Panduranga Seetahal-Maraj1, Narindra Ramnarine1
1Department of Neurosurgery, San Fernando General Hospital
Corresponding Author
Dr. Panduranga Seetahal-Maraj
San Fernando General Hospital
Paradise Pastures, Independence Avenue,
San Fernando
Email: [email protected]
DOAJ: https://doaj.org/article/ef02ee371b92457b890389e7d9acb745
Copyright: This is an open-access article under the terms of the Creative Commons Attribution License which permits use, distribution, and reproduction in any medium, provided the original work is properly cited.
©2021 The Authors. Caribbean Medical Journal published by Trinidad & Tobago Medical Association
ABSTRACT
Tumours of the foramen magnum are infrequent compared to other locations within the neuraxis. Meningiomas are one of the most frequently encountered tumours of the nervous system, but only 1.8 to 3.2% actually originate within the foramen magnum. However, they account for almost 50% of all tumours in this region.
We report a case of a large foramen magnum meningioma in a 16-year-old female, the diagnostic difficulty it presents due to its rarity and indolent course, and the surgical strategies employed to manage this case.
This was the first performance of a far-lateral craniotomy in San Fernando General Hospital. The use of a staged procedure to facilitate this skull base tumour resection resulted in an excellent outcome.
CASE REPORT
A 16-year-old female presented to the emergency department due to a two-month history of progressive lower limb weakness and unsteadiness when ambulating. She denied having upper limb weakness and bowel/bladder symptoms. She had a cough, mild dyspnea and rhinorrhea, but no fever. The remainder of the history did not reveal any significant positive findings.
Physical examination of her gait was unremarkable at this time. Sensation was intact and she had grade 5/5 power in all limbs. However, there was increased tone globally with hyper-reflexia. Both plantars were upgoing but a Hoffmann’s sign was not elicited. Romberg’s test was negative. A CT brain scan was performed, and no abnormalities detected. The patient was admitted by the medical team for investigation of her upper motor neuron signs, with differential diagnoses of demyelinating diseases and transverse myelitis.
During her hospital admission, the patient’s gait and power progressively deteriorated to the point where she became bed-bound. On repeat examination, the patient appeared to have lost significant muscle bulk and needed assistance to sit up in bed. She was hypertonic in all limbs, with clonus present. Power was now 3/5 in the upper myotomes, and 2/5 in the lower myotomes. Reflexes were 3+ with clonus present, and both her plantars were upgoing. An urgent MRI scan of the entire neuraxis was performed, which revealed a lesion within the foramen magnum. She was subsequently referred to the neurosurgical team.
MRI scans of the brain and C-spine showed a contrast enhancing mass arising from the ventral foramen magnum (FM), with extension inferiorly to the base of C3 vertebral body. The dimensions were 4.7 (craniocaudal) x 2.0 (anteroposterior) x 2.1 (mediolateral) centimetres. Dural tails were noted at the base of the clivus and posterior aspect of C3 vertebral body. Compression of the ventral medulla and upper cervical cord was significant. Notably, there was tumour extension into the right C1-2 foramen. In spite of the remarkable degree of brainstem compression, the patient’s pulse remained in a range of 60-80 beats per minute, and she had no episodes of hypotension or respiratory distress on the ward.
Differentials included a foramen magnum meningioma (FMM) and schwannoma/neurofibroma. The patient did not fulfil any clinical criteria for the diagnosis of neurofibromatosis type 1, however, genetic testing for the NF1 and NF2 genes was not readily available.
Figure 1: Top row: Sagittal T1 MRI pre- (left) and post-(right) gadolinium, displaying ventral FM tumour, from base of clivus to posterior C2-3 border, and causing significant brainstem and cord compression.
Bottom row: T1 axial (left) and coronal (right) post-gadolinium MRI images showing the extension of the tumour into C1-2 neural foramen.
Figure 2: Postoperative axial (left) MPRAGE and sagittal (right) T1 post-gadolinium images showing significant tumour resection and brainstem decompression. Yellow arrow indicates decompressed upper cervical cord.
The goals of treatment were brainstem decompression and maximal safe tumour resection. To facilitate this, surgery would be performed as a staged procedure, with the first stage being a far-lateral craniotomy and foramen magnum decompression. The second stage would address the upper cervical portion of the tumour, including the extension into the right C1-2 foramen. Microsurgery on tumours of the skull base require a high degree of concentration to avoid neurovascular injury, and avoidance of surgeon fatigue plays a key role in attaining good outcomes.
After extensive counselling, consent was obtained for a far-lateral craniotomy, C1-2 hemilaminectomy, foramen magnum decompression and tumour debulking. Included in the consent was occipitocervical fusion, depending on the degree of condylar drilling performed, and if subsequent instability ensued. Due to the patient’s age, avoidance of fusion would allow her to maintain a higher quality of life. The potential for lower cranial nerve compromise and subsequent need for tracheostomy and feeding gastrostomy was emphasized.
