and careful multidisci-

plinary perioperative planning, allowing radical tumor resection, with a decrease in the rate of complications and improvement in survival rates (1–4, 6, 12, 13, 18–27).

Surgical approaches

Traditionally, posterior midline suboccipital approaches and C1 laminectomy have been used in the operative treatment of ventral foramen magnum meningioma (12, 28). Some authors still advocate the traditional lateral suboccipital approach with total resection in 82–96% of cases. However, no attempts are made in this approach to resect the dura widely or to excise involved bone (14, 16) and other authors have found that residual tumor after initial suboccipital approach had to be resected with far lateral approach (17). The advantage of suboccipital

Fig. 4 – Classification of foramen magnum of Bruneau and George. Foramen magnum meningiomas are classified according to their compartment of development, their dural insertion, and their relation to the vertebral artery. The relation to the vertebral artery permits to anticipate the displacement of the lower cranial nerves. Tumors growing below the vertebral artery push the lower cranial nerves at the superior aspect of the lesion. On the other hand, tumors developed above or on both sides of the vertebral artery displace the lower cranial nerves in all directions and their position can then not be anticipated. Reproduced with permission from Bruneau M, George B (2008) Foramen magnum meningiomas: detailed surgical approaches and technical aspects at Lariboisière Hospital and review of the literature. Neurosurg Rev 31:19–33.


craniotomy is the familiarity of most surgeons with this simple and rapidly performed craniotomy. Criticisms of this approach primarily relate to the interposition of brain stem, cranial nerves, and vessels between an anterior tumor and the surgeon for its access (7). Some authors advocate judging the “surgical corridor” using the transcondylar approach when considered necessary to create an appropriate surgical corridor otherwise, using the suboccipital craniotomy when they consider is likely sufficient (7). Bruneau and George (8) choose the approach according to their classification of the tumor: posterior midline is used for posterior intradural lesions, posterolateral approach for lateral and anterior lesions, and posterolateral or anterolateral for intraex-tradural or pure extradural. Transoral approach (10, 29) has serious limitations in cases of intradural lesions: poor access to laterally placed or broad-based tumors, crossing of a contaminated operative field (oropharynx) causing meningitis or a cerebrospinal fluid (CSF) fistula, difficult dural closure, and destabilization of the cranio-cervical junction (10). We firmly believe the transcon-dylar approach is greatly advantageous in the treatment of ventral foramen magnum meningiomas. It is impera-tive in obtaining total removal and lessening complica-tions (9). It should, of course, be tailored to fit the local anatomy and tumor characteristics in each patient.

Perioperative protocol

The perioperative protocol for surgery of ventral foramen meningiomas is designed for maximum visua-lization of the lesion and adjacent bony and neurovas-cular structures and their relation to the tumor, as well as accessing and protection of general and neurological functions particularly relevant to the area and to the special care of each individual patient. The neuroradio-logical workup consists of magnetic resonance (MR) imaging, MR angiography (both arterial and venous), and computed tomography (CT) scanning. Recently 3D computed tomography and angiography have been used, enabling better 3D visualization of the lesion and its relation to bony and vascular structures (Fig. 5). Gadolinium-enhanced sequences help to precisely deli-neate the dural attachment and the presence of the dural tail, the tumor size, and consistency (firm, soft, or cystic) and its relation to neural and vascular structures (Fig. 6). On T2-weighted images, the presence of an arachnoid plane between the tumor and the neuroaxis is sometimes visible (Figs. 7–8). Bone windows CT scan is helpful depicting bony invasion.

The surgeon must carefully analyze the local anatomy of the foramen magnum, the condyles, the C1–2 complex, the area of tumor origin, the tumor features, the regional vascular anatomy, the bilateral VA patency, and the dominance of venous sinuses. Four-vessel angiography is not used unless MR angiography revealed particularly unusual findings that required further visualization. Intraoperative use of image-guided frameless stereotaxy is particularly helpful in skull base surgery, including surgery for ventral foramen magnum meningiomas, as there is no shift of vital structures upon opening the skull and draining cerebrospinal fluid. Perioperative evaluations include speech pathology and otolaryngological evaluations, including a formal or at least bedside swallowing study, and visualization of the vocal cords. If a patient has swallowing difficulties, appropriate actions such as instigation of parenteral nutrition, insertion of Dobb-hoff feeding tube, vocal cord injections, or medializa-tion will assist in preventing the serious complication of aspiration.

