Meningioma Treatment & Management

Medical care for meningiomas has been disappointing. It is restricted either to perioperative drugs or to medications that are used after all other means of treatment have failed. ^[30]

The use of corticosteroids preoperatively and postoperatively has significantly decreased the mortality and morbidity rates associated with surgical resection.

Antiepileptic drugs should be started preoperatively in supratentorial surgery and continued postoperatively for no less than 3 months.

The current experience with chemotherapy is disappointing.

• This modality of treatment is reserved for malignant cases after failure of surgery and radiotherapy to control the disease.

• The main drugs studied include temozolomide, which had no effect against recurrent meningiomas in a phase 2 study ^[31] , and hydroxyurea (ribonucleotide reductase inhibitor); RU-486 (synthetic antiprogestin); and interferon-alpha. The last 3 drugs also showed disappointing results. A recently published prospective phase 2 study of irinotecan (CPT-11) also failed to demonstrate any efficacy.

• The combination of interferon alpha and 5-fluorouracil synergistically reduces meningioma cell proliferation in culture and warrants further investigation.

• Some studies have shown a possible role of COX-2 inhibitors in the treatment of recurrent meningiomas. ^[11]

• The role of targeted chemotherapy to block the tumorogenic pathways of meningiomas at specific sites is being extensively investigated. ^[32]

• Molecules to block specific growth factors or enzymes are being developed. Atypical meningioma (WHO grade II) and anaplastic meningioma (WHO grade III) showed increased fatty acid synthase (FAS) expression. FAS inhibitor (cerulein) decreased meningioma cell survival in vitro. Thus, increased FAS expression in human meningiomas represents a novel therapeutic target for the treatment of unresectable or malignant meningiomas. ^[33]

Although most meningiomas grow slowly and have a low mitotic rate, clinical benefit has been reported in many case series with either tumor regression or stasis after radiotherapy; however, these results have not been confirmed in randomized trials. Oya et al reported on the natural history of meningiomas. ^[34] The prospect of benign meningioma growth is an important factor to consider in their proper management. Approximately 40% of 273 meningiomas (in 244 patients) grew within a 4-year period. Lack of calcification, hyperintensity in T2 MRI, and peritumoral edema were predictors of growth in follow up. In addition, age younger than 60 years and tumor size larger than 25 mm (diameter) were also associated with a greater risk.

Radiotherapy is mainly used as adjuvant therapy for incompletely resected, high-grade and/or recurrent tumors. It can also be used as primary treatment in some cases (optic nerve meningiomas ^[35] and some unresectable tumors). ^{[36, 37]}

In general, the ideal treatment of a benign meningioma is surgical resection if possible. Hasegawa et al treated 46 patients with gamma knife radiation (GKR) as the initial treatment modality. ^[38] The lesions were falcine, convexity, or parasagittal. The study found GKR to be effective. The main caveat was tumor size. Large tumors had the possibility of severe postirradiation edema. This was actually more likely to occur with significant, baseline peritumoral edema. GKR may be selected over surgery in patients with significant medical comorbidities.

Stereotactic radiosurgery has been shown to provide excellent local tumor control with minimal toxicity. ^{[3, 4]}

• It is mainly used for small (< 3 cm in diameter) residual or recurrent lesions when surgery is considered to carry a significantly high risk of morbidity.

• It has been advocated as an effective management strategy for small meningiomas and for meningiomas involving the skull base or the cavernous sinus.

• It is used primarily to prevent tumor progression.

• In a recently published series, the long-term follow up after radiosurgery was reported; a tumor control rate of 94% was found after an average of 103 months.

Patients who undergo operation for meningiomas should receive regular follow-up with enhanced MRI to check for possible recurrences. ^[39] Patients who are discharged home with antiepileptic agents should be monitored by a neurologist.

Before or after surgery, patients with skull-base meningiomas may have numerous disabilities, such as diplopia, dysphasia, dysphagia, or motor weakness. These problems should be managed with a multidisciplinary approach (eg, occupational therapy, physiotherapy, speech therapy).

