sign in sign up
<<
Home , Bone, Foramen magnum, Occipital bone

Neurosurg Focus 14 (6):Article 10, 2003, Click here to return to Table of Contents

Foramen magnum : concepts, classifications, and nuances

MELFORT R. BOULTON, M.D., PH.D., AND MICHAEL D. CUSIMANO, M.D., PH.D., F.R.C.S.(C) Division of Neurosurgery, St. Michael’s Hospital, and the University of Toronto, Ontario, Canada

Foramen magnum meningiomas represent a common histological tumor in a rare and eloquent location. The authors review the clinical presentation, relevant anatomical details of the foramen magnum region, neuroimaging features, the posterior and posterolateral surgical approaches for resection, and outcomes. Based the experiences of the senior author (M.D.C.) and a review of the literature, they introduce the concept of a “surgical corridor,” discuss the classification of these tumors, and the nuances of care for patients with these challenging lesions.

KEY WORDS • • foramen magnum • craniovertebral junction • • suboccipital craniotomy

Meningiomas are slow-growing benign tumors that from the lower third of the , to upper margin of the arise at any location where arachnoid cells reside. Al- body of C-2, laterally from the jugular to the though meningiomas account for a sizable proportion of upper margin of the C-2 laminae, and posteriorly from the all primary intracranial neoplasms (14.3–19%),46 only 1.8 anterior edge of the squamous occipital to the C-2 to 3.2% arise at the foramen magnum.2 Their indolent spinous process. development at the craniospinal junction makes clinical The foramen magnum contains several critical neu- diagnosis complex and often leads to a long interval be- roanatomical and vascular structures of which the surgeon tween onset of symptoms and diagnosis. The sensitivity of must be aware. The neural structures include the cerebel- this region to surgical manipulation has sparked recent lar tonsils, inferior vermis, , caudal aspect debate as to the most advantageous surgical approach. The of the medulla, lower cranial (ninth–12th), rostral intent of this paper is to provide an overview of the rele- aspect of the , and upper cervical nerves (C-1 vant surgical , clinical features, and nuances of and C-2). The ninth through 11th arise as a the management of foramen magnum meningiomas. We series of rootlets along the anterior medulla, with the introduce the concept of the “surgical corridor” and dis- spinal component of the 11th cranial arising mid- cuss its importance in the management of these challeng- way between the anterior and posterior spinal rootlets of ing lesions. the spinal cord. The spinal accessory rootlets coalesce and ascend rostral to join the ninth, 10th, and the cranial por- tion of the 11th nerve. Together, these nerves exit the skull FORAMEN MAGNUM ANATOMY through the . The 12th cranial nerve exits the medulla more anteriorly than the other lower cranial Several excellent reviews of foramen magnum anatomy 3,10,14–17,29–31 nerves and passes anterior to the ipsilateral VA on its have been published. By definition, foramen course to the hypoglossal , located within the superi- magnum meningiomas arise from arachnoid at the cra- or and anterior–most portion of the occipital . niospinal junction. The borders of this zone, as defined 14,17 Major arterial structures located within the foramen by George and George and colleagues range anteriorly magnum include the VAs, PICAs, anterior and posterior spinal , and the meningeal branches of the verte- Abbreviations used in this paper: CSF = cerebrospinal fluid; bral, external, and internal carotid arteries. The VA cours- CT = computerized tomography; GKS = gamma knife ; es through the foramen tranversalis until reaching C-1 MR = magnetic resonance; PICA = posterior inferior cerebellar where it curves above the lateral aspect of the posterior ; QOL = quality of life; VA = . arch and proceeds rostral to pierce the dura mater just

Neurosurg. Focus / Volume 14 / June, 2003 1

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC M. R. Boulton and M. D. Cusimano inferior to the lateral edge of the foramen magnum adja- cent to the occipital condyle. Its intradural portion typi- cally gives rise to the and PICA, although the origin of the PICA has been reported to vary, arising at, above, or below the foramen magnum.13

