Oligodendroglioma Workup

Updated: Jan 02, 2015
  • Author: ABM Salah Uddin, MD; Chief Editor: Stephen A Berman, MD, PhD, MBA  more...
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Workup

Laboratory Studies

Routine laboratory workup is not helpful. If seizures are noted, include EEG, serum electrolyte studies, and if necessary a lumbar puncture in the metabolic workup for seizure, after excluding intracranial pathology with an imaging study. These routine tests help exclude other causes of seizure (eg, electrolyte imbalance, metabolic abnormalities).

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Imaging Studies

Diagnostic imaging studies are the most important part of the workup.

  • MRI (with and without gadolinium) is the preferred modality.
    • T1 images generally demonstrate a hypointense or mixed hypointense and hyperintense mass.
    • T2 images reveal a hyperintense mass with or without surrounding edema.
    • With contrast administration, the LGO generally does not enhance, while an anaplastic oligodendroglioma does enhance. These tumors also tend toward calcification. See the image below.
      Sagittal gadolinium-enhanced T1-weighted magnetic Sagittal gadolinium-enhanced T1-weighted magnetic resonance image of a low-grade oligodendroglioma. This image demonstrates no contrast enhancement.
  • A study by Megyesi et al compared the MRI characteristics of oligodendroglioma with 1p/19q loss with those without 1p/19q loss. Tumors with 1p/19q loss were significantly more likely to have indistinct borders, a mixed signal intensity on T1- and T2-weighted images, paramagnetic susceptibility effects, and intratumoral calcification compared with oligodendroglioma without 1p/19q loss, which more often had a distinct border and a uniform signal on T1- and T2-weighted images. [4]
  • A study by Brown et al, using noninvasive quantitative MRI with and without contrast, reliably predicted the co-deletion of chromosomes 1p and 19q with high sensitivity and specificity in suspected low-grade glioma. [5]
  • CT scans reveal a hypodense, reasonably well-demarcated mass with moderate surrounding edema.
    • Intratumoral calcification is common, and hemorrhage is noted occasionally.
    • As with contrast MRI, the tumor does not enhance unless it is behaving unusually aggressively or has an anaplastic astrocytic component. See the images below.
      Contrast-enhanced computed tomography scan in a 44 Contrast-enhanced computed tomography scan in a 44-year-old man with a 3-year history of epileptic seizures. This image reveals a calcified hypoattenuating lesion that is invading the corpus callosum.
      Computed tomography scan of a low-grade oligodendr Computed tomography scan of a low-grade oligodendroglioma. This image reveals a well-demarcated, left frontal hypoattenuating lesion with a small calcification.
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Other Tests

Definite diagnosis in confirmed by stereotactic or open biopsy of the lesion. Currently, MR spectroscopy is performed regularly in some centers to differentiate the tumor from other benign lesions and to define the aggressiveness of the tumor, although this is in the investigational phase. In the future, it may offer another noninvasive modality of investigation.

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Histologic Findings

Macroscopic

Grossly, oligodendrogliomas appear as well defined, solid, and pinkish grey, frequently with areas of calcification and sometimes with areas of necrosis and cystic degeneration. Intratumoral hemorrhage may be present and in some patients may be massive and responsible for sudden death.

Microscopic

Oligodendrogliomas are distinctive, consisting of homogeneous, compact, rounded cells with distinct borders and clear cytoplasm surrounding a dense central nucleus, giving them a "fried egg" appearance. See the image below.

Classic histologic image of oligodendroglioma. Thi Classic histologic image of oligodendroglioma. This image shows monomorphous tumoral proliferation that consists of round, regular cells with a small, central, hyperchromatic nucleus surrounded by clear cytoplasm. Few calcifications are present.

Oligodendrogliomas usually arise in the subcortical location but infiltrate diffusely into cortex around normal neuronal elements and, in superficially located lesions, may extend to the leptomeninges. Within the tumor, branching blood vessels are highly characteristic and divide the cells into discrete clusters. Many oligodendrogliomas have some component of astrocytoma within them; however, distinguishing neoplastic astrocytes from reactive astrocytes may be very difficult. Clearly, some tumors are truly mixed oligoastrocytic tumors; both cell types are believed to arise from a common oligodendrocyte precursor termed the oligodendrocyte type-2 astrocyte.

To call a tumor a mixed oligoastrocytoma, the minimum proportion of astrocyte is variable but ranges from 10-25%. In most instances, the diagnosis of oligodendroglioma is apparent. Confusion can arise with intraventricular oligodendrogliomas, which can appear similar to central neurocytoma. Under light microscopy, neuronal differentiation (eg, Homer Wright rosette formation) can indicate a diagnosis of central neurocytoma, but immunohistochemical markers such as synaptophysin may be necessary to confirm the diagnosis. [6]

Most oligodendrogliomas are slow-growing indolent tumors; however, they occasionally behave in a more malignant manner when initially diagnosed, or an indolent tumor may evolve into an aggressive one. Malignant tumors demonstrate increased cellularity, nuclear pleomorphism, endothelial proliferation, mitotic activity, and necrosis. Different grading systems are available for malignant tumors, but most pathologists use a simple two-tier grading system, diagnosing tumors without anaplastic features as oligodendroglioma tumors and as anaplastic oligodendroglioma if several of the malignant features are present. [7] See the image below.

Smear preparation of anaplastic oligodendroglioma. Smear preparation of anaplastic oligodendroglioma. This image reveals increased nuclear pleomorphism and vascular proliferation.
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Staging

No other staging workup is required.

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