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Central neurocytoma (CN) is classically defined by its intraventricular location, neuronal/neurocytic differentiation, and histological resemblance to oligodendroglioma. Extraventricular neurocytoma (EVN) shares similar histological features with CN, while it distributes any site without contact with the ventricular system. CN and EVN have distinct methylation landscapes, and EVN has a signature fusion gene, FGFR1-TACC1. These characteristics distinguish between CN and EVN. A 30-year-old female underwent craniotomy and resection of a left intraventricular tumor at our institution. The histopathology demonstrated the classical findings of CN. Adjuvant irradiation with 60 Gy followed. No recurrence has been recorded for 25 years postoperatively. RNA sequencing revealed FGFR1-TACC1 fusion and methylation profile was discrepant with CN but compatible with EVN. We experienced a case of anatomically and histologically proven CN in the lateral ventricle. However, the FGFR1-TACC1 fusion gene and methylation profiling suggested the molecular diagnosis of EVN. The representative case was an "intraventricular" neurocytoma displaying molecular features of an "extraventricular" neurocytoma. Clinicopathological and molecular definitions have collided in our case and raised questions about the current definition of CN and EVN., (© 2023. The Author(s).)

Cerebellar liponeurocytoma (cLNC), categorized as a World Health Organization grade II tumor, is a rare neoplasm characterized by advanced neuronal/neurocytic differentiation and focal lipid accumulation in neuroepithelial tumor cells. However, the expression and genetic profiling of cLNC have been poorly studied. A 44-year-old woman with a three-year history of cerebellar ataxia and numbness in lower extremities underwent radiological examination revealing multiple contrast-enhancing tumors at the floor of the fourth ventricle and in the lower vermis, and spinal dissemination. The high uptake of 11 C-methionine in positron emission tomography (Met-PET) supported the preoperative cLNC diagnosis. Subtotal removal of the tumor around the obex and inferior vermis was performed. Histologically, the tumor was composed of small, uniform cells with round nuclei in a sheet-like fashion. Tumor cells were diffusely reactive for the neuronal markers synaptophysin and neurofilament. Vacuolate cells with a displacement of nuclei suggested the accumulation of lipid, which was further supported by immunohistochemical staining of S-100. These findings confirmed the diagnosis of cLNC. Next-generation sequencing of tumoral DNA detected a splice site mutation in the ATRX gene. Further reports of cLNC cases with detailed expression and genetic profiles are essential for precise diagnosis and clarifying the oncogenic pathway in cLNC., (© 2021. The Japan Society of Brain Tumor Pathology.)

To discuss the clinicopathological features of liponeurocytoma, we retrospectively reviewed three liponeurocytoma cases and compared their immunophenotypes and genotypes with those of similar tumors. Furthermore, we reviewed the literature and compared the similarities and differences between cerebellar and intraventricular liponeurocytomas. Two cerebellar and one intraventricular liponeurocytomas were included in the present study. The liponeurocytomas comprised small tumor cells and lipomatous cells. The tumor cells expressed SYN, MAP-2, and NeuN. One case showed atypical histological features. By reviewing the literature, we found that cerebellar liponeurocytoma tended to be more common in females, whereas the converse was true for intraventricular liponeurocytoma. Compared with cerebellar liponeurocytoma, intraventricular liponeurocytoma was more commonly noted in younger adult patients. A high MIB-1 index (>10%) and incomplete tumor resection might represent adverse prognostic factors in patients with liponeurocytoma. We suggest that 'central liponeurocytoma' should be used to include all putative liponeurocytoma sites. The present study identified several morphological, immunohistochemical, and genetic features that may aid in the differential diagnosis of liponeurocytoma. In addition, surgery should be the preferred treatment, and complete tumor resection should be the goal. Additional cases with long-term follow-up are needed to develop optimal management protocols for liponeurocytoma.

Cerebellar liponeurocytoma is a rare tumor that usually develops in adult patients, and is categorized as World Health Organization grade II. Because of the small number of reports on its radiological and pathological features, the disease remains poorly characterized. The current case involved a 59-year-old man with tumor in the upper cerebellar vermis. Preoperative positron emission tomography (PET) showed high uptake on (11)C-methionine PET, but low uptake on (18)F-fluorodeoxyglucose PET. These findings resemble those of central neurocytoma and oligodendroglioma, but are incompatible with other brain tumors. Subtotal tumor removal was performed by suboccipital craniotomy. Histopathological examinations showed sheets of small, isomorphic cells with round nuclei and clear cytoplasm, and focal vacuolated cells resembling adipose cells. On immunohistochemistry, tumor cells were positive for synaptophysin and NeuN. Vacuolated cells were immunoreactive for perilipin. Based on these findings, cerebellar liponeurocytoma was diagnosed. Genetic analyses revealed absences of both chromosome 1p/19q loss and isocitrate dehydrogenase 1 mutation, further ruling out oligodendroglioma. These radiological and genetic aspects of cerebellar liponeurocytoma, which are mostly in common with central neurocytoma, should prove helpful in differentiating this rare tumor from other tumors with similar morphology.

