J Neurosurg 72:493-496, 1990
Foramen magnum meningioma: transoral resection with a bone baffle to prevent CSF leakage Case report JANUSZ A. B O N K O W S K I , M.B.,B.S., F.R.C.S., F.R.A.C.S., ROBIN D. GIBSON, M.B.,Cn.B., F.R.C.R., F.R.A.C.R., AND LESLIE SNAPE, F.R.C.S., F.R.A.C.D.S., F.F.D.R.C.S. Department of Neurosurgery and Unit of Oral and Maxillofacial Surgery, Christchurch Public Hospital and Department of Radiology, Christchurch Medical School, Christchurch, New Zealand ~" A case of meningioma situated at the anterior rim of the foramen magnum with successful removal via a transoral approach is reported. A new technique of preventing cerebrospinal fluid leakage is described utilizing fascia lata and a bone baffle without any attempt to close the dura, either by primary suture or tissue sealants. KEY WORDS
* foramen magnum operative technique 9 bone graft
HE transoral approach for lesions in the region of the anterior rim of the foramen m a g n u m has, over the last two decades, assumed an increasing role in the neurosurgical a r m a m e n t a r i u m . Progressive technical refinements have broadened the range of pathology which can be successfully managed by this operative technique. 2'8'11 For some time the problem of wound breakdown and intractable postoperative cerebrospinal fluid (CSF) leakage has hampered application of the approach to intradural lesions, specifically to aneurysms and tumors. 1,6,11 The introduction of biological tissue sealants has provided a new stimulus to the utilization of transoral surgery for intradural pathology. 3's'9 While the sealants have demonstrated an improvement in primary healing, they are blood-derived products and despite presumed stringent checks on their safety there is, in the current climate, some residual concern about long-term safety as regards viral and other infective complications. 12 We report a case of successful transoral removal of a foramen m a g n u m m e n i n g i o m a in which simple autograft material provided an effective seal against postoperative CSF leakage, despite lack of primary dural suture. Baffling of CSF pulsation is suggested as the potential mechanism whereby this new technique is successful.
T
J. Neurosurg. / Volume 72/March, 1990
9 meningioma 9 transoral surgery 9 cerebrospinal fluid leakage
9
Case Report
This 49-year-old w o m a n came to neurological attention with a 2-year history of severe headaches, initially radiating up the fight side of the occiput but becoming bilateral. She developed associated hyperpathic sensations of the occiput and also evolved sensory symptoms radiating down the fight side of the body. The right leg and foot became "raw and hot" with reduced temperature sensation of the entire lower limb. The occipital and skull base pains had rendered the patient virtually bedridden. She also developed diplopia on upward gaze and progressive unsteadiness. E x a m i n a t i o n . The patient demonstrated no cranial nerve deficit save nystagmus on right lateral gaze. She had a mild degree of truncal ataxia with an unsteady gait. There was a hyperesthetic response to pinprick of the entire right side with diminished sensation to light touch down the right leg. There was no objective m o t o r deficit. A computerized tomography (CT) scan of the head obtained 1 year previously had been unremarkable, but had not included views of the foramen m a g n u m and skull base. A cervical myelogram with instillation of O m n i p a q u e at C 1-2 and subsequent CT scanning were reported as showing some a b n o r m a l relationship 493
J. A. Bonkowski, R. D. Gibson, and L. Snape between the dens, C-1, and the spinal cord, but concentration of contrast material was suboptimal in the foramen m a g n u m region and further views were suggested. Analysis of CSF removed at this examination was positive for oligoclonal banding, although subsequent visual evoked responses and brain-stem auditory evoked potentials were normal. Computerized tomography scanning with a higher concentration ofintrathecal contrast material showed a n u m b e r of "ossicles" above the dens, and the medulla and cord were displaced posteriorly, with a soft tissue gap between "ossicles" and lower medulla. Further CT scanning with intravenous contrast m e d i u m showed an enhancing hemispherical soft tissue mass, 3 cm in diameter, centered on the previously demonstrated calcified nodules (Fig. 1). Vertebral angiography showed both vertebral arteries to be displaced laterally around the mass as they passed forward at the foramen m a g n u m . The pre-
FIG. 1. Computerized tomography reconstruction, sagittal projection, showing the foramen magnum tumor.
operative diagnosis was of a foramen m a g n u m meningioma.
