A 62-year-old male presented with headache, nausea and vomiting. Imaging showed a lobulated, peripherally enhancing mass in the left parietal-occipital lobe with surrounding edema. The mass was surgically resected. Pathology revealed sheets of uniform small blue cells consistent with a Primitive Neuroectodermal Tumor (PNET), a rare and aggressive brain tumor seen more commonly in children. Immunohistochemical staining supported the diagnosis of PNET.

1. Harbor-UCLA Neuro-Radiology Case Conference Sahar Farzin, M.D. Department of Radiology, Harbor UCLA Medical Center Thu Tran, M.D. Department of Pathology, Harbor UCLA Medical Center

2. History: 62 year old male presents with headache, nausea and vomiting

3. Imaging Axial head CT with contrast

4. Imaging Axial T1WIs post-gadolineum

5. Imaging Coronal T1WIs post-gadolineum

6. Imaging Sagital T1WI post-gadolineum

7. Imaging Axial FLAIR

8. Discussion of Imaging Findings CT with contrast shows a lobulated, peripherally enhancing mass in the left parietal-occipital lobe. Surrounding vasogenic edema extends to the splenium of the corpus callosum. There is mass effect on the trigone of the left lateral ventricle. MR images show a 3.7 x 3.8 x 4.0cm lobulated mass with heterogenous peripheral enhancement and central low signal intensity in the left parietal-occipital lobe with extension to the cortex. Anteriorly there is vasogenic edema extending into the splenium of the corpus callosum. There is no morphologic evidence of tumor extension into the corpus callosum. Differential Diagnosis based on imaging: Glioblastoma Multiforme vs. Metastasis

9. Operative procedure performed: Left parieto-occipital craniotomy and resection of mass

10. Pathology Hematoxylin-Eosin, 4x: The tumor is comprised of sheets of uniform small blue cells with focal necrosis

11. Pathology Hematoxylin-Eosin, 20x: The tumor cells are rounded with irregular hyperchromatic nuclei and small amounts of eosinophilic or clear cytoplasm

12. Pathology MIB-1 Immunohistochemical Stain, 4x: Proliferation index is 20% to 50%

13. Pathology CD99 Immunohistochemical Stain, 10x: Strong membranous staining of tumor cells

14. Pathology Glial Fibrillary Acidic Protein (GFAP) Immunohistochemical Stain, 4x: Tumor component showing focal positivity

15. Pathology CAM 5.2 Synaptophysin AE1-3 CD45 Immunohistochemical Stains, 4x: No immunoreactivity

16. Diagnosis Primitive Neuroectodermal Tumor, (PNET) WHO GRADE 4

17. Discussion Supratentorial PNETs were once known as cerebral neuroblastomas. They are classified as a WHO grade IV, aggressive tumor. These tumors are typically solitary, well-circumscribed with irregular enhancement, and show cytic or necrotic areas. Calcifications and hemorrhagic components are not uncommon. PNETs are usually seen in children, and 80% occur in those less than 10 years of age. Only sporadic cases of PNETs in adults have been reported in the literature. Less than 1% of adult brain tumors are PNETs.