Intraoperative neurophysiological monitoring

Introperative neurophysiological monitoring includes the use of somatosensory evoked potential, motor evoked recording and brain stem auditory evoked potentials bilaterally. The CN X is monitored via an electromyo-graphic endotracheal tube. CN XI and CN XII are also monitored, unilaterally, or bilaterally as needed by the direct insertion of EMG needles in the corresponding muscle.

Operative management

Awake endoscopic intubation is performed routi-nely to avoid neck flexion or extension. Perioperative spinal cord trauma steroid drug protocol (for 24 hours) may be administered and prophylactic antibiotics (48 hours) are administered to the patient when anesthesia is induced. The technique is tailored to each patient according to the findings on preoperative imaging, indi-vidual anatomy, and the tumor extension. If necessary, the approach is extended or combined with other skull base approaches.

This approach is greatly influenced by microsurgical anatomical studies of this complex area and has been described in detail before (6, 11, 18–20, 24, 26).


Fig. 5 – 3D CT angiography demonstrating the vertebral artery encasement by calcified ventral foramen meningioma.

Fig. 6 – MRI is the diagnostic mean of choice. On enhancement it demons-trates tumor size, vessel encasement and neurovascular displacement. A. Sagittal MRI with typical homo-genous enhancement of menin-gioma. B. Postoperative. C. Vertebral artery encasement on coronal cut. D. Postoperative.

A B

C D


Fig. 7 – T2-weighted images MRI is very useful in depicting an arachnoidal dissecting membrane between the tumor and brain stem. A. Coronal preoperative MRI. B. Coronal postoperative MRI.

Fig. 8 – Axial T2 MRI demonstrating the arachnoidal dissecting membrane and the position of the vertebral artery. A. Axial preope-rative MRI. B Axial postoperative MRI.

Patient position

The patient is logrolled and placed in a semilateral position 45° from horizontal (Fig. 9). The neck is kept in neutral position, without rotation, to maintain the normal anatomic course of the VA. The shoulder is pulled gradually downward and taped. The position allows the surgeon a lateral view of craniovertebral junction, exposing the laminae of C1 and C2, while it does not obstruct access to the field.

Skin incision

A curvilinear incision is made two fingers breadths behind the mastoid and extended down along the ster-nomastoid muscle into a skin crest in the neck. This is a well-vascularized incision that provides wide exposure and can incorporate other approaches when necessary. The greater auricular nerve is identified at the surface of the sternomastoid muscle and preserved.

A B

A B


Exposing the vertebral artery

The small muscles of the deep triangle are sectioned off the transverse process of C1 and removed. They should be resected in superiosteal fashion so that no remnants obstruct the field. The artery is usually crossed by the anterior branch of the second cervical nerve, which is followed laterally to find the artery between C1 and C2. The nerve may be sectioned for exposure if needed (Fig. 10). The VA above C1 is then exposed. The poste-rior arch of the atlas is exposed in subperiosteal fashion from the transverse process to the midline. The inser-tions of the small muscles are first detached from their inferior margin at C1 and then are detached from the superior margin. The horizontal segment of the VA is fully exposed and carefully freed between the surroun-ding periosteal sheath and the bone of the arch.

The entry of the VA into the dura can be identified as it courses superiorly and anteriorly by the thicke-ning of the bone of the posterior arch of C1 and the muscular branch that originates from the artery and runs medially.

Fig. 9 – A. Illustration demonstrating patient position for the transcondylar approach. B. Skin incision.

Fig. 10 – Shows the vertebral artery in the suboccipital cavernous sinus (SCS) and the surrounding vertebral plexus (VAVP) and lateral ring (LR); jugular vein (JV), lateral jugular vein (LJV), posterior jugular vein (PJV), external vertebral venous plexus (EVP). Reproduced with permission from Arnautovic KI, al-Mefty O, Husain M (2000) Ventral foramen magnum menin-giomas. J Neurosurg (Spine 1)92:71–80.

A B


Transposing the vertebral artery, drilling the bone, and opening the dura

The transposition of the VA complex depends on the encasement of the VA by the tumor, the extension of the tumor inferiorly beyond C1, the ventral and contra-lateral extension of the tumor, and the involvement of the other side VA. The transverse foramen of C1 is opened by drill or rongeurs to expose the VA. In this fashion, the VA is identified throughout its course but remains surrounded by the venous plexus supported by its periosteal sheath and the fatty tissue around it. The venous plexus can be troublesome leaving the fatty tissue around the vessels minimizing the potential of bleeding from this plexus. The plexus is prominent on the ante-rior and medial aspect of the VA. Occasionally oversized and particularly troublesome is the subcondylar vein, which requires repeated obliteration of its foramen with Gelfoam powder. The complex venous compartment in the subocciptal area (6, 20, 29) which cushions the VA complex, was previously named the suboccipital caver-nous sinus. Its engorgement, which cannot be predicted by using current diagnostic modalities, can be trouble-some, causing prolonged VA complex dissection and transposition (Fig. 10). The freed segment of the artery from C2 to the dural entry is elevated and held medially with caution not to kink the artery (Fig. 11).

