Approach Considerations
Meningioma can present a different set of clinical symptoms based on its size, location, and its intrinsic aggressiveness. Besides some nonspecific symptoms such as headache, a convexity meningioma in close proximity to motor/sensory areas of the brain may manifest motor/sensory disturbances or seizures. On the other hand, olfactory groove meningioma may present with loss of smell, personality changes, or visual deficit. Spheno-orbital meningioma may present with unilateral proptosis and/or visual deficit. Therefore, it is important to realize the normal surrounding structures that may be affected by the tumor. Appropriate work-up should focus on testing the structural and functional integrity of those normal intracranial, or sometimes extracranial, structures.
Clinical examination should include a detailed neuro-ophthalmic assessment, together with a dilated fundal examination of the optic nerve head and retina. Orbito-sphenoid meningiomas recurrences often are associated with involvement of the optic nerve. [78]
Laboratory Studies
Laboratory studies may be indicated to rule out other differential diagnoses (eg, metabolic panel including calcium, bone-specific alkaline phosphatase, urine hydroxyproline).
Imaging Studies
Plain radiography of the skull
Abnormalities have been found in 30-60% of patients with sphenoid wing meningioma. Hyperostosis, thinning of bone, and irregular foci of calcification can be seen. [79]
CT scanning of the bone window
CT scanning of the bone window typically shows thick, hyperdense, intradiploic lesion expanding the calvaria and destroying the cortical layers of the skull. The bony expansion and ground-glass appearance of sphenoid wing meningioma complicates differentiation from fibrous dysplasia71; however, the inner table of the skull looks smooth in fibrous dysplasia, whereas sphenoid wing meningiomas often demonstrate irregularity of the inner table associated with a dural reaction. Clinically, fibrous dysplasia usually presents in younger individuals and stops growing after puberty, in contrast to meningioma, which typically develops in older individuals. Among sphenoid wing meningiomas, 59% are osteoblastic, 10-35% are osteolytic, and 6% are a mixed picture of both osteolytic and hyperostosis. [75, 80]
CT scan brain bone window showing intraosseous meningioma involving left sphenoid wing, lateral orbital, superior orbital fissure, and the anterior part of the middle fossa floor.
MRI
MRI allows better delineation of the soft tissue component of the tumor and dural involvement, as well as delineation of intraorbital extension or growth. There might be no dural tail in sphenoid wing meningioma, especially the en plaque variant. [81]
MRI brain T2W (left) and T1W Fat-Sat (right) sequences showing involvement of the left sphenoid wing associated with dural thickening and the periorbita. Notice proptosis of the left globe secondary to left orbital wall thickening.
Angiography
Angiography is not necessary in sphenoid wing meningioma. When performed, it usually shows tumor blush of the en masse component and tortuous external carotid artery feeders. [81]
C-PiB and F-FDG positron-emission tomography scanning
Two patients who had undergone contrast-enhanced MRI scans that revealed extra-axial tumors next to the sphenoid wing were examined using C-PiB and F-FDG positron-emission tomography (PET) scanning. The researchers concluded that C-PiB could be used as a meningioma marker. [82]
Other Tests
Other tests may include the following:
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Preoperative evaluation of patients with anterior basal meningiomas, including formal visual field and acuity testing.
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Metastatic work-up, such as CT scanning of the chest, abdomen, and pelvis; skeletal survey; radionucleotide scanning; and PET scanning
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Intraoperative radiodetection of somatostatin receptors is feasible, especially in bone-invasive meningiomas using gamma probe. [83]
Histologic Findings
According to the WHO, in 2007 and 2016, 3 types of meningiomas exist based on malignant behavior, as follows [61, 84, 85] :
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Grade I (benign), with a recurrence rate of 7-25%, does not meet atypical or malignant meningioma criteria. Despite involvement of the adjacent bony structures, grade I meningiomas do not invade the brain parenchyma. Grade I meningiomas include 9 histologic subtypes: meningothelial, fibrous, transitional, psammomatous, angiomatous, macrocystic, secretory, lymphoplasmacyte-rich, and metaplastic.
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Grade II (atypical), with a recurrence rate of 29-52%, includes atypical, clear cell, and chordoid histologic subtype or increased mitotic activity (4-19 mitoses per 10 high-powered fields) or brain invasion, or 3 or more of the following features: increased cellularity, small cells with a high nuclear:cytoplasmic ratio, prominent nucleoli, uninterrupted patternless or sheetlike growth, or foci of spontaneous or geographic necrosis.
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Grade III (malignant), with a recurrence rate of 50-94%, includes anaplastic, papillary, and rhabdoid histologic subtypes. Anaplastic meningiomas have 20 or more mitoses per 10 high-powered fields or malignant characteristics resembling carcinoma, sarcoma, or melanoma.