CLASSIFICATION OF FORAMEN MAGNUM MENINGIOMAS We describe foramen magnum meningiomas as having originated primarily from within the confines of the fora- men magnum or having secondarily invaded the region but originating elsewhere. We also classify the primary tumors according to their anteroposterior and lateromedi- al orientations. The spinal dentate delineates the anterior and posterior compartments. Most lesions (68– 98%)2 arise anterolaterally; a posterolateral origin is the second most frequent, purely posterior lesions the third, Fig. 1. Illustration of the surgical corridor. A: Normal rela- and least common are entirely anterior. We also classify tionship of brainstem to foramen magnum. oc = occipital condyle; these lesions based on their size relative to that of the fora- cmj = cervicomedullary junction. B–D: As the tumor (T) en- men magnum (small, one third the transverse dimen- larges, it displaces the brainstem posteriorly and typically to one sion of the foramen magnum; medium, one third to one side, naturally creating a widened surgical corridor. B: A narrow half its dimension; large, one half). corridor of less than 1 cm between the condyle and cervicomed- Most importantly, when managing these lesions, we de- ullary junction. C: Adequate corridor with a 1- to 2-cm distance. D: Large corridor ( 2 cm) that allows relatively easy access to the fine an avenue that we term the “surgical corridor.” This anterior foramen magnum. is defined as “the space for surgical access to a lesion.” It describes the space that the surgeon will work through to access the lesion. The surgical corridor can be enlarged naturally by a tumor displacing normal structures like the undeniable, and lead to significant and often permanent in a confined space such as the fora- neurological deficit. Early features of foramen magnum men magnum. Alternatively, one goal of a surgical route meningiomas include occipital headache and upper cervi- such as the transcondylar approach would be to enlarge cal pain, which is often exacerbated by flexion or the surgical corridor. Valsalva maneuvers. Classic foramen magnum syndrome In the management of foramen magnum meningiomas, is defined by development of unilateral sensory and the surgical corridor involves the space between the later- motor deficits, which progress to the ipsilateral , then al margin of the cervicomedullary junction and the medi- the contralateral leg, and finally contralateral upper ex- al aspect of the occipital condyle. The corridor can and tremity. Long tract findings characteristic of upper motor should be assessed on preoperative imaging. In these le- lesions are found paradoxically in the presence of atrophy sions, the corridor represents the view of a lesion that a in the intrinsic muscles of the . Later findings surgeon obtains via a posterolateral approach after remov- include spastic quadriparesis and lower cranial nerve pal- ing only the and leaving the condyle intact. sies. Slowly progressive lesions such as these allow the We define a corridor as “narrow” if it provides a diameter development of accessory muscles to replace of access to the tumor of less than 1 cm; “adequate” if it is and sternocleidomastoid . We therefore highly re- greater than 1 cm but less than 2 cm; and “large” if greater commend that the patient be undressed and the sternoclei- than 2 cm (Fig. 1). Thus, a tumor arising primarily from domastoid and trapezius muscles be closely inspected for the posterior of the foramen magnum and extending atrophy. Likewise, the should be inspected at rest laterally has a large corridor of access, whereas one pure- for atrophy and fasciculation. Close attention to sensory ly anterior with no displacement of the cervicomedullary testing of the C-2 dermatome will help establish the diag- junction has a narrow corridor. Most tumors, once ad- nosis. Patients attest to initial sensory disturbances such as vanced enough to produce symptoms, have at least an ade- cold or burning dysesthesias, astereognosis, and anesthe- quate corridor. sia but often do not seek medical attention until intractable pain, motor deficits, or ensue. Terminal progression includes quadriplegia, an inability to maintain airway pro- CLINICAL PRESENTATION tection with secondary pneumonitis, and ultimately respi- ratory arrest. The clinical presentation of foramen magnum meningi- omas is protean, and the mean length of symptoms prior IMAGING FEATURES to diagnosis is 30.8 months, even in the era of MR im- aging.16 The clinical differential diagnosis includes multi- The role of neuroimaging is to confirm the clinical ple sclerosis, amyotrophic lateral sclerosis, syringomyelia, diagnosis and to allow the planning of a surgical approach. and cervical spondylosis.11,20,36 In a cursory examination Magnetic resonance imaging is the modality of choice for the physician may miss subtle findings early in the stage defining tumors of the foramen magnum because it pro- of the progression, but later symptoms are often advanced, vides high-resolution images of soft- anatomy that is

2 Neurosurg. Focus / Volume 14 / June, 2003

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC Foramen magnum meningiomas not susceptible to degradation by the surrounding skull resect tumor safely because of the sharp contrast between base, a pitfall of CT scanning. Although plain T1-weight- bone and soft tissues. It is sometimes difficult to outline ed MR images demonstrate excellent anatomical detail, bone margins on MR images, and this technique may they provide little discrimination between tumor and - overestimate the size of the surgical corridor available for stem because the former may appear isointense, mild- extirpation. It is clearly evident that optimal surgical plan- ly hypointense, or hyperintense to surrounding brain. On ning requires both CT and MR imaging to assess appro-

T2-weighted images meningiomas appear as isointense to priately bone and soft tissues, respectively. slightly hyperintense compared with brain (Fig. 2 left). An additional imaging modality that may assist surgery

The T2-weighted images should be carefully inspected for is conventional angiography with optional embolization the presence of an arachnoid plane between the tumor, of vessels that supply tumor exclusively. The dural blood brainstem, and spinal cord. Edema depicted within the supply typically arises as posterior and anterior meningeal neuroparenchyma on T2-weighted sequences suggests that branches from the VAs with the support of meningeal the pial membrane has been invaded; this should prompt branches via ascending pharyngeal and occipital arteries. an attempt at function preservation in which a near-total The tumor may derive its vascular supply from a domi- resection of leaves a small thin plating of tumor intact.38 nant vessel, which when subjected to contrast injection, is