Operation. Following preliminary tracheostomy and insertion of a lumbar subarachnoid drain, a midline approach to the foramen m a g n u m and atlantoaxial region was performed through the posterior pharyngeal wall, using a transoral approach and splitting the soft palate vertically. The t u m o r was entered by drilling away and removing the lower clivus, anterior arch of the atlas and dens, and associated ligaments. The t u m o r was debulked centrally by removal of the calcified "ossicles," and resected until arachnoid was identified posteriorly. The t u m o r had been split centrally and the two lateral plaques of residual t u m o r could be rotated into the field and cut away from their dural attachment. The medulla and cord could be identified through the residual dural defect and there was no possibility of closing the dura by primary suture. A 4 • 1-cm graft of fascia lata was placed intradurally and a single suture was passed across the middle of the dural defect to prevent the fascia from prolapsing into the wound. A rectangle of corticocancellous bone, measuring 4 x 1 cm, was harvested from the inner iliac cortex and placed in the defect over the fascia. The upper and lower ends of the graft were thinned to leave cortex only and were wedged, above and below, behind the clivus and body of C-2, after an extradural pocket had been fashioned behind the clivus and a lower pocket between the posterior longitudinal ligament and the body of C-2 (Fig. 2). Postoperative Course. The patient's postoperative recovery was unremarkable. The lumbar drain was left to drain continuously for 48 hours then removed. The tracheostomy was removed after 7 days. The patient received a week's course of prophylactic antibiotics. At
FIG. 2. Schematic representation of the bone graft as visualized in the sagittal (left) and coronal (right) plane. 494
J. Neurosurg. / Volume 72/March, 1990
Prevention of CSF leakage in transoral meningioma resection no stage were there any problems with leakage or bulging of the pharyngeal wound and the patient was mobilized with no apparent complications. Subsequent follow-up findings have remained unremarkable. She has made a full recovery of neurological function save some slight residual sensory s y m p t o m s in the fight leg. Subsequent t o m o g r a m s of the foramen m a g n u m performed 1 m o n t h postoperatively showed the bone graft to be in a satisfactory position (Fig. 3). Subsequent CT scanning and review at 12 m o n t h s have revealed no evidence of t u m o r recurrence. Histological examination of the excised specimen revealed it to be a transitional meningioma. Discussion This case illustrates the clinical and radiological difficulties encountered in the diagnosis of lesions of the foramen m a g n u m region. 7 Magnetic resonance imaging would undoubtedly have been diagnostic but was not locally available. The absence of a postoperative CSF leak, despite the lack of dural sealing by either tissue sealant or primary dural closure might be chance or partly helped by CSF drainage; however, due to the almost invariable diff• culties previously reported, we suggest that the fascial graft and bone baffle had a significant role to play. Cerebrospinal fluid drainage is r e c o m m e n d e d routinely in these procedures but has been reported as failing to prevent breakdown even when instituted on a prolonged basis. 3 It has even been r e c o m m e n d e d that permanent CSF diversion by lumboperitoneal drainage is the only technique to reduce pressure for a suitable length of time to allow sealing of the area to o c c u r . 9 We propose that the primary mechanism for the wound breakdown that has frequently been reported
FIG. 3. Postoperative midline tomogram, sagittal projection, illustrating cortical bone lying across the defect between the clivus and the posterior body of C-2. J. Neurosurg. / Volume 72/March, 1990
even in the face of high-quality primary closure is related to pulsatile effects of the CSF, both regular transmitted vascular pulsation and intermittent higher displacement pulses associated with Valsalva maneuvers and the like. 4'~~Waves are a mechanism for transmitting energy, and each CSF pulsation results in the transmission of energy to the surrounding m e m b r a n e . This is absorbed as potential energy, which can then be dissipated back to the CSF during diastolic pressure troughs if the m e m b r a n e is elastic; or will be utilized internally as kinetic energy in the case of an inelastic m e m b r a n e such as dura. Normally, dura has little requirement for elastic recoil since