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Multinodular and vacuolating neuronal tumor of the cerebrum is a rare supratentorial brain tumor described for the first time in 2013. Here, we report 11 cases of infratentorial lesions showing similar striking imaging features consisting of a cluster of low T1-weighted imaging and high T2-FLAIR signal intensity nodules, which we referred to as multinodular and vacuolating posterior fossa lesions of unknown significance. No relationship was found between the location of the lesion and clinical symptoms. A T2-FLAIR hypointense central dot sign was present in images of 9/11 (82%) patients. Cortical involvement was present in 2/11 (18%) of patients. Only 1 nodule of 1 multinodular and vacuolating posterior fossa lesion of unknown significance showed enhancement on postcontrast T1WI. DWI, SWI, MRS, and PWI showed no malignant pattern. Lesions did not change in size or signal during a median follow-up of 3 years, suggesting that multinodular and vacuolating posterior fossa lesions of unknown significance are benign malformative lesions that do not require surgical intervention or removal. ABBREVIATIONS: IQR interquartile range; MVNT ¼ multinodular and vacuolating neuronal tumor of the cerebrum; MV-PLUS ¼ multinodular and vacuolating posterior fossa lesions of unknown significance M ultinodular and vacuolating neuronal tumor of the cerebrum (MVNT) is a rare brain tumor described for the first time in 2013 and added in the World Health Organization Classification of Tumors of the Central Nervous System in 2016. 1,2 Its prevalence and pathophysiology are unknown. It is often asymptomatic and discovered incidentally. It remains unclear whether MVNT should be considered a true neoplasm or a malformative lesion. 1-7 MVNTs have been reported to show highly suggestive imaging features, especially with MR imaging. 8-16 MVNT consists of the coalescence of small T2-weighted imaging and T2-FLAIR

lithiasis >0.5 cm, intact, and visible via simple radiography. A sample of 245 lithiases was obtained, with 87 rejected as they did not fulfill the inclusion criteria. Initially the three main actual diameters of each lithiasis were measured with a calibrator, then a plain X-ray and a CT scan were taken of the samples to determine the surface size in cm(2) for simple radiography; surface size and volume in cm(3) for CT scan, in bone window and soft tissue (Toshiba Aquillion 64, sections of 0.5 mm, 120 Kv, 250 mA). The tomographic area was calculated by employing the formula recommended by the European Association of Urology and scanner software. The actual, radiographic and tomographic measurements were taken by three different researchers who were unaware of the results obtained by the each other. The statistics program IBM SPSS Statistics(®) 19 was used. Differences were analyzed using the Wilcoxon sign test. The bone window CT scan slightly overestimated the actual lithiasic size (0.12 vs. 0.17 cm(3)), while in soft tissue window the actual volume was practically doubled (0.12 vs. 0.21 cm(3)) (p < 0.05). We did not find statistically significant differences in the comparison between actual surface size (0.39 cm(2)) and bone window CT scan size when using the EAU formula or scanner software (0.36/0.37 cm(2)). Resulting measurements in soft tissue window tended to significantly overestimate the surface size, although only slightly (0.42/0.44 cm(2)), whilst the plain radiography underestimated it slightly but significantly (0.37 cm(2)). CT scan, using the bone window, is the technical methodology with which the greatest in vitro accuracy in which actual lithiasis measurements can be estimated, although the craniocaudal diameter measurement will be overestimated. Using soft tissue window gives an overestimated size.

Background and purpose Multinodular and vacuolating neuronal tumor (MVNT) of the cerebrum is a rare brain lesion with suggestive imaging features. The aim of our study was to report the largest series of MVNTs so far and to evaluate the utility of advanced multiparametric magnetic resonance (MR) techniques. Methods This multicenter retrospective study was approved by our institutional research ethics board. From July 2014 to May 2019, two radiologists read in consensus the MR examinations of patients presenting with a lesion suggestive of an MVNT. They analyzed the lesions’ MR characteristics on structural images and advanced multiparametric MR imaging. Results A total of 64 patients (29 women and 35 men, mean age 44.2 ± 15.1 years) from 25 centers were included. Lesions were all hyperintense on fluid‐attenuated inversion recovery and T2‐weighted imaging without post‐contrast enhancement. The median relative apparent diffusion coefficient on diffusion‐weighted imaging was 1.13 [interquartile range (IQR), 0.2]. Perfusion‐weighted imaging showed no increase in perfusion, with a relative cerebral blood volume of 1.02 (IQR, 0.05) and a relative cerebral blood flow of 1.01 (IQR, 0.08). MR spectroscopy showed no abnormal peaks. Median follow‐up was 2 (IQR, 1.2) years, without any changes in size. Conclusions A comprehensive characterization protocol including advanced multiparametric magnetic resonance imaging sequences showed no imaging patterns suggestive of malignancy in MVNTs. It might be useful to better characterize MVNTs.

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