The use of T1-weighted Gd-enhanced contrast imaging is visualized as a “blush.” If the vessel is accessible to endo- particularly helpful in defining the dural attachment site vascular catheterization, one might opt for preoperative of the tumor; additionally it provides ready discrimina- embolization to diminish intraoperative during tion between tumor and brainstem, with often dramatic tumor debulking.33 demonstration of brainstem distortion (Fig. 2 right). Mag- netic resonance angiography should also be performed with an autotriggered elliptic centric-ordered sequence,12 PREOPERATIVE ASSESSMENT if available, to help demonstrate vascular anatomy, collat- eral vessels, and the effect of the tumor on the VAs. A VA As is true with all oncology, all neurosurgeons must that is encased and narrowed suggests that the adventitia remember that they are treating people and not just resect- of the artery has been invaded, and the surgeon needs to ing tumors. Sometimes this requires consideration of sub- assess whether residual tumor will be left in the adventitia total resection or monitoring. In initial discussions about or whether reconstruction is necessary. In our experience, surgery one must not assume that patients wish to under- subtotal resection is the preferred approach in this in- go surgery because they are present at a neurosurgeon’s stance. office. Often patients seek consultation to gather informa- Although MR imaging provides clearly superior soft- tion about their situation, and depending on their age, eth- tissue assessment, CT scanning with osseous algorithms nic background, and personal values, their decision-mak- remains the tool of choice for identifying , ing process may not coincide with that of a neurosurgeon. , and osseous anatomy. Axial CT scanning It is therefore vital to reach an understanding of the pa- allows planning of the extent of bone resection required to tient’s expectations of surgery as well as his/her philoso- phy regarding QOL issues. The possibility of residual tumor and subsequent treatment must also be discussed in relation to the risks of surgery. A careful and detailed history will often demonstrate that symptoms appeared long before the chief complaint. As the lesion progresses in size, the clinical course may seem to accelerate because compensatory mechanisms are exhausted and the neural compromise reaches critical lev- els. A history in which symptoms are rapidly progressive without a longer prodrome should raise clinical suspicion that lesions such as carcinoma or infectious/inflammatory entities may be present. Potential surgery-related risks are not insignificant, and a careful assessment will give the astute clinician a better understanding of them in a particular patient. Care should be directed to lower cranial nerve examination. Deficits of any magnitude suggest neural compression and potential vasa nervosum involvement, thereby making the nerves Fig. 2. Left: Sagittal T2-weighted MR image obtained in a 48- more vulnerable to surgical manipulation. The ninth and year-old man, demonstrating an anteriorly situated foramen mag- 10th cranial nerves represent the afferent and efferent num meningioma (long arrow) causing compression and displace- of the gag reflex, respectively, and play a pivotal role ment of the rostral spinal cord (short arrow). Right: Axial in protecting from aspiration pneumonia. Patients with T1-weighted Gd-enhanced MR image obtained at the level of the foramen magnum. The homogeneously enhancing tumor arises unilateral preoperative gag deficits are often able to adapt predominantly in an anterior location with some left lateral contri- because of the deficit’s slow growth pattern and its chron- bution. The large tumor occupies slightly more than half of the ic , which allow time for compensatory mechanisms transverse diameter of the foramen magnum and affords an ade- to develop. An acute disruption of the gag reflex, howev- quate surgical corridor of approximately 1 cm. The rostral spinal er, can be lethal due to aspiration pneumonia. Thus, pre- cord (arrow) is compressed and displaced posteriorly. operative and immediate postoperative endoscopic in-

