Multinodular and vacuolating neuronal tumors in epilepsy: dysplasia or neoplasia?

Abstract

Multinodular and vacuolating neuronal tumor (MVNT) is a new pattern of neuronal tumour included in the recently revised WHO 2016 classification of tumors of the CNS. There are 15 reports in the literature to date. They are typically associated with late onset epilepsy and a neoplastic vs. malformative biology has been questioned. We present a series of ten cases and compare their pathological and genetic features to better characterized epilepsy-associated malformations including focal cortical dysplasia type II (FCDII) and low-grade epilepsy-associated tumors (LEAT). Clinical and neuroradiology data were reviewed and a broad immunohistochemistry panel was applied to explore neuronal and glial differentiation, interneuronal populations, mTOR pathway activation and neurodegenerative changes. Next generation sequencing was performed for targeted multi-gene analysis to identify mutations common to epilepsy lesions including FCDII and LEAT. All of the surgical cases in this series presented with seizures, and were located in the temporal lobe. There was a lack of any progressive changes on serial pre-operative MRI and a mean age at surgery of 45 years. The vacuolated cells of the lesion expressed mature neuronal markers (neurofilament/SMI32, MAP2, synaptophysin). Prominent labelling of the lesional cells for developmentally regulated proteins (OTX1, TBR1, SOX2, MAP1b, CD34, GFAPδ) and oligodendroglial lineage markers (OLIG2, SMI94) was observed. No mutations were detected in the mTOR pathway genes, BRAF, FGFR1 or MYB. Clinical, pathological and genetic data could indicate that MVNT aligns more with a malformative lesion than a true neoplasm with origin from a progenitor neuro-glial cell type showing aberrant maturation.

Keywords: Multinodular; epilepsy; neuronal; tumour; vacuolating.

Figure 1

Neuroimaging features of multinodular and vacuolating neuronal tumour. A. Case 1 (as reported in the original case report45) showing marked signal change in the left temporal lobe, parahippocampal gyrus and hippocampus on coronal FLAIR but with minimal mass effect; little change was noted over 8 years. B. Case 8. Abnormality was observed in the right mesial temporal region with hyperintensity on coronal FLAIR sequence. C. Case 5. Initial FLAIR MRI sequences at presentation highlighted a lesion in the right posterior temporal lobe as a diffuse cortical abnormality, which did not show significant growth on MRI, as shown in (D) at 21 months following the initial scan. E. Case 6 shown with T2 and (F) FLAIR sequences, highlighting a hyperintense abnormality and the cortical, white matter interface in the left temporal lobe.

Figure 2

Macroscopic and low power histological features of multinodular and vacuolating neuronal tumours (MVNT). A. Macroscopic features of the temporal lobe specimen from Case 1 show areas of breakdown/cavitation in the gyral cores and focal translucency of the white matter. B. Luxol fast blue/cresyl violet stained section from Case 1 confirms lack of myelin in some gyral cores (arrow) and pale hypomyelinated nodules at the cortical white matter junction extending into the white matter (arrowhead). C. SMI94/myelin basic protein confirms diffuse regions of poor myelination (arrow) and nodular like patterns (arrowhead) in the white matter in Case 1. D. Abnormal nodular islands of cells in the subiculum in Case 1, present on both sides of the pyramidal cell layer, although predominantly in the subcortical region (arrowhead). E. Macroscopic appearance of fixed 5 mm sections of the temporal lobe in Case 2 shows islands of grey tissue in the white matter of the inferior medial part of the specimen with an overlying normal‐appearing cortex. F. Synaptophysin labelling in Case 4 highlights the nodules encroaching on the deep cortical layers with reduced labelling compared to the adjacent cortex. G. Neuropeptide Y in Case 4 at low power shows reduction of labelling within the cortical nodules compared to adjacent cortex (arrowheads). H. MAP2 staining in Case 8 in the temporal cortex shows variable patterns with reduced MAP2 labelling in some nodules (arrowhead) compared to others (arrows). I. Myelin basic protein staining (SMI94) in Case 4 highlights abutting, myelin‐poor nodules. J. The abnormal white matter regions are populated by single scattered cells with a neuronal/ganglion cell appearance and prominent vacuolation of the cytoplasm or vacuoles surrounding the cells. K. Occasional binucleated cells were seen (arrowhead) and cells with more eosinophilic cytoplasm were observed in MVNT after H&E staining. L. In some cases alignment of the atypical cells along vessels was noted in the nodules (Case 4). M. The border (arrowhead) between a nodule in MVNT(top half of figure) and the white matter (lower half of figure) on cresyl violet stain gives the impression of overall reduced cellularity, particularly for small oligodendroglial‐like cells in the nodules, compared to the adjacent white matter. N. In Case 8, a focal area in the mesial temporal lobe showed more typical appearances of a ganglioglioma, with dysplastic neurones and eosinophilic granular bodies. Bar = 1cm for macroscopic images in A and E; = 3mm for B–D, F–H; =0.5mm for I; = 100 microns for J, L–N and =50 microns for K (approximate based on original magnifications).