The patient was placed in the park-bench position with the right side exposed, and all bony prominences padded. The head was secured using three-point pinion fixation, and hair shaved over the operative site. Intraoperative nerve monitoring and free-running electromyography were utilised to aid in avoiding iatrogenic injury to the neural tissue. CSF release via a lumbar drain was not required for this case. Intraoperative imaging adjuncts were not deemed to be necessary, due to the large size and location of this lesion.
A hockey-stick incision was made, with the curve extending to the right mastoid process and the straight limb down to C4. A right-lateral suboccipital craniotomy with C1 hemi-laminectomy was performed. There was no need to perform significant condylar drilling to obtain adequate exposure, and less than 20% was removed. Control of the ipsilateral vertebral artery and PICA was obtained, and the right vertebral artery transposed away from the operative corridor.
After durotomy, CSF release from the lateral cerebello-medullary cisterns facilitated brain relaxation, and the tumour was identified. The tumour was firm, almost rubbery in consistency and likely to be a meningioma. A combination of sharp dissection and use of the ultrasonic aspirator was employed to debulk the tumour, without injuring the brainstem and lower cranial nerves. Neuromonitoring did not reveal any neurologic compromise at any point in the procedure, and values actually increased from baseline as the surgery progressed. This was in keeping with brainstem decompression. Watertight dural closure was performed at this time, with the use of dural substitutes (DuraGen/DuraSeal) to reinforce this. There was no postoperative CSF leak.
After a successful first stage, the patient was taken to the ICU and a postoperative MRI was done. Radiological findings confirmed medullary decompression. The second stage of surgery to remove a portion of the tumour posterior to C2 vertebral body was planned to be done within 24 hours, since the patient remained physiologically stable.
The following day, the patient was taken back to theatre, and extension of the incision was performed along the posterior midline, up to the level of C5. Laminectomy of C2 was done, followed by durotomy and tenting of the dura. Debulking of the intradural, extramedullary component of the tumour was performed with sharp dissection and the ultrasonic aspirator, with removal of the portion extending into the right C1-2 foramen. There was no need for fusion. Watertight dural closure was followed by layered muscle and fascial approximation. Neuromonitoring did not detect any neurologic compromise throughout the second stage of the procedure.
The patient spent several days in the ICU postoperatively but was rapidly stepped down to the surgical ward. Nutritional optimization and physiotherapy were commenced, and rapid improvement in function was noted. There was no CSF leak postoperatively.
At six weeks postoperatively, she was ambulant with assistance. At one-year follow-up, the patient has returned to normal activity, and resumed schooling.
DISCUSSION
Tumours of the foramen magnum (FM) are infrequent, compared to other regions in the neuraxis. Meningiomas are one of the most frequently encountered tumours of the nervous system, but only 1.8 to 3.2% actually originate within the foramen magnum. However, they account for almost 50% of all tumours in this region.1 Due to their typically indolent nature, they can become very large before symptoms manifest, and therefore causes difficulty with gross total resection.
Knowledge of the borders of the FM helps to determine if a meningioma is classified as arising from this region. Anteriorly, it extends from the lower third of the clivus to the upper border of C2, posteriorly the anterior edge of squamous occipital bone, and laterally the jugular tubercles and upper aspect of C2 laminae.2
Classification
A simple classification system was proposed by Bruneau and George,1 that assists in determination of the surgical approach. The compartment of development, insertion point into the dura/dentate ligament and relationship to the vertebral artery were used to create this.
Based on compartment, FMM can be intradural, extradural or intra- and extra-dural, with intradural being the most common. The insertion point dictates the degree of bony drilling required to expose the neural elements, whether anterior, lateral or posterior. Finally, meningiomas can be above, below or on either side of the vertebral artery. Typically, they are located inferior to the artery, which makes visualization of the lower cranial nerves easier. Sometimes, the dura surrounding the region of entry of the vertebral artery into the cranial space is involved, and a cuff of tumour may need to be left back.
Clinical presentation
Due to the location and nature of these tumours, they can grow to large sizes before becoming clinically symptomatic, with a mean timeframe of 30.8 months.3 Features include occipital headaches, upper cervical pain, and foramen magnum syndrome. This consists of unilateral sensorimotor upper limb deficits, which progresses to the ipsilateral lower limb, contralateral lower limb and, finally, the contralateral upper limb. Long tract signs, spastic quadriparesis and, finally, lower cranial nerve palsies occur (respiratory difficulty, aspiration).
Preoperative investigations
Imaging is necessary to determine the nature of the tumour, relationship to the brainstem and vertebral arteries, rostral and caudal extension and bony involvement. MRI pre- and post-gadolinium administration is the examination of choice.4 On T1-weighted sequences, one can identify a dural tail, and differentiate between normal brain and tumour. T2-weighted sequences display the degree of oedema, and can reveal an arachnoid plane surrounding the tumour.2 MR angiography and TOF sequences define the neurovasculature in the region of the tumour.
CT scan with bone windows is indicated when a far-lateral approach is proposed. This may require significant drilling of the occipital condyle that leads to atlanto-occipital instability and may necessitate fusion.
