ABSTRACT
Tissue sampling is an important consideration in rendering an accurate diagnosis in many of these cases. Gangliogliomas, for example, are tumors marked by an atypical ganglion cell
component and a glioma component. Both components of the tumor are generally not evenly distributed throughout the entire neoplasm. In fact, in some gangliogliomas, the ganglion cell component may be present in only a small part of the tumor; obviously, if this region of the tumor is not sampled, a correct diagnosis will not be made. The classic dysembryoplastic neuroepithelial tumor is a multinodular, cortical based microcystic tumor. Small biopsies make it quite difficult or impossible to recognize the architectural pattern which is a salient and useful diagnostic feature of this tumor. In such cases, the differential diagnosis expands to include other lowgrade tumors which can have a microcystic appearance and are comprised primarily of cells with rounded nuclei (such as microcystic oligodendroglioma and protoplasmic astrocytoma). Pilocytic astrocytomas classically have a biphasic appearance, which may not be readily apparent if a limited tissue sampling is obtained. Rosenthal fibers and granular bodies, which are useful diagnostic clues to a diagnosis of pilocytic astrocytoma, are not present in all cases, and their absence may also cause diagnostic confusion. To further complicate matters, occasional pilocytic astrocytomas can contain areas with small rounded cells marked by pericellular clearing, mimicking an oligodendroglioma.
