NI FEATURE: THE EDITORIAL DEBATE IV-- PROS AND CONS
|Year : 2018 | Volume
| Issue : 4 | Page : 962--963
Olfactory groove meningiomas: The expanding spectrum of operative approaches
Department of Neurosurgery, Institute of Neurosciences, Medanta – The Medicity, Gurugram, New Delhi, India
Dr. V P Singh
Department of Neurosurgery, Institute of Neurosciences, Medanta – The Medicity, Gurugram, Delhi National Capital Region, New Delhi
|How to cite this article:|
Singh V P. Olfactory groove meningiomas: The expanding spectrum of operative approaches.Neurol India 2018;66:962-963
|How to cite this URL:|
Singh V P. Olfactory groove meningiomas: The expanding spectrum of operative approaches. Neurol India [serial online] 2018 [cited 2020 May 27 ];66:962-963
Available from: http://www.neurologyindia.com/text.asp?2018/66/4/962/237008
The term 'olfactory groove meningiomas' (OGM) is sometimes used to describe all anterior cranial fossa midline meningiomas. While planum sphenoidale meningiomas often cannot be differentiated from olfactory groove meningiomas, especially when large – tuberculum sellae meningiomas are a distinct entity presenting with different clinical features and should not be included in them.
These tumors have often attained a large size at presentation in view of their indolent growth in a relatively non-eloquent location. They often present with mental disturbances. The challenges in their removal are their large size, invasion of paranasal sinuses, the risk of cerebrospinal fluid (CSF) leak and infection, and the need for skull base reconstruction. In addition, for large tumors, the pressure on visual pathways and encasement of the anterior cerebral artery and its branches pose a special challenge.
Surgical approaches required for excising these tumors have evolved over time and now the large bifrontal approaches have mostly been replaced by a unilateral frontal or pterional approach. The frontolateral approach provides a quick access to the tumor with less brain exposure, yet it enables total tumor removal with minimal morbidity and mortality even in large tumors.
A similar refinement in the surgical approaches has been described by Goel et al., in their paper published in this issue on their vast experience of 129 patients operated for an olfactory groove meningioma over a 29-year period. This is to date the largest single institution study of olfactory groove meningiomas (presuming that tuberculum sellae meningiomas are not included). They have assigned points to various clinical and radiological features and attempted to correlate the resultant scores with the difficulty encountered during surgery and the outcomes. They concluded that the factors important for causing difficulty during surgery are tumor size and location (posterior cribriform plate tumors being the worst tumors to excise), degree and duration of visual disturbances, extent of cerebral edema, extracranial extension and anterior cerebral artery encasement. They also found that all patients with subtotal excision who died had a high grade tumor based on their grading criteria. However, the clinical or radiological features selected and the number of points assigned to each parameter are arbitrary and based solely on the vast experience of the authors and their own beliefs and philosophy. It would have been scientifically appropriate if they had validated their judgement by doing a univariate and multivariate analysis of these factors to determine which of them are truly significant. It appears that a large number of their criteria are interdependent upon each other. At one stage they conclude that the major cause of surgical difficulty was the relationship of the tumor with the anterior cerebral artery complex and the optic nerves. They also state that all their patients who died had an intraoperative injury to the anterior cerebral artery or its major branches. It is likely that a multivariate analysis might have revealed that this is the most important determinant of outcome and the size or location of the tumor or the degree of visual loss only reflect more probability of ACA encasement. The purpose of a grading system is to make a surgeon aware preoperatively of the difficulties he may face during surgery. The grading system proposed by Goel et al., is too cumbersome and unwieldy to be adopted widely on a large scale.
The paper nicely describes the surgical nuances of the procedure – no doubt aided by the senior author's long experience. The advice to resect the frontal pole in a large tumor is very apt. One often sees that extensive retraction of the frontal lobe to remove a large tumor only results in an edematous frontal lobe which hampers recovery in the postoperative period. The only caveat to such a resection would be the utilisation of skull base techniques (orbitozygomatic basal approaches) which may obviate the need for frontal lobe retraction. There is also controversy over removal of hyperostotic bone with some authors advocating radical removal of this bone to prevent recurrence and then repairing the skull base with vascularised grafts.
One is a little perturbed by their 33% subtotal excision rate and their reluctance to use radiosurgery in these cases. This is likely to be related to tumor excision in the early part of their experience. It would have been nicer if the authors had subdivided their data into the early and late periods and demonstrated how refinement in surgical techniques has resulted in more complete excisions and reduced complications.
The previous largest series of olfactory groove meningiomas was by Pallini et al., who reported the outcomes in 99 patients. Comparing different surgical approaches, they found that the fronto-orbito- basal approaches offered the highest percentage of Simpson grade 1 or 2 excisions, no retraction related brain swelling, and the least number of life threatening complications. However, CSF leaks were more common. The bifrontal approach had the highest number of life threatening complications. A good overall survival was associated with age <70 yrs, the tumor size smaller than 6 cms diameter, pre- and post-surgery Karnofsky Performance Status (KPS) >80, Simpson grade 1 and 2 excision and World Health Organisation (WHO) histological grade 1. On multivariate analysis, only age and WHO histologic grade were independent prognostic factors for survival.
The endoscopic extended endonasal approaches – transcribriform for olfactory groove meningiomas, and transtuberculum and transplanar for tuberculum sellae meningiomas have been introduced in the last decade and are gaining popularity. They involve removal of bone of the skull base at strategic points to expose the tumor attachment directly without the need for retraction of the brain. The endoscopic route offers better visual outcomes and lesser chances of worsening of deficit or development of newer deficit, as retraction of the brain is not needed at all. The advantages of the transcranial route are more frequent complete resections, reduced CSF leaks and the possibility of removing tumors of any size. Loss of olfaction has been considered inevitable in endoscopic removal of these tumors. Recently, contralateral olfaction preservation is being attempted by using a unilateral transcribriform endonasal approach and using septal transposition to widen the exposure.
A detailed meta-analysis of 64 studies (after 2004) comparing the endonasal transphenoidal approach with the microscopic transcranial approach for excision of olfactory groove and tuberculum sellae meningiomas has recently been published. This included 891 patients with olfactory groove meningiomas and 1444 patients with tuberculum sellae meningiomas. The gross total resection rates were significantly higher with microsurgery compared to endoscopy for olfactory groove meningiomas (88.5% vs 70.9%). For tuberculum sellae meningiomas, the total resection rates were similar – 85.8% for microscopy and 83.0% for endoscopy. Visual improvement was significantly higher with endoscopic removal of tuberculum sellae meningiomas as compared to microsurgery but not for olfactory groove meningiomas. Endoscopy fared much worse for CSF leaks for both tuberculum sellae meningiomas (19.3% vs 5.81% microsurgery) and for olfactory groove meningiomas (25.1% vs 10.5% microsurgery). Intraoperative arterial injury was significantly more common with endoscopy for tuberculum sellae meningiomas (4.89% vs 1.86% for microsurgery) but the difference was not significant for olfactory groove meningiomas (3.88% vs 1.62%). Mortality rate differences were not significant in both the groups – 5.15% for endoscopy to 2.67% for microscopic resections. The operating time, operative blood loss and hospital stay were similar in both the groups. To conclude, endoscopic techniques for these meningiomas are so far not superior to the microscopic transcranial approaches. A subset of tumors, possibly small tuberculum sellae tumors, may be suitable candidates for endonasal surgery. Olfactory groove meningiomas, on the other hand, may be at a disadvantage for endonasal surgery because the restricted angle of the scope may result in a suboptimal view.
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