A Rare, Mixed Neuronal-glial Tumor of the Central Nervous System

Diagnosis

Ganglioglioma

Ganglioglioma is a rare mixed, neuronal-glial tumor that is composed of mature, neoplastic neurons and glial cells. This tumor occurs mainly in children and young adults. However, in one series of 27 patients with ganglioglioma, the age range was from 3 to 52 years ¹. Thus the age of occurrence of this tumor in our patient is not unusual. The location of the tumor, in the temporal lobe as well as the relationship of our patient's tumor to a seizure disorder is not unlike the presentation and location of most gangliogliomas. Gangliogliomas may also be found in the frontal and parietal lobes as well as in the cerebellum and suprasellar regions of the brain.

The MRI features of gangliogliomas can be either that of a solid or a cystic lesion with a mural, enhancing nodule ^{2, 3, 4}. When the MRI features of the ganglioglioma is that of a cystic lesion, then other central nervous system (CNS) with similar features, such as hemangioblastoma, a pilocytic astrocytoma and an infectious or inflammatory cyst, should be considered as possible diagnoses. Hemangioblastomas are usually located in the cerebellum and the patients with this lesion are in their third to fifth decade. Cystic, pilocytic astrocytomas are usually centrally located CNS tumors of young children. An atypical location for a cystic pilocytic astrocytoma would be in the temporal lobe. The possibility of an infectious/inflammatory cyst is a reasonable consideration because our patient is on steroid therapy. Thus, although location and age are helpful in distinguishing between hemangioblastomas and pilocytic astrocytomas, biopsy of the lesion will provide a definitive diagnosis.

In tissue sections, it is important to be able to distinguish the neoplastic neurons from neurons that are entrapped in an infiltrating glioma. Loss of polarity of the neurons as well as binucleation are helpful features that would indicate a diagnosis of ganglioglioma. Immunohistochemistry aids in the detection of neurons in a ganglioglioma since the neurons stain with antibodies for chromogranin A, vasoactive immunopeptide and synaptophysin. Staining of neurons for synaptophysin and chromogranin have been proposed as features that distinguish neoplastic neurons from normal neurons.