Case Study 15 Gabrielle Yeaney, M.D.

Question 1 25-year-old man with history of seizures. Describe the MRI findings (location, enhancement, mass effect).

Axial T1

FLAIR

Axial T1 post contrast

Coronal T1 post contrast

Answer There is a well-defined, intra-axial, partially-cystic, NON- enhancing mass (2.6cm) in the left inferior temporal lobe. There is no mass effect or midline shift.

Question 2 What is in your differential diagnosis based on MRI/ age?

Answer Ganglioglioma, Pleomorphic xanthoastrocytoma, Dysembryoplastic neuroepithelial tumor, Oligodendroglioma, Extraventricular neurocytoma.

Question 3 Describe the cytologic features of the smear. Click here to view slide.

Answer The tissue is more cellular than normal cortex.  There are cells with round to ovoid nuclei and fibrillary processes with admixed larger cells with round nuclei and prominent nucleoli (neurons).  Several calcifications are present.  Mitotic figures and anaplasia are not seen.

Question 4 What is your intraoperative diagnosis (A. Neoplastic / Defer / Non-neoplastic, B. ______)?

Answer Neoplastic Low-grade neuroglial neoplasm; If you hadn’t seen the imaging prior to looking at the smear, you might defer and consider cortical dysplasia in your differential.

Question 5 Review the permanent section and describe the histologic features. Click here to view slide.

Answer The tumor shows numerous dysmorphic neurons (ganglion cells) mixed with atypical astrocytes (enlarged elongated nuclei with irregular nuclear contours).  Mitotic figures are not seen.  There are foci of dystrophic calcification of neurons and vessels.

Question 6 You order some immunostains to further classify the tumor cells and look for proliferative activity. Review the immunohistochemical studies. Click here to view slides.

Answer NeuN and synaptophysin highlight the neuronal component of the tumor.  Vimentin and GFAP (overstained) highlight astrocytic processes of the tumor cells.  The proliferative activity of the tumor cells is very low (Ki-67 = 1-2%).

Question 7 What is your final diagnosis?

Answer Ganglioglioma

Question 8 What is the most important histologic feature that distinguishes pilocytic astrocytoma with trapped neurons from ganglioglioma?

Answer The cortical neurons overrun by an infiltrating glioma (oligo or astro) will appear cytologically normal, in contrast to neuronal cells in a ganglioglioma which should be dysmorphic.  Dysmorphic neurons may have ganglioid cytology, more than one nucleus, cytoplasmic vacuolation, abnormally clumped Nissl and/or abnormal processes.  These abnormal neurons usually stain with synaptophysin (surface positivity), chromogranin (cytoplasmic positivity), NeuN (nuclear and cytoplasmic), CD34.  These stains are not specific, so assessment of the morphology of the stained cell is important.  Co- expression of synaptophysin and GFAP is not uncommon and is a sign of an abnormal neuron.  Crysl violet may be helpful in highlighting cells with Nissl substance.