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Case 14 - Discussion

Surgical Pathology Case

Diagnosis: Meningothelial Meningioma (WHO grade I)

Meningioma

The Key Features

  • Lobules of syncytial epithelioid cells, meningothelial whorls, psammoma bodies

  • EMA +, Vimentin +, CK18 +, S100 + (50%), CD20 -, GFAP -

  • EM: interdigitating processes, desmosomes

  • Loss of the NF2 gene on chromosome 22q

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 septa

  • 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

  • Chordoid Meningioma

    • Grade II meningioma

    • Mostly young adults, 30-40 years of age, female predominance

    • Common location: supratentorial

    • May be associated with systemic inflammatory disorders linked to Castleman’s syndrome in young patients

    • Histology:

      • Cords and nests of medium-sized epithelioid cells with bland cytological features

      • Tumor cells contain mucin-rich chordoid elements

      • Myxoid stroma: pale basophilic mucin with vacuolar appearance

      • Stromal hyalinization may be present

      • PAS and mucicarmine stains were positive in all cases and

    • Differential diagnosis: chordoma, conventional chondrosarcoma and myxoid chondrosarcoma, chordoid glioma, myxopapillary ependymoma, and clear cell meningioma

    • Positive: GFAP, vimentin, EMA, CD34, NSE and CK-7

    • Negative: synaptophysin, S-100 protein, neurofilament, and estrogen and progesterone receptors

  • 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)

  • I, Typical (90%), low risk of recurrence and aggressive growth

    • Meningothelial meningioma, fibrous (fibroblastic) meningioma, transitional (mixed) meningioma, psammomatous meningioma, angiomatous meningioma, microcystic meningioma, secretory meningioma, lymphoplasmacyte-rich meningioma, metaplastic meningioma.

  • II, Atypical (5-7%), increased recurrence and/or aggressive behavior

    • Brain invasion, and/or

    • 4 ≤ Mitoses/HPF<20, and/or

    • Three or more of the following

      • Increased cellularity

      • Small cell change

      • Prominent nucleoli

      • Loss of lobular architecture (Sheeting)

      • Neoplastic necrosis

    • Chordoid or clear cell subtype

  • III, Anaplastic (3-5%), increased recurrence and/or aggressive behavior

    • Overt anaplastic, and/or

    • Mitoses/HPF≥20, and/or

    • Rabdoid or papillary subtype

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