Cerebral meningiomas are among the most common primary brain tumors in adults. They are considered extra-axial, intradural tumors originating from the arachnoid cap cells. Meningiomas typically grow by displacement and only rarely infiltrate the surrounding brain parenchyma. The genetic mutations leading to the development of these brain tumors are the subject of intensive research. Apart from ionizing radiation (e.g., after whole-brain irradiation in children with leukemia) and patients diagnosed with neurofibromatosis type II (NF2), there are no clear risk factors.

Epidemiology

Meningiomas account for about 13–19% of all brain tumors. They represent the largest group of benign intracranial tumors. The peak incidence is between 45 and 50 years of age. Women are more frequently affected than men, with a ratio of 3:2. In 19–24% of cases, cerebral meningiomas in adolescence are associated with NF2. Neuropathology distinguishes between the common WHO grade I (benign), the rarer WHO grade II, and the very rare and clinically malignant anaplastic meningiomas WHO grade III (grades II & III account for about 2–5% of all cases).

Clinical presentation

Small meningiomas are often incidental findings, diagnosed during cranial imaging performed for other reasons (e.g., trauma). Depending on the location, larger tumors may cause symptoms such as first-time epileptic seizures and/or neurological deficits like speech disorders, paralysis, visual disturbances, or personality changes. Headaches are also common, usually as a result of mass effect and possibly associated with brain edema or disturbances in cerebrospinal fluid circulation.

Radiological findings

The diagnostic method of choice is MRI with contrast agent, which typically shows a contrast-enhancing, dura-attached tumor with a characteristic “dural tail” in 70% of cases. Meningiomas usually do not show signs of infiltrative growth into the brain parenchyma. Vascular supply is mainly via the dural attachment points, occasionally also via peritumoral vessels. Normal vessels around the tumor can sometimes be seen as “flow voids.” MRI T2 sequences may show a thin fluid rim (“cleft sign”) around the mass. On native CT, meningiomas are usually hyper- or isodense lesions. Calcifications occur in about 20% of cases (psammoma bodies). The inner cortex of the bone may show erosions or hyperostosis. CT with contrast also shows an enhancing tumor. The larger the meningioma, the more likely peritumoral brain edema is present. Intraventricular meningiomas are located in the trigone of the lateral ventricles in 80% of cases (left > right). Intraventricular meningiomas, as well as tumors of the skull base and anterior fossa, tend to have more calcifications.
Note: Dural metastases, especially from breast carcinoma, can also form a “dural tail.”

Differential diagnoses

• Hemangiopericytoma
• Cerebral metastasis
• Gliosarcoma
• Cerebral lymphoma
• Vestibular schwannoma (if located in the cerebellopontine angle)
• Hemangioblastoma (differential diagnosis to tentorial meningioma)

Special consederations

Localization

About 21% parasagittal, 16% at the convexity, 13% tuberculum sellae (TS-M), 12% sphenoid wing (KBF-M), 10% olfactory meningioma (OF-M), 9% falx, and the rest in the cerebellopontine angle, intraventricular, tentorium, or other locations.

Sphenoid wing meningioma

When large, these (as well as clinoidal meningiomas) are often associated with visual disturbances. Even smaller KBF-meningiomas may warrant early surgical resection. Tumorous encasement of vascular structures (e.g., middle cerebral artery) or cranial nerves (e.g., optic nerve) with involvement of the cavernous sinus can be prevented by early intervention. Complete resection is often not possible in extensive cases.

Tuberculum sellae meningioma

Pre- or postoperative pituitary insufficiency may occur. TS-M usually displaces the optic chiasm supero(laterally), while OF-M displaces it infero(laterally).

Olfactory meningioma

Up to 100% of patients have irreversible anosmia after resection, and there is a high risk of postoperative cerebrospinal fluid fistula at the skull base. Careful intraoperative closure of the skull base is essential. Large olfactory meningiomas often present with Foster Kennedy syndrome (ipsilateral, compression-induced optic atrophy and contralateral papilledema). Mortality and morbidity increase with size >3 cm.

Foramen mangnum meningioma

Clinical findings are often diffuse and difficult to interpret, depending on location.

Tentorial meningioma

Often associated with an enlarged A. Bernasconi & Cassinari—a branch of the cavernous segment of the internal carotid artery. Frequently, a vascular branch supplies petroclival meningiomas.

Radiation

1–2% of all patients with a meningioma may develop another (multiple) meningiomas; in irradiated patients, up to 30%. Radiation (e.g., whole-brain irradiation) is a risk factor for developing meningiomas (5x more frequent than gliomas or sarcomas).

Blood supply of meningiomas

Localization	Main blood supply
Convexity meningioma	Middle meningeal artery
Sphenoid wing meningioma	Middle meningeal artery
Tentorium/cerebellopontine angle	Bernasconi-Casanari artery
Olfactory meningioma	Branches of the ophthalmic artery
Foramen magnum meningioma	Anterior meningeal artery
Posterior fossa/falx cerebelli	Posterior meningeal artery

Indication for surgery

To confirm the diagnosis, surgical resection should be performed in unclear cases. Surgery is also indicated for symptomatic patients or documented tumor growth >1 mm/year. Small meningiomas near the superior sagittal sinus, cavernous sinus, sella, and other vital structures qualify for resection regardless of size due to the risk of progression and involvement of adjacent structures. Up to 30% of parasagittal meningiomas infiltrate the superior sagittal sinus. Literature reports that 30% of all meningiomas grow ~2–3 mm/year, exceeding the 1 mm/year threshold for a wait-and-see approach. Preoperative embolization may be helpful, especially for skull base meningiomas where complete resection is often not possible.

Simpson Classification

The Simpson grade of meningioma resection was described in 1957 and correlated the degree of surgical resection completeness with symptomatic recurrence rate (%).

• Grade I (~9%): Macroscopic, complete tumor resection including involved bone, dura, sinus.
• Grade II (~19%): Macroscopic, complete tumor resection with coagulation of dural attachments.
• Grade III (~29%): Macroscopic, complete tumor resection without coagulation of dura or bone.
• Grade IV (~44%): Partial resection with residual tumor in situ.
• Grade V (~98%): Simple decompression (+/– biopsy).

Outcome

Overall 5-year survival is 91%. Perioperative morbidity is 3.5% for patients <70 years and 23% for those >70 years. The overall recurrence rate after 20 years is 20–50%, depending on the Simpson resection grade. The 5-year recurrence rate after partial resection is between 37 and 85%. Postoperative radiation can reduce recurrence rates but is not indicated for benign meningiomas (WHO grade I). Malignant meningiomas (WHO grades II and III) have a much higher recurrence rate; postoperative radiation is possible. Skull base meningiomas generally have an increased risk of recurrence (about 30% after 5 years, 40% after 10 years).

References

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