Alveolar rhabdomyosarcoma is a common malignant soft tissue tumor in child and adolescents. Intracranial alveolar rhabdomyosarcoma in adults is rare, especially in the pineal region. We present a case of primary alveolar rhabdomyosarcoma of the pineal gland in a 36-year-old Chinese male with a chief complaint of dizziness, headache and a loss of balance when walking. Imaging identified a space-occupying mass in the pineal region with obstructive hydrocephalus. An endoscopic-assisted pineal mass resection was performed. Pathology revealed a solid, sheet-like growth of medium-sized, round or oval cells with map-like necrosis and some rhabdomyoblasts. The tumor cells were diffusely positive for desmin, myogenin, MyoD1, ALK, and OLIG2. Fluorescence in situ hybridization (FISH) detected FOXO1 gene rearrangement. This rare case is presented to expand the knowledge of pineal gland tumors and alert us to pay attention to the differential diagnosis of OLIG2-positive round-cell tumors of the central nervous system.

Diffuse midline glioma with histone H3-K27M mutation is a new tumor entity defined by the 2016 WHO Classification of Tumors of the Central Nervous System. A 51-year-old Chinese woman presented with neck pain for a month. Subsequent MRI revealed an intramedullary neoplasm extending from C5 to C7. Histologically, the cellular area of the tumor was composed of primitive, poorly differentiated, small cells with scant cytoplasm, nuclear molding, and brisk mitotic activity, exhibiting PNET-like appearance, while in the hypocellular area, oligodendroglioma-like cells were observed. More importantly, neuropil-like islands were observed in the cellular area. Microvascular proliferation was noted, with no necrosis. Besides histone H3K27M mutation, immunohistochemical staining also showed that the tumor cells were positive for oligodendrocyte lineage transcription factor 2 and ATRX. The neuropil-like areas were positive for synaptophysin, intermingled with scattered neuronal nuclear antigen positive cells. The Ki-67 proliferation index was about 30%, and tumor cells were highly immunopositive for p53. Sequencing for IDH1 codon 132 and IDH2 codon 172 gene mutations showed negative results. Furthermore, fluorescent analysis revealed 1p deletion in the lesion but no 19q deletion. Based on these findings, the tumor was diagnosed as diffuse midline gliomas with histone H3-K27M mutation in the spinal cord, corresponding to WHO grade IV. After 4 months of remission, the tumor recurred; 2 months later, the patient died. Herein, we report an extremely rare case of diffuse midline glioma with histone H3K27M mutation, which was morphologically characterized simultaneously by primitive neuroectodermal tumor-like appearance and neuropil-like islands.

The term \"long-term epilepsy-associated tumor (LEAT)\" encompasses brain lesions associated with drug-resistant epilepsy over a long duration (≥2 years). Notably, some LEATs do not fit into any of the classifications of the World Health Organization (WHO). Herein, we report a LEAT that occurred in the left amygdala of a 16-year-old patient with intractable epilepsy. Histological examination of the resected amygdala revealed diffusely infiltrating tumor cells in the cortex. Perineuronal satellitosis and perivascular aggregation of tumor cells were apparent, along with mild nuclear enlargement and cytologic atypia. Tumor cells were positive for oligodendrocyte transcription factor 2 and neuronal markers including NeuN, neurofilaments, and synaptophysin, but were negative for CD34 and nestin. The most intriguing finding was intranuclear filaments, which appeared as rod- or needle-like shapes under high-power view. Ancillary ultrastructural analysis revealed thin filamentous intranuclear structures in tumor cells. Based on the glioneuronal nature of these cells as well as the infiltrative growth pattern, a diagnosis of LEAT was rendered that was deemed WHO grade I to II; however, the clinicopathological implications of the intranuclear inclusions remain unknown. The patient is currently alive and well without seizures.

Primary intraventricular oligodendroglioma (IVO) is a rare form of clear cell neoplasm and diagnosis is challenging because other clear cell neoplasms such as central neurocytoma must be ruled out. We report a case of primary IVO in which Olig2 immunohistochemistry was useful for the diagnosis. A 33-year-old man was admitted to our hospital with severe headaches due to an intraventricular mass lesion and underwent total resection of the mass lesion. The histological diagnosis was oligodendroglioma because the tumor was negative for synaptophysin and positive for Olig2. IVO is rare and differential diagnoses must be considered. The correct pathologic diagnosis is essential for anticipating the prognosis and selecting adjuvant therapy. In this case, Olig2 was useful for the diagnosis of oligodendroglioma.