Figure 3

Neuronal and glial marker expression in vacuolated cells (VC). A. NeuN staining showed labelling of normal interstitial neurons in the white matter, but the vacuolated cells (VC) were typically weak or more often negative (arrowheads). Labelling of VC with (B) neurofilament, (C) MAP2, (D) synaptophysin is shown. E. Overall, reduced labelling with synaptophysin was observed in the cortical nodules. F. TBR1 neuronal lineage marker shows nuclear labelling of t VC and strong cytoplasmic labelling noted with (G) OTX and (H) MAP1b. I. GFAPδ highlighted small glial cells primarily in the nodules at low power; inset (top) multipolar GFAPδ cells in proximity to VC), inset (bottom) GFAP conventional isoform shows opposite pattern with more extensive labelling of the gliosis around the lesions. J. Nuclear labelling of VC with OLIG2 whereas (K) PDGFRbeta highlighted small multipolar cells in the nodules but not the VC. L. SMI94 for myelin basic protein, as well as demonstrating the diminished myelination in the white matter nodules (see also Figure 2), also showed membranous labelling of the VC (arrow).Bar = 80 microns (A, C, D, F–H, J) = 40 microns (I) and 140 microns (B, K) and 200 microns (E and I) (approximate, based on original magnifications).

Figure 4

Immature and interneuronal markers in multinodular and vacuolating neuronal tumour. A. PAX6 was negative in vacuolated cells (VC) but labelled nuclei of small cells within the lesion. B. SOX2 showed strong labelling of the nodules and VC highlighting the regions of involvement at low magnification (C) CD34 showed variation in the staining between cases, but as shown here in Case 5, prominent multipolar cells and processes were evident in the regions with VC. D. Occasional doublecortin positive (DCX) VC were seen. E. VC were mainly nestin negative but occasional positive cells were seen (inset left). Small nestin expressing cells were noted in the lesion and occasional bipolar cell (inset right). F. NPY showed reduced labelling in nodules of one MVNT (Case 4), arrows showing the edge of the nodule; NPY staining labelled scattered interneurons in the lesion of normal morphology but the VC were negative (arrowed in inset). G. Case 3 showing strong labelling of VC for parvalbumin. H. Cationic chloride transporter ((N/KCC1) with distinct cytoplasmic labelling of the VC. I. AT8 labelling for phosphorylated tau in Case 4 with Alzheimer's disease pathology, and dense cortical tau in tangles and threads showed a marked sparing of the VC and nodules on MVNT for tau accumulation (arrows). J. VC were strongly positive with p62 and (K) anti‐mitochondrial antibodies. L. VC were not positive with both pS6 markers pS6 Ser240/244 (shown here) and pS6 Ser 235/236, apart from occasional dot‐like positivity in the cytoplasm of uncertain significance (insert left); in contrast the overlying cortex (insert left) showed strong scattered neuronal positivity. M. A high proportion of VC were MCM2 nuclear positive. Bar = 50 microns (A, D, E, G, H, K–M) = 20 microns (B, F, I, J) (approximate based on original magnifications).