Tumors of Nervous System and Meninges – Pathoanatomy

Depending on the localization the tumors are distinguished into the tumors of the central nervous system – Neuroectodermal tumors, the tumors of peripheral nervous system, meninges and ganglias are ependymal tumors, choroid epithelial, neuronal, meningovascular poorly differentiated and embryonic tumors.

Features of tumors of the nervous system. All tumors of the central nerv ous system are clinically malignant due to the lesions of the vital centers. The designation of a tumor is formed from its name of the derived cells (tissues) by adding the word “cytoma” in benign tumors and “blastoma” in malignant tu mors.

For example, astrocytoma (glioma) and astroblastoma, ganglioneuroma (gangliocytoma) and ganglioneuroblastoma (neuroblastoma), and depending on the function of the derivative of the tissue they may be called differently, for ex ample meningioma (arachnoidendothelioma) and anaplastic (malignant) menin gioma.

Macroscopic tumor sizes may be the size of a pea to a considerable size of 5-10 cm; even benign tumors do not have clear boundaries. Cut benign tumors are uniform; sometimes cysts can occur; there may be foci of necrosis and hem orrhage.

Malignant tumors metastasize through invasion into the surrounding brain tissue or neurocanal, i.e. within the osteocranum, in the cerebrospinal fluid pathways, but later hematogenous metastases may be. For malignant tumors of the central nervous system the development of secondary changes as the foci of necrosis, hemorrhage, angiomatosis, cyst are characteristic, that is why macro scopically they have mottled appearance, soft texture, indistinct borders, charac teristic infiltrative growth. Malignant tumors are characterized by marked cellular atypism, polymorphism, and rapid growth. Macroscopic and microscopic changes are determined by the localization of the process in the nervous system parts, clinical features, and the presence of secondary changes in the tumor tissue. Secondary changes in the tumor tissue may be in the form of vascular proliferation, hemorrhage, foci of necrosis, for mation of cysts, inflammation, dystrophic changes of neurocytes, foci of petrifi cation, hemosiderosis and other changes.

Neuroectodermal tumors of the central nervous system. Benign neuroectodermal tumors are astrocytoma (glioma), oligodendroglioma. Astrocytoma is a macroglial benign tumor from astrocytes. There are the following histological forms of astrocytomas: fibrillary, protoplasmatic, mast cell (giant cell) astrocytoma, and mixed. Macroscopically the formation of intracerebral foci differing in density and pallor is possible; or they may have soft consistency, gray-pink colour, gelati nous surface of the cut; the formation of cysts is possible. In cystic astrocytoma they are characterized by the formation of a large cavity to diameter which compressing the cerebellum tissue leads to its atrophy (Fig. 132).

Figure 132. Cystic astrocytoma, presented with cavitary lesion, the tissue of the cerebellum is atrophied around it.

Macroscopic impression in anaplastic astrocytoma (Fig. 133) is characterized that the margins of the tumor is indistinct with the foci of multiple diapedet ic and confluent hemorrhages and hemosiderosis.

Figure 133. Anaplastic astrocytoma, the margins of the tumor is indistinct with the foci of hemorrhage and hemosiderosis

Microscopic changes in neuroectodermal tumors are defined with histological form of astrocytoma.

Fibrilar astrotsytomas consist of stellate or elongated cells that are rich in glial fibers arranged in bundles and astrocytes, blood vessels are sanguine; there are foci of perivascular hemorrhage; the formation cysts is marked (Fig. 134a, 134b, 135a).

Figure 134a. Neuroectodermal tumor: the fibrillar astrocytoma, rich in glial fibers in the form of bundles and astrocytes. Stained with hematoxylin and eosin. 200-fold

Figure 134b. Neuroectodermal tumor: the astroblastoma, cellular polymorphism, large cells, atypical cells. Stained with hematoxylin and eosin. 400-fold

Figure 135a. Neuroectodermal tumor: the fibrillar astrocytoma, the foci of hemorrhage, cyst formation. Stained with hematoxylin and eosin. 200-fold

Protoplasmatic astrocytoma consists of small cells with eosinophil cyto plasm and numerous dendrites. Mast cell (giant cell) astrocytoma is represented by large homogeneous multidendritic cells.

