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A Fully Endoscopic Supraorbital Suprafrontal Approach to Frontal and Frontoparietal Convexity/Parasagittal Meningiomas
By Mohamed S. Kabil, M.D. and Hrayr K. Shahinian, M.D.

Abstract

Traditional approaches, via open transcranial techniques to access meningiomas of the frontoparietal convexity often require relatively large craniotomies as well as excessive extra and intracranial surgical dissection. Thus, creating potential disfigurement and morbidity attributed to the approach itself, which is ultimately translated into longer operative times, more blood loss, increased postoperative discomfort and long-term convalescence. We report our experience with a minimally invasive supraorbital suprafrontal endsoscopic approach through the eyebrow that we utilized in resection of 2 (convexity and middle parasagittal) meningiomas.

Two males, aged 40 and 52 years, with frontoparietal convexity meningioma and parasagittal meningioma (middle third), respectively, were operated upon via a fully endsoscopic supraorbital suprafrontal approach utilizing a 2x2 cm keyhole craniotomy. Complete tumor removal was accomplished in both cases with no postoperative complications and minimal postoperative discomfort. The cosmetic outcome was excellent and both patients were discharged home within 48-hours of their operation.

This preliminary experience demonstrates the feasibility of resecting frontoparietal convexity/parasagittal meningiomas using endoscopic techniques. The endoscope with its suprerior visibility and the approach being a more targeted one, has allowed both the approach and resection to be done with minimal disturbance to the surrounding brain tissue. Therefore, we believe that our experience with the reported technique does not only advocate the expanding use of the supraorbital approach as a minimally invasive alternative for open craniotomies, but also as a more anatomic alternative leading to superior results and surgical outcomes.

Keywords
Endoscopic, Supraorbital, Suprafrontal, Eyebrow, Minimally invasive

Introduction

Meningioma, a term coined by Harvey Cushing in 1922 [1] referring simply to the close proximity of these tumors to the meninges, are extra axial mostly benign tumors that originate from the leptomeninges, specifically the arachnoidal cap cells. They are typically single, globular masses with a broad, flattened base abutting the dural surface [2,3]. The incidence of intracranial meningiomas among primary intracranial neoplasms is approximately 15-20%, and they are more commonly identified in older and female patients [4]. They represent the most common extra-axial tumor of the brain in adults and the most common non-glial primary neoplasm of the brain [5].

Ninety percent of intracranial meningiomas are supratentorial, and are most often parasagittal arising from the dura of the superior sagittal sinus (SSS), the second most common location is the cerebral convexities [6]. Presenting signs and symptoms depend on the tumor's size and location, these include headaches, seizures and neurological deficits usually due to the direct mass effect they exert. As a result of the ever-increasing use and accuracy of cross-sectional brain imaging, smaller and even incidental meningiomas are discovered more commonly during imaging evaluation for various symptoms [6], for which large open craniotomies or major surgical operations seem undesirable or greatly injurious.

In 1938, Cushing and Eisenhardt established a landmark categorization of meningiomas[7], and since then the common practice has been to classify meningiomas by their site of origin. The term "convexity meningioma" describes those tumors whose attachment does not occur on the dura of the skull base and does not involve the dural venous sinuses or the falx cerebri. Convexity meningiomas of the cerebral hemispheres may arise from any area of the dura over the convexity, but they are more common along the coronal suture and near the parasagittal region [5,6]. Parasagittal meningiomas are those that involve the sagittal sinus and the adjacent convexity dura and falx and they are classified into two general categories; the first involves only the lateral edge of the sagittal sinus and adjacent convexity dura and the second extensively involves the sinus, adjacent falx, and convexity dura [8]. A less common morphological appearance of meningiomas is that of a flat lesion, referred to as a "meningioma en plaque."