Neurosurg. Focus / Volume 14 / June, 2003 3

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC M. R. Boulton and M. D. Cusimano spection of the should be performed to assess Careful identification of PICA during routine posterior laryngeal function. New postoperative dysfunction should neck dissection is indicated if the PICA originates extra- be treated using aggressive support measures, primarily durally. by placing a gastric or jejunal feeding tube, and early tra- cheostomy if necessary. We routinely order an early oto- laryngology and speech consultation to SURGICAL MANAGEMENT patients for vocal cord and swallowing functions. Acute Surgical dissection in which the cranial nerves and vas- 11th cranial nerve deficits are sure to be problematic for cular structures are preserved is integral to foramen mag- the patient especially in terms of abduction, but num tumor management (Fig. 3). Every attempt should be often the only symptom is shoulder pain. Patients with made to keep the arachnoid with these structures and to foramen magnum meningiomas rarely present preopera- perform surgery on the tumor’s side of the nerves and ves- tively with an acute disturbance of this nerve, and its pres- sels during dissection. Even in cases involving encase- ence should lead one to consider alternate lesions. Uni- ment of the VA, if the dissection is deliberate and selec- lateral paralysis of the 12th cranial nerve may also be tive, an arachnoid cuffing of the artery may often be overlooked if the tongue is not inspected at rest within the identified and allow successful dissection of the VA free mouth. Ipsilateral tongue deviation and furrowing are late from tumor. It may be tempting to cauterize small vessels and often irreversible signs of 12th cranial nerve palsy. overlying tumor capsule, in light of the concept that the Planning for resection of foramen magnum meningio- tumor is parasitizing blood supply from the . If mas relies heavily on imaging findings and the clinical possible, however, these vessels should be left intact in the scenario.27,39,44 Because the two posterior approaches to arachnoid because they may actually mislead the surgeon anterior foramen magnum meningiomas require dissec- into moving outside the ideal plane where coagulation tion of and muscles in anatomically distinct regions, could potentially produce brainstem perforator ischemia. one must decide preoperatively which approach is most Intraoperative monitoring is intended to aid the neuro- suitable for the given tumor. Selection is based on the surgeon in preserving neurological function. Somatosen- basic skull base surgery principle of removing bone to sory evoked potentials provide a measure of ascending provide a corridor of access to the tumor to allow total pathways within the surgical field, whereas electromyo- tumor resection and to preclude retraction of neurological graphic recordings in the sternocleidomastoid muscle and structures. Evaluation of MR imaging data allows one to determine the relationship of tumor to the brainstem and its possible site of dural attachment. Computerized tomog- raphy scans provide data regarding the osseous anatomy in relation to tumor. Most importantly, an assessment of the surgical corridor is made at this stage. Because the ma- jority of foramen magnum meningiomas are anterolateral- ly situated, their growth tends to displace the brainstem in a posterior and contralateral direction. It is our opinion that this in situ retraction creates an adequate surgical cor- ridor for resection of most of these lesions. In our ex- perience, no drilling of the occipital condyle has been ne- cessary to achieve resection, and in the cases in which residual tumor remained, resection of the condyle would not have affected the degree of resection. Imaging also clearly displays the relationship of tumor to vascular structures. Encasement of the VA is not un- common and should not be surprising intraoperatively during tumor debulking. Provided that encasement of the VA exists, proximal control of the vessel is prudent and may require mobilization of the VA at the C-1 transverse foramen or, rarely, below, particularly if a transcondylar approach is needed. Assessment of the PICA is also of importance in some cases, particularly those in which one encounters an encased VA. Magnetic resonance angiogra- phy/auto-triggered elliptic centric-ordered or CT angiog- raphy provides the best degree of noninvasive resolution and should be used to assess for encasement, contratlater- al VA, and focal narrowing that could indicate adventitial invasion. If it is hypoplastic, the surgeon may decide to Fig. 3. Intraoperative photograph demonstrating resection of an anterior foramen magnum meningioma. A standard suboccipital leave residual tumor on the vessel if necessary or perform craniectomy was performed without resection of the condyle. a bypass, rather than simply resect the affected segment. Tumor (asterisk) is noted through intact arachnoid to the left of the Conventional angiography with greater resolution is rostral spinal cord and is draped with various nerve rootlets sometimes necessary. An additional advantage of preoper- (arrows) and blood vessels. CH = cerebellar hemisphere; CT = ative imaging is to determine whether the PICA originates ; FM = rim of foramen magnum; C1 = C-1 seg- at above, at, or below the level of the foramen magnum.13 mental nerve root.

4 Neurosurg. Focus / Volume 14 / June, 2003

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC Foramen magnum meningiomas tongue reflect 11th and 12th cranial nerve activity, respec- tively. If either of these modalities demonstrates a change, then the surgeon is alerted to a potentially threatening maneuver and may pursue a different manner of dissec- tion. Although we have found electromyographic moni- toring of the 11th cranial nerve useful, stimulation of the 12 cranial nerve occasionally will cause protrusion of the tongue, which, if not returned to position by the anesthe- sia staff, can lead to postoperative swelling. There is insuf- ficient evidence to support the use of routine evoked potential monitoring in this location. Currently, these mo- dalities have not gained absolute clinical acceptance; their use instead is based on surgeon preference.

SURGICAL APPROACHES TO FORAMEN MAGNUM MENINGIOMAS Fig. 4. Surgical approach to an anterior foramen magnum me- The foramen magnum can be approached via anterior, ningoma. A: Suboccipital craniotomy (red) with a narrow corri- lateral, and posterior approaches. Each approach serves an dor does not provide adequate exposure of the tumor for resection. important function and each was developed to deal with B: Tumor growth naturally widens the surgical corridor, allowing specific problems. The anterior transoral approach to the its safe and effective removal via suboccipital craniotomy without foramen magnum is rarely conducted to reach intradural drilling of the condyle. C: Transcondylar exposure (blue) widens lesions such as meningiomas because of problems with the corridor by removing the medial condyle (red arrow represents dural repair, risk of CSF leakage, and meningitis. Debate very narrow corridor before excision of the condyle, green arrow about foramen magnum meningioma resection primarily represents adequate corridor after this resection). D: Access to involves the posterior suboccipital craniectomy and pos- much of the tumor has been created. terolateral approaches, which necessitate drilling of the occipital condyle (Fig. 4). We limit our discussion to these approaches. To simplify understanding of approaches to this region, The VA is easily identifiable as it curves above the arch we advocate the use of the terms of suboccipital crani- of the , in the depth of the suboccipital triangle, pro- otomy and transcondylar approach. Both require lami- viding proximal vascular control if required. We use neu- nectomy, although the transcondylar is more commonly ronavigation to help determine the extent of the cranioto- associated with mobilization of the VA from its lateral my needed. Although some authors prefer to conduct a attachments to widen the surgical corridor. craniectomy, we prefer a craniotomy because the inci- Suboccipital Craniotomy dence of postoperative occipital pain, we believe, is limit- ed by replacing a firm protective covering over the dura, Suboccipital craniotomy, or craniectomy, with or with- even if it only covers a fraction of the exposed dura.37 If out cervical represents the classic approach the surgical corridor to the tumor cannot be safely ac- to the foramen magnum meningiomas and is familiar to cessed as determined by neuronavigation prior to dura op- most neurosurgeons. For posteriorly situated lesions we ening, more bone can be removed laterally toward the place the patient prone. For lateral or anterolateral lesions, condyle. The craniotomy almost always has to be com- the patient is placed in the lateral decubitus position with bined with a laminectomy to the inferior aspect of the the of the head displaced slightly downward to tumor. At C-1 the laminectomy should encompass at least open the space between occiput and the cervical spine. We the vertebral groove in the lateral aspect of the C-1 lami- also turn the head approximately 20 to 30° toward the na. Care should be taken to not injure the thin-walled ver- floor, depending on the extent to which the tumor is later- tebral plexus of that surround the thick-walled VA. ally situated. The surgical corridor defined on preopera- Of help in this procedure is bipolar coagulation with con- tive imaging must be easily within reach of the surgeon. stant saline irrigation to avoid sticking of the tips of the The corridor should not be hidden under a large bulk of instrument. paracervical muscles deflected laterally. Sufficient soft- The advantage of suboccipital craniotomy includes vi- tissue dissection to create access to the corridor is essen- sualization of the VA, brainstem, cranial nerves, and tu- tial. Routine use of computerized neuronavigation helps mor in a safe, simple, and rapid manner. Criticisms of this to demonstrate subtle variations of anatomical distortions approach primarily relate to the interposition of brainstem, caused by these sessile meningiomas. cranial nerves, and vessels between an anterior tumor and For midline posterior lesions, we make a midline in- the surgeon. The purely anterior midline tumor without an cision. For posterolateral lesions that require exposure adequate surgical corridor is completely obscured by these up to the condyle, we make a “hockey-stick” or inverted structures. The unmodified suboccipital craniotomy ap- L–shaped extension laterally at the superior end of our in- proach necessitates undue retraction of critical neurologi- cision just beneath the superior nuchal line. Whichever the cal structures in cases in which the lesion is purely anteri- incision, cutting of the C-2 nerve branches and the 11th or. Fortunately, these purely ventrally located tumors are cranial nerve distally in the neck should be avoided. the rarest.

