This CT scan shows a ganglioglioma in the right temporal lobe; note the arrow pointing to a cystic lesion. The presenting symptom was seizure.

Gangliocytomas are composed of neuronal cells scattered within a glial component, which usually resembles a pilocytic astrocytoma or fibillary astrocytoma. Rosenthal fibers and eosinophilic granular bodies (not seen here) may occasionally be present.

Two populations of cells are present: (1) atypical ganglion cells which tend to cluster haphazardly and lack polarity, occasionally bizarre and binucleate forms are seen; (2) glial cells -- this component usually resemble fibrillary or pilocytic astrocytoma and rarely, oligodendroglioma. Eosinophilic granular bodies and Rosenthal fibers may be seen in tumor periphery (Fletcher).

The ganglion cells are atypical, with abnormal distribution of Nissl substance, cytomegaly and multinucleation (not seen here).

The stroma is delicate and fibrillary, with a lymphocytic infiltrate. The lymphocytes tend to cluster around the vessels

Tumor cells are strongly positive for GFAP and MAP-2. GFAP highlights the glial elements while MAP-2 is present within the dysplastic neurons. EGFR was negative.

Gangliogliomas are the most common mixed neuronal-glial tumor and comprise 1% of all brain tumors, but 4-8% of pediatric brain tumors (Fletcher, Prayson).

Gangliogliomas mostly arise in the temporal lobes, followed by the parietal and frontal lobes. Imaging demonstrate a well-demarcated tumor with cystic and calcified components; an enhancing mural nodule may be seen. Similar to dysembryoplastic neuroepithelial tumor (DNT), another type of tumor with glial and neuronal components, overlying and adjacent cortex may show dysplasia (Prayson).

The neurons can be highlighted with an IHC stain for neurofilament and synaptophysin; stains which highlight Nissl substance can also be helpful in detecting neuronal cells. The glial elements can be highlighted by GFAP, vimentin and S-100 (Fletcher). The stroma can be fibrous, fibrovascular or desmoplastic with a perivascular lymphocytic infiltrate.

Most occur prior to age 21 and the most common presentation is seizures. In fact, ganglioglioma is the most common tumor removed for seizures (Prayson).

The glial component determines the grade of this tumor, which is usually WHO Grade I. When Ki-67 is performed, it is confined to the glial elements (Fletcher). Anaplastic transformation occurs in about 10% of cases (WHO Grade III).