Brain Pathology Case of the Month - February 2007

DIAGNOSIS    Pleomorphic xanthoastrocytoma


This report demonstrates an atypical presentation of a pleomorphic xanthoastrocytoma that, based upon clinical and radiographic grounds, was most consistent with a meningioma. PXAs typically occur in younger patients, although there are several case reports of these neoplasms discovered in patients in the fourth and fifth decades of life [5,9,12]. Seizures represent the typical clinical presentation. In the 1996 review of the 80 case reports (with clinical symptoms) available in the literature by Van Roost, et al., symptoms of increased intracranial pressure, headache and paresis were found in 15%, 10% and 1% of patients, respectively [13]. Typically PXAs are contrast enhancing lesions which by MRI are T1 hypo or isointense and T2 hyperintense. Cystic change and peritumoral edema are found in approximately one-half and one-third of cases, respectively [13]. While PXAs and meningiomas share some radiographic findings, the presence of a solid mass with a dural tail is typical of meningioma. Although Kepes [6] states that PXAs involve the leptomeninges, but "as a rule not the dura mater," there have been a handful of cases, in addition to the current case, which have reported dural attachment [2,3,12]. This case represents the very rarely reported circumstance of a dural-based PXA with no apparent cerebral cortical component (including leptomeningeal), either radiographically, surgically or histologically. Cytologic preparations are routinely used alone or in conjunction with frozen sections in intraoperative pathologic consultations. While PXAs are capable of being diagnosed based upon an intraoperative cytologic preparation alone [1], the diagnosis of meningioma in this case likely reflected a non-representative sampling of the lesion including a portion of the reactive meningeal proliferation. The histologic appearance of the permanent tissue specimens raised a number of diagnostic possibilities. Immunopositivity for GFAP excluded the possibility of an unusual pleomorphic variety of meningioma. Other gliomas, including glioblastoma and gliosarcoma, were considered in light of the cellular pleomorphism. The well-circumscribed nature of the lesion and the absence of mitoses mitigated against the diagnosis of glioblastoma. Additionally the uniform GFAP immunopositivity would not be a feature of gliosarcoma. With the presence of convincing eosinophilic granular bodies, pilocytic astrocytoma, ganglioglioma and pleomorphic xanthoastrocytoma were considered. While pilocytic astrocytomas can have a spectrum of histologic appearances, the degree of pleomorphism in the current case would be truly exceptional for that diagnosis. Although the histologic features of pleomorphic GFAP immunoreactive cells, xanthomatous cells and an exuberant reticulin network are diagnostic of PXA [4], a co-existing gangliogliomatous component has also been reported [10]. No regions suggestive of ganglion cell tumor histology were found; a synaptophysin immunostain was also negative.


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Contributed by Terri Haddix, MD, Steven Chang, MD and Hannes Vogel, MD

International Society of Neuropathology