Anaplastic oligodendroglioma (WHO III)
Anaplastic oligodendroglioma (WHO III) is a highly cellular diffuse infiltrating glioma with histologic features of malignancy. Patients with anaplastic oligodendroglioma are likely to respond to chemotherapy (5). Oligodendroglioma is made up of monotonous cells with well-defined borders and prominent clear cytoplasm ("perinuclear halo") surrounding hyperchromatic nuclei and resulting in a classic "fried-egg" appearance. On H&E, characteristic, small, branching vessels with a "chicken-wire" pattern and vasculare proliferation with necrosis are visible. Around neurons in grey matter, olygodendrocytes, exhibiting "perineuronal satellitosis".
The molecular genetic signature of oligodendrogliomas at the DNA level is combined 1p/19q loss, typically involving the entire chromosomal arm at both sites. Combined 1p/19q loss has been reported in 50% to 80% of cases carrying a diagnosis of oligodendroglioma, with frequencies as high as 90% when using strict diagnostic criteria (1). 1p/19q status is a predictive marker of response to PCV chemotherapy and is also a prognostic marker (1). Moreover, the presence of IDH1 mutations is present in high frequency in diffuse gliomas as oligodendroglioma. This mutation is a very significant prognostic factor in anaplastic oligodendroglioma, for overall survival but without evidence of a predictive significance for outcome to PCV chemotherapy. IDH1 mutations were strongly associated with 1p/19q codeletion and MGMT promoter methylation (8). However our case showed negativity for 1p19q codelation and presence of MGMT methylation.
Radiologically, anaplastic oligodendroglioma presents as a calcified cortical-subcortical frontal lobe mass. Calcifications are seen in 90% of oligodendroglioma, (the most common glioma to present this feature); the calcifications can be nodular or gyriform. Cystic degeneration is also frequently noted (4) and blood products may be seen. Anaplastic oligodendroglioma enhances much more commonly than low grade oligodendroglioma. Otherwise there are not reliable measures to differentiate on the imaging between low and high grade oligodendroglioma.
The case herein presented showed some oligodendroglioma features, i.e. calcifications, cystic degeneration and superficial location. The marked vascularity, the gyriform calcifications and the cystic degeneration are all features which can be encountered in brain arteriovenous malformations. The presence of solid enhancement, which is lacking in AVM, allowed the radiological presurgical diagnosis of high grade glioma.
The association of intracranial arteriovenous malformations with brain neoplasms is extremely rare, and data are limited to case reports. It has been postulated that the hyperangiogenic environment of high-grade tumors induces abnormal arteriovenous connections. Also a glial tumor mimicking AVM has been previously reported (2). The association of AVM and a cerebral glioma has been reported infrequently (3, 7). Usually these two diseases are sufficiently distinctive histologically to cause no diagnostic difficulty. Their potential coexistence in the same lesion requires careful scrutiny to avoid over-interpretation. Also, the presence of swollen oligodendroglial cells in AVM is quite common. Typically, these cells have abundant clear cytoplasm, a distinct plasma membrane, and a centrally placed round nucleus. They are usually scattered through the lesion, admixed with reactive astrocytes, and are interpreted as being part of the reactive process (3). Regarding the association between gliomas and AVM, a few different conditions should be considered, which are a hypervascularized glioma and coexistence of an AVM with a glioma in two adjacent contiguous regions (7, 6).
The marked vascularity seen on the MRI, the gyriform calcifications and the cystic degeneration are all features which can be encountered in brain arteriovenous malformations. The presence of solid enhancement, allowed the radiological presurgical diagnosis of high grade glioma. This case illustrates that highly vascular malignant gliomas can simulate vascular lesions by radiology and may require an angiogram for diagnosis.
Contributed by Eytan Raz, MD, Manila Antonelli, MD, Luca Saba, MD, Francesca Caramia, MD, Pier Luigi Di Paolo, MD, Luigi Bozzao, MD, Felice Giangaspero, MD, Marco Fiorelli, MD