The constant principles in meningioma resection are the following: If possible, all involved or hyperostotic bone should be removed. The dura involved by the tumor as well as a dural rim that is free from tumor should be resected (duraplasty is performed). Dural tails that are apparent on MRI are best removed, even though some may not be involved with the tumor. Make a provision for harvesting a suitable dural substitute (pericranium or fascia lata). The surgeon also can use commercially available dural substitutes. If feasible, always start by coagulating the arterial feeders to the meningioma. See the images below.

Surgical strategies for managing meningiomas in specific locations are discussed in the sections that follow. It should be noted that there is a significant amount of experience reported regarding surgical resection of menigiomas in their various locations and the goal of avoiding complications during and after these procedures. ^[40]

Convexity meningioma

Opening the scalp and skull may be bloody because of the hypertrophy of blood vessels originating from the external circulation.

The tumor may breach the sanctity of the dura and the bone, thus appearing subcutaneously.

The dural blood vessels should be coagulated before opening the dura to decrease tumor vascularity.

Usually the tumor is separated from underlying brain parenchyma by an arachnoid layer. This layer may not be complete at the depth of the tumor. In this location, separating the tumor from the brain may be difficult.

Unless the tumor is small and can be removed in 1 piece, the best strategy for excising convexity meningiomas is to find the arachnoidal plane and dissect it gently.

Placing patties circumferentially around the tumor allows quick identification of this crucial plane at a later time.

Coagulate the surface of the tumor, then core it and invaginate the outer layer to allow further circumferential dissection.

Perform dural grafting. (See the video below.)

Parasagittal meningiomas

These tumors may arise from the convexity and involve the superior sagittal sinus (SSS) by medial extension, or they may arise from the falx and involve the SSS by upward extension. The former subgroup is easier to treat surgically because of its superficial location.

The foremost consideration in surgically treating parasagittal meningiomas is to decide what to do with the SSS. MRV is not yet sensitive enough to confirm unequivocally the complete occlusion of the SSS.

The diagnostic test of choice is still endovascular angiography with late venous images to look for a possible delayed filling of the involved portion of the SSS. If the SSS is completely obliterated by tumor, it can be ligated safely and excised. The surgeon should be careful not to injure the veins that run anteriorly and posteriorly to the tumor. These veins may provide crucial collateral circulation for the venous drainage of the cerebrum and should be preserved at all costs.

If the SSS is only partially involved, the decision of whether to sacrifice it depends on the involved segment.

The anterior third of the SSS can usually be sacrificed with impunity; the middle third, sacrificed at times; and the posterior third, never ligated. In this author's experience, the SSS is never sacrificed beyond the anterior third.

Some surgeons resect a partially involved sinus and reconstruct it later (either with a vein or prosthetic graft).

The author's opinion is that explaining to the patient that some tumor was left behind that may need further resection at a later date is better than taking undue risk of neurological deficit by obliterating more of the SSS. If the sinus is occluded gradually by the tumor, the venous drainage will be diverted over time through parasagittal veins.

Olfactory groove and tuberculum sellae meningiomas

To avoid undue retraction of the frontal lobes, these tumors are best approached through a low craniotomy. This is achieved by removing the supraorbital rim.

A unilateral approach is usually sufficient. The midline burr hole should be placed just above the frontonasal suture. By entering the frontal sinus and removing the orbital rim, a low approach is provided.

To allow adequate visualization, the falx should be sectioned after ligating the most anterior aspect of the SSS. Every attempt should be made to preserve at least one of the olfactory nerves.

These tumors receive their blood supply through various sources: the ethmoidal branches of the ophthalmic arteries, branches from the middle meningeal artery, and the carotid arteries.

These tumors often invade the ethmoid sinuses and, at times, the sphenoid sinus.

Care should be taken to identify and preserve both optic nerves. Note that the usual relationship between the optic nerves and the carotid arteries might not hold true owing to displacement of these vital structures by tumor.

Tumor arterial supply and perforator arteries to the hypothalamus must be differentiated because both arise from the anterior circulation. (See the video below.)

