Answer and Discussion of Quiz Set: N-017

4.    Which of the following is not true regarding oligodendroglioima?

A.  Oligodendroglioma (WHO grade II) typically occurs as a solitary hypointense or mixed hypointense and hyperintense mass on T1-weighted images, and a hyperintense mass on T2-weighted images. Edema in surrounding tissue is variable and these tumors, in general, do not enhance,

B.  Calcifications are typical findings in oligodendroglioma.

C.  Tumor cells are always negative for glial fibrillary acidic protein (GFAP).

D.  Tumor cells are often positive for Olig2.

E.  Mitoses are either scant or not found.

Answer and Discussion: The answer is (C). GFAP is expressed in oligodendroglioma particularly in minigemistocytic cells. However, the expression is often patchy. Interpretation of the sections should be careful as the residual parenchyma around tumor cells can be positive and these immunoreactivity should not be interpreted as genuine positivity. Olig2 is a markers that are extensively expressed in diffuse gliomas. Calcifications are characteristic findings in oligodendrogliomas and far less common in either astrocytic tumor or ependymal tumors. In general, WHO grade II oligodendrogliomas or astrocytomas do not enhance. Mitosis should not be more than scant. Increased mitotic rate is an indication of grade III diffuse gliomas.

References:

1.   Okada M, Yano H, Hirose Y, Nakayama N, Ohe N, Shinoda J, Iwama T. Olig2 is useful in the differential diagnosis of oligodendrogliomas and extraventricular neurocytomas. Brain Tumor Pathol. 2011 Apr;28(2):157-61.

2.   Preusser M, Budka H, Rössler K, Hainfellner JA. OLIG2 is a useful immunohistochemical marker in differential diagnosis of clear cell primary CNS neoplasms. Histopathology. 2007 Feb;50(3):365-70.

3.   Ligon KL, Alberta JA, Kho AT, Weiss J, Kwaan MR, Nutt CL, Louis DN, Stiles CD, Rowitch DH. The oligodendroglial lineage marker OLIG2 is universally expressed in diffuse gliomas. J Neuropathol Exp Neurol. 2004 May;63(5):499-509.