In spite of its mostly benign nature and its rewarding potential for cure, access to meningiomas of the frontoparietal convexity traditionally has required wide exposure of the surgical field via open craniotomies, thus adding potential morbidity and cosmetic disfigurement attributed to the surgery itself. Non invasive alternatives such as gamma knife surgery (GKS), due to a higher incidence of post-irradiation peritumorous imaging changes, have not been advocated by many authors for meningiomas of the cerebral convexity, parasagittal region, or falx cerebri [9,10] additionally a prompt relief from the mass effect is often required and surgery remains the primary treatment in the majority of cases.

During the past decade, the practice of minimally invasive endoscopic skull base and brain surgery has evolved as a result of technological advancement and accrued experience with these techniques. These improvements have permitted the adoption of safe and effective techniques to become the standard of care in the treatment of many common tumors of the skull base and the pituitary gland carrying the advantage of superior visibility, simpler resection, less invasiveness, and minimization of the injurious effects of brain retraction while avoiding the use of potentially disfiguring skin incisions.

In late 2002 our group converted to the routine use of the fully endoscopic supraorbital approach for accessing and resecting tumors of the anterior and middle cranial base [11]. In this report we present our experience with a fully endoscopic supraorbital suprafrontal approach to access the frontal and frontoparietal convexity.

Surgical technique

The details, utilities and indications of the minimally invasive supraorbital approach are relatively well known and have previously been reported [11-14] and will be briefly discussed in this report with emphasis on the fully endoscopic technique and the necessary modifications which enable suprafrontal access to the cerebral convexity via the supraorbital approach. The operation starts with the patient placed in the supine position on the operating table and the head of the bed is slightly raised. Following the induction of general anesthesia, the patient's neck is flexed approximately 20-30 degrees and slightly rotated laterally towards the surgeon who operates from the front. The head being positioned at level higher than that of the heart improves venous drainage from the cranium and helps maintain a clean surgical field. Flexion of the head helps open a supraftontal subdural pathway for the endoscope and endosccopic instrumentation as the frontal lobes "relax" downwards once cerebrospinal fluid (CSF) is drained. Thus positioned, the head is fixed in place using a three-pin clamp and the frontal and para-nasal areas are cleansed with an aqueous antiseptic solution and then draped. The base of a pneumatically powered endoscope holding arm (Mitaka Kohki Co., Tokyo) is fastened to the operating room table opposite the surgeon; the arm extends to hold the endoscope firmly. A 4.0 mm 0° rigid endoscope (Karl Storz of America, Culver City, CA, USA) is attached to the holding arm.

A standard skin incision is placed within the hair of the eyebrow few mms above the orbital rim, the position of the eyebrow incision is not absolutely constant as it depends on the anatomy of the patient's skull. The incision is bounded medially by the supraorbital notch and laterally by the lateral end of the eyebrow anterior to the frontozygomatic suture. Subsequent to skin and soft tissue incision the upper end of the incision is retracted upward and a 2cm supraorbital craniotomy is performed with its upper border as high as possible to facilitate suprafrontal access to the cerebral convexity. Following that, the dura is incised and CSF is slowly drained; a combination of mild hyperventilation, positioning and CSF drainage opens a suprafrontal subdural space as the frontal lobe "relaxes" downwards. The endoscope is then introduced through the keyhole and advanced over the frontal convexity in a subdural plane.

A panoramic view of the meningioma arising from the dura and pushing downward on the brain is displayed as the endoscope is advanced in the suprafrontal subdural plane, arachnoid bands hanging from the surface of the convexity are coagulated and sharply divided, thus promoting further brain relaxation. Using a combination of custom designed endoscopic instrumentation, bipolar electrocoagulation and a micro cavitron ultrasonic surgical aspirator (CUSA) the tumor is gradually resected. Its originating part from the dural surface is identified and dealt with last after which the dura is coagulated.

Following tumor removal, the keyhole bone flap is repositioned using absorbable microplates and screws. The skin incision is closed with careful attention to the aesthetic repair.

