Brain Tumors Classification and Biology of Brain Tumors M.R.Ehsaei M.D Department of Neurosurgery of MUMS

Methods for Tissue Sampling and Study Open Biopsy Needle Biopsy Frozen Section Immunohistochemistry Electron Microscopy Cytology Cytogenetic and Molecular Biological Studies Quantitation of Cell Proliferation

Open Biopsy. For lesions that are favorably situated, open cerebral resection can provide a true total resection of the tumor for which classification and grading are of academic interest.

Needle Biopsy. The size of such specimens ranges from small fragments or only scattered cells when a thin needle is used to more substantial tissue fragments when a large, hollow core needle with a cutting side port is employed.

Frozen Section. Frozen sections of open or needle biopsy specimens provide a means to ensure that adequate material is obtained or to establish a specific histological diagnosis.

Immunohistochemistry. As it has for pathological diagnoses for other organ systems, immunohistochemistry has had a major impact on operative pathology of the nervous system. This technique is employed to recognize antigens on or within neoplastic cells by immunofluorescence or, more commonly, by the immunoperoxidase method, which can be used on paraffin- embedded material.

S-100 is a soluble protein found within the cytoplasm and nuclei of cells of the central and peripheral nervous system. It is expressed strongly in Schwann cells and is useful in establishing this cellular origin for acoustic and spinal schwannomas.

The strong S-100 staining of melanocytes is also helpful in identifying amelanotic metastatic malignant melanomas. Other applications of immunohistochemistry include the characterization of germ cell neoplasms in the pineal region, characterization of the hormones produced by pituitary adenomas, and differentiation in medulloblastomas

Cytogenetic and Molecular Biological Studies. There is increasing interest in the chromosomal abnormalities of human neoplasms because of the possibility that such changes are related etiologically to the neoplasms by means of certain oncogenes and tumor suppressor genes.

Quantitation of Cell Proliferation. The estimate of a neoplasm's proliferative potential is done inferentially by study of the cytological characteristics of the cells or more directly by determination of a mitotic index. A monoclonal antibody, MIB-1, recognizes the same antigen as Ki-67 but retains strong reactivity in paraffin sections (Fig ).

Clinicopathological Entities

FIBROUS DYSPLASIA Fibrous dysplasia is a disorder of unknown etiology that usually is manifested as an enlargement of the bones in and about the orbit. Occasionally, more discrete lesions appear as isolated osteolytic areas in the cranial vault. The natural history of fibrous dysplasia has not been studied in detail; many lesions stabilize in adolescence.

CHORDOMA The chordoma is a destructive neoplasm generally arising at either end of the axial skeleton, in the clivus or the sacrum. Evidence indicates that the lesion originates from notochordal nests, which are frequently observed in the clivus, although it is not clear why these neoplasms are not more common along the thoracic and lumbar spine, where these same nests are frequently encountered in the center of the intervertebral discs. Chordomas in the clivus are often situated somewhat off the midline and can produce unilateral cranial nerve deficits.

LANGERHANS CELL HISTIOCYTOSIS Langerhans cell histiocytosis is a uni- or multifocal disorder of bone or soft tissue, or both, that most often comes to neurosurgical attention as a lytic lesion of the skull. The common solitary lesion of the skull is known as an eosinophilic granuloma, and the multiple lesions of the skull that are often associated with diabetes insipidus are part of the Hand-Schüller-Christian syndrome (Fig ). Extensive involvement of soft tissue characterizes the historical but ill-defined entity of Letterer- Siwe disease.

The common solitary lesion of bone is a benign condition responding to radiation therapy. The multifocal lesions of the base of the skull are in many cases also cured by irradiation, although they may be associated with variable morbidity.

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Histologically, the lesions are distinctive because of the mixture of histiocytes (Langerhans cells), lymphocytes, and eosinophils (Fig ). In some cases, the histiocytes are engorged with fat, and the lesions are macroscopically yellow. The Langerhans cells have markedly convoluted nuclei and, by electron microscopy, contain the distinctive Birbeck granule diagnostic of this cell type (Fig ).

CRANIOPHARYNGIOMA The craniopharyngioma is a radiographically discrete, calcified, often cystic neoplasm that is seen most frequently in childhood. A noncalcified lesion with a slightly different histological pattern is usually seen in adults

Microscopically, cells anastomose in ribbons to produce the adamantinomatous pattern (Fig ). Keratinized nodules, seen as white flecks with the naked eye or operating microscope, are also typical. During resection, pieces of the floor of the third ventricle can be avulsed, and microscopic study often reveals infiltration of the neoplastic cells. It is not surprising that total excision is difficult and that late recurrences can occur. The recurrent lesion is more widely adherent to local structures and is difficult or impossible to remove.

The histological pattern of the craniopharyngioma seen most frequently in adults has been termed a "papillary craniopharyngioma" or "suprasellar squamous papillary epithelioma" (Fig )

MENINGIOMA