Neurosurg. Focus / Volume 14 / June, 2003 5

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC M. R. Boulton and M. D. Cusimano

Transcondylar Approach PERSONAL EXPERIENCE In an attempt to offer effective and safer resections par- Between 1992 and 2002, 10 (3.4%) of 296 patients with ticularly in cases of more anteriorly situated lesions, the meningiomas underwent resection of the lesion from the transcondylar approach was developed.41 A number of dif- foramen magnum at our institution. Six of these arose ferent names exist for the variations in this approach, and from the anterior or anterolateral rim, three were predom- this leads to significant confusion regarding nomencla- inantly posterior, and one had a lateral origin. Eight of the ture.4,5,8,27 In the literature on foramen magnum menin- 10 patients were women, and the mean age was 55 years giomas, two major variations have evolved: 1) the far-lat- (range 34–72 years) in the entire series. The most com- eral approach, which necessitates removal of the foramen mon complaint was occipital pain with progression to magnum rim toward the condyle and excision of the ipsi- paresthesias. Typically the mean duration of these lateral atlantal arch, and 2) the transcondylar approach, in symptoms was 10 months (range 3–24 months). which resection of some or all of the occipital condyle is All patients underwent preoperative CT, MR, or both required. The first of these is ultimately a suboccipital CT and MR imaging. In cases of predominantly anterior- approach involving an appropriate soft-tissue dissection to ly located lesions, a suboccipital craniotomy and hemi- allow access to the surgical corridor. laminectomy were undertaken. An adequate surgical cor- The transcondylar approach requires an inverted ridor was obtained in all patients, and retraction of neural U–shaped incision with one of the U in the midline elements or resection of the occipital condyle was deemed and the other along the anterior border of the sternoclei- unnecessary in all cases. Total excision of the tumor was domastoid muscle. The sternocleidomastoid muscle is de- achieved in nine patients, and there was no recurrence as tached from the mastoid process and reflected as lateral- of the last follow-up examination. In one patient with MR ly as possible to avoid hindering access to the skull base. imaging–documented residual tumor growth GKS was The superficial splenius capitis, semispinalis capitis, and performed 7 years after resection. Subtotal resection was longissimus capitis muscles are reflected downward to not necessitated by the poor quality of the surgical corri- expose the underlying suboccipital triangle. Bordered by dor but rather by the lesion’s adherence of the VA and the the superior and inferior oblique muscles and the rectus perceived risk of damage to the vessel if total excision capitis posterior muscles, the VA courses in the of the were attempted. suboccipital triangle below the occipital condyle. All three Cerebrospinal fluid leakage and transient worsening muscles are released from their vertebral attachments and of preoperative symptoms were the only surgery-related reflected toward the midline. The craniotomy should in- complications. In two patients CSF leakage developed, in clude the bulk of the lesion and often be extended from one of whom meningitis with hydrocephalus was also pre- near the midline, to just medial to the , and sent. Treatment required antibiotic therapy and placement to just above the rim of the foramen magnum. The re- of a ventriculoperitoneal shunt. To treat the uncomplicat- sidual bone over the sigmoid and foramen magnum is ed CSF leak duraplasty was conducted. No patient suf- removed using rongeurs or high-speed . The C-1 lami- fered permanently worsened postoperative cranial nerve nectomy is more extensive than the suboccipital cranioto- deficits, but one patient sustained a mild Brown–Sé- my and extends out into the foramen transversarium. The quard syndrome. There was no surgery-induced death. At posteromedial aspect of the occipital condyle and C-1 lat- a mean of follow-up period of 33 months (range 2–70 eral mass are removed by drilling or careful rongeuring. If months, median 30 months) improved functional was evi- necessitated by the anatomy of the lesion, the foramen dent in seven patients and relatively unchanged status was transversarium and C-2 lamina are also decompressed. demonstrated in two. Of the two patients with unchanged The VA is freed from collagenous tissue at the C-1 fora- status, one continues to experience unilateral leg weak- men transversarium and adjacent to the condyle by using ness that was present preoperatively, and in the other fol- a high-speed drill under surgical magnification. A fine low-up period is too short (2 months) to determine final prolene stitch can be used to secure the VA in a medial functional status. The one patient with residual enlarging position. Guided by preoperative planning of the surgical tumor who underwent GKS is experiencing hand ataxia corridor and supplemented intraoperatively, if necessary, and subtle neurocognitive difficulty. by computerized neuronavgation, the condyle is progres- sively removed in a mediolateral direction. Anterior con- dylar resection can include liberating the hypoglossal NONSURGICAL MANAGEMENT nerve from its canal if necessary to create an adequate sur- We have tended to err on the side of recommending re- gical corridor. Because bone removal is extended much section to patients with reasonably sized tumors in the for- more laterally than in the suboccipital craniotomy, the amen magnum (even with minimal symptoms in younger ipsilateral VA is situated in the center of or medially in patients) because of the lack of space for future tumor the “surgical corridor” prior to dural opening. The dura is growth or swelling during other treatments such as radio- opened by making an incision that parallels the lateral therapy. The ideal treatment of meningiomas is a safe and margins of the craniotomy, with the base of the flap locat- complete resection. If contraindications to surgery exist or ed medially. A ring of dura can be left attached to the VA if the patient elects not to undergo surgical resection, then where it is pierced. This maneuver allows the artery to be radiotherapy should be considered. Because of the critical retracted away from the surgical corridor, thereby provid- anatomy within the foramen magnum and the size of most ing a clear view of the anterior portion of the brainstem tumors ( 3 cm in maximum dimension), we usually rec- and rostral cord. Occipitocervical fusion is recommended ommend focused GKS rather than standard conformal in condylar resections of 50% or greater.45 radiotherapy.28 Patients with small residual tumors under-

