This patient presented with chronic headache and right-sided weakness. Imaging revealed a heterogeneous mass centered in the splenium of the corpus callosum, with significant edema. Histopathology of a biopsy showed features of a high-grade glioma such as cellular atypia, endothelial proliferation, and a high Ki-67 proliferation index. Immunohistochemistry was positive for GFAP. Features were consistent with glioblastoma multiforme.

1. HARBOR UCLA NEURO CASE # 6 Anton Mlikotic, MD, Department of Radiology Marcia Cornford, MD, PhD, Department of Pathology Los Angeles County Department of Health Sciences

2. History This patient is a 67 year old woman presenting with chronic headache and gradually increasing right sided weakness

3. A screening non-enhanced CT study of the brain revealed a bilateral, heterogeneous mass centered about the splenium of the corpus callosum (arrows). There is significant associated vasogenic edema which extends high into the left centrum semiovale.

4. A selected trans-axial MRI FLAIR image demonstrates the anatomy of the normal superior right brain. The precentral gyrus is anterior to the central sulcus and controls motor function. The postcentral gyrus is posterior to the sulcus and houses the sensory strip. The pars marginalis is an anatomic landmark that helps to identify the central sulcus, which is directly anterior.

5. FLAIR T1WI T1WI + GAD The MRI FLAIR image on the left shows the mass to be heterogeneous in signal intensity, containing water content centrally and there is high signal in the surrounding white matter of the forceps major, more so on the left, reflecting vasogenic edema. On the T1-weighted image with contrast on the right, there is irregular contrast enhancement along the periphery with low signal and lack of enhancement centrally, a finding related to a necrotic neoplasm.

6. T1-weighted images + contrast A collage of contrast-enhanced MRI images in orthogonal planes shows the extent of the tumor .

7. Diffusion weighted image ADC map The diffusion-weighted sequence detects a few areas of increased signal intensity restricted diffusion along the peripheral aspects of the mass, confirmed by the Apparent Diffusion Coefficient (ADC) map on the right with corresponding darker areas (arrows).

8. Questions: What is the differential diagnosis? What term has been coined to describe the typical appearance of this lesion? Are there imaging features that would support a particular diagnosis? Can imaging accurately define the extent of local disease? What is the role of MR diffusion imaging to narrow the differential diagnosis? How do immunohistochemical markers assist in making a diagnosis?

9. Differential diagnosis: Glioblastoma multiforme (GBM, high grade astrocytoma) Lymphoma Metastasis Tumefactive demyelination Toxoplasmosis

10. This is a needle core biopsy procured during surgery following staining with haematoxolin and eosin (H and E) which shows hypercellularity and lack of necrosis (Magnification 10X)

11. At higher power, there is endothelial cell proliferation in a small venule (arrows), against a background of appreciable cellular atypia. (H and E, Magnification 40X)

12. Even higher magnification more clearly demonstrates variation in both cell size and nuclear appearance. Of note is the absence of “round cells,” which would identify an oligodendrocytic lineage (H and E, Magnification 400X)

13. An immunohistochemistry stain (IMHC) for gliofibrillary acidic protein (GFAP), shows localization within multinucleated cells (arrows) and many smaller cells. (Magnification 400X)

14. A Ki-67 IMHC proliferation index reveals nuclear localization in up to 20% of cells, consistent with a high grade malignancy.

15. Summary of histopathologic findings The mass is characterized by extreme cytologic atypia, with noticeable absence of round conformation cells containing round nuclei, precluding the presence of oligodendrocytic cells. There is no pseudopalisading necrosis and only a slight area of focal necrosis, although there is prominent endothelial proliferation and a high proliferation index over 20%, including actively mitotic polyploid cells. The tumor shows positivity for glial fibrillary acidic protein (GFAP).

17. Discussion Processes that infiltrate or involve the corpus callosum are traditionally referred to as “butterfly lesions,” with a characteristic imaging appearance.

18. The coned-down T2-weighted coronal image demonstrates the “butterfly” configuration of a mass that infiltrates the corpus callosum, and a schematic for comparison.

19. Discussion The corpus callosum consists of densely myelinated fibers that usually interconnect homologous territories of the two cerebral hemispheres. The compact nature of the white matter tracts, relative to the adjacent white matter, creates a natural barrier to the spread of neoplasm and flow of interstitial edema. Therefore, only high grade neoplasms, which exhibit aggressive behavior, tend to cross or involve the corpus callosum. Composed primarily of myelinated axons, it can also involve demyelinating processes. The differential diagnosis for masses involving the corpus callosum includes high grade astrocytomas (in particular, Glioblastoma multiforme), lymphoma, metastatic disease, tumefactive demyelination, and occasionally, toxoplasmosis.

20. Discussion Glioblastoma, also referred to as Glioblastoma multiforme (GBM), is a WHO Grade 4, malignant, rapidly progressive, and ultimately fatal astrocytic neoplasm. It is an extremely aggressive diffuse astrocytic tumor that may arise in any region of the central nervous system with a predilection for the supratentorial white matter. They are the most common primary brain tumor and account for 10-15% of all intracranial tumors and 40-50% of all glial tumors. They may arise de novo or develop from a less-malignant diffuse astrocytoma. Glioblastoma occurs in all age groups, with a peak incidence between 45 and 70 years. There is no sex predilection and the mean survival ranges from less than one year to 18 months, with less than 2% surviving longer than 3 years. Glioblastomas commonly spreads via direct extension along white matter tracts that include the corpus callosum although hematogenous, subependymal and subarachnoid spread can also be seen.