A lateral posterior fossa craniotomy is done to open the foramen magnum. The sigmoid sinus and jugular bulb are skeletonized fully. The C1 and occipital condyle are drilled medial to the VA.

The portion of the condyle drilling is directly propor-tional to the tumor location and extension to the contralateral side, allowing its safer dissection from vital anatomical structures. In other words, the more medial the tumor, or the more it extended across the midline, the more the condyle is drilled.

As the bony work is completed, the insertion of the VA into the dura will be the center of the exposure. The incision is made along posterior edge of the sigmoid sinus, crossing posterior to the jugular bulb in the foramen magnum and circling around the insertion of the VA. The incision is continued caudally into the upper cervical dura.

Exposing tumors located laterally

Laterally placed tumors require only partial drilling of the condyle, and it is unlikely that there is a need to transpose the VA. The tumor is exposed after opening and tenting the dura laterally. The medullary spinal

junction is usually displaced backwards and frequently to the other side. The 11th nerve is stretched over the lateral aspect of the tumor. The VA is usually deep to the tumor in these cases and is not seen on initial expo-sure. The cerebellum is supported slightly to expose the upper pole of the tumor. The arachnoid is opened over the capsule of the tumor (Fig. 11).

Exposing ventrally located tumors

Ventrally located tumors require extensive drilling of the condyle and transposition of the VA. After the dura is opened, the tumor is exposed. The VA is visible on the lateral aspect of the tumor as the artery may pierce the tumor and be totally encased by it.

Devascularizing and debulking the tumor

The tumor is devascularized by coagulating its inser-tion. It is then debulked with an ultrasonic aspirator or suction and bipolar coagulation. Ultrasonic aspiration should be used with care to avoid injuring the VA and the PICA when they are embedded in the tumor. Once the tumor is debulked, intra-arachnoidal dissection is completed by separating the upper pole of the tumor from the lower cranial nerves and the lower pole of the tumor from its extension into the spinal canal (Fig. 12). Care is taken to preserve the spinal rootlets of the CN X, which are usually spread out on the lateral wall of the tumor.

Fig. 11 – Intraoperative illustration demonstrates the relationship of a foramen magnum tumor with the neurovascular elements. Tumor covered with the arachnoid, vertebral artery, and cranial nerves. Reproduced with permission from Arnautovic KI, al-Mefty O, Husain M (2000) Ventral foramen magnum menin-giomas. J Neurosurg (Spine 1)92:71–80.


Tumor dissection

The piece of tumor lodged against the intramedullary portion is separated, and the arachnoid plane over the spinal cord and the medulla is preserved. Particular attention is made to preservation of the anterior spinal artery. Depending on its location, the VA is meticu-lously separated and followed cephalad to the vertebral junction. If the junction is involved, it is also carefully separated, exposing both the junction and the contrala-teral VA. The PICA is dissected carefully, as is the ante-rior spinal artery (Fig. 13) The tumor may extend into the canal of the 12th nerve, requiring the canal to be

unroofed if this has not already been done. Occasionally, the tumor originates at the midline; then the 12th nerve is seen on the lateral aspect of the deep-seated tumor.

The dura over the insertion is coagulated with the laser or bipolar, or excised if involvement is obvious. Any hyperostotic bone is drilled. Sometimes the whole tumor is a bony mass that needs extensive drilling. The dura is then closed and a patch graft is used to cover any defect around the VA. A fat graft is applied over the defect, and muscles are closed in tight layers. If the condyle was totally removed in meningiomas, it is very unlikely that stabilization is needed. Most patients with less than 70% resection of the condyle remain stable without need for surgical fixation (30, 31). Occipitocervical fusion is indicated if there is clinical instability defined by the presence of a painful head tilt, radiological instability on flexion–extension films, or complete resection of the occipital condyle (30). It is also indicated after a bilateral condyle resection with 50% removal (31). If and when fixation is needed, a construct made of plate-rod system is used with a plate fixed to the occiput with inside–outside screw (32) and a rod fixed to the pedicle of C2 and C3, with bone graft extending from the occiput to the upper cervical spine lamina.