Patients and Methods: History Patient 1

A 40-year-old gentleman with a long (five years) history of chronic headaches for which he has undergone numerous investigations including CT and MRI of the brain that revealed a right sided frontoparietal supratentorial convexity menigioma. He had no history of seizures, visual disturbances or other neurological symptoms or deficits. His menigioma was therefore monitored for several years, but recently his headaches have increased in both frequency and intensity and have become resistant to regular analgesic medications and only resolved with intravenous steroids. The patient was seen locally by surgeons and was advised to undergo an open craniotomy for excision of his tumor. The patient seeked a minimally invasive alternative and was presented to our practice where he was advised that he would be a candidate for excision of his tumor endoscopically via an eye brow approach.

Examination/Preoperative Testing

A known case of right sided frontoparital supratentorial convexity meningioma. On examination, the patient was noted to be awake and conversant with no focal neurological deficits and his vital signs were within normal limits; the rest of his neurological examination was unremarkable.

A new MRI brain was obtained demonstrating a right sided dural based extra axial tumor with dense uniform enhancement but with no apparent perifocal oedema or other abnormal reaction of the underlying brain consistent with a meningioma in the opercular cortex below the right posterior frontal bone and in close proximity to the superior saggital sinus (SSS). When compared to his previous MRI brain performed 2 years ago, the tumor was noted to have increased by at least 1.5 cm to become 3.8x2.7 cm in size. Computerized tomographic (CT) scanning with contrast was obtained revealing hyperostosis of the overlying bone, the hyperostosis was judged as reactionary rather than direct bony involvement with tumor.

Surgery

Under general anesthesia, after positioning, prepping, draping, and initial tumor exposure in the previously described manner, a zero-degree endoscope was introduced and advanced in a suprafrontal subdural plane directly to the tumor, which was clearly visible. Some arachnoid adhesions were taken care of using the bipolar electrocautery followed by sharp division of the arachnoid bands and the tumor was circumferentially dissected off the surrounding normal brain. At this point, utilizing microdissection techniques and microinstruments, the surrounding veins were electrocoagulated and divided, and the tumor was completely freed from the underlying normal brain but was still attached to its dural base. Following that, disconnection of the tumor from its dural attachments and some minor blood vessels was pursued. The surface of the tumor was then electrocoagulated and a piece of it was sent for frozen section confirming that it was a meningioma. Using a combination of custom designed endoscopic instrumentation, bipolar electrocautarization and the CUSA, the tumor was gradually resected, first resecting its inner portions in order to collapse, following which its capsule was electrocoagulated and gradually resected till a gross total resection of the tumor was obtained. A small piece of Gelfoam was left on the brain surface where the tumor was sitting, following which the area was copiously irrigated and since no bleeders were identified, the endoscope was slowly withdrawn from the field and out of the supraorbital keyhole. Closure was then carried out in the previously described manner. The patient was extubated and was found to be moving all four extremities to command and had no neurological deficits. He was taken to the recovery room in a stable condition.

History patient 2

A 52-year-old male with recent onset of severe throbbing headache, there was no history of nausea, vomiting, focal weakness or visual changes. Since no apparent etiology for his headaches could be identified a CT scan brain followed by an MRI were performed revealing a 3 x 2.5 cm left sided parasaggital meningiomas along the middle third of the falx cerebri. The patient was seen in surgical consultation locally and advised to undergo a formal craniotomy. The patient was interested in a minimally invasive alternative to open surgery, and was presented to our practice for evaluation where he was advised that he would be a candidate for minimally invasive endoscopic resection of his meningiomas via a supraorbital approach.

Examination/Preoperative Testing

Bilateral early papilledema was noted on fundus examination otherwise the patient was neurologically intact and the rest of his examination was unremarkable.

CT scan demonstrated a high left homogenous frontal/frontoparietal mass along the convexity in close proximity to the falx cerebri and with a wide dural base as well as mild hyperostitic reaction of the overlying bone, consistent with a parasaggital meningioma of the middle third of the falx cerebri. An MRI and MRA were performed in which the tumor was noted to be abbutting rather than invading the falx with good venous flow along the SSS. There was no significant mass effect exerted by the tumor and no additional abnormalities were identified.

