ReviewUpdate on the diagnosis, pathogenesis, and treatment strategies for central neurocytoma
Introduction
The term central neurocytoma (CNC) was first coined by Hassoun et al. in 1982 when they described two patients with intraventricular tumors with neuronal features on electron microscopy.1 These rare tumors have been thought to originate from the septum pellucidum; however, their precise origin remains elusive. Multiple hypotheses regarding their cellular origin have been proposed, including stemming from neuronal cells, neuronal progenitor cells and bi-/multipotent precursor cells.2, 3, 4, 5, 6
CNC are benign tumors that are categorized as World Health Organization grade II. Many of the histopathologic characteristics of CNC mimic those of oligodendrogliomas and ependymomas. As a result, they have been previously misdiagnosed.7, 8 The definitive diagnosis of CNC rests upon immunohistochemistry and electron microscopy to confirm the neuronal characteristics of the tumor.3, 9 Accurate diagnosis is important because patients with CNC generally have a good prognosis, and complete resection has been found to be curative for most patients.10, 11, 12 However, there have also been reports of atypical CNC with atypical histological features and/or high mitotic activity, which have been associated with a worse prognosis and a higher rate of recurrence.12, 13 Extraventricular neurocytomas have typical features but a worse prognosis, generating significant interest in the use of various adjuvant therapies.14, 15 Radiation therapy seems to be effective in improving outcomes in many patients with CNC.10, 11, 12, 13 However, it is hard to establish any standards for such therapies as most of the accounts are limited to small series and case reports. There has also been recent interest in the molecular characteristics of CNC, as they may provide insight to novel targets for new therapies.2
Section snippets
Epidemiology
CNC represent approximately 0.1–0.5% of all primary brain tumors.7, 9, 16, 17 More than 500 cases have been reported since Hassoun et al. originally described them.2 These tumors typically affect adolescents and young adults with the highest incidence occurring in the third decade, followed by the second and fourth decades.17 They seem to be equally prevalent in both males and females.16, 17, 18 The majority of CNC are located in the lateral ventricle,3, 19 with most being located in the
Clinical presentation
Although CNC are most common in adolescents and young adults, they have been reported in very old and very young patients as well.18, 25 A common presentation of most neurocytomas is hydrocephalus, caused by obstruction of the foramen of Monro by the tumor.26, 27 Presenting symptoms stem from increased intracranial pressure and include headache, vision problems and nausea or vomiting.18, 19, 26 There are many other symptoms, including weakness, balance problems, paresthesias, tinnitus,
Radiological findings
On radiological studies, CNC generally appear as well demarcated, lobulated masses located in the lateral ventricles.9, 31 On CT scans, CNC typically appear as an iso- to hyper-dense or mixed-dense mass within the lateral ventricles, close to the septum pellucidum and foramen of Monro (Fig. 1).8, 19, 31 Tumors tend to be attached to the superior and lateral walls of the ventricles, and on imaging the septum pellucidum is typically not clearly demarcated.20 Mild to moderate contrast enhancement
Pathologic characteristics and molecular pathogenesis
Histopathologic diagnosis of CNC under light microscopy can be difficult as many of the histopathological features of CNC mimic other central nervous system neoplasms. Because of this, CNC have been frequently misdiagnosed.9, 17, 36 A definitive diagnosis of CNC rests upon immunohistochemistry and electron microscopy to demonstrate the neuronal origin of these tumors.3, 9, 17 CNC usually present with benign histology which may vary within the same specimen.37 CNC tend to have small, round to
Surgical resection
Surgical resection is the mainstay of therapy with gross-total resection (GTR) as the goal. Complete curative resection offers the best chance of minimizing recurrence.10 The main objectives of surgery are to perform maximum resection with minimal neurologic impairment, to establish and/or restore cerebrospinal fluid (CSF) pathways, and to provide tissue for definitive pathologic diagnosis of CNC.20, 45 Most CNC are intraventricular and do not invade surrounding parenchyma, allowing for the
Conclusions
CNC are benign tumors that typically affect young adults and tend to have favorable outcomes. The precise origin of these tumors remains elusive; however, significant progress has been made in unraveling distinct characteristics of these rare tumors, which has opened new doors for the diagnosis and treatment of these lesions. Currently, surgery is the primary treatment for most CNC and GTR is associated with a favorable prognosis. In patients where GTR is unattainable, STR with adjuvant RT or
Conflicts of interest/disclosures
The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
Acknowledgements
We would like to thank Dr. Ada Baisre for providing the histopathology images for this manuscript.
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