Pilocytic astrocytoma with abundant oligodendroglioma-like component
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- Utsuki, S., Oka, H., Kijima, C. et al. Brain Tumor Pathol (2012) 29: 103. doi:10.1007/s10014-011-0074-9
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An 18-year-old girl presented with a history of visual disturbance without headache, nausea, or vomiting in May 2010. In July 2010, the patient visited our hospital because of visual disturbance. Head magnetic resonance images revealed hydrocephalus caused by a ring-enhancing mass lesion located in the vermis. Total tumor removal was performed. Histological findings revealed that honeycomb cells resembling oligodendrocytes accounted for most parts of the tumor. Rosenthal fibers and hyaline droplets were seen in a small portion. The tumor cells were immunoreactive for GFAP and Olig2, but none of the tumor cells were immunoreactive for Symaptophysin, EMA, or IDH 1. according to these findings, the tumor was diagnosed as pilocytic astrocytoma with an abundant oligodendroglioma-like component. Pilocytic astrocytoma is known to be associated with an oligodendroglioma-like component; however, the differential diagnosis for oligodendroglioma may be difficult when an oligodendroglioma-like component occupies most of the tumor.
KeywordsCerebellar tumorHoneycomb structureIDH1OligodendrogliomaPilocytic astrocytoma
The histology of pilocytic astrocytoma shows a characteristic biphasic pattern, with compact and microcystic areas, and sometimes there are oligodendroglioma-like areas that closely resemble oligodendrogliomas. Chronic degenerative findings such as Rosenthal fibers, eosinophilic granular bodies, and hyaline droplets aid in diagnosis . Blood vessels also develop in the interstitium and may show hyperplasia of microvessels, with hyalinization of vessel walls and a glomerular capillary-like structure. Sometimes, a large polymorphic nucleus appears; however, cells closely resembling oligodendrogliomas are less frequently seen .
However, the ratio of tumor to cells resembling oligodendrocytes is unknown. We herein report a case of pilocytic astrocytoma with abundant honeycomb cells such as oligodendrogliomas as well as a few Rosenthal fibers and hyaline droplets.
Fluorescence in situ hybridization (FISH) analysis was performed from archived paraffin blocks for 1p/19q status, and 1p/19q had intact alleles.
There were no specific findings, and structures such as microvilli or junctions were not observed by electron microscopic examination.
Various tumors have a morphologic honeycomb structure, such as pilocytic astrocytoma, oligodendroglioma, clear cell ependymoma, extraventricular neurocytoma, and rosette-forming glioneuronal tumor; these tumors should be differentiated. This tumor had differentiated to glia, but not to neuronal cells, and it was unknown whether the honeycomb structure that constituted most of the tumor tissues showed the origin of the kind of tumor. This tumor was diagnosed as pilocytic astrocytoma with abundant oligodendroglioma-like cells, since a small portion of this tumor accorded with pilocytic astrocytoma histologically. The results of immunohistological studies (MGMT-positive and IDH1-negative) and FISH analysis (1p/19q had intact alleles) supported that the tumor was pilocytic astrocytoma, too. Pilocytic astrocytoma is associated with an oligodendroglioma-like component; however, the differential diagnosis of oligodendroglioma may be difficult when an oligodendroglioma-like component occupies most of the tumor. There is no detailed statement about the ratio of honeycomb structure cells to tumor cells in pilocytic astrocytoma. In this case, almost all tumor tissues were investigated as specimens, and most of the tumor was occupied by oligodendroglioma-like cells showing a honeycomb structure. The reason the diagnosis of this case was difficult is that tissue of a conventional pilocytic astrocytoma was found in only a small portion.
These tumors may be misdiagnosed as oligodendroglioma when all of the tumor tissue obtained by subtotal resection or biopsy contains oligodendroglioma-like cells indicating a honeycomb structure. Our case is a valuable one as it shows that pilocytic astrocytoma must be distinguished, even if tumor tissue appears at a glance to be oligodendroglioma. It is difficult to differentiate oligodendroglioma and a tumor with oligodendroglioma-like morphology only with honeycomb structure morphologically. Also, immunohistochemistry with glial markers such as the oligodendroglial marker Olig2 was not useful in this situation, since oligodendroglioma-like cells in the pilocytic astrocytoma were immunopositive for Olig2 .
The immunostaining of IDH1 is useful to distinguish oligodendroglioma from oligodendroglioma-like cells of pilocytic astrocytoma [4, 5]. In oligodendroglioma, the immunopositive rate of IDH1 is 70–90%. In contrast, the immunopositive rate is 0% for a tumor with an oligodendroglioma-like morphology, except in oligodendroglioma that includes oligodendroglioma-like cells of pilocytic astrocytoma [4, 5]. If tumor cells are immunopositive for IDH1, the tumor will be an oligodendroglioma. Also, if tumor cells are immunonegative for IDH1, the tumor is more likely to be a tumor with oligodendroglioma-like morphology. For a tumor in which most tumor cells have oligodendroglioma-like morphology, immunohistology of IDH1 helps in differentiating them from oligodendroglioma.
There are few previous reports about cerebellar oligodendroglioma [6–10]. The clinical feature of cerebellar oligodendrogliomas is more common in children than cerebral oligodendroglioma and is often associated with cyst formation. These features seem to resemble features of cerebellum pilocytic astrocytoma. Therefore, the differential diagnosis should be done carefully. Immunohistochemistry and genetic techniques are utilized for a convincing adjuvant diagnosis of the brain tumor diagnosis, and then, the diagnosis is more objective and certain. This case is valuable because it shows that in case of a tumor, differentiation between cerebellar oligodendroglioma and pilocytic astrocytoma is difficult.