The Mickey Mouse's hand sign in brain MRI points out multinodular and vacuolating neuronal tumors in mesial temporal lobe structures.

Purpose: Multinodular and vacuolating neuronal tumor (MVNT) is a rarely diagnosed neoplastic lesion often associated with adult-onset focal seizures. In some situations, atypical MRI features of MVNT may mimic other long-term epilepsy associated tumors (LEATs) or diffuse low-grade gliomas. In such a context, the identification of distinct clinical markers is recommended.

Methods: We retrospectively analyzed the neuroimaging features of histologically confirmed MVNT lesions of our epilepsy surgery cohort. All the identified MVNT patients had a mesial temporal lobe location. The MRI features from the MVNT population were compared to those from non-MVNT lesions randomly selected in our cohort. Non-MVNT lesions consisted of (i) other tumoral lesions belonging to LEATs group, (ii) infiltrative tumoral lesions such as grade 2, IDH-mutant Gliomas, and (iii) non-tumoral, highly epileptogenic lesions, such as hippocampal sclerosis.

Results: MRI analysis of patients with MVNT noticed an unusual FLAIR hyperintense signal extending from the uncus to the anterior white commissure through the sublenticular region. This neuroimaging abnormality visually mimicked "Mickey Mouse's hand" on coronal plane. The "Mickey Mouse's hand" sign was identified in 6 patients out of 9 (66.7%) MVNT patients. We did not identify the Mickey Mouse's hand sign in other control lesions (0/11 ganglioglioma, 0/11 glioma, 0/150 hippocampal sclerosis), except in one patient with dysembryoplastic neuroepithelial tumors (DNET) (1/15; 6.7%). All patients showing the "Mickey Mouse's hand" sign were seizure-free after surgery.

Conclusions: The Mickey Mouse's hand sign represents a straightforward and easy-to-remember neuroimaging feature, that does not require advanced MRI sequences and that could help clinicians facing mesial temporal lesions to rapidly raise the suspicion of MVNT diagnosis.