Malignant transformation is rare. Originally, malignancy was seen in anaplastic tumors, but they may arise from any of the meningioma variants or atypical meningiomas. Papillary histopathology is associated with local aggressiveness and an increased incidence of late distant metastasis. The papillary type is considered malignant by definition and is encountered more frequently in children. [86]
Earlier classification schemes used the term angioblastic meningioma for what is now considered to be a hemangiopericytoma. This neoplasm is distinctly separate from a meningioma, and it shows extremely high propensity for recurrence and metastasis. Hemangiopericytoma is a sarcoma in the new WHO classification. [85, 87]
Meningiomas generally are slow growing. Growth patterns of meningioma in a 2011 series of incidentally diagnosed meningioma included no growth, linear growth, or exponential growth. The presence of calcification, T2-weighted MRI tumor hypointensity, and older age at onset were associated with slower growth rate. [88]
In a large series of 603 asymptomatic meningiomas, 63% did not increase in size, and only 6% of patients eventually experienced symptoms over a mean follow-up of 3.9 years. [89]
Another series of 273 incidental meningiomas in 244 patients with a mean follow-up period of 3.8 years observed a 2 mm or greater increase in maximum diameter in 120 tumors (44% of the cases). [90]
True metastases are extremely uncommon, and dissemination usually is believed to occur hematogenously, with the lungs as the most common site. [91]
Bony invasion is not evidence of malignancy in meningiomas, and invasion of mesenchymal components (eg, bone, muscle, dura) can occur with benign meningiomas. [92]
Procedures
The operative approach for meningioma depends largely on the tumor location, size, shape, and involvement of the critical neurovascular structures. In general, the operative procedure to remove meningioma requires opening of the skull (craniotomy) in the most accessible location where it can facilitate removal of the meningioma without aggressive retraction of the brain. For instance, convexity meningioma typically will require a craniotomy directly over the tumor. The margin of the craniotomy should be larger than the tumor in order to completely resect the tumor. Tumors involving the anterior/middle skull base (meningioma of tuberculum sella, planum sphenoidale, sphenoid wing, clinoidal) typically can be approached via a standard frontotemporal approach. With the advancement of endoscopic techniques and technologies, expanded endoscopic endonasal approaches are being popularized for removal of these tumors. However, tumors that are saddling the petrous and the clival bone (also known as petroclival meningioma) may require additional skull base drilling (such as partial or complete petrosectomy) in order to gain access. [93] Olfactory groove meningioma may require bifrontal craniotomy and subfrontal approach for resection.
Staging
Staging typically is not done for meningioma, which is confined to areas within the meninges and typically does not metastasize to distant organs.
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Coronal T1-weighted MRI with gadolinium enhancement of a sphenoid wing meningioma with some degree of encasement of bilateral cavernous sinuses.
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T1-weighted MRI with gadolinium (coronal section) of same patient with sphenoid wing meningioma. A better visualization of en plaque growth of the meningioma along the convexity of the cerebral hemisphere on the left side is seen, in addition to better illustration of intracavernous carotid arteries bilaterally and en plaque growth of meningioma inferiorly and laterally around both temporal lobes.
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T1-weighted gadolinium enhanced (sagittal section) of same patient with meningioma of the sphenoid wing.
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CT scan brain bone window showing intraosseous meningioma involving left sphenoid wing, lateral orbital, superior orbital fissure, and the anterior part of the middle fossa floor.
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MRI brain T2W (left) and T1W Fat-Sat (right) sequences showing involvement of the left sphenoid wing associated with dural thickening and the periorbita. Notice proptosis of the left globe secondary to left orbital wall thickening.
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This is a typical appearance of a sphenoorbital meningioma on the MRI. The image depicts a contrasted MRI of the brain which shows an enhancing mass along the sphenoid ridge, orbital apex, and even the temporalis muscle. The orbital involvement of the tumor causes significant proptosis of the affected eye.
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After elevation of the myocutaneous flap; note the underlying bone is infiltrated with tumor.
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A frontotemporal craniotomy is performed to elevate the affected bone. Underlying it, dura is seen. The dura is also infiltrated with the tumor.
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The tumor debulking is performed using the micro-instruments and high-speed diamond drill bit.
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The dura is opened. Any intradural portion of the tumor is resected, if any. The involved dura is cut and discarded.
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Important neurovascular structures are decompressed including the orbit, orbital apex, superior orbital fissure. The tumor has also infiltrated the periorbita. Some periorbital fat can be seen.
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After gross total resection of the tumor (star = orbit, circle = frontal lobe, triangle = temporal lobe).
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After closing the dura with a synthetic dural substitute, cranium is replaced and secured with titanium hardware. Medpore cranioplasty (white plates) are placed for further reconstruction and to restore cosmesis.
