Multinodular and Vacuolating Posterior Fossa Lesions of Unknown Significance

Abstract

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.

Fig 1.

A 38-year-old man presenting with headache. 3D-T2-FLAIR reformatted in the axial (A), coronal (B), and sagittal (C) planes shows a high-signal intensity lesion (white arrow) of the posterior part of the left cerebellar peduncle, consisting of a coalescence of small nodules, highly suggestive of MV-PLUS. The lesion is hypointense on axial T1WI (D) and does not enhance on postcontrast T1WI (E). SWI (F) shows no blooming or intratumoral susceptibility signal. High-resolution T2WI (G) shows hypointensity in the center of hyperintense nodules (black arrows), consistent with a central dot sign. Note the small mass effect and distortion of the lateral margin of the fourth ventricle.

Fig 2.

A 31-year-old woman presenting with headache. 3D-T2-FLAIR reformatted in the sagittal (A) and axial (B) planes shows a high signal intensity multinodular lesion (arrow) of the upper vermis, highly suggestive of an MV-PLUS. Almost all clustered nodules are hypointense on 3D-T1WI reformatted in the sagittal (C) and axial (D) planes and do not enhance on postcontrast 3D-T1WI reformatted in the sagittal (E) and axial (F) planes. One anterior nodule (arrowhead) shows a substantially higher T2-FLAIR and lower T1 signal intensity than all the others, with a marked enhancement after contrast injection. Note the T2-FLAIR hypointense central dot sign does not enhance on postcontrast T1WI.