21. Discussion On radiologic imaging, they typically present as heterogeneous masses that, when large enough, have central necrosis. A peripherally enhancing, irregular ring represents the more cellular and vascularized portions of the tumor, and the central T1 low signal intensity and T2 high signal intensity portions correspond to areas of necrosis. The classic radiographic “butterfly” pattern is caused by spread of the tumor across the corpus callosum into the opposite hemisphere. The presence of associated vasogenic edema suggests infiltration by tumor that extends beyond the bulk mass itself. Unfortunately, the absolute margins of the mass are not well-appreciated on current imaging techniques. It is purported that the lesion contains microscopic tendrils that are occult on routine contrast-enhanced MR imaging, necessitating a wide margin of surgical resection.

22. Discussion On MR spectroscopy, a neoplastic signature is elicited, with a rise in choline and decrease in N-acetyl-aspartate, as well as lipid and lactate peaks corresponding to necrosis. Similar to neoplasms with high nuclear to cytoplasmic ratios, such as lymphoma and primitive neuroectodermal tumor, the solid components of the mass may show areas of restriction on diffusion-weighted imaging. In addition, the mass may occasionally be multi-centric with neighboring satellite lesions and may spread to the ventricular systems and the intracranial and spinal subarachnoid spaces, warranting a contrast-enhanced evaluation of the entire neuroaxis to assess for distal seeding of tumor.

23. Discussion Macroscopically, glioblastomas appear as well-defined mass lesions although there is invariably significant microscopic infiltration of tumor into the surrounding parenchyma. They sometimes form multiple lesions, and this “multicentric” type of glioma has an estimated frequency between 2-7%. Although they sometimes extend into the subarachnoid space or ventricles with the potential for cerebral spinal fluid dissemination, extra-cranial extension and hematogenous dissemination are quite rare.

24. Discussion On microscopic analysis, all glioblastomas display the histologic features of high cellularity, marked nuclear atypia, mitoses, microvascular proliferation, and necrosis. However, their appearance may be highly variable, with considerable regional heterogeneity. There may be considerable nuclear and cytoplasmic pleomorphism, with multinucleated giant cells whereas others may consist mainly of small, undifferentiated cells with scant cytoplasm. Occasionally, cells with glandular or epithelioid features, oligodendrocyte-like cells, granular cells, and lipidized cells may be present. Necrosis is characteristic, with large, confluent areas or small, band-like or serpiginous, geographic foci surrounded by densely packed tumor cells, which imparts a highly diagnostic “pseudopalisading” pattern. Capillary endothelial proliferation with or without central thrombosis is commonly encountered.

25. Discussion CNS Immunohistochemistry provides an important adjunct to the diagnosis of CNS neoplasms. (see chart on next slide) Most glioblastomas show positivity for glial fibrillary acidic protein (GFAP), and proliferation indices are typically prominent, averaging 15% to 20%, and are usually greatest in tumors composed predominantly of small, undifferentiated cells.

26. Examples of Immunohistochemistry (IMHC) Profiles for Various CNS Neoplasms GFAP = Glial fibrillary acidic protein NSE = Neuron specific enolase SNPTN = Synaptophysin var = variable staining Chart derived from information posted on Pathologyoutlines.com Neoplasm Lineage Type GFAP Vimentin EMA NSE SNPTN Alpha FP OCT4 S-100 CD 3 CD20 CD68 CD99 GBM Astrocytic Glial + - - - - - - - - - - - Oligodendroglioma Oligodendroglial Glial s - - - - - - + - - - - Ependymoma Ependymal Glial + + slight - - - - - - - - - Astroblastoma Neuroepithelial Glial + + focal - - - - + - - - - Ganglioglioma Neuronal Glial + - - + + - - - - - - - PNET Embryonal Nonglial + - - - - - - - - - - + Choroid plexus papilloma Choroid plexus Nonglial - + var - slight - - + - - - -- Pineoblastoma Pineal Nonglial - - - + + - - + - - - - Meningioma Meningeal Nonglial - + + - - - - + - - - - Melanoma Metastatic Nonglial - + - - - - - + - - - - Germinoma Germ cell Nonglial - - - - - - + - - - - - Pituicytoma Sellar Nonglial slight + - - - - - + - - - - B cell lymphoma Hematopoietic Nonglial - - - - - - - - - + - + T cell lymphoma Hematopoietic Nonglial - - - - - - - - + - - + Histiocytic sarcoma Hematopoietic Nonglial - - - - - - - var - - + - Chordoma Mesenchymal Nonglial - + + - - - - + - - - -

27. References Lesions of the Corpus Callosum: MR Imaging and Differential Considerations in Adults and Children. American Journal of Radiology July 2002 Volume 179, number 1, 251-257. EC Bourekas, K Varakis, D Bruns, et al. Escourolle and Poirier Manual of Basic Neuropathology: Fourth Edition. F Gray, U De Girolami, J Poirier. Tumors of the Central Nervous System. Pages 24 – 28.