Low-Grade Astrocytoma Workup

Updated: Oct 27, 2014
  • Author: George I Jallo, MD; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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Workup

Laboratory Studies

No specific laboratory test is available for the diagnosis or follow-up of low-grade gliomas. There are promising studies which aim to detect circulating tumor DNA in human malignancies. Although this technology hasn't been applied to low-grade gliomas it could potentially be implemented in the future as a screening, diagnostic or follow-up tool. [8]

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Imaging Studies

Both CT scan and MRI can aid in the diagnosis of low-grade glioma. Generally, MRI is considered the study of choice. However, in an emergency setting a noncontrast CT scan may be ordered first.

Computed tomography

Patients with new-onset headache, seizure, weakness, or numbness frequently undergo a CT scan first. Typical CT findings of a low-grade glioma show lower attenuation than the surrounding brain (see image below). A mild mass effect may be noted. Obstructive hydrocephalus can be confirmed. Low-grade gliomas also may show evidence of calcification (more common in oligodendroglial tumors). Low-grade astrocytomas are usually non-enhancing lesions, although the presence of contrast enhancement doesn´t preclude their diagnosis.

PET and SPECT

Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging sometimes are used to try to differentiate low-grade gliomas from either high-grade tumors or other types of pathology. Typically, low-grade gliomas show hypometabolism via PET or SPECT while high-grade gliomas are hypermetabolic. This information may be useful in guiding further therapy.

A 28-year-old male taxi driver presented to the em A 28-year-old male taxi driver presented to the emergency department after having a seizure. Noncontrast head CT scan was obtained showing the typical appearance of a low-grade astrocytoma. The lesion in the mesial left frontal lobe was hypodense on CT scan.

Magnetic resonance imaging

On MRI, low-grade astrocytomas show decreased signal relative to surrounding brain on T1 sequences (see following images).

Preoperative MRI of the brain of a 28-year-old mal Preoperative MRI of the brain of a 28-year-old male taxi driver who presented to the emergency department after having a seizure. On T1-weighted sequences, the tumor does not enhance and shows decreased signal intensity compared to normal brain. These findings are consistent with low-grade astrocytoma.
For tumors, MRI has the advantage of showing the l For tumors, MRI has the advantage of showing the lesion in multiple planes. This image, a T1-weighted sagittal image of the brain of a 28-year-old male taxi driver who presented to the emergency department after having a seizure, shows the tumor along the mesial aspect of the frontal lobe. Note that mass effect is minimal, typical of a low-grade lesion.
Coronal T1-weighted gadolinium-enhanced MRI of the Coronal T1-weighted gadolinium-enhanced MRI of the brain shows the tumor of a 9-year-old boy who presented with headaches and gradual onset of a right hemiparesis. Note the heterogeneous enhancement of the tumor.
Sagittal T1-weighted MRI of the brain shows juveni Sagittal T1-weighted MRI of the brain shows juvenile pilocytic astrocytoma of a 9-year-old boy who presented with headaches and gradual onset of right hemiparesis. Stereotactic surgery has made resection of these low-grade tumors in this deep location feasible.
A 3-year-old boy presented with speech regression. A 3-year-old boy presented with speech regression. MRI of the brain revealed a tumor in the left mesial temporal lobe. This T1-weighted gadolinium-enhanced image shows an enhancing tumor involving the hippocampus, uncus, and amygdala. The surgical pathologic studies revealed a low-grade mixed tumor of astrocytes and atypical neurons, a ganglioglioma.

On T2 sequences, higher signal reflects both the tumor and surrounding edema (see following images). Pilocytic astrocytomas often are associated with a cyst, which may be particularly prominent on T2-weighted sequences.

T2-weighted sequences of an MRI of the brain of a T2-weighted sequences of an MRI of the brain of a 28-year-old male taxi driver who presented to the emergency department after having a seizure show increased signal intensity compared with normal brain. The radiologic appearance is typical of low-grade astrocytoma.
A 9-year-old boy presented with headaches and grad A 9-year-old boy presented with headaches and gradual onset of right hemiparesis. MRI of the brain was obtained. The T2-weighted sequence in this MRI shows a tumor in the left thalamus, which is a typical location for a juvenile pilocytic astrocytoma. Note the relatively well-circumscribed nature of the lesion.

MRI of the spinal cord is also the study of choice if an intramedullary low-grade astrocytoma is suspected. On MRI, widening of the spinal cord and frequently an associated cyst are noted. The tumor may show a variable degree of enhancement.

Functional magnetic resonance imaging (fMRI) can provide information about the relationship and localization of a low-grade glioma and eloquent structures such as speech centers and motor pathways. This may help in planning the operation. Recently, the use of digital tractography has allowed to pre-operatively assess the relationship of tumors to important white matter tracts (e.g. descending corticospinal tract) prior to resection.

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Other Tests

Electroencephalography (EEG) may be performed on a patient with new-onset seizures; however, no EEG findings are specific to low-grade glioma. However, generalized, diffuse slowing and/or epileptogenic spikes can be seen over the area of the tumor.

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Procedures

Lumbar puncture is generally contraindicated in patients with elevated intracranial pressure, which may occur in the setting of a brain tumor. Cerebrospinal fluid (CSF) studies do not aid in the diagnosis of low-grade astrocytomas.

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Histologic Findings

The histologic findings in low-grade astrocytomas vary according to the specific tumor type. As reviewed before, the absence of high-grade lesion characteristics like necrosis, microvascular proliferation and high mitotic indices are common to the group as a whole.

Pilocytic astrocytomas show the presence of bipolar piloid cells with long hair-like processes and Rosenthal fibers. Pilomyxoid astrocytomas are dominated by the presence of a mucoid matrix, monomorphous bipolar cells and an angiocentric cell arrangement. Pleomorphic xanthoastrocytomas have a variable histological appearance, hence the name. The term xanthoastrocytoma is derived from the presence of xanthomatous cells which show intracellular accumulation of lipids. Diffuse astrocytomas are composed of well differentiated fibrillary or gemistocytic neoplastic astrocytes on the background of a loosely structured microcystic tumour matrix. [1]

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Staging

There are currently no valid staging systems in clinical use.

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