Indications for surgery
Once symptomatic, surgical excision is offered. In patients in whom a contraindication to surgery exists (high anaesthetic risk, poorly controlled comorbidities) or if the patient refuses surgery, then Gamma Knife Surgery/ Stereotactic Radiosurgery is offered. Focused radiation is necessary, due to the critical and delicate structures in the foramen magnum, and the typically low tumour volume (<14 cc). (2,3)
Surgical approach
This is based on tumour location. If posterior or postero-lateral, a midline suboccipital/far-lateral/trans-condylar approach gives adequate exposure. If ventrally placed, then the transoral/transcervical route may be preferable. However, most neurosurgeons are familiar with the suboccipital/far-lateral approach, and it has been shown to provide a working corridor, even in ventrally placed tumours.5,6 A brief description of these are given here.
The suboccipital approach requires the patient to be placed prone in a Mayfield head clamp, and a midline incision is performed, to expose from the inion to C2. For more laterally placed tumours, the patient is positioned laterally/park-bench, and a hockey stick extension of the incision, towards the side of the tumour, is added.1,2 C1 laminectomy and craniotomy are performed, to give exposure of the vertebral artery, lower cranial nerves, brainstem and tumour.
In the far-lateral/transcondylar approach, lateral extension of bone removal to include the occipital condyle is performed, with the goal of increased exposure in postero-lateral lesions. Between 30-50% of the condyle can be removed without causing instability requiring fusion.2-4
After dural opening, identification of the lower cranial nerves and brainstem is done, and tumour debulking performed, usually with a combination of bipolar cautery, sharp dissection and the ultrasonic aspirator. Neuromonitoring aids with the prevention of neural injury when near critical structures. Watertight dural closure is the aim after tumour removal, with bone replacement.
Postoperative care
These patients are monitored in the ICU after surgery, with special attention to ventilation and feeding. Manipulation of the lower cranial nerves may cause transient worsening of these patients in the immediate postoperative phase, and counselling regarding tracheostomy and gastrostomy tubes is necessary.
Outcomes
Early series on surgical excision of FM meningiomas had mortality ranging from 5-13%, and morbidity of 36%.2 The major complications are CSF leak, lower cranial nerve palsies, aspiration pneumonia and worsening hemiparesis or quadriparesis.
However, excellent results can be achieved in specialised centres, as evidenced by George et al in Hospital Lariboisiere, Paris. In a series of 40 cases, the clinical condition improved in 90%, worsened in 7.5%, and did not change in 2.5%. Over the last 20 years, the overall mortality is 6.2%.1,7 Due to the nature of these tumours, there is significant heterogeneity in data as to the approach selected. Extent of resection is dependent on multiple factors, including adherence to the vertebral artery and cranial nerves, tumour location and size, and lack of arachnoid planes.1,4
Relevance to local setting
Skull base pathologies are not frequently encountered locally. Compared to high resource settings, there are no dedicated centres in the region for the management of these tumours, which have been shown to be associated with favourable outcomes. However, in select patients and with meticulous pre-operative planning and intraoperative adjuncts (neuromonitoring), these tumours can be successfully managed. Staged procedures are useful in preventing surgeon fatigue, which facilitates improved microsurgical technique and thus better patient outcomes.
CONCLUSION
FM meningiomas present unique and complex challenges in their management. This is due to the anatomy of the region, which includes the brainstem, vertebral arteries and lower cranial nerves. Several surgical approaches are possible, each one with specific indications. While data on the best approach is not clear, comprehensive pre-operative planning and tailoring of the approach to the tumour location gives the best outcome. Postoperative complications can be devastating, and patients need to be counselled as such.
Informed consent statement: Informed consent was given to us by the patient and her parents, for use of images and writing of case report.
Conflict of interest statement: Not applicable
Ethical approval statement: Not applicable
Funding statement: None
Authors contribution: Both authors were responsible for the performance of surgery, conception and drafting/editing of the manuscript.
REFERENCES
- Bruneau M, George B. Foramen magnum meningiomas: Detailed surgical approaches and technical aspects at Lariboisière Hospital and review of the literature. Neurosurg Rev. 2008;31(1):19–33.
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- Michael D. Cusimano, Ahmed Faress YC, Luong W. Foramen Magnum Meningiomas. In: Al-Mefty’s Meningiomas. 2011. p. 297.
- LANDEIRO JA, SILVEIRA RL, REIS CVC DOS. Surgical Management of Tumours of the Foramen Magnum. In: Schmidek and Sweets Operative Neurosurgical Techniques: Indications, Methods and Results. 2012. p. 517–28.
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- Colli BO, Carlotti-Junior CG, Assirati-Junior JA, Borba LAB, Coelho-Junior V de PM, Neder L. Foramen magnum meningiomas: Surgical treatment in a single public institution in a developing country. Arq Neuropsiquiatr. 2014;72(7):528–37.
- George B, Lot G, Boissonnet H. Meningioma of the foramen magnum: a series of 40 cases. Surg Neurol. 1997 Apr;47(4):371–9.
