Intraoperative imprint cytology of central neurocytoma: The great oligodendroglioma mimicker

Cytopathology of glioneuronal and neuronal tumours with histological correlations

Glioneuronal and neuronal tumours constitute a diverse group of tumours that feature neuronal differentiation. In mixed glioneuronal tumours, a glial component is present in addition to the neuronal component. With a few exceptions (eg diffuse leptomeningeal glioneuronal tumour) they are well-circumscribed and slow-growing tumours, which is why their prognosis is intrinsically favourable after gross total resection. Rendering an intraoperative diagnosis of glioneuronal/neuronal tumour is therefore important-neurosurgeons should remove them to prevent the persistence of clinical symptoms and/or recurrence. In this context, cytopathological examination can be especially useful for assessing cellular details when frozen section artefacts render poor-quality preparations, as is the case for this group of tumours, which are frequently mistaken for infiltrating gliomas (eg diffuse astrocytoma infiltrating grey matter, oligodendroglioma) on frozen section slides. The aim of this article is to review the cytomorphological features of glioneuronal and neuronal tumours according to the 2021 World Health Organization classification of central nervous system tumours, 5th edition. Additionally, since interpretation in intraoperative cytology relies on intuiting tissue patterns from cytology preparations, representative histological figures of all discussed entities have been included. Clues for specific diagnoses and the primary diagnostic problems encountered during intraoperative procedures are also discussed.

Cytologic Features of Ventricular Tumors of the Central Nervous System: A Review with Emphasis on Diff-Quik Stained Smears

BACKGROUND

Neoplasms from the ventricular system share a common location but have highly variable histogenesis. Many are slowly growing tumors that behave in a benign fashion. They can be classified as primary and secondary tumors. The most common primary tumors are ependymomas, subependymomas, subependymal giant cell astrocytomas, central neurocytomas, choroid plexus tumors, meningiomas, germinomas, pineal parenchymal tumors, papillary tumors of the pineal region, chordoid gliomas, rosette-forming glioneuronal tumors of the fourth ventricle, and craniopharyngiomas. Pilocytic astrocytomas, medulloblastomas, and atypical teratoid/rhabdoid tumors often show secondary involvement of the ventricular system.

SUMMARY

Advances in neurosurgery have facilitated access to the ventricular system increasing the number of cases in which such tumors can be biopsied. In this context, cytology has been proven to be an extremely useful diagnostic tool during intraoperative pathologic consultations. Many ventricular tumors are infrequent, and the cytologic information available is limited. In this review, we describe the cytologic features of the uncommon ventricular tumors and report on unusual findings of the more common ones. For the cytologic evaluation of brain tumors, many neuropathologists prefer formalin fixation and hematoxylin and eosin staining. In this review, we highlight the cytologic findings as seen with Diff-Quik, a very popular staining method among cytopathologists. In fact, when pathologists are unfamiliar with cytology, it is common to request the assistance of cytopathologists during the evaluation of intraoperative procedures. Key Message: Ventricular tumors of the central nervous system comprise a group of heterogeneous tumors with very different cytologic features. The cytomorphology of these tumors, including rare entities, is often very characteristic, allowing a precise recognition during intraoperative pathologic consultations. Diff-Quik is a valuable staining method that can be used alone or as a complement to hematoxylin and eosin staining. Diff-Quik allows for clear visualization of the overall architecture, cytoplasmic details, and extracellular material.

Intracytoplasmic dot-like inclusions as cytopathologically useful findings of ependymoma: Case report of adolescent supratentorial anaplastic ependymoma with clear cell morphology

Pediatric supratentorial ependymomas often have a clear cell morphology and reveal a RELA fusion. When a clear cell neoplasm is intraoperatively diagnosed, intracytoplasmic dot-like inclusions by cytology are a useful cytopathological feature of ependymoma.

Differential hypermethylation of death-associated protein kinase promoter in central neurocytoma and oligodendroglioma

BACKGROUND

Central neurocytoma and oligodendroglioma are rare tumors of the central nervous system. However, diagnosis between these two types of tumors is challenging due to their many cytological and histological similarities. Death-associated protein kinase (DAPK) is a calcium/calmodulin-regulated serine/threonine protein kinase involved in many apoptosis pathways, and repressed expression of DAPK by promoter hypermethylation has been found in a variety of human cancers. The purpose of this study was to assess DAPK protein expression and promoter hypermethylation in central neurocytoma and oligodendroglioma.