Extent of resection

Complete surgical removal (Simpson grade I and II) of ventral foramen magnum meningiomas is reported in recent literature to be between 56 and 100% with a perioperative mortality between 0 and 20% (1, 3, 6, 7, 15, 17, 22, 27, 33). Radical tumor surgery should be pursed with zeal at initial surgery, as this time is best to affect a “cure.” A radical tumor resection is proved to be a feature with a statistically significant impact on favo-rable clinical outcome. On the other hand, the feasibility of radical resection cannot be predicted prior to surgery in patients presenting with a recurrent tumor, and it is less likely to be achieved. Nonetheless, the surgeon should still endeavor to seek maximum removal (9). This strategy appeared to contribute to a relatively long period in which the patient’s condition is stable.

The tumor is usually removed in one session. However, if dissection of the suboccipital cavernous sinus and transposition of the VA complex were difficult because of the significant engorgement of the suboccipital caver-nous sinus, the intradural stage of surgery is postponed 1 to 5 days after the first stage. Especially if the patient had previous radiation, the tumor might be adherent to the VA and the lower cranial nerves, and an arachnoidal plane might not be established. Persistence in separating

Fig. 12 – During tumor resection. Reproduced with permission from Arnautovic KI, al-Mefty O, Husain M (2000) Ventral foramen magnum meningiomas. J Neurosurg (Spine 1)92:71–80.

Fig. 13 – After resection of the tumor and preserving the neuro-vascular elements. Reproduced with permission from Arnautovic KI, al-Mefty O, Husain M (2000) Ventral foramen magnum meningiomas. J Neurosurg (Spine 1)92:71–80.


these structures might lead to rupture of the VA, which should be repaired by microsurgical sutures. Radiation induced angiopathy is a source of serious risks and surgical difficulties because of the subsequent pulmo-nary complications.

Surgery-related complications

Preoperative lower cranial nerve deficits may worsen postoperatively or patients may develop new lower cranial deficits after surgery. The most common deficits are of lower cranial nerves, CN IX and CN X in parti-cular. These deficits are the most morbid (3, 27, 33–35). These patients may undergo vocal cord medialization or vocal cord injection with collagen as necessary. Fortu-nately, almost all patients recover or compensate with time progressing from a dysphagia diet to a regular diet within a range of 10 days to 8 months (mean 66 days) (9). The 11th nerve is more resilient and it is anatomi-cally preserved and manipulated “cautiously” during surgery. It usually recovers well. Patients who develop a 12th nerve deficit usually recover completely or partially. Other complications include CSF leak. Although water-tight closure after transposition of the VA complex may be difficult, meticulous dural closure with fascial and fat autografts remains the only way to prevent this poten-tially dangerous complication. Hydrocephalus may be the underlying case of the leak and requires insertion of a shunt. If a CSF leak occurs, additional sutures and external lumbar drainage should be attempted first. If this approach fails, revision is needed.

Clinical outcomes

Most patients (89%) present with a Karnofsky Perfor-mance Scale (KPS) score of 60 and higher. KPS scores are observed to improve during a follow-up period of 12, 18, and 24 months compared with the preoperative scores. In patients who undergo near-total or subtotal tumor resection a stable tumor size is usually demons-trated on yearly follow-up MR images but tumor progress might occur and lead to death. Use of Cox’s proportional-hazard model revealed that radical tumor resection (gross total or near total), and higher preope-rative KPS score were factors that had statistically signi-ficant impact on the favorable outcome, whereas gender and, interestingly, age did not (9). Low preoperative KPS score, a progressive clinical course, and quadriparesis are

factors that portend a poor prognosis and a significant risk. Hence, early diagnosis and operative treatment is recommended (9).

Histological examination

The histological subtype differs among different reports (3, 5, 9, 13). Meningotheliomatous was the most common type in some reports (39–68%) (3, 9, 13), while the psammomatous comprised the majority in others (5). Although the histological type of menin-gioma may have had some yet unknown impact on the extent of tumor removal it does not seem to influence the clinical outcome (9). A clear cell meningioma that is WHO Grade II and known with aggressive behavior and recurrence in foramen magnum is reported in one of five children with foramen magnum meningioma, it recurred 12 years later with metastasis in the sacrum with complete destruction of the S2 and S3 vertebral bodies (36).

Radiosurgery

Because of the low incidence of ventral foramen magnum meningioma, the number of reported cases is limited (37–39). Because of the irregular tumor volumes along the inferior clivus, multiple isocenters of irradia-tion were required (39). This treatment modality would be considered in nonsurgical candidates.

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