Case of the Week

MVNT is included in the 2016 World Health Organization Tumor Classification as a newly recognized architectural pattern. It is possibly related to ganglion cell tumors and is comprised of multiple nodules with vacuolation and glial and/or neuronal differentiation. It is a low-grade lesion that may be malformative rather than neoplastic. 

MVNT was initially described in 2013 in the neuropathology literature as being a distinct, seizure-associated, purely neuronal lesion with WHO grade I benign behavior.

 

The neuropathology literature shows the lesion as being highly associated with seizures.      

In a more recent cohort of patients with imaging findings similar to those described in the neuropathology literature, approximately 20% may have had a presenting seizure. Most had nonfocal headaches or another reason for imaging and MVNT was thought to be incidental.

The discrepancy between the neuropathology and radiology literature is likely from reporting and referral bias. Asymptomatic patients may be unaware they have MVNT, and if it is discovered incidentally based on imaging obtained for another reason, they will usually not have it biopsied or resected.

Characteristic imaging features are variably sized (1–5 mm) groupings of nodular round to ovoid foci in the cortical ribbon and juxtacortical white matter, which may be discrete, clustered, and/or coalescent. The nodular foci are T2 hyperintense with no suppression on T2 FLAIR, no mass effect, no diffusion restriction, and rare reported contrast enhancement. 

Characteristic histopathology includes neuroepithelial cells with stromal vacuolation arranged in nodules within the deep cortical ribbon and superficial subcortical white matter. The dysplastic cells have immunopositivity indicative of an earlier stage of neuronal development (positive for HuC/HuD and Olig2), supportive of a malformative lesion. Markers for mature neurons (synaptophysin, neuronal nuclear antigen (NeuN), neurofilament) are either negative or weakly positive. Genetic analysis has failed to demonstrate a specific tumor type. Histology is distinct from dysembryoplastic neuroepethelial tumor (DNET) and ganglioglioma. 

 

Prior to being described as a distinct entity, interpreting radiologists included the following as potential diagnoses: DNET, focal cortical dysplasia, focal cerebritis, contusion, glioma, hamartoma, and enlarged perivascular spaces

DNET may appear similar. Multicystic appearance usually involves more cortical thickness compared to MVNT, often with gyral expansion. There is usually some suppression of signal on T2 FLAIR, sometimes with a rim of T2 FLAIR hyperintensity.

Ganglioglioma more commonly has an associated cyst. However, it can appear solid, typically with T2 prolongation involving the cortex diffusely with lack of the distinct nodularity of MVNT.

Cortical dysplasia usually has more confluent and ill-defined white matter T2 prolongation, sometimes with appreciable associated cortical thickening and/or abnormal sulcal patterns.              

 

MVNT has been shown to be a benign, nonaggressive lesion that remains stable over time. Therefore, when incidentally discovered, surveillance imaging is adequate.

If proven to cause symptoms such as seizure, surgery may be considered.