Other types of astrocytic tumors are a pilocytic astrocytoma (spongioblas toma) which contains parallel and interlacing bundles of bipolar cells giving the impression of hair strands, the formation of cysts occurs often; subependymal giant-cell astrocytoma (SEGA) is in the form of small scleroid nodules (tuber ous sclerosis) in the wall of the lateral ventricles with polymorphism of cells, in cluding large, giant cells, spindle or pyramidal cells, the formation of perivascular pseudorosette is characteristic. Astroblastoma is a rare tumor of the cerebral hemispheres in young people. Microscopically cellular polymorphism is characteristic in malignant variant of Malignant neuroectodermal tumors include astroblastoma (malignant as trocytoma) and malignant oligodendroglioma.

the tumor; tumor cells with one long and several short dendrites directed to the vessels form pseudorosettes. Atypical cells are arranged chaotically, they are various sizes and shapes with nuclei and nucleoli (Fig. 135b).

Figure 135b. Neuroectodermal tumor: the bundles of glial fibers, the groups of cells such as astrocytes, edema of the tissue. Stained with hematoxylin and eosin. 400-fold

Poorly-differentiated and embryonic tumors Glioblastoma multiforme (glioblastoma, multiform spongioblastoma, and astrotcytoma of grade III and IV) is a high grade tumor, often of astrocytic and rarely of oligodendroglial or ependymal origin.

Grossly mottled appearance of the tumor is characteristic; the combination of yellow and gray areas of necrosis is in the center; gray and red vitalized tis sue at the periphery; brown and red foci of old and fresh hemorrhages. Microscopically a tumor is presented chaotically arranged polymorph atypical cells with an abundance of pathologic mitosis, necrosis, the formation of perivascular rosettes, vascular proliferation with the formation of choroid glomi (Fig. 136).

Medulloblastoma is a high grade tumor, usually occurs in children. It is localized in the cerebellum, in the lateral inversion of the IV ventricle, in the cerebellar hemispheres. Macroscopically it looks gray-pink with very soft consistency, semiliquid and semitransparent mass.

Microscopically the abundance of small cells with a poor cytoplasm with a round or oval nucleus is observed, multiple mitosis is identified; pseudoro settes and structures in the form of a column in a combination of series of dark nuclei and light bands of cytoplasm may occur.

Histological forms of medulloblastoma: a) a desmoplastic medulloblasto ma is characterized by the developed reticular and collagenous stroma; b) a medullamioblastoma is an extremely rare high-grade tumor which occurs in striated muscle cells, and this tumor relates to a teratoma. Meningovascular tumors are tumors which develop from the meninx vasculosa and related tissues.

Meningioma is a benign meningovascular tumor which develops from the cells of the meninx vasculosa. Histological forms of meningiomas are a fibrous (fibroblastic) meningioma is formed from the cells bundles and connective fi bers (Fig. 137a); an arachnoidendothelioma is from covering cells of the arach noid membrane (Fig. 137b); a menigotheliomatous meningioma is from endo thelial cells, concentric structures of “corpora psammosa” may form; transi tional (mixed) meningioma; psammous meningiomas. In the presence of the vascular component in the tumor tissue the following forms of meningiomas are distinguished: angiomatous, hemangioblastic, hemangiopericytoma and papil lary meningiomas.

Malignant meningovascular tumors have the following histological forms: anaplastic (malignant), meningeal sarcoma, fibrosarcoma, polymorphcellular sarcomatous tumor, diffuse sarcomatosis of meninges. Tumors of the peripheral nervous system occur from the nerve sheath. Benign tumors of the peripheral nervous system include neurilemmomas (schwannomas); neurofibromas, neurofibromatosis or “Recklinghausen dis ease”. Malignant tumors of the peripheral nervous system are malignant schwannomas, or neurogenic sarcoma.

Macroscopically they are in the form of single or multiple dense nodular formations. Microscopically neurilemmoma (schwannoma) is characterized by the formation of spindle with cells rod-shaped nuclei. The cells and fibers form bundles or “palisade” structures, alternating parallel nuclei “Verocay bodies”

(Fig. 138a, 138b).

Neurofibromatosis or “Recklinghausen disease” is a systemic disease with the development of multiple neurofibromas.