Low-grade gliomas in adults have an incidence of 0.8 to 1.2 per 100 000, and their causes are unknown. Despite their histological classification as low-grade, they cannot be cured by any current treatment mode, and no class I evidence exists to guide initial treatment of these tumors. Median survival ranges between 7.5 years and 10 years, with a 5-year survival probability between 55% and 86%. The prognosis depends on age, World Health Organization (WHO) tumor grade, Karnofsky performance score, cytological type (oligodendroglioma vs astrocytoma), and, potentially, the extent of resection. Oligodendrogliomas with loss of heterozygosity on chromosomes 1p and 19q have a distinctly more favorable prognosis and therapeutic response rate. Low-grade tumors progress to high-grade gliomas with aggressive biological behavior at increasing frequency with advancing age. Ms P is a young woman with a previously treated oligodendroglioma, WHO grade II, with loss of heterozygosity on chromosomes 1p and 19q, which at a third resection had transformed into an oligodendroglioma of WHO grade III. She wants to know her current and future therapeutic options.
A, Fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) of Ms Q's tumor at diagnosis. The white signal-intense areas in the right temporal lobe correlate with the tumor. Note the lack of a clear demarcated border. B, Left panel, FLAIR MRI of Ms Q's tumor at first recurrence. The tumor has regrown in the dorsal wall of the previous resection cavity, seen as a small dark zone (yellow arrowhead) in front of the FLAIR signal. Note the more circumscribed appearance, suggesting a more delineated tumor growth. Right panel, arterial spin-labeling (ASL) MRI reflecting blood flow at first recurrence of Ms Q's tumor. The dark areas in the region of the tumor (blue arrowhead) reflect reduced blood flow indicative of a low-grade tumor. C, Arterial spin-labeling MRI at second recurrence of Ms Q's tumor. The tumor still appears dark (blue arrowhead), signifying reduced blood flow compared with the surrounding cortex and white matter, compatible with a low-grade glioma.
The 3 peaks from left to right represent choline, creatinine, and N -acetylaspartate. In normal brain, N -acetylaspartate is the prevalent peak. In tumors of higher grade, the choline peak becomes the largest and the ratio of choline to creatinine is indicative of the grade. Ratios of 2 or higher are associated with more malignant phenotypes in gliomas. Here, the ratio is 2.87. The tumor otherwise had features consistent with a low-grade recurrence; the magnetic resonance spectroscopy was the only indicator of a malignant regrowth.
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