Meningiomas

Overview

Meningiomas are the most common primary brain tumors in adults and comprise a group of mostly benign, slow-growing solid neoplasms that likely originated from meningothelial or arachnoid cells of the arachnoid layer that cover the brain and spinal cord. Meningiomas are dural based in location and can occur anywhere in the central nervous system (CNS). At least 15 different subtypes of meningiomas based on histology have been defined, some with unique molecular genetic features. Malignant meningioma, a rare variant, can metastasize outside of CNS, especially to the lung or liver.

	Age range (Yr) (mean)	Female: Male	Cell of origin	WHO Grade	Molecular/genetic markers	Prognosis
Typical (Nine subtypes)	45-85 (65)	3:1	Meningothelial or arachnoid cap cells of arachnoid layer	I	Monosomy 22	Favorable; low risk of recurrence
Atypical (Three subtypes)	35-44	1:2		II	NF2	Less favorable; moderate risk of recurrence
Malignant (Three subtypes)	35-44	1:2		III	NF2	Poor; high risk of recurrence

Typical Meningiomas (WHO Grade I)

Definition: Mostly benign, slow-growing solid tumors arising from the arachnoid membranous layer of the meninges, which surrounds the brain and spinal cord.

Epidemiology: Most common primary brain tumor in adults, accounting for 36% of all brain tumors but comprise less than 3% of pediatric brain tumors. The vast majority occur as a solitary tumor (>90%) but can be multiple in the setting of prior radiation exposure or underlying syndrome such as neurofibromatosis type 2. Up to 70% of all meningiomas are benign, WHO grade I tumors, with grade II and grade III tumors accounting for 20%-25% and 1%-6%, respectively. Grades II and III tumors occur more frequently in men. Median age at diagnosis is 65 years, with higher incidence in women than in men with approximate ratio of 2.2:1. The incidence of meningioma is even higher in premenopausal women aged 35-44 years, where the ratio of women to men is 3.15:1. 2016 WHO central nervous system (CNS) Classification defines 15 different variants of meningioma based on histologic features:

Regardless of histologic features, meningiomas can be classified into at least 15 subtypes based on the anatomic location of tumor:

Cavernous sinus, suprasellar/tuberculum sellae, cerebellopontine angle, cerebral convexity, intraorbital, intraventricular, olfactory groove, parasagittal, falcine, tentorium, petrous ridge/face, posterior fossa, sphenoid, foramen magnum and spinal.

Affected age group: Although meningioma is the most common primary brain tumor in adults, it occurs very rarely in children with predilection for clear cell and rhabdoid subtypes.

Molecular and genetic profile: There are at least 15 different histologic subtypes of meningiomas (Table 2.1). Several molecular and genetic abnormalities have been detected (Table 2.1), with characteristic differences between WHO grade I and WHO grade II/III tumors: monosomy 22, deletion of 1p, losses of chromosomes 6q, 9p, 10, 14q, and 18q, NF2 gene → truncated and presumably nonfunctional merlin protein (a.k.a. schwannomin).

Cerebrospinal Fluid (CSF) markers: None

Clinical features and standard therapy: Symptoms of meningioma depend mainly on size, location, and growth rate of tumor. Meningiomas are usually slow growing, benign, and clinically indolent. For grade I meningiomas, gross total resection of tumor leads to cure although recurrence can be seen in rare cases. For grade II and III meningiomas, gross total resection does not necessarily ensure cure because they can recur both at the site of original tumor or at a distant site.

To minimize local recurrence, adjuvant radiation therapy is often used, especially when there is any residual tumor, but it does not prevent distant recurrence.

