Pleomorphic xanthoastrocytoma and oligodendroglioma: collision of 2 morphologically and genetically distinct...

With the exception of oligoastrocytoma, mixed gliomas are rarely encountered, and the astrocytic component of mixed oligoastrocytoma is almost always fibrillary and diffusely infiltrative. Pleomorphic xanthoastrocytoma (PXA) has occasionally been described in conjunction with ganglioglioma, as well as in 1 case of oligodendroglioma. In this latter case, described by Perry et al., 1p/19q codeletions were not detected. The authors report on a 25-year-old woman with a combined PXA/oligodendroglioma in which concurrent 1p/19q codeletions were detected in the oligodendroglial component only. The patient presented with a 1-month history of headaches. Neuroimaging revealed a heterogeneous left temporal mass with focal enhancement, cystic changes, hemorrhage, and left-to-right midline shift. The patient underwent a craniotomy and gross-total resection. Pathological examination revealed a glial tumor composed of 2 apparently distinct components. The largest component exhibited a prominent fascicular, reticulin-rich, spindle cell arrangement admixed with areas of highly pleomorphic cells, with bizarre cytological features reminiscent of PXA. A smaller component was composed of cellular sheets and lobules of oligodendroglial cells. Both components were characterized by anaplastic features. Dual-color fluorescence in situ hybridization for 1p/19q codeletions was performed. Only the oligodendroglial component showed the combined 1p/19q deletions. This case represents the first instance in which PXA has been reported in conjunction with an oligodendroglioma exhibiting the "molecular signature" characteristic of oligodendroglial neoplasms. The different genetic alterations seen in the 2 components of this neoplasm argue in favor of a "collision tumor" rather than a mixed glioma of the same genotype.