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Convexity meningiomas develop from the leptomeninges of the cerebral convexities over all lobes of the brain and represent 15-20% of intracranial meningiomas. Due to their accessible location, distance from the skull base and the dural venous sinuses, they offer the greatest potential to achieve their radical gross total resection. Their excision should encompass a wide dural margin and the involved bone, especially for young patients, to decrease the risk of tumor recurrence.
Similarly, convexity meningiomas were among the earliest accessible surgical targets in our profession.
Clinical presentation is largely dependent on tumor location. Tumors situated away from the eloquent cortices may reach a large or giant size before presenting with symptoms of raised intracranial pressure.
Convexity meningiomas are frequently found incidentally on unrelated imaging studies, but may present with focal neurologic findings or epileptic activity of the underlying cortex. Hyperostotic tumors may present with cosmetic deformity of the skull.
Magnetic resonance imaging (MRI) with contrast enhancement is the main diagnostic study of choice for these tumors. Their imaging characteristics are similar to other meningiomas: homogeneous enhancement and an enhancing dural tail. The T2/FLAIR sequences allow evaluation of underlying brain edema and presence of a subarachnoid plane between the tumor and the pia.
Large cortical vasculature (large parasagittal veins or vein of Labbe) and their involvement should be studied preoperatively through the use of complementary studies such as a computed tomography (CT) angiogram or MR venogram. Preservation of these veins is fundamental to securing a desirable outcome after meningioma surgery.
CT scans allow evaluation of bony involvement and may also identify calcification in some tumors. Bone erosion must be considered during preoperative planning. Hyperostosis suggests tumor infiltration and requires resection.
Other lesions mimicking a convexity meningioma include hemangiopericytomas, primary bony tumors, dural-based metastases, and potentially lymphoma.
Indications for Surgery
Older patients with small, asymptomatic lesions may be observed with serial imaging. Younger patients’ asymptomatic tumors may be observed until growth is identified, but if the patient has a large or symptomatic lesion, surgical resection is the primary treatment modality.
Radiosurgery may be used for small residual or recurrent tumors, for adjuvant treatment of higher-grade meningiomas, and for palliation in patients unable to tolerate surgical resection.
Small lesions do not require special consideration beyond standard cranial neuroanesthesia and navigation. Dexamethasone, anticonvulsant medications, and mannitol are administered at the start of the surgery, especially if the patient has underlying brain edema.
Large lesions invading the dural sinuses often lead to significant bleeding during surgery and preoperative hematologic studies and precautions for intraoperative venous air embolism detection and management are warranted. Preoperative embolization is unnecessary because the tumor’s meningeal vascular supply is addressed readily after craniotomy through transdural coagulation and circumcision of the tumor’s dural attachments.
Due to this tumor’s accessibility, every effort should be made to achieve a gross total resection, with consideration of excision of dural margins 1-2 cm beyond the points of attachment/dural tail. Hyperostotic bone on the craniotomy flap should be resected. If preoperative studies suggest significant bony involvement, a custom synthetic skull flap or titanium mesh cranioplasty is prepared in advance, depending on the size of the defect.
RESECTION OF CONVEXITY MENINGIOMAS
Please refer to the Cranial Approaches volume for details of the craniotomy. Each tumor requires a unique bony exposure based on its location. Neuronavigation allows a tailored incision that provides adequate exposure for wide dural excision. Although a long linear incision may provide adequate exposure, a curvilinear or horseshoe incision is usually more appropriate for wide-based convexity meningiomas.
At the end of the operation, a large dural defect is often apparent. Therefore, during the early parts of the operation, I routinely harvest a large piece of pericranium to be used for postresection dural closure. I avoid using synthetic dural allografts because they lead to an increased risk of infection and aseptic inflammation. These risks are especially heightened when an allograft is used for large dural defects.
Careful epidural hemostasis is necessary before proceeding with intradural surgery.
Preoperative edema indicates pial violation by the tumor. Intraoperative dissection should carefully preserve the subpial contents and aggressive bipolar coagulation should be avoided. The tumor may be debulked so that the tumor rather than the brain is retracted to advance the dissection planes. If excessive brain tension is present causing excessive cerebral herniation along the craniotomy edges, medical management for increased intracranial pressure should be instituted and the tumor expeditiously debulked and removed to relieve its mass effect.
Larger tumors or those with a dominant deep tumor nodule should be internally enucleated to allow the tumor capsule to be collapsed into the resection cavity; this method avoids excessive brain retraction or manipulation. As the tumor is decompressed, the capsule is reflected away from the surrounding brain tissue. This maneuver enables me to predict the extent of tumor removal possible at the lower depth of the same dissection plane.
Papaverine-soaked Gelfoam pledgets are temporarily placed on arteries that may be in spasm.
Other Related Techniques
Mobilization and en bloc resection of large convexity meningiomas during their dissection can place the surrounding cortices under untoward forces, leading to neurovascular injury. A bulb syringe connected to a standard surgical suction device may be used to handle the bulk of the tumor mass using the vacuum-assisted en bloc resection technique.
The patient is observed in the intensive care unit overnight for frequent neurologic evaluations and pain and blood pressure control. A postoperative CT scan is obtained. Steroids are weaned slowly postoperatively.
Tumors with a large amount of underlying cerebral edema may lead to malignant postoperative cerebral swelling; patients with such tumors should be maintained on steroids for a longer postoperative period. Prophylactic anticonvulsants are administered perioperatively, but stopped one week after surgery if the patient has not suffered from a seizure.
Patients with meningiomas have an increased risk of postoperative deep vein thrombosis. These patients should be treated with aggressive preventive measures including early mobilization.
Pearls and Pitfalls
- A preoperative CT scan evaluates the extent of bony involvement. Resection of the affected bone is an important goal of surgery. In addition, a wide craniotomy should allow generous removal of the affected dura.
- Cortical arteries and veins that are draped over the tumor capsule should be inspected and preserved if they are not terminal tumor vessels. Pial violation should be avoided and dissection should be maintained along the extrapial subarachnoid planes.
- Large lateral frontotemporal meningiomas may adhere to the middle cerebral artery (MCA) branches at their depth. These tumors should be carefully mobilized and MCA branches sharply dissected.
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