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|NI FEATURE: THE EDITORIAL DEBATE IV-- PROS AND CONS
|Year : 2018 | Volume
| Issue : 4 | Page : 964-966
Olfactory groove meningiomas: The surgical approaches and factors influencing prognosis
Ramesh C Mishra1, Shashwat Mishra2
1 Department of Neurosurgery, Global Rainbow Healthcare, Agra, Uttar Pradesh, India
2 Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
|Date of Web Publication||18-Jul-2018|
Dr. Ramesh C Mishra
Department of Neurosurgery, Global Rainbow Healthcare, Agra, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Mishra RC, Mishra S. Olfactory groove meningiomas: The surgical approaches and factors influencing prognosis. Neurol India 2018;66:964-6
Goel et al., have described their surgical experience with olfactory groove meningiomas (OGMs) and have proposed a scoring system to grade the surgical difficulty in treating these tumours that also helps in assisting in tumor prognostication following surgery.
OGMs are among the commonest meningiomas that arise from the anterior skull base. Comprising about 3% of all intracranial meningiomas, their incidence is marginally lower than that of the tuberculum sellae meningiomas. However, since the site of meningeal origin of these OGMs is away from the optic apparatus, the tumour size is significantly larger when they are brought to clinical attention as compared to other anterior skull base meningiomas. It is not uncommon to find large OGMs that are discovered during the routine imaging performed to exclude an organic cause, as a part of the psychiatric evaluation of a patient suffering from behavioral abnormalities. An early devascularisation of the tumour, preservation of the integrity of frontal lobes, protection of the optic apparatus and dissection of the anterior cerebral artery complex from the tumour are the four essential steps for addressing the formidable surgical challenges that these large sized OGMs pose.
The clinical presentation of OGMs in this series is unremarkable and is fairly reflective of the observations reported in the previous published series on OGMs.,
Paralleling the evolution of neurosurgical techniques, the surgical approaches to these tumours have changed. The trend towards minimalism has dominated the surgical trajectory for excision of these tumors. The approaches that help in achieving an early brain relaxation through the cisternal drainage of cerebrospinal fluid have gained in popularity. This evolution in the approaches to these tumors has also been reflected in the experience of the authors, which spans almost 3 decades. Initially, they performed a bifrontal craniotomy for these meningiomas but later switched to mainly a unifrontal (frontolateral) craniotomy, which they found was sufficient to address the majority of these tumours. The bifrontal craniotomies were performed without utilizing a combined bilateral anterior skull base dural exposure by division of the anterior part of the superior sagittal sinus and the falx cerebri. A unilateral exposure despite a bifrontal craniotomy could be accomplished by division of the anterior portion of the falx cerebri. Division of the superior sagittal sinus was avoided to prevent compromise of venous drainage of the frontal lobes.
We would, therefore, plan a bifrontal craniotomy only if the transverse expanse of the dural attachment of the OGM along the anterior skull base is plaque-like and extensive (extending far beyond bilateral optic foramina). Also, such an exposure would also be indicated if there is bilateral paranasal sinus involvement. This necessitates drilling of the involved bone bilaterally and a careful reconstruction of the skull base with a vascularized pericranial flap to avoid leakage of the cerebrospinal fluid though the skull base into the nasal cavity. A bifrontal exposure is useful in these situations to maximize the Simpson's grade of excision. Whenever a bilateral frontal exposure is being performed, a lumbar subarachnoid drain is helpful because the access to the basal cisterns is difficult beyond the tumour mass [Figure 1]. The drain can be opened upon performing the craniotomy and before the durotomy, which theoretically minimizes the risk of brain herniation as compared to when the drain is kept open right from the time the lumbar drain is instituted prior to positioning of the patient for the craniotomy. A slack brain towards the beginning of tumour excision is tremendously important in protecting bilateral frontal lobes from retraction injury. This is an important part of the surgical strategy and obviates the need for an elective brain resection in large tumours, as has been suggested by the authors.