it is largely backed by a layer of bone which is well able to reflect the energy of cerebral pulsations. However, if dura loses this bone backing then it poorly tolerates distortion and m o v e m e n t , and the progressive absorption of strain energy can result in stretching of the connective tissue junctions of the dura with a propensity to dehisce. If there is a dural incision, the suture junction is even less tolerant of repetitive strains and, with a dural defect, an onlay fascia graft will have almost no capacity to repair under strain. When a lesion has been removed by the anterior approach, there is a resultant cavity in the bone, a rectangular dead space over 1 cm deep, into which the energy of CSF pulsations will push the dura or any other soft-tissue graft irrespective of the primary repair (Fig. 4). Furthermore, the muscular layer anterior to this bone space also has poor tensile characteristics and will not prevent progressive anterior propulsion of the pseudomeningocele which m a y eventually dehisce and rupture the mucosa. Even if the mucosa does hold then, there m a y still remain a residual retropharyngeal CSF meningocele; this complication has also been reported. 6 The ideal repair therefore provides a hard bed flush with the posterior face of the bone excision against which the CSF can pulsate and, by preventing any anterior m o v e m e n t into the defect, allows spontaneous m e m b r a n e healing to seal any CSF leak. In this case, the bone graft was thinned down to provide a plug approximately 5 m m thick, but sufficiently thin to avoid interfering with movement. The patient's neck
FIG. 4. Schematic representation showing the pressure of cerebrospinal fluid pulsations (direction of arrows) after removal of a lesion by the anterior approach. 495
J. A. Bonkowski, R. D. Gibson, and L. Snape m o v e m e n t s have recovered fully. W e w o u l d presume that this b o n e graft will, over a long p e r i o d o f time, either resorb o r f o r m a local p s e u d o a r t h r o s i s which s h o u l d n o t interfere with f u n c t i o n o f t h e craniocervical articulations. T h e r e have been p r e v i o u s r e p o r t s o f b o n e grafts t h r o u g h the region, T M b u t these a p p e a r to have largely consisted o f o n l a y i n g or p a c k i n g c a n c e l l o u s bone into the defect to try to achieve b o n e u n i o n a n d stability. W e w o u l d suggest that this t e c h n i q u e o f a thin, wedged, o r l o c k e d i n l a y graft to baffle C S F p u l s a t i o n s is an a l t e r n a t i v e to tissue sealants a n d l o n g - t e r m C S F drainage in the a c h i e v e m e n t o f w a t e r - t i g h t closure for intrad u r a l lesions in this area.
References 1. Chono Y, Abe H, Iwasaki Y, et al: [Transoral anterior approach to foramen magnum meningioma - - a case report and review.] No Shinkei Geka 13:109-114, 1985 (Jpn) 2. Crockard HA: The transoral approach to the base of the brain and upper cervical cord. Ann R Coil Surg Engl 67: 321-325, 1985 3. Crockard HA, Bradford R: Transoral transclival removal of a schwannoma anterior to the craniocervical junction. Case report. J Neurosurg 62:293-295, 1985 4. du Boulay GH: Pulsatile movements in the CSF pathways. Br J Radiol 39:255-262, 1966
496
5. Hadley MN, Martin NA, Spetzler RF, et al: Comparative transoral dural closure techniques: a canine model. Neurosurgery 22:392-397, 1988 6. Hayakawa T, Kamikawa K, Ohnishi T, et al: Prevention of postoperative complications after a transoral transclival approach to basilar aneurysms. Technical note. J Neurosnrg 54:699-703, 1981 7. Howe JR, Taren JA: Foramen magnum tumors: pitfalls in diagnosis. J A M A 225:1061-1066, 1973 8. Menezes AH, VanGilder JC: Transoral-transpharyngeal approach to the anterior craniocervical junction. Tenyear experience with 72 patients. J Neurosurg 69: 895-903, 1988 9. Miller E, Crockard HA: Transoral transclival removal of anteriorly placed meningiomas at the foramen magnum. Nenrosurgery 20:966-968, 1987 10. O'Connell JEA: Cerebrospinal fluid mechanics. Proc R Soc Med 63:507-518, 1970 11. Pfisztor E, Vajda J, Piffk6 P, et al: Transoral surgery for craniocervical space-occupying processes. J Neurosurg 60:276-281, 1984 12. Watts C: Comment on Miller E, Crockard HA: Transoral transclival removal of anteriorly placed meningiomas at the foramen magnum. Neurosurgery 20:968, 1987 Manuscript received April 19, 1989. Address reprint requests to: Janusz A. Bonkowski, M.B., B.S., F.R.C.S., F.R.A.C.S., Department of Neurosurgery, Christchurch Hospital, Private Bag, Christchurch, New Zealand.
