Microscopic Description: Multiple sections show sheets of epithelioid cells, many of which are arranged in whorled bundles. An occasional psammoma body is present, but these are not common. There are portions of the tumor which have increased vascularity with thickened vessel walls. The majority of the neoplastic cells have oval to slightly spindle-shaped nuclei with finely dispersed chromatin. An occasional nucleus shows a prominent nucleolus. An occasional cell shows mild nuclear atypia. The mitotic rate is low, approximately 1 per 10/high power fields. No necrosis is identified. Immunostaining with Ki-67 demonstrates approximately 1% positive staining (counted with automated quantitive analysis). EMA staining demonstrates focal positively staining meningothelial cells (membranous). An occasional neoplastic cell contains melanin pigment. No brain invasion is identified (WJH).

Meningioma

CLINICAL FEATURES

• Derived from meningothelial (arachnoidal) cells; typically occur in adults, but children are sometimes affected;

• Location: mostly Intracranial; also involves optic nerve sheath, spinal cord (mainly cervicothoracic segments), rarely lumbosacral

• T2-weighted images: usually isointense (gray) or even hypointense (dark);

GROSS FINDINGS

• Soft, discrete, smooth-surfaced masses broadly attached to the dura;

• Fibrous lesions are firmer, more discrete, even more smooth surfaced, and tougher;

• Lesions of the microcystic subtype are more likely to be macrocystic, and attached to the brain.

• Dense calcification is common, and calcified or ossified lesions may be gritty;

• Lipidized meningiomas are bright yellow, whereas myxomatous tumors are gray and semigelatinous. 

MICROSCOPIC FINDINGS

• Classic and common variant of meningioma;

• Tumor cells form lobules which are surrounded by thin collagenous septae;

• Typically, they are composed of bland syncytial epithelioid cells;

• The nuclei are oval, with distinct nuclear membrane, and fine chromatin. A single nuclear groove is seen sometimes;

• Pseudonuclear inclusions resulting from protrusion of cytoplasm into the nuclei are often present. Nucleoli are indistinct, if present;

• Meningothelial whorl formation;

• Psammoma body is commonly present.

SUBTYPES

• Meningothelial Meningioma:

  • Densely packed cells, arranged in sheets and lobules in variable size, indistinct cell borders in a syncytial appearance;

  • Cytologically, round to oval nuclei, delicate chromatin, small solitary nucleoli;

  • Frequent nuclear-cytoplasmic invaginations (pseudoinclusions), round, circumscribed, and intranuclear areas surrounded by marginated chromatin. They can be found in almost any meningioma variant;

  • Fibrous tissue is typically scant in meningothelial meningiomas;

  • Whorls and psammoma bodies.

• Fibrous (Fibroblastic) Meningioma :

  • Less cellular and consists of sheets of interlacing, fascicular spindle cells in a collagen-rich matrix;

  • Nuclei are hyperchromatic and much more elongated than the meningothelial-type cells;

  • Unlike transitional tumors, whorls, psammoma bodies, and intranuclear pseudoinclusions are infrequent, but calcification of fibrous stroma or the vasculature may be prominent.

• Transitional meningioma

  • Prominent lobules, whorls, psammoma bodies, and collagenized vessels;

  • Syncytial cells are commonly in the the centers of the small lobules, and spindle cells in the periphery.

• Microcystic Meningioma

  • The cobweb microcystic quality of the tumor is the result of elongated cell processes enclosing intercellular fluid-filled spaces and neoplastic cells with xanthomatous change.

  • Often hypocellular, conspicuous loose-textured quality, vascular hyalinization, foamy cells, and scattered large pleomorphic nuclei.

• Secretory Meningioma

  • Hyaline inclusions (pseudopsammoma bodies): eosinophilic, hyaline, often multiple, intracytoplasmic structures. 

  • Distinguished from psammoma bodies that are larger, blue, laminated, basophilic, extracellular and generally originate in the center of the whorls;

  • Periodic acid–Schiff (PAS) positive and diastase resistant.

  • No prognostic significance is attached to secretory meningioma, although these lesions are usually well differentiated and, in principle, may be associated with a better prognosis.

• Clear cell meningioma

  • Grade II meningioma;

  • Generally clear cells throughout with clear PAS positive cytoplasm.

  • Focal and poorly formed whorls, if present. Psammoma bodies are not expected.

  • Bands of connective tissue course through the mass, and some lesions are densely and almost exclusively sclerotic;

  • Often subtentorial (cerebellopontine angle or lumbosacral meninges), and may not be dura based.

• Rhabdoid Meningioma

  • Grade III meningioma;

  • Focally or globally rhabdoid cells, with a rather discrete hyaline or faintly fibrillar cytoplasmic mass;

  • Almost all have an elevated mitotic rate or other prognostically unfavorable features.

• Papillary meningioma

  • Grade III meningioma;

  • Rare, sometimes pediatric. Monotonous neoplastic cells that are meningothelial in appearance;

  • Nuclei generally rounder and more uniform than in the typical meningothelial lesion;

  • Perivascular orientation of tumor cells that mimics the perivascular pseudorosettes in ependymoma. In contrast to those of ependymoma, the cells that approximate the vessel are usually,separated by delicate reticulin fibers in a perivascular stellate pattern.

HISTOLOGICAL GRADING (WHO Grades)

DIFFERENTIAL DIAGNOSES

• Schwannoma: Antoni A and B patterns, long club-shaped nuclei, EMA-;

• Solitary fibrous tumor: brightly eosinophilic bands of collagen, no whorls or psammoma bodies, CD34+, BCL2+, EMA-;

• Hemangiopericytoma: EMA-.

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS

• EMA +

• Vimentin +

• S100 + (50%)

• CK18 +

• CK-AE1/3 +

• CAM5.2 +

• CD20 -

• GFAP -

ELECTRON MICROSCOPIC FINDINGS

• Interdigitating processes

• Desmosomes

• Cytoplasmic intermediate filaments

CYTOGENETIC STUDIES

• Meningiomas are seen in about 50% of NF2, but not associated with NF1;

• Loss of the NF-2 gene (NF2) on chromosome 22q. NF2 encodes a tumor suppressor known as merlin (schwannomin).

• Up to 60% of sporadic meningiomas were found to harbor NF2 mutations.

TREATMENT AND PROGNOSIS

• 10-year recurrence and overall survival rates: Grade I, 70% and 80%; Grade II, 60% and 34%; Grade III, 0% and 0%.

REFERENCES

• AFIP, tumor of the central nervous system, series 4;