We report a case of oligodendroglioma showing marked neuronal differentiation, which arose in the right frontal lobe of a 46-year-old woman. The resected tumor was composed of a mixture of oligodendroglioma, gangliocytoma, and neurocytoma areas with predominance of gangliocytoma-like areas. The oligodendroglioma areas showed immunoreactivity for Olig2 and mutant isocitrate dehydrogenase 1 protein, whereas the gangliocytoma and neurocytoma areas were positive for synaptophysin and NeuN. Ki-67 labeling index was approximately 5% to 10% in the oligodendroglioma areas. Molecular cytogenetic analyses demonstrated chromosomal losses of 1p and 19q and a mutation of isocitrate dehydrogenase 1 (G395A, R132H) in both the oligodendroglioma and gangliocytoma areas. These data suggest that this tumor is an oligodendroglioma associated with prominent neuronal differentiation. There seems to be a close relationship between oligodendroglial progenitor cells and neuronal cells.

We report a rare case of epileptogenic glioma composed of glial progenitor cells that differentiated into an astrocytic and oligodendrocytic tumor. This 4-year-old girl presented with a 1-year history of complex partial seizure. MR scan showed a mass in the left temporal lobe with a cyst and a contrast-enhanced component. Subtotal resection of the tumor was achieved. Histological examination revealed that the tumor exhibited low cellularity composed of astrocytic and oligodendrocytic components, as well as low mitotic activity (MIB-1 = 1%). Immunohistochemical examination revealed GFAP positivity within the astrocytic cells, olig2 positivity within the oligodendrocytic cells, and S100 positivity in both cell types. MAP2 and CD34 were negative, and neurofilament was only positive in preexisting neurons. The pathological diagnosis was epileptogenic glioma (grade I) composed of glial progenitor cells. The postoperative course has been uneventful with good seizure control for 3 years.

A case of unclassified, pediatric cerebral neuroepithelial tumor in a 10-year-old girl that showed remarkable radiosensitivity is reported. MRI revealed a brain tumor of mixed intensity with heterogeneous enhancement in the medial temporal lobe, extending to the basal ganglia. The tumor was partially removed. On pathology, the main part of the tumor showed immature features: the tumor cells had a chromatin-rich large nucleus and less cytoplasm, and mitoses and fragmentation of the nuclei were frequent. On immunohistochemistry, the tumor cells were negative for glial fibrillary acidic protein (GFAP) and synaptophysin and positive for Olig2. The maximum MIB-1 index was 70%. The part invading into the surrounding brain showed similarities in form to a highly anaplastic astrocytoma. The infiltrating tumor cells were positive for GFAP and less positive for Olig2. After 40 Gy radiation, the residual tumor was markedly reduced. Neuroepithelial tumors rarely show such high radiosensitivity, and the reason for the radiosensitivity in the present case may have been the immaturity of the tumor cells.

BACKGROUND: Extraneural metastasis of oligodendroglioma is extremely rare and is diagnosed primarily by biopsy or autopsy and very occasionally by fine needle cytologic examination. We report a case of metastatic oligodendroglioma diagnosed by cytologic examination of a pleural effusion. Such a diagnosis has not been reported before.
METHODS: A 64-year-old woman developed anemia and bilateral pleural effusion 7 years after an operation for an oligodendroglioma over the left frontal lobe. Cytologic examination of the pleural effusion showed aggregates of atypical polygonal cells containing round, hyperchromatic nuclei and scanty, granular cytoplasm in Liu\'s and Papanicolaou stain and cell blocks. Immunohistochemical staining of the tumor cells revealed a positive reaction for antibodies to glial fibrillary acidic protein, S-100 and Olig2. Pleural biopsy confirmed the cytologic diagnosis of pleural effusion. A pathologic fracture of the right humeral and femoral bones was noted 1 month later, and the specimen also showed infiltrating oligodendroglioma cells in bone tissue.
CONCLUSIONS: To the best of our knowledge, this is the first metastatic oligodendroglioma diagnosed by pleural cytology. Fine needle cytology can provide a reliable and rapid way to detect an extracranial metastatic oligodendroglioma in different organs.