Sphenoid-wing meningiomas

Sphenoid-wing meningiomas present either as en plaque meningiomas or as globular masses.

Removing the zygoma and the orbital rim allows wider exposure of the sphenoid wing, the middle cranial fossa, the anterior cranial fossa, and the anterior clinoid.

Medial tumors may extend within the cavernous sinus.

Tentorial and torcular meningiomas

Tentorial meningiomas may be supplied by a multitude of vessels that arise from the tentorial leaf. These should be coagulated thoroughly before one attempts to remove the tumor.

A major supply may be the Bernasconi-Cassinari artery, which arises from the cavernous portion of the carotid artery and runs posteriorly to supply the tentorium.

This artery is usually not apparent on normal angiograms but may be conspicuous in angiograms of tentorial meningiomas.

A definite attempt should be made at recognizing the Bernasconi-Cassinari artery during surgery and coagulating it to decrease tumor vascularity.

Tentorial meningiomas often grow in both the infratentorial and supratentorial compartments and should be approached accordingly.

Studying the preoperative angiogram is imperative in cases of torcular meningiomas to delineate the patency of the different sinuses and the available collateral circulation. Removing these tumors completely is often impossible because of partial involvement of the venous sinuses.

Cerebellopontine angle meningiomas

In acoustic neuromas, the facial nerve usually lies anterosuperiorly to the tumor and is encountered late in surgery. This relationship is lost in cerebellopontine angle meningiomas, because the facial nerve may lie along the posterior tumor edge and can be injured early in surgery (unless care is taken to identify it).

Before attempting to remove the tumor, the surgeon should first diminish its blood supply by coagulating its supplying arteries from the dura. To do so, the interface of the tumor and the petrous bone should be followed. A partial cerebellar resection may be necessary to avoid undue retraction of the brain.

Meningiomas involving the cavernous sinus

The issue of meningiomas involving the cavernous sinus is currently an area of intense interest in neurosurgery. No one doubts that, in experienced hands, such meningiomas can be treated successfully.

The debate centers on 2 points: when to operate and how aggressive the resection should be. The following opinion is a personal reflection on the matter, and diverging views may be found in the literature.

• Asymptomatic cavernous sinus meningiomas should not be operated but should be monitored carefully by means of repeated physical examination and serial MRI.
• Symptomatic meningiomas in otherwise healthy patients should be resected by neurosurgeons who are trained for such procedures.

Avoid injuring the cranial nerves or the carotid artery. This author does not believe in the benefit of bypassing and resecting the cavernous carotid artery in these cases.

The surgeon should remember that a multitude of processes may affect the cavernous sinus and mimic a meningioma, including sarcoidosis and infection/inflammation that lead to the Tolosa-Hunt syndrome.

Gamma knife may be a good treatment option in parasellar meningiomas. ^[41]  Large tumors can be partially resected and treated with gamma knife after resection. In a report by Jensen et al, a good outcome was obtained, with an impressive 69% local tumor growth control.

Clival and petroclival meningiomas

These tumors represent some of the greatest challenges in neurosurgery; although partial resection is relatively straightforward, complete resection remains a daunting task.

Partial resection usually does not translate into any benefit for the patient and only renders further surgeries more difficult; therefore, every attempt should be made to complete the resection. If surgery has to be interrupted for logistical reasons, the second operation should be scheduled the earliest possible opportunity.

A multitude of approaches has been devised for these tumors. The traditional approaches such as the suboccipital or the subtemporal are usually insufficient to allow complete removal. More extensive approaches, such as the petrosal approach, are needed. This approach consists of combined supratentorial and infratentorial craniotomies, associated with a simple mastoidectomy down to the solid angle (ie, the bone encasing the inner ear). After the tentorium is split, the petroclival meningioma can be visualized in its entirety.

If the patient has neurofibromatosis, the neurosurgeon may want to refer the patient for genetic counseling and for audiometric testing.

If the radiologic diagnosis is not clear cut, a detailed discussion with the radiologist should attempt to rule out other pathologic entities, such as neurofibromas or sarcomas.

In specific cases, consulting a radiation oncologist may be appropriate.