Surgery

Following the previously described initial steps, a zero-degree endoscope was introduced and navigated all the way to the parasagittal area in a suprafrontal subdural plane. Immediately a yellowish-purplish tumor was identified and biopsied and frozen section confirmation of a meningioma was obtained. Of note, and throughout the procedure, the motor cortex was monitored continuously.

Following that, the tumor's surface was electrocoagulated, and gradually dissected and resected off the underlying normal brain. The tumor was then followed superiorly towards the falx and the SSS, which were identified. The superior medial aspect of the tumor was dealt with last as this portion of the tumor was felt to be the most dangerous due to the location of the SSS. Using microdissection techniques and microinstruments and with great care not to injure the SSS the tumor was gradually resected and shaved off the falx cerebri till it was cleared of all apparent tumor. The surface of the falx as well as the origin of the tumor from the adjacent convexity dura were then electrocauterized and minor venous bleeders were electrocoagulated. Following that the area was copiously irrigated, hemostasis assured, and closure was then carried out in the previously explained fashion. The patient was extubated and taken to the recovery room where he was noted to be moving all four extremities to command, and had no apparent neurological deficits.

Discussion

There are generally three treatment options for meningiomas, these are observation, surgery, and radiation whether GKS or less commonly conventional radiotherapy; however, if the tumor cannot be completely excised, treatments can be combined. Although surgery is generally accepted to be the primary treatment among these lines especially with larger tumors, those with symptoms or those that show progressive growth, and complete tumor removal is the ideal result, the frequency of recurrence of meningiomas even after the most aggressive and radical surgeries has not been as low as expected [15-17] and continuous attempts to improve both surgical and functional outcomes are being made.

Moreover, traditional surgery, not promising "no recurrence" and carrying the disadvantage of being a major operation where significant mobilization of non-pathological tissues is required in order to access the tumor, often results in undesirable functional and cosmetic morbidity that is seldom acceptable for a mostly benign lesion that is generally associated with a good prognosis. The details of the traditional transcranial technique are well known and have been long reported by several authors [18-20]. However, the key considerations in the traditional transcranial approach are considered as disadvantages; these include that the incision and bone flap must be large enough to enable excision of a good margin of dura around the tumor attachments and to insure that all the margins of the tumor could be accessed, and, that with the standard transcranial techniques the surface of the tumor and the plane separating it from the normal cerebral cortex could not be easily visualized without placing retraction on the cortex yielding potential long-term morbidity and inferior quality of life and increasing the incidence of postoperative seizures[21]. Additionally, as the tumor arises originally from the dura and only compresses the brain, anatomical planes are partly lost when the tumor is approached "externally" and major draining or bridging veins are often unnecessarily sacrificed. In contrast, when the tumor is approached "internally", as in the reported approach, the pathology could be dealt with directly and the tumor resected with virtually no disturbance to the underlying brain tissue.

In this report although Simpson Grade I removal [22], which entails excising the meningioma along with its dural/sinus/bone attachments and which is generally believed to be associated with the lowest rate of recurrence, has not been followed and instead Simpson Grade II removal (macroscopic complete removal of the meningioma with endothermy coagulation of its dural attachements) was percieved, preliminary excellent functional, cosmetic, and patient sastisfaction outcome along with a minimal postoperative discomfort were achieved, yet long term follow-up is necessary.

Nevertheless, many meningiomas elicit hyperostosis without invasion of the calvarium, however, some lesions will actually penetrate the skull, causing extensive bony thickening and osteoblastic reaction and may even penetrate the entire skull and present as a scalp mass. The latter type may require extensive bone removal and are generally not suitable for the reported technique. .In general, changes in adjacent bony structures take a variety of appearances ranging from mild reactive hyperostosis to actual osseous invasion and bone destruction [6], The cause, management, and prognosis of these bony have long been a a point of controversy [23], therefore a standard surgical procedure may not suit these wide varieties. Furthermore, technology has improved the surgeon's ability to precisely locate the tumor, define its borders, and confirm the best technique for its removal preoperatively. Although the authors of this report agree that the objective of the operation is total removal of the meningioma and the involved dura/bone, the first priority remains to preserve and improve function as every treatment type has its own set of risks and benefits. Other factors that will affect the treatment choice are age, overall state of health, which medical center you turn to for treatment, as well as involving and informing the patient about different alternatives, risks and benefits.