6 Neurosurg. Focus / Volume 14 / June, 2003

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC Foramen magnum meningiomas go monitoring to assess growth rate, and in the event that ically relevant issues such as the surgical corridor. When the residual lesion grows we recommend GKS.19,24,26 In the transcondylar approach is considered necessary to cre- patients with multiple recurrent tumors or in whom the ate an appropriate surgical corridor, it should to be per- aforementioned contraindications exist, we administer hy- formed. Otherwise, the suboccipital craniotomy is likely droxyurea therapy, with or without Cox II inhibitor man- sufficient. agement.7 Unfortunately, no authors have reported functional out- comes in terms of multidimensional QOL measures. It behooves all neurosurgeons treating these patients to con- CLINICAL OUTCOMES sider issues of QOL foremost in decision making and in discussion of preoperative planning with patients and their Early reports of resection in cases of foramen magnum families.9 meningiomas were associated with a surgery-related mor- 43,47 23 tality rate of 5 to 13% and morbidity rate of 36%. Acknowledgment Postoperative complications include intracranial hemato- mas, CSF leakage, meningitis, lower cranial nerve palsies, We gratefully acknowledge the contribution of the intraoperative hemiparesis, quadriparesis, and aspiration pneumonia.40 In photograph from Dr. Paul Muller, St. Michael’s Hospital. the past decade, greater than 75% gross-total resection has been reported in series, and morbidity rates have been References lower than previously documented (Table 1). Outcome has been similar in series involving condylar drilling and 1. Akalan N, Seckin H, Kilic C, et al: Benign extramedullary tu- mors in the foramen magnum region. Clin Neurol Neurosurg those in which it has not been an aspect of approaching the 96:284–289, 1994 lesion. No randomized controlled trial of the two principal 2. Arnautovic KI, Al-Mefty O, Husain M. Ventral foramen mag- approaches has been conducted nor is one likely to be per- num meninigiomas. J Neurosurg (Suppl 1) 92:71–80, 2000 formed. Surgeons will have to continue managing patients 3. Arnautovic KI, Al-Mefty O, Pait TG, et al: The suboccipital as individuals by undertaking careful assessments of crit- cavernous sinus. J Neurosurg 86:252–262, 1997

TABLE 1 Summary of recent series addressing the management of foramen magnum meningiomas*

No. of Cases No. of (No. of Condyle Mortality Authors & Year Lesions) FM location Resections Tumor Resection Major Morbidity Rate (%) Postop QOL

