Multinodular and vacuolating neuronal tumors (MVNT) are lesions with distinct cytoarchitectural patterns. They are often considered part of the heterogeneous group of tumors known as long-term epilepsy-associated tumors (LEATs).
Radiologically, MVNTs appear as small "bubbly" indolent subcortical tumors that sometimes present with seizures. These tumors have been most frequently identified in the temporal lobe, although that is likely to be due to that location being more likely to result in seizures than necessarily a predilection for that lobe 1-4.
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Terminology
Lesions with identical imaging features have been described in the cerebellum without histological proof, and have initially been given the name of multinodular and vacuolating posterior fossa lesions of unknown significance (MV-PLUS) 7. A few case reports of MVNT in the cerebellum have been published 10,11 and as such it is likely that MV-PLUS will be abandoned at some point in favor of generalizing the term MVNT to include the cerebellum 12.
Epidemiology
The true epidemiology of these tumors is unknown as they have only been known since 2013 and most are asymptomatic, so are likely undiagnosed or misdiagnosed as other lesions (see differential diagnosis below) further confounding epidemiology.
Reported cases are mostly in young to middle-aged individuals with adult-onset epilepsy, or identified incidentally 1-4,7.
Clinical presentation
Other than some of these lesions being epileptogenic, it is likely that most are asymptomatic 1-4,7.
Pathology
MVNTs are considered as one of the glioneuronal and neuronal tumors in the 2021 WHO classification of CNS tumors 9.
Microscopic appearance
The histopathological hallmark of MVNT is of neuroepithelial cells with conspicuous stromal vacuolation arranged in nodules principally within the deep cortical ribbon and superficial subcortical white matter 1-3.
Immunophenotype
Immunostaining is positive for synaptophysin, HuC/HuD neuronal antigens and p62 but negative for other markers (e.g. IDH1, nestin, NeuN, neurofilament, GFAP, and CD34) 1-4.
Genetics
Alterations in the MAPK pathway are important molecular characteristics 9.
Radiographic features
CT
Smaller lesions are difficult to identify, but if seen will appear as non-enhancing low attenuation lesions deep to the cortex in the subcortical white matter.
MRI
These tumors appear as a cluster of well-circumscribed high T2 signal "bubbles" located predominantly in the subcortical white matter but can involve the overlying cortex 1,3,4.
T1: hypointense to adjacent gray and white matter
-
T1 C+ (Gd)
usually no enhancement
some faint focal enhancement may be seen 3,4
-
T2
hyperintense to grey and white matter, almost as high as CSF
occasional central hypointense dot (also hypointense on FLAIR) 7,8
FLAIR: does not suppress (remains high signal)
In the cerebellum (MV-PLUS) these lesions most commonly involve the vermis, often extending cerebellar hemispheres, but not the brainstem 7.
Treatment and prognosis
MVNTs appear to be benign tumors with very indolent biological behavior which can, if asymptomatic, be followed by imaging alone. In symptomatic patients (e.g. where the MVNT is causing epilepsy) surgical resection often controls seizures, with no tumor regrowth reported 1-4.
History and etymology
MVNTs were first described in 2013 3 and included in the 2016 revised 4th edition of the WHO classification of CNS tumors as an "architectural pattern" but recognized as a distinct entity in the 2021 5th edition 9.
Differential diagnosis
Possible considerations include:
-
dysembryoplastic neuroepithelial tumor (DNET)
can appear similar with a soap bubble appearance but usually is mostly cortical (rather than subcortical)
often has bright FLAIR rim
-
focal cortical thickening or blurring of the gray-white junction, sometimes associated with a radial glial band (transmantle sign)
-
location can be similar
usually more elongated along vessel long axis
fully attenuating on FLAIR
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