In our experience, despite the small size of the craniotomy, the thin caliber of the endoscope together with its wide range of view and ability to navigate and access remote areas within the skull via a small key hole, as well as exploration followed by slow CSF drainage provided a space large enough for safe access to the frontoparietal convexity from a suprafrontal subdural pathway, thus, reserving the integrity of as much normal tissue as possible. The endoscope allows the surgeon to position it directly at the level of dissection, effectively reducing the viewing and operating distances and unnecessary manipulation or brain retraction/dissection was not needed. The advantages that the described approach offers over conventional craniotomy are significant including a hidden skin incision completely within the eyebrow, the lens of the endoscope being at its tip and just in front of the tumor, minimizes unnecessary brain retraction and finally a smoother , more pleasant postoperative course and an earlier return to work for the patient.

However, despite the mentioned advantages, in our opinion the most significant advantage provided by the reported approach is that the layer of arachnoid that usually separates meningiomas from the brain could be easily identified and followed as the pathology is addressed from within the dura, therefore enabling the surgeon to stay within this surgical plane which ultimately decreases the chances of neural and/or vascular injury as wall as ensuring gross total removal. Furthermore, a clean field with minimal bleeding was noticed during the course of both operations, this was attributed to the fact that the feeding meningeal arteries are easily identified from within the dura and occluded early in the course of the operation, preoperative embolization was not needed.

The general disadvantages of the supraorbital approach have been previously discussed by other authors and ourselves [11-14], these mainly include scalp anesthesia due to section or stretch of the supraorbital and supratrochlear nerves; transient frontalis muscle palsy due to transmitted stretch on the frontal branch of the facial nerve; or occurrence of an internal fistula through an occult frontal sinus opening leading to rhinorrhea. To avoid these complications the mini-craniotomy should be far enough from the frontal sinus and the nasofrontal duct should be obliterated and the sinus cranialized in case of accidental opening. The medial limit of the incision should always be kept lateral to the supraorbital notch, bearing in mind that palsy of the supraorbital and supratrochlear nerves may be a handicap for the patient.

Conclusion

Most meningiomas grow inward from the dura and toward the brain as discrete, spherical or lobulated, well-defined, dural-based masses, therefore the endoscopic approach offers a more targeted access to the site of pathology with dissection starting directly at the dural level. In both reported cases, the fully endoscopic supraorbital suprafrontal approach allowed excellent visualization of the tumor and the surrounding vascular and neural structures. A macroscopic complete removal was obtained in both cases. The skin scar was virtually invisible in both patients at one month postoperatively and they were both discharged home within 48 hours of their operation. In addition, the maneuverability of the endoscope allows the surgeon to position it directly at the level of dissection, effectively reducing the viewing and operating distances. Endoscopic imaging thereby facilitates complete tumor resection via a minimally invasive technique.

In the latter part of the previous century it became apparent that the functional cost (morbidity) related to gaining access to many skull base and brain tumors was very significant and the practice of minimally invasive brain surgery, aided by successive technological advancements started to evolve. We believe that direct access to these tumors with virtually no brain retraction provided by the fully endoscopic supraorbital approach minimizes the risk of injury to brain tissue and vascular structures and directs the focus on preserving neurological function and reducing morbidity. The described approach has the potential for lowering the rate of surgical complications and greatly reducing hospital stays and it appears to be much less painful and much less uncomfortable for the patient when compared to conventional approaches. These cases demonstrate a further application for the supra orbital approach that, in indicated cases, can eliminate the need for traditional open techniques without compromising surgical success. Further applications and usefulness of the technique could be envisioned, and larger studies with long-term follow-up are recommended.

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