Abstract
WHO Grade II glioma (low-grade glioma [LGG]) is increasingly diagnosed as an incidental finding in patients undergoing MRI for many conditions. Recent data have demonstrated that such incidental LGGs are progressive tumors that undergo clinical transformation and ultimately become malignant. Although asymptomatic LGG seems to represent an earlier step in the natural course of a glioma than the symptomatic LGG, it is nonetheless impossible to predict at the individual level when the tumor will become malignant. The authors report the case of a 43-year-old woman with a right operculo-insular LGG that was incidentally diagnosed because of headaches. No treatment was proposed, and repeated MRI scans were performed for 6 years in another institution. Due to a slow but continuous growth of the lesion, the patient was finally referred to our center to undergo surgery. Interestingly, objective calculation of the velocity of the tumor's diametric expansion demonstrated a sudden acceleration of the growth rate within the 5 months preceding surgery, with the development of contrast enhancement. Remarkably, the patient was still asymptomatic. An awake resection was performed with intraoperative electrical mapping. There was no functional worsening following surgery, as assessed on postoperative neuropsychological examination. Removal of 92% of signal abnormality on FLAIR MRI was achieved, with complete resection of the area of contrast enhancement. Neuropathological examination revealed a glioblastoma, and the patient was subsequently treated with concomitant radiotherapy and chemotherapy. Although a "wait and see" attitude has been advocated by some authors with respect to incidental LGG, our original case demonstrates that acute transformation to glioblastoma may nonetheless occur, even before the onset of any symptoms. Therefore, because the lack of symptoms does not protect from malignant transformation, we propose consideration of earlier resection in a more systematic manner in cases of incidental LGG.