Kratimenos & 8 ant none 80% total, 20% aspiration pneu- 25 NA Crockard, 1993 subtotal monia Akalan, et al., 1994 8 1 ant, 7 anterolat none 100% total none 0 88% improved, 12% unchanged Bertalanffy, et al., 1996 19 ant & anterolat 19 100% total none 0 NA Samii, et al., 1996 38 15 spinocranial, 7 63% total, 37% 30% morbidity 5.3 improved mean (40) 25 craniocervical, subtotal (hydro, pneumonia, performance 11 ant, 12 lat, 2 pst CN palsy) George, Lot, & 40 18 ant, 21 lat, yes (NA) 94% total intra- pulmonary embolism, 7.5 90% improved, Boissonnet, 1997 1 pst dural; 50% total air embolism 7.5% worsened, extradural 2.5% unchanged Sharma, et al. 1999 (20) 5 ant, 5 pst none 100% total CN palsy, CSF leak, 15 NA for menin- hydro, spinal insta- giomas bility Salas, et al., 1999 24 24 ant or 24 66% total, 33% hydroc, CSF leak, 0 approach depen- anterolat subtotal CN palsy dent, slightly improved Arnautovic, et al., 2000 18 18 ant 18 75% total, 25% 4 CSF leak, 1 shunt, 0 89% improved, subtotal 10 CN palsies 11% unchanged Goel, et al., 2001 17 17 ant or 2 82% total, 18% 6% (CN palsy) 0 100% improved, anterolat subtotal 100% active & independent Roberti, et al., 2001 21 NA NA 76% total, 24% 21.5% (CN palsy, 9.5 improved mean subtotal CSF leak, me- performance ningitis) Marin Sanabria, et al., 7 5 ant, 2 pst 2 100% total tetraparesis, CN 14 NA 2002 palsy Nanda, et al., 2002 6 6 ant none 100% total none 0 100% improved present experience, 2003 10 6 ant, 3 pst,1 lat none 90% total, 10% 40% (CSF leak, 0 70% improved, subtotal worsened hand 20% unchanged, ataxia, urinary 10% worsened frequency) * ant = anterior; CN = cranial nerve; FM = foramen magnum; hydro = hydrocephalus; NA = not available for meningioma data; pst = posterior.

Neurosurg. Focus / Volume 14 / June, 2003 7

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC M. R. Boulton and M. D. Cusimano

