Gliosarcomas are rare and have an incidence 1.8–2.8% that of GBMs [18
]. Similar to other glial based tumors, PGS affects adults in the sixth to seventh decade of life, with a significantly higher proportion found in men than in women (M:F ratio 1.4–1.8:1) [12
]. The presenting signs and symptoms reported are consistent with those of a rapidly expanding intracranial tumor, including aphasia, headache, hemiparesis, seizures, and cognitive decline, depending on its location. The clinical similarities to GBM have led many authors to conclude that these tumors are clinically indistinguishable [12
]. However, there are a number of important and distinct features of PGS that suggest that it is a separate entity.
The striking features of PGS that distinguish it from GBM include its location and its differential radiographic and gross appearance. Gliosarcoma is almost never found infratentorially and the majority of the reports describe its temporal lobe predilection [18
] while a few report a higher incidence in the frontal lobe [12
]. The published experience describes two distinct appearances of PGS grossly at operation. The early case series by Feigin and Morantz noted the gross appearance of PGS were often firm, well-circumscribed masses commonly found at the periphery in contact with the dura mater, falx cerebri or the skull [3
]. However, the series by Perry and colleagues reported that most cases of gliosarcoma [12
] were diffusely infiltrating with ill defined margins (exact proportions not given). In contrast the series by Parekh and colleagues found only 2 of 15 cases had such characteristics on gross appearance [12
]. These three series illustrate the variety of potential appearances of PGS, despite the use of the same diagnostic criteria described by the WHO.
The findings on imaging are also variable. On computed tomography (CT), the lesions can appear with large necrotic areas and heterogenous contrast enhancement, similar to that of GBMs, or as hyperdense lesions with well-defined margins and homogenous enhancement, mimicking the appearance of a meningioma [23
]. In a small case series of five patients, Maiuri and colleagues [24
] reported that PGS resembling meningiomas on CT appeared similar to meningiomas on gross pathology as well. However, this correlation was not found in a subsequent report that included 15 patients with PGS who received surgical resection [21
]. Of the 14 patients who were imaged by CT, only 3 showed homogenous enhancement, similar to a meningioma. Of 15 tumors that were excised, 13 showed firm lesions with well demarcated margins, and two were necrotic and infiltrating with ill defined borders. Detailed descriptions of appearance on Magnetic Resonance Imaging (MRI) are lacking, as the majority of large case series were reported during the era when CT was the primary method of imaging. Hence, reports of clinical correlation with findings on MRI are also lacking. Recent case reports show that findings on MRI are similar to those on CT, with masses having heterogeneous enhancement and sharply demarcated or irregular borders [4
]. A prominent and common feature of gliosarcomas seen on MRI is marked peritumoral edema [18
]. The difficulty in establishing the diagnosis of PGS radiologically underscores the importance of establishing methods to make the diagnosis histopathologically. The variability of radiographic and pathologic presentations of gliosarcoma suggests a potential need for an update of the WHO criteria reflecting these potential clinical subtypes.
Despite its variable appearance, initial data have supported uniform aggressive treatment of PGS. Morantz and Feigin as well as Parekh and colleagues [3
] warn that an attempt to shell out PGS that resemble meningiomas will likely result in persistence of tumor tissue with subsequent recurrence. Currently, a reasonable approach to these tumors is an attempt at gross total resection when possible. However unlike GBM, there currently are no well controlled studies to support the advantage of a gross total resection of PGS over biopsy or subtotal resection followed by adjuvant therapy.