METHOD

Central neurocytoma and oligodendroglioma samples were obtained from age- and sex-matched patients. DAPK protein expression was performed using immunohistochemical assays in formalin-fixed, paraffin-embedded sections. DAPK promoter hypermethylation was carried out using bisulfite-modified genomic DNA in methylation-specific PCR followed by separation in agarose gels.

FINDINGS

A statistically significant difference (P = 0.021) in DAPK promoter hypermethylation between central neurocytoma (76.9%) and oligodendroglioma (20%) was observed. High levels of DAPK protein expression were generally found in oligodendroglioma (90%), compared with 38.5% in central neurocytoma (P = 0.054; not statistically significant). There was an inverse correlation between DAPK protein expression and DAPK promoter hypermethylation in the cohort of 23 patients (P = 0.002).

CONCLUSIONS

The results show that DAPK promoter hypermethylation and repressed expression of DAPK protein were more common in central neurocytoma than in oligodendroglioma. Thus, DAPK promoter hypermethylation could be useful for differential diagnosis between these two types of tumors, whereas DAPK protein expression might be less predictive. The role of DAPK promoter hypermethylation in the pathogenesis of central neurocytoma warrants further study.

Cytologic features during intraoperative assessment of central neurocytoma: a report of three cases and review of the literature

BACKGROUND

Central neurocytomas (CNs) are infrequent intraventricular tumors with features of neuronal differentiation that affect young adults and have an excellent prognosis after total resection. The main differential intraoperative diagnoses are oligodendrogliomas, ependymomas and non-Hodgkin's lymphomas; therefore, an accurate and precise intraoperative diagnosis is essential, making the cytologic features the hallmark for cytopathologists, surgical pathologists and neurosurgeons alike. Seven previous reports have described 18 cases of CNs and have addressed the cytodiagnostic criteria during intraoperative assessment in the English medical literature.

CASES

Three patients (23 years old/male, 29 years old/female and 28 years old/male) were evaluated during intraoperative assessment as CNs. They showed intraventricular tumors that measured 6.5, 3.5 and 6.6 cm, respectively. The cytologic features common in these cases were: (1) monotonous or isomorphic round cells, (2) small nuclei with stippled or granular chromatin, and (3) acellular fibrillary areas or neuropil (islands). Other cytologic features often encountered were: rosette-like structures, micronucleoli, perinuclear haloes, well-formed capillary-sized vessels and calcifications.

CONCLUSION

Differential diagnosis of CNs can be a diagnostic challenge. The integration of radiologic imaging and touch preparations taking into account specific cytologic features and frozen sections is necessary for an optimal intraoperative assessment.

Intraoperative cytology of central neurocytoma mimicking oligodendroglioma

Central neurocytomas (CNs) are uncommon tumors of the central nervous system. These tumors have a predilection for the lateral ventricles of young adults and are known to display characteristic neuroimaging and histomorphologic features. Typically, CNs are associated with a favorable outcome, although cases with more aggressive clinical course with recurrences are not unknown. Most descriptions of this tumor are available in the form of isolated histopathology-based case reports and small series. Cytology-based publications of CN are rare. Here, we report a case of CN in a 22-year-old girl. Intra-operative squash cytology and subsequent histopathology of the tumor simulated an oligodendroglioma and a clear cell ependydoma. Final confirmation was obtained on immunohistochemistry. This paper discusses the salient cytological, histomorphological and immunohistochemical features of CN that are useful in distinguishing from its mimickers.

Clinicopathological analysis of central and extraventricular neurocytoma: a report of 17 cases

Neurocytoma, a rare brain tumor, is characterized by a mass located mainly in cerebral ventricles. It is prone to be misdiagnosed as oligodendroglioma or ependymoma due to their similar histopathological features in clinical practice. This study aimed to examine the clinicopathological features and differential diagnosis of central and extraventricular neurocytoma. The clinical and histopathological data of 17 patients (male: female=7:10; age: 4-41 years; mean age: 27.4 years) with central or extraventricular neurocytoma were retrospectively analyzed. These patients showed typical radiological, histopathological and immunohistochemical features of neurocytoma. The tumor tissue was found to be composed of small uniform cells with round nuclei and clear cytoplasm resembling that of oligodendroglioma and ependymoma. Immunohistochemistry revealed the tumor tissues were positive for neuronal markers such as synaptophysin (SYN) and neuronal nuclear antigen (NeuN). It was concluded histopathological features of neurocytoma overlaps with some tumors in the central neural system. Immunopositivity for SYN and NeuN can help differentially diagnose neurocytoma.