- - anaplastic a. intermediate grade a. characterized by increased cellularity, nuclear pleomorphism, mitoses, and variable vascular endothelial proliferation.- cerebellar a. a variant of a. located in the cerebellum occurring mostly in children, consists of two architectural patterns on microscopy including a loose reticular pattern and a more compact often spindled cell pattern. SYN: juvenile cerebellar a..- desmoplastic cerebral a. a rare variant of a. most frequently occurring in infancy, the tumor has a spindled cell appearance.- fibrillary a. a. derived from fibrillary astrocytes.- gemistocytic a. an a. composed primarily of gemistocytic-type astrocytes. SYN: gemistocytoma.- grade I a. solid or cystic a. of low grade; World Health Organization (WHO) designation including pilocytic a. and other low-grade a. variants.- grade II a. a. of low grade; World Health Organization (WHO) designation including well-differentiated fibrillary a..- grade III a. a. of intermediate grade; World Health Organization (WHO) designation. SEE ALSO: anaplastic a..- grade IV a. a. of high grade; World Health Organization (WHO) designation. SEE ALSO: glioblastoma multiforme.- low grade a. a. characterized by an increased cellularity of uneven distribution and mild nuclear pleomorphism.- pilocytic a. a slowly growing a. composed histologically of elongated astrocytes; often located in the optic chiasm region of the third ventricle, hypothalamus, or cerebellum, predominantly in younger individuals. SYN: piloid a..- piloid a. SYN: pilocytic a..- protoplasmic a. a neoplasm composed primarily of protoplasmic-type astrocytes.- subependymal giant cell a. a rare a., frequently located in the wall of the lateral ventricle, comprised of large glial cells with abundant eosinophilic cytoplasm and intermixed elongated astrocytes, associated with tuberous sclerosis.
* * *as·tro·cy·to·ma .as-trə-sī-'tō-mə n, pl -mas also -ma·ta -mət-ə a nerve-tissue tumor composed of astrocytes
* * *n.a brain tumour derived from non-nervous cells (glia), which - unlike the neurones - retain the ability to reproduce themselves by mitosis. All grades of malignancy occur, from slow-growing tumours whose histological structure resembles normal glial cells, to rapidly growing highly invasive tumours whose cell structure is poorly differentiated (see glioblastoma). In adults astrocytomas are usually found in the cerebral hemispheres but in children they also occur in the cerebellum.
* * *as·tro·cy·to·ma (as″tro-si-toґmə) a tumor composed of astrocytes; it is the most common type of primary brain tumor and is also found throughout the central nervous system. One classification groups astrocytomas according to their histologic appearance and distinguishes pilocytic, protoplasmic, gemistocytic, and fibrillary types. Another classification groups them in order of increasing malignancy as Grade I, Grade II, Grade III, and Grade IV types. Called also astrocytic glioma.
Medical dictionary. 2011.