Astrocytoma Biopsy

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]

Tumor biopsy findings associated with astrocytoma include microcystic tumor matrix, gemistocytes, rosenthal fibres and hyalinization of blood vessels. High grade tumors are characterized by high cellularity, pleomorphism, nuclear atypia, increased mitotic activity, necrosis and microvascular proliferation.

• If doctors think there may be an astrocytoma, a biopsy may be done to remove a sample of tissue. For tumors in the brain, a part of the skull is removed and a needle is used to remove tissue. Sometimes, the needle is guided by a computer. A pathologist views the tissue under a microscope to look for cancer cells. If cancer cells are found, the doctor may remove as much tumor as safely possible during the same surgery. Because it can be hard to tell the difference between types of brain tumors, you may want to have your child's tissue sample checked by a pathologist who has experience in diagnosing brain tumors.
• The following test may be done on the tissue that was removed:

• Immunohistochemistry : A test that uses antibodies to check for certain antigens in a sample of tissue. The antibody is usually linked to a radioactive substance or a dye that causes the tissue to light up under a microscope. This type of test may be used to tell the difference between different types of cancer. An MIB-1 test is a type of immunohistochemistry that checks tumor tissue for an antigen called MIB-1. This may show how fast a tumor is growing.
• Sometimes tumors form in a place that makes them hard to remove. If removing the tumor may cause severe physical, emotional, or learning problems, a biopsy is done and more treatment is given after the biopsy.
• Children who have NF1 may not need a biopsy or surgery to remove the tumor.

• Diffuse low grade astrocytomas are predominantly composed of a microcystic tumour matrix within which are embedded fibrillary neoplastic astrocytes with mild nuclear atypia and a low cellular density.
• Often microcystic spaces containing mucinous fluid are present, a typical finding in fibrillary astrocytomas, but even more characteristic and pronounced in protoplasmic astrocytomas.
• The occasional occurrence of gemistocytes in a diffuse astrocytoma does not justify the diagnosis of gemistocytic astrocytoma. Gemistocytic astrocytomas tend to progress more rapidly to anaplastic astrocytoma and secondary glioblastoma than fibrillary astrocytoma although they share the WHO grade II.
• Mitoses, microvascular proliferation and necrosis are absent (if present they suggest a high grade tumor). Like all tumors derived from astrocytes, fibrillary astrocytomas stain with glial fibrillary acidic protein (gFAP).

• The key feature present in anaplastic astrocytomas, absent in low grade tumors is mitotic activity and cellular pleomorphism.

• The term pilocytic refers to the the elongated hair-like projections from the neoplastic cells. The presence of eosinophilic Rosenthal fibres is a characteristic feature, and hyalinisation of blood vessels is also common.^[3]

• Features typically found in pilocytic astrocytomas, such as and rosenthal fibres, eosinophilic granular bodies and calcification are uncommon or absent in pilomyxoid astrocytomas^[4][5]. These tumors also lack the biphasic appearance (dense cellular areas alternating with loose cystic areas) usually present in pilomyxoid astrocytomas.

• Histologically, subependymal nodules and subependymal giant cell tumors are indistinguishable, and the distinction lies in the potential of a subependymal giant cell tumor for growth and mass effect.^[7]

• Microscopically the margins are not as well defined. Spindle cells, polygonal cells, multi-nucleated cells and lipid laden xanthomatous astrocytes are identified. Even more pleomorphic is the appearance of the nuclei. Endothelial proliferation is rare.

• Malignancy histologic features such as high cellularity, pleomorphism, nuclear atypia, and increased mitotic activity are usually found in the OA anaplastic. Necrosis and microvascular proliferation may also be present.

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