4. Babu RP, Sekhar LN, Wright DC: Extreme lateral transcondy- 27. Pirotte B, David P, Noterman J, et al: Lower clivus and foramen lar approach: technical improvements and lessons learned. J magnum anterolateral meningiomas: surgical strategy. Neurol Neurosurg 81:49–59, 1994 Res 20:577–584, 1998 5. Banerji D, Behari S, Jain VK, et al: Extreme lateral transcondy- 28. Plowman PN: Stereotactic intracranial radiotherapy/radiosur- lar approach to the skull base. Neurology India 47:22–30, gery has come of age. J R Coll Physicians Lond 34:273–281, 1999 2000 6. Bertalanffy H, Gilsbach JM, Mayfrank L, et al: Microsurgical 29. Rhoton AL Jr: The far-lateral approach and its transcondylar, management of ventral and ventrolateral foramen magnum me- supracondylar, and paracondylar extensions. Neurosurgery 47 ningiomas. Acta Neurochir Suppl 65:82–85, 1996 (Suppl 3):195–209, 2000 7. Black PM: , radiosurgery and virtual reality: new as- 30. Rhoton AL Jr: The foramen magnum. Neurosurgery 47 (Suppl pects of meningioma management. Can J Neurol Sci 24: 3):155–193, 2000 302–306, 1997 31. Rhoton AL Jr: Meningiomas of the cerebellopontine angle and 8. Cantore G, Ciappetta P, Delfini R: Choice of neurosurgical ap- foramen magnum. Neurosurg Clin N Am 5:349–377, 1994 proach in the treatment of cranial base lesions. Neurosurg Rev 32. Roberti F, Sekhar LN, Kalavakonda C, et al: Posterior me- 17:109–125, 1994 ningiomas: surgical experience in 161 cases. Surg Neurol 56: 9. Cusimano MD: Quality-of-life assessment in patients with le- 8–21, 2001 sions of the cranial base. Skull Base Surg 9:259–264, 1999 33. Rosen CL, Ammerman JM, Sekhar LN, et al: Outcome analy- 10. David CA, Spetzler RF: Foramen magnum meningiomas. Clin sis of preoperative embolization in cranial base surgery. Acta Neurosurg 44:467–489, 1997 Neurochir 144:1157–1164, 2002 11. Dodge HW Jr, Love JG, Gottlieb CM: Benign tumours at the 34. Salas E, Sekhar LN, Ziyal IM, et al: Variations of the extreme- foramen magnum: surgical considerations. J Neurosurg 13: lateral craniocervical approach: anatomical study and clinical 603–617, 1956 analysis of 69 patients. J Neurosurg (Spine 2) 90:206–219, 12. Farb RI, Scott JN, Willinsky RA, et al: Intracranial venous sys- 1999 tem: gadolinium-enhanced three-dimensional MR venography 35. Samii M, Klekamp J, Carvalho G: Surgical results for me- with auto-triggered elliptic centric-ordered sequence-initial ex- ningiomas of the craniocervical junction. Neurosurgery 39: perience. 226:203–209, 2003 1086–1095, 1996 13. Fine AD, Cardoso A, Rhoton AL Jr: Microsurgical anatomy of 36. Sawaya RA: Foramen magnum meningioma presenting as amyo- the extracranial-extradural origin of the posterior inferior cere- trophic lateral sclerosis. Neurosurg Rev 21:277–280, 1998 bellar artery. J Neurosurg 91:645–652, 1999 37. Schessel DA, Rowed DW, Nedzelski JM, et al: Postoperative 14. George B: Meningiomas of the foramen magnum, in Schmidek pain following excision of acoustic neuroma by the suboccipi- HH (ed): Meningiomas and Their Surgical Management. tal approach: observations on possible cause and potential ame- Philadelphia: WB Saunders, 1991, pp 459–470 lioration. Am J Otol 14:491–494, 1993 15. George B, Lot G: Lateral approaches, in Janecka P, Tiedemann 38. Sekhar LN, Babu RP, Wright DC: Surgical resection of cranial K (eds): Skull Base Surgery: Anatomy, Biology, and Tech- base meningiomas. Neurosurg Clin N Am 5:299–330, 1994 nology. Philadelphia: Lippincott-Raven, 1997, pp 243–260 39. Sekhar LN, Swamy NK, Jaiswal V, et al: Surgical excision of 16. George B, Lot G, Boissonnet H: Meningioma of the foramen meningiomas involving the clivus: preoperative and intraoper- magnum: a series of 40 cases. Surg Neurol 47:371–379, 1997 ative features as predictors of postoperative functional deterio- 17. George B, Lot G, Velut S: [French Language Society of Neu- ration. J Neurosurg 81:860–868, 1994 rosurgery. 44th Annual Congress. Brussels, 8-12 June 1993. 40. Sekhar LN, Wright DC, Richardson R, et al: Petroclival and Tumors of the foramen magnum.] Neurochirurgie 39 (Suppl foramen magnum meningiomas: surgical approaches and pit- 1):1–89, 1993 (Fr) falls. J Neurooncol 29:249–259, 1996 18. Goel A, Desai K, Muzumdar D: Surgery on anterior foramen 41. Sen CN, Sekhar LN: Surgical management of anteriorly placed magnum meningiomas using a conventional posterior suboc- lesions at the craniocervical junction—an alternative approach. cipital approach: a report on an experience with 17 cases. Neu- Acta Neurochir 108:70–77, 1991 rosurgery 49:102–107, 2001 42. Sharma BS, Gupta SK, Khosla VK, et al: Midline and far later- 19. Hartford AC, Loeffler JS: Radiosurgery for benign tumors and al approaches to foramen magnum lesions. Neurol India 47: arteriovenous malformations of the central . 268–271, 1999 Front Radiat Ther Oncol 35:30–47, 2001 43. Stein BM, Leeds NE, Taveras JM, et al: Meningiomas of the 20. Honch GW: Spinal cord and foramen magnum tumors. Semin foramen magnum. J Neurosurg 20:740–751, 1963 Neurol 13:337–342, 1993 44. Strang RD, Al-Mefty O: Small skull base meningiomas. Sur- 21. Kratimenos GP, Crockard HA: The far lateral approach for ven- gical management. Clin Neurosurg 48:320–339, 2001 trally placed foramen magnum and upper cervical spine tu- 45. Vishteh AG, Crawford NR, Melton MS, et al: Stability of crani- mours. Br J Neurosurg 7:129–140, 1993 overtebral junction after unilateral occipital condyle resection: 22. Marin Sanabria EA, Ehara K, Tamaki N: Surgical experience a biomechanical study. J Neurosurg (Spine 1) 90:91–98, 1999 with skull base approaches for foramen magnum meningioma. 46. Wara WM, Sheline GE, Newman H, et al: of Neurol Med Chir (Tokyo) 42:472–480, 2002 meningiomas. Am J Roentgenol Radium Ther Nucl Med 23. Meyer FB, Ebersold MJ, Reese DF: Benign tumors of the fora- 123:453–458, 1975 men magnum. J Neurosurg 61:136–142, 1984 47. Yas¸argil MG, Mortara RW, Curcic M: Meningiomas of basal 24. Muthukumar N, Kondziolka D, Lunsford LD, et al: Stereotactic posterior . Adv Tech Stand Neurosurg 7:1–115, radiosurgery for anterior foramen magnum meningiomas. Surg 1980 Neurol 51:268–273, 1999 25. Nanda A, Vincent DA, Vannemreddy PS, et al: Far-lateral ap- proach to intradural lesions of the foramen magnum without re- section of the occipital condyle. J Neurosurg 96:302–309, Manuscript received April 16, 2003. 2002 Accepted in final form May 14, 2003. 26. Nicolato A, Foroni R, Pellegrino M, et al: Gamma knife radio- Address reprint requests to: Michael Cusimano, M.D., Ph.D., surgery in meningiomas of the posterior fossa. Experience with Division of Neurosurgery, St. Michael’s Hospital, University of 62 treated lesions. Minim Invasive Neurosurg 44:211–217, Toronto, 38 Shuter Street, Toronto, ON, M5B 1A6, Canada. email: 2001 [email protected].

8 Neurosurg. Focus / Volume 14 / June, 2003

Unauthenticated | Downloaded 10/01/21 10:34 AM UTC