|Year : 2018 | Volume
| Issue : 2 | Page : 368--369
Extra-ventricular neurocytoma: An enigmatic tumor
C Komal Prasad
Department of Neurosurgery, Narayana Hrudayalaya Institute of Neurosciences, Bangalore, Karnataka, India
Dr. C Komal Prasad
Department of Neurosurgery, Narayana Hrudayalaya Institute of Neurosciences Mazumdar Shaw Medical Center, NH Health City, 258/A, Bommasandra Industrial Area, Hosur Road, Bangalore - 560 099, Karnataka
|How to cite this article:|
Prasad C K. Extra-ventricular neurocytoma: An enigmatic tumor.Neurol India 2018;66:368-369
|How to cite this URL:|
Prasad C K. Extra-ventricular neurocytoma: An enigmatic tumor. Neurol India [serial online] 2018 [cited 2019 Nov 14 ];66:368-369
Available from: http://www.neurologyindia.com/text.asp?2018/66/2/368/227286
Extra-ventricular neurocytoma (EVN) is defined as “a tumour composed of small uniform cells that demonstrate neuronal differentiation but are not isocitrate dehydrogenase (IDH)-mutant, and that presents throughout the central nervous system, without apparent association with the ventricular system”. However, we should note that because most cases reported before 2012 were not screened for IDH mutations, it is difficult to be certain of the diagnosis of extraventricular neurocytoma in most of the referenced articles. On histopathological examination, EVN exhibit uniform round cells with a clear cell morphology and neuronal differentiation. As a clear cell morphology is also a classic feature of oligodendrogliomas, difficulty in histologically distinguishing EVN from an oligodendroglioma may arise. This is especially because EVNs have also been reported to be having a fairly ubiquitous origin mainly in the cerebral hemispheres, occurring commonly in the frontal and parietal lobes but also in the thalamus, cerebellum, pineal region and the spinal cord. Myung et al., have listed the differential diagnoses of EVN to include an oligodendroglioma with neurocytic differentiation, oligoastrocytoma with neurocytic differentiation, ganglioglioma, dysembryoplastic neuroepithelial tumor, and pineal parenchymal tumor of intermediate differentiation.
Apart from neuronal features like rosette and neuropil formation, immune expression of multiple markers of neuronal differentiation, particularly Syn in a diffuse manner may occur. The absence in EVN, of gene mutation of IDH1, the absence of Olig2 (a transcription factor that regulates oligodendroglial development), p53 immunoexpression, glial fibrillary acid protein and MGMT (O 6-Methylguanine-DNA-methyltransferase) promoter methylation as well as a low frequency of EGFR gene amplification, are also features that may distinguish EVNs from astrocytic and oligodendroglial tumors.
In the article by Mallick et al., on extraventicular neurocytoma (EVN), although the intention of the article, to review all the available literature on extra-ventricular neurocytoma, is commendable, it would not qualify to be an 'individual patient data meta-analysis' in a strict sense. The authors have identified 108 relevant publications to analyse but have listed only 21 in the references. The master table with all the individual patient data-an essential element in analysis of this nature is not available.
Technical issues apart, the authors have provided a good narrative review of the rare entity of extraventricular neurocytoma. Though the optimal treatment of EVN is gross total excision, it is not always feasible, as in the case of tumours located in eloquent areas. The role of surgery (gross total and subtotal), as well as the role of radiotherapy in the review is deduced from the limited data available from disparate studies. Furthering the study by collating the missing data on treatment and follow-up from all the identified studies on EVN would aid in the management of these rare tumours.
EVN is essentially a WHO Grade II tumour. The reported grade I in 20 patients and grade III in two patients may not be compatible with the definition. However, EVN have been classified into the typical or atypical tumor types. The atypical histological criteria are designated by an MIB-1 labelling index that is greater than 3% or features consistent with higher grade tumors. These tumors may occasionally exhibit atypical features that may be associated with an aggressive clinical behavior. The recurrence risk of an atypical EVN may be twice that of a typical tumor. Another factor that significantly contributes to the risk of recurrence is the tumor proximity to the surrounding structures and its invasion into the brain parenchyma. Adjuvant radiotherapy is advised in cases following subtotal resection/biopsy or for recurrent disease. Drop metastasis may occasionally occur during surgical excision of the aggressive forms of these tumors and, therefore, care needs to be taken to prevent this tumor from disseminating during its surgical excision. A greater focus on its radiological hallmarks, its histological and molecular distinguishing features, the subtle variations in the tumor replication rate and the adjuvant chemo-radiotherapeutic regimens possible would go a long way in deciphering the characteristic features of this enigmatic tumor and in its management. The article by Mallick et al., has served the commendable purpose of directing attention towards the need for further multicentric research on this entity.
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