Olig2 is useful in the differential diagnosis of oligodendrogliomas and extraventricular neurocytomas
- First Online:
- Cite this article as:
- Okada, M., Yano, H., Hirose, Y. et al. Brain Tumor Pathol (2011) 28: 157. doi:10.1007/s10014-011-0017-5
- 204 Views
A 42-year-old woman had suffered from headaches since April 2009. Computed tomography revealed a tumor with marked calcification in the left frontal lobe adjacent to the left anterior horn of the lateral ventricle. T1-weighted gadolinium-enhanced magnetic resonance imaging showed a well-enhanced tumor at the lesion. Dynamic methionine positron emission tomography showed no delayed methionine attenuation. Initial preoperative diagnosis was extraventricular neurocytoma (EVN). However, oligodendroglioma was determined upon a second diagnosis. The patient underwent total tumor removal. Hematoxylin and eosin staining showed the characteristic fried egg-like cells, round nuclei, and immunohistochemically, the tumor cells were positive for glial fibrillary acidic protein, synaptophysin, neuronal nuclear antigen, microtubule-associated protein 2 and Olig2. The MIB-1 labeling index was 20%, which suggested malignancy. Although these findings demonstrated that the tumor had glioneuronal character, it was difficult to differentiate between EVN and oligodendroglioma. There have been reports that Olig2 immunohistochemistry is generally positive in cases of oligodendroglioma, but not in cases of neurocytoma. We completed the diagnosis as oligodendroglioma. Subsequent electron microscopy results presented oligodendroglial but not neuronal characteristics. We concluded that Olig2 is useful in the differential diagnosis of oligodendrogliomas and EVNs.
KeywordsOlig2Electron microscopyOligodendrogliomaExtraventricular neurocytoma
Extraventricular neurocytomas (EVN) are newly included in the fourth edition of the WHO Classification of Tumours of the Central Nervous System . EVN are defined as neoplasms that occur in brain parenchyma outside the ventricular system with biological behavior and histopathological characteristics similar to central neurocytomas, although the histopathological characteristics appear to exhibit a somewhat larger morphological spectrum [1–3]. It is, however, difficult to distinguish EVNs from oligodendrogliomas, which are both likely to appear in the frontal lobe because of their neuroradiological and pathological similarities. Differentiating between these conditions for treatment strategy and prognostic evaluation is essential. In this paper, we present a case in which immunostaining for Olig2 was useful in a differential diagnosis between oligodendroglioma and EVN.
Formalin-fixed, paraffin-embedded tissue sections were used for hematoxylin and eosin (HE) staining and immunohistochemistry. The following primary antibodies were used: synaptophysin (Syn) (Progen), MIB-1/Ki-67 (DAKO), neuronal nuclear antigen (NeuN) (Chemicon), glial fibrillary acidic protein (GFAP) (DAKO), microtubule-associated proteins-2 (MAP2) (Lab Vision Corporation), and Olig2 (Immuno-Biological Laboratories). Nonimmunized mouse IgG (DAKO) was used for a negative control. An immPRESS system (Vector) was used in staining for Syn, MAP2, NeuN as a source of secondary antibody, and 3,3′-diaminobenzidine was used as the chromogen. An automatic immunohistochemical staining system (Ventana HX) was used in staining for MIB-1, GFAP and Olig2 according to the manufacturer’s protocol. A tissue sample was created from the formalin-fixed, paraffin-embedded tissue for electron microscopic examination.
An electron micrograph (EM) showed that the tumor cells possessed a plump and rounded cytoplasm without forming cellular processes. No synaptic structuring and dense core granules were discerned. The cytoplasm was rich in intermediate filaments; a few microtubules were observed. A few lysosome-like, electron-dense granules measuring around 300 nm were dispersed in the cytoplasm. Free polysomes were noted, but only a poorly developed endoplasmic reticulum system was seen. Vesicular cristae were observed in the mitochondria. These results were consistent with an oligodendroglioma rather than a neurocytoma (Fig. 2i, j) and we diagnosed the case as an anaplastic oligodendroglioma.