We present the first case of central neurocytoma with a component suggesting ependymal-like differentiation as an unclassified glioneuronal tumor. The patient was a 26-year-old Japanese man with a brain tumor extending from the frontal wall of the bilateral lateral ventricles to the corpus callosum. Histologically, the tumor's neuronal component consisted of small bland looking cells with fine, delicate, neuropil-like processes forming a rosette structure; its glial component consisted of tumor cells with thick processes arranged around the thinly walled vessels, resulting in a perivascular pseudo-rosette formation and indicating ependymal-like differentiation. Immunohistochemically, the cytoplasm of the tumor cells with ependymal-like features was positive for glial fibrillary acidic protein and negative for synaptophysin, while the tumor component with neuronal features showed the opposite immunohistochemical staining pattern. Most of the tumor cells were positive for Olig2, but EMA, D2-40, CD99, p53, and mutant IDH-1 (R132H) were totally negative. Its Ki-67 labeling index was less than 1 %. Histologically, this tumor was diagnosed as a central neurocytoma with an ependymoma-like glial component, and its tumor grade was estimated at grade II. The tumor location, infiltrating the corpus callosum, and histology were distinctive and might represent a peculiar subtype of glioneuronal tumor.

Extraventricular neurocytoma (EVN) is a rare tumor that mainly occurs in the cerebral hemispheres and spinal cord. Sellar neurocytoma is extremely rare, with only two previously reported cases. We report a sellar EVN in a 48-year-old man presenting with visual impairment. This tumor was partially resected. The residual tumor disappeared on MRI with adjuvant radiotherapy. However, 2 years later the tumor recurred with craniospinal dissemination, which is also very rare, with only four previously reported cases. The recurrent tumor showed atypical features with an MIB-1 LI score of 3 %. It is suggested that postoperative adjuvant radiation therapy with long-term follow-up is required for incompletely resected EVN.

Extraventricular neurocytoma is an uncommon neuronal tumor, located outside the cerebral ventricles, which shows histological features similar to those of central neurocytoma. Most extraventricular neurocytomas are situated in the intraaxial regions of the central nervous system. We report a rare case of an extraaxial neurocytoma in the sphenocavernous-petroclival region that was successfully treated by radiation therapy following partial removal and pathological evaluation of the tumor.

A 42-year-old woman had suffered from headaches since April 2009. Computed tomography revealed a tumor with marked calcification in the left frontal lobe adjacent to the left anterior horn of the lateral ventricle. T1-weighted gadolinium-enhanced magnetic resonance imaging showed a well-enhanced tumor at the lesion. Dynamic methionine positron emission tomography showed no delayed methionine attenuation. Initial preoperative diagnosis was extraventricular neurocytoma (EVN). However, oligodendroglioma was determined upon a second diagnosis. The patient underwent total tumor removal. Hematoxylin and eosin staining showed the characteristic fried egg-like cells, round nuclei, and immunohistochemically, the tumor cells were positive for glial fibrillary acidic protein, synaptophysin, neuronal nuclear antigen, microtubule-associated protein 2 and Olig2. The MIB-1 labeling index was 20%, which suggested malignancy. Although these findings demonstrated that the tumor had glioneuronal character, it was difficult to differentiate between EVN and oligodendroglioma. There have been reports that Olig2 immunohistochemistry is generally positive in cases of oligodendroglioma, but not in cases of neurocytoma. We completed the diagnosis as oligodendroglioma. Subsequent electron microscopy results presented oligodendroglial but not neuronal characteristics. We concluded that Olig2 is useful in the differential diagnosis of oligodendrogliomas and EVNs.

We report an unusual case of extraventricular (cerebral) neurocytoma with a long, 25-year history, and which appeared to transform to neuroblastoma. In 1978, an 18-year-old woman was treated for right frontal oligodendroglioma. Eighteen years later (in 1996), recurrence of tumor in the fourth ventricle was noted and was treated with gamma-knife radiotherapy. The tumor shrunk transiently, but 7 years later (in 2004), MRI study demonstrated a second recurrence and ventricular dissemination. Partial removal was performed, and histological examination revealed that tumor cells had round or oval nuclei with halos. Frequent mitoses and vascular proliferation were observed. The MIB-1 LI was 80%. Despite postoperative whole-brain radiotherapy to a total dose of 30 Gy, the tumor progressed, and she died at 4 months after the second surgery.

Central neurocytomas (CNs) are usually considered benign; however, some subsets of these tumors with histologic atypia and elevated proliferation potential have been reported to have a poor outcome. It has been proposed that those CNs exhibiting a MIB-1 labeling index (LI) greater than 2% and/or vascular proliferation be defined as atypical central neurocytoma (ACN). Two cases of ACN are reported here. Case 1 was a 13-year-old male who complained of headache. An MRI showed an enhancement of the tumor in the third ventricle and left lateral ventricle. The tumor was completely removed transcortically by a left frontotemporal craniotomy. The tumor showed anaplastic features, including microvascular proliferation, mitosis, and necrosis. The MIB-1 LI was 7.8%. The patient received 50Gy of focal irradiation. After 16 months of follow-up, no recurrence was observed. Case 2 was a 17-year-old female who presented with headache. An MRI showed an enhancement of the tumor in the right lateral ventricle. To preserve the internal cerebral vein, the tumor was partially removed by the transcingulate approach after a bifrontal craniotomy. Histologically, the tumor displayed the typical features of a CN. The MIB-1 LI was 7.0%. Complete remission was achieved through 50Gy of focal irradiation. After 15 months of follow-up, there was no recurrence. The differences in the histopathological findings in these two cases indicate the presence of a variety of histopathological features among ACNs.

A case of central neurocytoma that was confirmed with ultrastructural and immunohistochemical studies has been reported. Ultrastructurally, thin cytoplasmic processes of tumor cells showed differentiation into neuronal cells containing parallel bundles of microtubules and abortive synapses with dense-core vesicles and/or clear vesicles. It was frequently found that the clusters of tumor cell processes were close to or around the microvessels. Microvessels were composed of endothelial cells without fenestrations and had tight junctions in the endothelial clefts. Neurosecretory granules in thin cell processes appeared close to microvessels and may have been secreted around microvessels.