J. Neurosurg. / Volume 7 2 / M a r c h , 1990
Foramen magnum meningioma: transoral resection with a bone baffle to prevent CSF leakage Case report JANUSZ A. B O N K O W S K I , M.B.,B.S., F.R.C.S., F.R.A.C.S., ROBIN D. GIBSON, M.B.,Cn.B., F.R.C.R., F.R.A.C.R., AND LESLIE SNAPE, F.R.C.S., F.R.A.C.D.S., F.F.D.R.C.S. Department of Neurosurgery and Unit of Oral and Maxillofacial Surgery, Christchurch Public Hospital and Department of Radiology, Christchurch Medical School, Christchurch, New Zealand ~" A case of meningioma situated at the anterior rim of the foramen magnum with successful removal via a transoral approach is reported. A new technique of preventing cerebrospinal fluid leakage is described utilizing fascia lata and a bone baffle without any attempt to close the dura, either by primary suture or tissue sealants. KEY WORDS
* foramen magnum operative technique 9 bone graft
HE transoral approach for lesions in the region of the anterior rim of the foramen m a g n u m has, over the last two decades, assumed an increasing role in the neurosurgical a r m a m e n t a r i u m . Progressive technical refinements have broadened the range of pathology which can be successfully managed by this operative technique. 2'8'11 For some time the problem of wound breakdown and intractable postoperative cerebrospinal fluid (CSF) leakage has hampered application of the approach to intradural lesions, specifically to aneurysms and tumors. 1,6,11 The introduction of biological tissue sealants has provided a new stimulus to the utilization of transoral surgery for intradural pathology. 3's'9 While the sealants have demonstrated an improvement in primary healing, they are blood-derived products and despite presumed stringent checks on their safety there is, in the current climate, some residual concern about long-term safety as regards viral and other infective complications. 12 We report a case of successful transoral removal of a foramen m a g n u m m e n i n g i o m a in which simple autograft material provided an effective seal against postoperative CSF leakage, despite lack of primary dural suture. Baffling of CSF pulsation is suggested as the potential mechanism whereby this new technique is successful.
T
J. Neurosurg. / Volume 72/March, 1990
9 meningioma 9 transoral surgery 9 cerebrospinal fluid leakage
9
Case Report
This 49-year-old w o m a n came to neurological attention with a 2-year history of severe headaches, initially radiating up the fight side of the occiput but becoming bilateral. She developed associated hyperpathic sensations of the occiput and also evolved sensory symptoms radiating down the fight side of the body. The right leg and foot became "raw and hot" with reduced temperature sensation of the entire lower limb. The occipital and skull base pains had rendered the patient virtually bedridden. She also developed diplopia on upward gaze and progressive unsteadiness. E x a m i n a t i o n . The patient demonstrated no cranial nerve deficit save nystagmus on right lateral gaze. She had a mild degree of truncal ataxia with an unsteady gait. There was a hyperesthetic response to pinprick of the entire right side with diminished sensation to light touch down the right leg. There was no objective m o t o r deficit. A computerized tomography (CT) scan of the head obtained 1 year previously had been unremarkable, but had not included views of the foramen m a g n u m and skull base. A cervical myelogram with instillation of O m n i p a q u e at C 1-2 and subsequent CT scanning were reported as showing some a b n o r m a l relationship 493
J. A. Bonkowski, R. D. Gibson, and L. Snape between the dens, C-1, and the spinal cord, but concentration of contrast material was suboptimal in the foramen m a g n u m region and further views were suggested. Analysis of CSF removed at this examination was positive for oligoclonal banding, although subsequent visual evoked responses and brain-stem auditory evoked potentials were normal. Computerized tomography scanning with a higher concentration ofintrathecal contrast material showed a n u m b e r of "ossicles" above the dens, and the medulla and cord were displaced posteriorly, with a soft tissue gap between "ossicles" and lower medulla. Further CT scanning with intravenous contrast m e d i u m showed an enhancing hemispherical soft tissue mass, 3 cm in diameter, centered on the previously demonstrated calcified nodules (Fig. 1). Vertebral angiography showed both vertebral arteries to be displaced laterally around the mass as they passed forward at the foramen m a g n u m . The pre-
FIG. 1. Computerized tomography reconstruction, sagittal projection, showing the foramen magnum tumor.
operative diagnosis was of a foramen m a g n u m meningioma.