Oligodendroglial tumors are well-known and well-characterized clinicopathological entities. However, a diagnosis of oligodendroglioma may be challenging, because there have been no reliable immunohistochemical markers available for the specific and sensitive recognition of human oligodendroglial tumor cells [5–7].
On the one hand, EVN, a differential diagnosis of oligodendroglioma, is likely to arise in the frontal lobe. In neuroradiological findings, both tumors have significant overlap , present with well-enhanced lesions in CT and MRI, and frequently show calcification in CT. It is sometimes difficult to differentiate them by CT or MRI. Dynamic methionine PET was reported to be useful for the diagnosis of oligodendrogliomas . The methionine accumulation gradually reduced 20 min after administration in cases of oligodendroglioma. It had been reported that other astrocytic tumors did not show the abovementioned findings. The result of the dynamic methionine PET study in the present case did not support a diagnosis of oligodendroglioma. An MRI showed a small cyst in the tumor, which is a finding compatible with EVN. Therefore, our first preoperative diagnosis was EVN rather than oligodendroglioma.
Oligodendrogliomas closely resemble neurocytomas in their pathological characteristics, as they have cells with small round nuclei and a surrounding halo of empty-appearing cytoplasm . Despite immunostaining, it is difficult to differentiate between oligodendrogliomas and EVNs. It has been reported that oligodendrogliomas can possess neuronal differentiation, and oligodendrogliomas could be immunostained for MAP2 and NeuN, and synaptophysin, all of which are markers of a neuronal tumor [11, 12]. Oligodendrogliomas are also immunoreactive for GFAP as gliomas. In this way, oligodendrogliomas have the potential to be glioneuronal. There has also been a case report of an EVN demonstrating glioneuronal differentiation, so the possibility that glioneuronal differentiation is present in an EVN is presented in the same way as an oligodendroglioma . GFAP, Syn, and NeuN are reliable markers for glial and neuronal differentiation. They were not so useful for the differential diagnosis of this particular case, because the tumor is an oligodendroglioma with neuronal differentiation. Olig2 has been identified as a transcription factor that regulates oligodendroglial development [14, 15]. Recently, it was reported that the polyclonal antibody to human Olig2 is useful in the diagnosis of oligodendroglioma . The authors obtained positive immunohistochemical results from 40 cases of oligodendroglial tumors . The study also showed that central neurocytomas were immunohistochemically negative for Olig2 . Therefore, if tumor cells are positive for Olig2, it is inappropriate to regard the tumor as a neurocytoma. We diagnosed the present case as an oligodendroglioma on the strength of positive staining for the Olig2 antibody. EM is essential for differentiating between oligodendrogliomas and other similar tumors, including EVNs . The ultrastructural evidence of neuronal differentiation such as synapse or dense-core vesicles has been regarded as a key point in discriminating neurocytomas from oligodendrogliomas , and the present case did not show the characteristic neuronal EM findings. The subsequent findings supported our diagnosis of an oligodendroglioma.
Perry et al.  found the characteristic oligodendroglioma-associated chromosome 1p and 19q codeletion pattern in just 2 (17%) of 12 cases of EVN. In contrast, it was reported that 1p and 19 codeletions are observed in up to 80% of oligodendroglioma cases . The absence of a 1p and 19q codeletion pattern may negate a diagnosis of oligodendroglioma. However, immunohistochemistry is more generally available in clinical settings than in EM and chromosomal studies.
It is suggested that Olig2 may be a helpful marker for distinguishing oligodendrogliomas from EVNs. There has been one report of an EVN where immunostaining for Olig2 was conducted . In that case, tumor cells were negative for Olig2 . However, it cannot be said that similar results will appear for all cases because there are few examples. The staining for Olig2 in further cases of EVN will be important.
In conclusion, we reported an anaplastic oligodendroglioma that was immunostained for Olig2, and that this was useful for the differential diagnosis of oligodendroglioma and EVN.