|Figure 1: Upper panel (a,b and c) shows the pre-operative contrast MRI images of large olfactory groove meningioma, operated by a bifrontal craniotomy with pre-operative insertion of a lumbar subarachnoid drain. Lower panel (d, e and f) The post-operative images shows complete tumour excision and minimal changes in the frontal lobes despite considerable peritumoural edema. Enhancement along the anterior cranial base is due to the vascularised pericranial graft|
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For the majority of these tumours, we prefer the pterional approach, popularized by Yasargil. Offering the shortest route to the suprasellar cisterns, this approach can facilitate brain relaxation at the beginning of surgery and spare the contralateral frontal lobe from injury [Figure 2]. Samii subscribed to the same philosophy and has described excellent results following excison of OGMs with the frontolateral modification of the pterional approach. Damage to bilateral frontal lobes is devastating for the social functioning of the patient, and therefore, conscious steps should be undertaken to guard against this mishap. Even elective brain resection, as advocated by the authors for some cases, can be avoided by following this strategy. Needless to say, the arterial supply to the tumour that is maintained through the ethmoidal arteries has to be divided early at the base of the tumour, for ensuring a smooth course of the surgery.
|Figure 2: (a) The contrast enhanced coronal MR scan of a lady with a large olfactory groove meningioma extending towards both sides of the midline; (b) The contrast enhanced axial image shows the extent of tumor arising from the anterior skull base; and (c) The post operative axial CT scan showing complete excision of the tumor from an unifronto-temporal approach|
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The authors have devised a scoring method for risk stratification and to gauge the perceived surgical difficulties encountered during the resection of these tumours. They also share with the readers the outcome of surgery performed for excision of these tumours. However, they have clearly mentioned that the grading did not decide the surgical approach. It appears that the grading system is of questionable relevance in surgical planning. The most important factor correlating with post-operative mortality is injury to the anterior cerebral artery in this series, which has also been observed by other authors. It would have been immensely helpful if the authors could have clarified their strategy for avoiding this devastating complication. Personally, we would attempt an aggressive resection of the tumour despite the tumor having encased the anterior cerebral arteries, provided the tumour had a favorable consistency and did not violate the arachnoidal planes. The integrity of the arachnoidal envelope around the tumour remains fairly consistent for a particular case. Tumour dissection from the anterior cerebral arteries should be attempted at the end of tumour resection, when only a thin maneuverable shell of the tumour remains. Firm tumours impede the aggressive debulking needed for safe dissection of the tumor capsule from vascular structures. It would be prudent to resect these tumours while leaving a small portion of the tumor in situ, especially the portion that intimately encases important blood vessels.
The authors have asserted that the scoring system predicts the surgical outcome following excision of OGMs but have provided insufficient evidence to support their contention. The differential outcome of patients falling under different grades is not clearly evident. Several of the factors incorporated in the grading system are reflective of the size of the tumour rather than being representative of any specific feature of the biological behavior of the tumour or its resectability. Although the surgical difficulty clearly correlates with the size of the tumour, the latter does not significantly influence the outcome. Further, these tumours sometimes do extend into the paranasal sinuses, which are the frequent sites where a residual tumour may be left and subsequently lead to a recurrence. Still, inexplicably, the posterior extension of the tumor along the anterior cranial fossa (which is easily accessible through a traditional craniotomy) carries a similar weightage in the proposed scoring system as the paranasal sinus extension. Although the authors have included in their reference list, several endoscopic series, they have not commented upon the feasibility of endoscopic methods for the comprehensive management of OGMs with paranasal sinus extension, especially in the modern era.
This paper presents a fairly large experience with OGMs from the developing part of the world. Tumours in this region come to clinical attention quite late in the course of the disease and have frequently been found to compromise vision and higher mental functions by the time they are surgically treated. Large OGMs pose a formidable surgical challenge but an excellent prognosis can be ensured for the patient if these tumors are resected safely and completely. This paper points out the specific challenges posed by an increasing tumour size in OGMs. These challenges are incorporated into the comprehensive scoring system that includes parameters such as the involvement of anterior cerebral arteries by the tumour, the visual symptoms, the behavioral changes, the extension into the paranasal sinuses, etc. The readers could have gained extensively from the experience of the prolific surgeon, who is also the lead author of this paper, if the surgical strategies adopted by him to address these challenging lesions were more clearly elaborated.
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. Olfactory groove meningiomas: An analysis based on surgical experience with 129 cases. Neurol India 2018;66:1081-6. [Full text]
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[Figure 1], [Figure 2]