Operation. Following preliminary tracheostomy and insertion of a lumbar subarachnoid drain, a midline approach to the foramen m a g n u m and atlantoaxial region was performed through the posterior pharyngeal wall, using a transoral approach and splitting the soft palate vertically. The t u m o r was entered by drilling away and removing the lower clivus, anterior arch of the atlas and dens, and associated ligaments. The t u m o r was debulked centrally by removal of the calcified "ossicles," and resected until arachnoid was identified posteriorly. The t u m o r had been split centrally and the two lateral plaques of residual t u m o r could be rotated into the field and cut away from their dural attachment. The medulla and cord could be identified through the residual dural defect and there was no possibility of closing the dura by primary suture. A 4 • 1-cm graft of fascia lata was placed intradurally and a single suture was passed across the middle of the dural defect to prevent the fascia from prolapsing into the wound. A rectangle of corticocancellous bone, measuring 4 x 1 cm, was harvested from the inner iliac cortex and placed in the defect over the fascia. The upper and lower ends of the graft were thinned to leave cortex only and were wedged, above and below, behind the clivus and body of C-2, after an extradural pocket had been fashioned behind the clivus and a lower pocket between the posterior longitudinal ligament and the body of C-2 (Fig. 2). Postoperative Course. The patient's postoperative recovery was unremarkable. The lumbar drain was left to drain continuously for 48 hours then removed. The tracheostomy was removed after 7 days. The patient received a week's course of prophylactic antibiotics. At
FIG. 2. Schematic representation of the bone graft as visualized in the sagittal (left) and coronal (right) plane. 494
J. Neurosurg. / Volume 72/March, 1990
Prevention of CSF leakage in transoral meningioma resection no stage were there any problems with leakage or bulging of the pharyngeal wound and the patient was mobilized with no apparent complications. Subsequent follow-up findings have remained unremarkable. She has made a full recovery of neurological function save some slight residual sensory s y m p t o m s in the fight leg. Subsequent t o m o g r a m s of the foramen m a g n u m performed 1 m o n t h postoperatively showed the bone graft to be in a satisfactory position (Fig. 3). Subsequent CT scanning and review at 12 m o n t h s have revealed no evidence of t u m o r recurrence. Histological examination of the excised specimen revealed it to be a transitional meningioma. Discussion This case illustrates the clinical and radiological difficulties encountered in the diagnosis of lesions of the foramen m a g n u m region. 7 Magnetic resonance imaging would undoubtedly have been diagnostic but was not locally available. The absence of a postoperative CSF leak, despite the lack of dural sealing by either tissue sealant or primary dural closure might be chance or partly helped by CSF drainage; however, due to the almost invariable diff• culties previously reported, we suggest that the fascial graft and bone baffle had a significant role to play. Cerebrospinal fluid drainage is r e c o m m e n d e d routinely in these procedures but has been reported as failing to prevent breakdown even when instituted on a prolonged basis. 3 It has even been r e c o m m e n d e d that permanent CSF diversion by lumboperitoneal drainage is the only technique to reduce pressure for a suitable length of time to allow sealing of the area to o c c u r . 9 We propose that the primary mechanism for the wound breakdown that has frequently been reported
FIG. 3. Postoperative midline tomogram, sagittal projection, illustrating cortical bone lying across the defect between the clivus and the posterior body of C-2. J. Neurosurg. / Volume 72/March, 1990
even in the face of high-quality primary closure is related to pulsatile effects of the CSF, both regular transmitted vascular pulsation and intermittent higher displacement pulses associated with Valsalva maneuvers and the like. 4'~~Waves are a mechanism for transmitting energy, and each CSF pulsation results in the transmission of energy to the surrounding m e m b r a n e . This is absorbed as potential energy, which can then be dissipated back to the CSF during diastolic pressure troughs if the m e m b r a n e is elastic; or will be utilized internally as kinetic energy in the case of an inelastic m e m b r a n e such as dura. Normally, dura has little requirement for elastic recoil since it is largely backed by