TABLE 2.1 Histologic Subtypes of Meningiomas

	WHO Grade	Histologic hallmark	Molecular alteration	Anatomic location	Imaging hallmark
Meningothelial	I	Medium-sized epithelioid tumor cells, abundant eosinophilic cytoplasm; Epithelioid, largely uniform cells with oval nuclei forming lobules demarcated by collagenous septa	Monosomy 22	Parasagittal	Most common subtype; classic imaging features-homogeneously enhancing dural based mass with isointense T1 and T2 signal
Fibrous or fibroblastic	I	Spindle cells with intercellular collagen	NF2 EMA	Convexity	Dark on T2
Transitional	I	Meningothelial, fibrous and transitional patterns; whorls and psammoma bodies; Lobular and fascicular foci of cells with conspicuous tight whorls and psammoma bodies	NF2	Parasagittal	Partially calcified
Psammomatous	I	Psammoma bodies, calcified masses; Confluent psammoma bodies replacing tumor cells and forming irregular calcified masses and bone	–	Thoracic spine	Heavily calcified mass
Angiomatous	I	Numerous blood vessels in greater proportion than tumor mass	Aneuploid, polysomies chromo-somes 5,13,20	Convexity	Marked tumor hypervascularity; prominent peritumoral edema
Microcystic	I	Spider-like cells with long thin processes; Cells with thin, elongated processes encompassing microcysts and creating a cobweb-like background	–	Convexity	Hyperintense on T2 & hypointense on T1; prominent peritumoral edema; micro- and macrocystic changes
Secretory	I	Pseudo-psammoma bodies with acid-Schiff-positive eosinophilic secretions and immunoreactivity for carcinoembryonic antigen and cytokeratin	KLF4 K409Q, TRAF7 mutations	Skull base	Prominent peritumoral edema
Lymphoplasmacyte-rich	I	Dense infiltrates of lymphocytes & plasma cells; Chronic inflammatory infiltrates	–	Convexity, skull base, parasagittal, spine	Markedly reduced on diffusion due to high cellularity
Metaplastic	I	Focal or widespread mesenchymal components- cartilaginous/chondroid, osseous, lipomatous, xanthomatous, myxoid patterns	–	Convexity	Scattered areas if calcium and fat within the tumor
Chordoid	II	Physaliferous-like cells resembling chordoma; Cords or trabeculae of eosinophilic, vacuolated cells set in an abundant mucoid matrix	–	–	High on T2
Clear cell	II	Polygonal cells with clear cytoplasm; prominent interstitial & perivascular hyalinization; pattern-less or sheeting architecture, glycogen-rich cytoplasm and prominent perivascular and interstitial collagen	Switch/Sucrose non-fermentable (SWI/SNF) Related, Matrix Associated, Actin Dependent Regulator of Chromatin, Subfamily E, Member 1 mutations	Spine, posterior fossa	High on T2 with exuberant cystic architecture
Atypical	II	Meningothelial cells invading into brain parenchyma; Increased mitotic activity, brain invasion with increased cellularity, small cells with a high nuclear-to-cytoplasmic ratio, prominent nucleoli, sheeting and foci of necrosis	Loss: 1p, 6q, 10, 14q, 18q Gain: 1q, 9q, 12q, 15q, 17q, 20q	–	Irregular border with neighboring brain
Papillary	III	Epithelioid tumor cells in a papillary or pseudopapillary pattern	–	Intraventricular, tuberculum sellae	Lobular contour; lack of dural tail
Rhabdoid	III	Rhabdoid cells with eccentric vesicular nuclei & prominent eosinophilic paranuclear inclusions	SMARCB1 retained	–	Reduced on diffusion; marked peritumoral edema; irregular border with neighboring brain
Anaplastic (malignant)	III	Cellular anaplasia and excessive mitoses	LOSS: 22q, 1p, 6q, 10, 14q, 18q, 9p; NF2 & TERT mutations	–	Reduced on diffusion; irregular border with neighboring brain; metastases to lung or liver

Imaging

Meningiomas are circumscribed, dural-based masses that have similar density or signal to brain parenchyma on CT or MRI, respectively, and enhance avidly following the administration of intravenous contrast, both iodine-based and gadolinium-based intravenous contrast agents. Meningiomas often show “dural tail” enhancement, which is contiguous with the primary mass but extends farther into the adjacent dura. Most meningiomas are solid masses, but some can contain prominent cystic components. The imaging appearance of meningiomas can vary widely depending on the histologic subtypes and presence and degree of intratumoral calcium. Prominent intratumoral hemorrhage is rare in meningioma. Meningiomas can be cellular and show homogeneous reduced diffusion on diffusion-weighted imaging, and some are hypervascular, showing markedly increased vascularity on perfusion MRI.

Figure 2.1. Imaging of meningothelial meningioma. A. Axial T2: hypointense mass. B. Axial T1-precontrast: hypointense mass. C. Axial T1-postcontrast: avid and homogeneous enhancement. D. Coronal T1-postcontrast: avid and homogeneous enhancement.

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