PMC3786386_01
Progression of findings on RSI over a 12-month period. Three coronal RSI images spanning a 12-month period following surgery and chemoradiation depict an enlarging area of restricted diffusion which eventually crosses the corpus callosum and extends into the contralateral frontal lobe.
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Over the next 18 months, this area of restricted diffusion became significantly larger and more confluent, eventually crossing the corpus callosum and extending into the contralateral frontal lobe (Figure 1).
(A,B) RSI and CBV maps in bevacizumab-related necrosis versus GBM. (A) is a side-by-side comparison of the RSI signal seen in our patient and the RSI signal seen in a typical GBM, with the two RSI images scaled identically (i.e., same window and level). (B) is a side-by-side comparison of the DSC MR perfusion-generated CBV map for this patient and the CBV map for the same patient with GBM shown in (A) (with adjacent color scales).
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However, on further inspection, it became clear that the degree and homogeneity of the restricted diffusion seen in this case was much greater than what is typically seen in high-grade glioma (Figure 2A), with GBM's usually demonstrating less intense and more heterogeneous restricted diffusion. In contradistinction, high-grade gliomas typically demonstrate markedly elevated CBV (Figure 2B).
Correlation of the gross pathology with imaging. Coronal gross pathologic specimen as well as matched coronal FLAIR (fluid attenuated inversion recovery), coronal T1 post-contrast, and coronal RSI sequences from the patient's last available MRI for correlation.
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Gross pathologic evaluation demonstrated yellow, caseous material in the left frontal lobe compatible with necrosis (Figure 3).
(A,B) Coagulative necrosis and negative Ki-67 stain. (A) Shows two H&E stains from the grossly necrotic region; the first demonstrates coagulative necrosis with a hyalinized fibrotic blood vessel in the center and the second demonstrates scattered gemistocytes on a background of edematous white matter. (B) is a Ki-67 stain of this region, which was completely negative.
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Histopathologic evaluation of this area revealed coagulative necrosis, gliosis, hyalinized blood vessels, and scattered atypical gemistocytes (Figure 4A). Although it is unclear if these gemistocytes represent tumor gemistocytes or reactive gemistocytic astrocytes, the Ki-67 stain was completely negative (Figure 4B), indicating that these are non-proliferating cells.