a layer of bone which is well able to reflect the energy of cerebral pulsations. However, if dura loses this bone backing then it poorly tolerates distortion and m o v e m e n t , and the progressive absorption of strain energy can result in stretching of the connective tissue junctions of the dura with a propensity to dehisce. If there is a dural incision, the suture junction is even less tolerant of repetitive strains and, with a dural defect, an onlay fascia graft will have almost no capacity to repair under strain. When a lesion has been removed by the anterior approach, there is a resultant cavity in the bone, a rectangular dead space over 1 cm deep, into which the energy of CSF pulsations will push the dura or any other soft-tissue graft irrespective of the primary repair (Fig. 4). Furthermore, the muscular layer anterior to this bone space also has poor tensile characteristics and will not prevent progressive anterior propulsion of the pseudomeningocele which m a y eventually dehisce and rupture the mucosa. Even if the mucosa does hold then, there m a y still remain a residual retropharyngeal CSF meningocele; this complication has also been reported. 6 The ideal repair therefore provides a hard bed flush with the posterior face of the bone excision against which the CSF can pulsate and, by preventing any anterior m o v e m e n t into the defect, allows spontaneous m e m b r a n e healing to seal any CSF leak. In this case, the bone graft was thinned down to provide a plug approximately 5 m m thick, but sufficiently thin to avoid interfering with movement. The patient's neck
FIG. 4. Schematic representation showing the pressure of cerebrospinal fluid pulsations (direction of arrows) after removal of a lesion by the anterior approach. 495
J. A. Bonkowski, R. D. Gibson, and L. Snape m o v e m e n t s have recovered fully. W e w o u l d presume that this b o n e graft will, over a long p e r i o d o f time, either resorb o r f o r m a local p s e u d o a r t h r o s i s which s h o u l d n o t interfere with f u n c t i o n o f t h e craniocervical articulations. T h e r e have been p r e v i o u s r e p o r t s o f b o n e grafts t h r o u g h the region, T M b u t these a p p e a r to have largely consisted o f o n l a y i n g or p a c k i n g c a n c e l l o u s bone into the defect to try to achieve b o n e u n i o n a n d stability. W e w o u l d suggest that this t e c h n i q u e o f a thin, wedged, o r l o c k e d i n l a y graft to baffle C S F p u l s a t i o n s is an a l t e r n a t i v e to tissue sealants a n d l o n g - t e r m C S F drainage in the a c h i e v e m e n t o f w a t e r - t i g h t closure for intrad u r a l lesions in this area.
References 1. Chono Y, Abe H, Iwasaki Y, et al: [Transoral anterior approach to foramen magnum meningioma - - a case report and review.] No Shinkei Geka 13:109-114, 1985 (Jpn) 2. Crockard HA: The transoral approach to the base of the brain and upper cervical cord. Ann R Coil Surg Engl 67: 321-325, 1985 3. Crockard HA, Bradford R: Transoral transclival removal of a schwannoma anterior to the craniocervical junction. Case report. J Neurosurg 62:293-295, 1985 4. du Boulay GH: Pulsatile movements in the CSF pathways. Br J Radiol 39:255-262, 1966
496
5. Hadley MN, Martin NA, Spetzler RF, et al: Comparative transoral dural closure techniques: a canine model. Neurosurgery 22:392-397, 1988 6. Hayakawa T, Kamikawa K, Ohnishi T, et al: Prevention of postoperative complications after a transoral transclival approach to basilar aneurysms. Technical note. J Neurosnrg 54:699-703, 1981 7. Howe JR, Taren JA: Foramen magnum tumors: pitfalls in diagnosis. J A M A 225:1061-1066, 1973 8. Menezes AH, VanGilder JC: Transoral-transpharyngeal approach to the anterior craniocervical junction. Tenyear experience with 72 patients. J Neurosurg 69: 895-903, 1988 9. Miller E, Crockard HA: Transoral transclival removal of anteriorly placed meningiomas at the foramen magnum. Nenrosurgery 20:966-968, 1987 10. O'Connell JEA: Cerebrospinal fluid mechanics. Proc R Soc Med 63:507-518, 1970 11. Pfisztor E, Vajda J, Piffk6 P, et al: Transoral surgery for craniocervical space-occupying processes. J Neurosurg 60:276-281, 1984 12. Watts C: Comment on Miller E, Crockard HA: Transoral transclival removal of anteriorly placed meningiomas at the foramen magnum. Neurosurgery 20:968, 1987 Manuscript received April 19, 1989. Address reprint requests to: Janusz A. Bonkowski, M.B., B.S., F.R.C.S., F.R.A.C.S., Department of Neurosurgery, Christchurch Hospital, Private Bag, Christchurch, New Zealand.
J. Neurosurg. / Volume 7 2 / M a r c h , 1990
