Astrocytoma Workup

Updated: Dec 07, 2017
  • Author: Benjamin Kennedy, MD; Chief Editor: Herbert H Engelhard, III, MD, PhD, FACS  more...
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Workup

Laboratory Studies

No laboratory studies are diagnostic of astrocytoma. Baseline laboratory studies that may be obtained for general metabolic surveillance and preoperative assessment include the following:

  • Basic metabolic profile
  • Complete blood cell count (CBC)
  • Prothrombin time (PT)
  • Activated partial thromboplastin time (aPTT)
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Imaging Studies

Computed tomography (CT) and magnetic resonance imaging (MRI), with and without contrast, are helpful in the diagnosis, grading, and pathophysiological evaluation of astrocytomas. MRI is considered the criterion standard, but a CT scan may be useful in the acute setting or when MRI is contraindicated.

On a CT scan, low-grade astrocytomas appear as poorly defined, homogeneous, low-density masses without contrast enhancement (see the image below). However, slight enhancement, calcification, and cystic changes may be evident early in the course of the disease.

Axial CT scan, precontrast and postcontrast, shows Axial CT scan, precontrast and postcontrast, shows a low-grade astrocytoma of the left frontal lobe. The tumor is nonenhancing.

In cases where a cortically based enhancing mass is discovered, particularly in cases where multiple lesions are identified, the possibility of metastatic disease must be considered. Systemic imaging, generally consisting of a contrast-enhanced CT scan of the chest, abdomen, and pelvis, may be warranted to evaluate for the possibility of an alternate primary lesion.

Like low-grade astrocytomas, anaplastic astrocytomas may appear as low-density lesions or inhomogeneous lesions, with areas of both high and low density within the same lesion. Unlike low-grade lesions, partial contrast enhancement is common. [19, 20]

Astrocytomas are generally isointense on T1-weighted images and hyperintense on T2-weighted images. (See the images below.) While low-grade astrocytomas uncommonly enhance on MRI, most anaplastic astrocytomas enhance with paramagnetic contrast agents. New methods are being developed to assess tumor vascularity by MRI, including techniques such as arterial-spin labeling (ASL) and dynamic contrast-enhanced MRI.

Coronal postcontrast T1-weighted MRI shows a low-g Coronal postcontrast T1-weighted MRI shows a low-grade astrocytoma in the right inferior frontal lobe just above the sylvian fissure. No enhancement is present post–gadolinium administration.
Axial T2-weighted MRI shows a low-grade astrocytom Axial T2-weighted MRI shows a low-grade astrocytoma of the inferior frontal lobe with mild mass effect and no surrounding edema.

Angiography may be used to rule out vascular malformations and to evaluate tumor blood supply. A normal angiographic pattern or a pattern consistent with an avascular mass that displaces normal vessels is usually observed with both low-grade and high-grade lesions. In rare instances, a tumor blush may be observed with high-grade lesions.

Imaging has also taken on a larger role in the operating room, as many procedures are now performed with intraoperative image guidance based on high-resolution MRIs. In addition, intraoperative MRI and CT scans are being tested for utility in guiding the extent of resection and presence of residual tumor during the surgical procedure.

The boundaries of infiltrating tumors extend far beyond what can be seen by imaging studies. New methods of tumor imaging are being developed to specifically tag or label tumor cells so they may be visualized in the operating room. Such methods include pretreatment of the patient with dyes or tumor-specific proteins tagged with fluorescent molecules.

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Other Tests

The following studies may be indicated in patients with astrocytoma:

  • Electroencephalography (EEG) may be employed to evaluate and monitor epileptiform activity in patients with seizures associated with astrocytoma
  • Radionuclide scans, such as positron emission tomography (PET), single-photon emission tomography (SPECT), and technetium-based imaging, can permit study of tumor metabolism and brain function; PET and SPECT may be used to distinguish a solid tumor from edema, to differentiate tumor recurrence from radiation necrosis, and to localize structures
  • Metabolic activity determined by radionuclide scans can be used to determine the grade of a lesion; hypermetabolic lesions often correspond to higher-grade tumors
  • An electrocardiogram (ECG) and chest radiograph are indicated to evaluate operative risk
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Procedures

Although cerebrospinal fluid analysis is not part of the diagnosis of astrocytoma, it may help in ruling out other possible diagnoses, such as metastasis, lymphoma, or medulloblastoma. However, lumbar puncture (LP) should be approached with extreme caution in patients with cerebral astrocytomas, because of the risk of downward cerebral herniation secondary to elevated intracranial pressure.

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Histologic Findings

Four histological variants of low-grade astrocytomas are recognized: protoplasmic, gemistocytic, fibrillary, and mixed. [21]

Gemistocytic astrocytomas are generally found in the cerebral hemispheres in adults and are composed of large round cells with eosinophilic cytoplasm and eccentric cytoplasm. Gemistocytic astrocytomas constitute 5-10% of hemispheric gliomas.

Diffuse astrocytomas, the most common histological variant, resemble cells from the cerebral white matter and are composed of small, oval, well-differentiated cells. The tumors are identified by a mild increase in cellularity and fibrillary background. Markers for glial fibrillary acidic protein (GFAP) are used to identify fibrillary astrocytomas.

Compared with low-grade lesions, anaplastic astrocytomas show a marked tendency for regional or diffuse hypercellularity. Furthermore, anaplastic astrocytomas show increased anaplasia, demonstrated by increased nuclear complexity, the presence of mitoses, increased cytoplasmic variability, and increased endothelial cell proliferation.

See the images below.

Low-grade diffuse astrocytoma and low cellularity Low-grade diffuse astrocytoma and low cellularity with minimal nuclear atypia.
Diffuse astrocytoma with microcyst formation. Diffuse astrocytoma with microcyst formation.
Gemistocytic astrocytoma tumor cells have eosinoph Gemistocytic astrocytoma tumor cells have eosinophilic cytoplasm with nuclei displaced to the periphery.
Characteristic pilocytic astrocytoma, long bipolar Characteristic pilocytic astrocytoma, long bipolar tumor cells, and Rosenthal fibers.
Anaplastic astrocytoma with high cellularity with Anaplastic astrocytoma with high cellularity with marked nuclear atypia.
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Staging

Staging is not performed or described for patients with astrocytoma. The histologic grade of the tumor is of primary importance when determining prognosis. Unlike other systemic tumors, distant or extracranial metastasis of astrocytomas is exceedingly rare. Clinical decline and tumor-associated morbidity and mortality are almost always associated with local mass effects on the brain by a locally recurrent intracranial tumor.

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