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Magnetic Resonance Imaging Findings of Radiation-induced Changes in Malignant Gliomas


Figure 4: Radionecrosis in a Right Frontal Anaplastic Astrocytoma Treated with Surgery and Temozolomide Chemoradiotherapy (Same Patient as in Figure 1)


AB


Figure 5: Radionecrosis in a Right Frontal Cystic Metastasis from Cervical Cancer


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CD CD


EF E F


G G


H


4 321 0


A: Axial fluid-attenuated inversion recovery (FLAIR) image showing elevated signal intensity in the frontal white matter (open arrow); B: Contrast-enhanced axial T1-weighted image revealing irregular and pseudonodular enhancement of the surgical margins, particularly on its posterior aspect and enhancement crossing the mid-line through the corpus callosum (solid arrows); C: Axial FLAIR image at follow-up study demonstrating a markedly increased right parietal and bifrontal oedema (*); D: Paired contrast-enhanced axial T1-weighted image showing increased areas of amorphous, irregular enhancement (Swiss-cheese pattern) in frontal white matter; E: Paired apparent diffusion coefficient (ADC) map demonstrating elevated ADC values as high as 1.81x10-3mm2/second; F: Paired relative cerebral blood volume (rCBV) map evidencing values under 0.7; G: Magnetic resonance spectroscopy (single voxel, echo time 35ms) showing slightly increased choline (Cho) levels, decreased N-acetyl aspartate (NAA) levels and large peaks of lipids/lactate (Lip/Lac). These findings are typical of radionecrosis.


Cho levels are typical of RN.4,7 Second, significant elevations of the


Cho/NAA and Cho/Cr ratios (with a concomitant reduction in the NAA/Cr ratio) in contrast-enhancing lesions represent tumour recurrence.8,9,11,12,15,17


with areas of radiation injury and normal adjacent tissue.4,7,9,15


In different studies, cut-off values of 1.71–1.8 (i.e. values >1.8 being diagnostic of recurrence) for either the Cho/NAA or Cho/Cr ratio are considered diagnostic of recurrence5,9,15


compared EUROPEAN ONCOLOGY & HAEMATOLOGY Third,


the presence of lipids (Lip), which reflects necrosis, and lactate (Lac), which indicates ischaemia and necrosis, may suggest both RN and recurrence. However, large Lip peaks and Cho/Lip-Lac ratios under 0.3 have a high positive predictive value for RN.4,5,7,17


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4


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A: Axial fluid-attenuated inversion recovery (FLAIR) image shows a right frontal mass with well-defined margins (*) and mild perilesional vasogenic oedema. Several chronic ischaemic foci in the deep white matter are also observed; B: Axial contrast-enhanced T1-weighted image evidences thin peripheral enhancement of the lesion. The patient underwent whole-brain radiation therapy and radiosurgery followed by surgical resection. Post-surgical axial FLAIR (C) and contrast enhanced T1-weighted images (D) demonstrated surgical changes in the tumoral bed, leucoencephalopathy and irregular peripheral enhancement of the surgical cavity (solid arrows). Four months later, paired axial FLAIR (E) and contrast- enhanced T1-weighted images (F) demonstrate how the surgical cavity presents thicker walls with pseudonodular enhancement. G: Perfusion map evidencing low relative cerebral volume values ranging between 0.31 and 0.72; H: Magnetic resonance spectroscopy (single voxel, echo time 35ms) shows markedly decreased choline levels with prominent lipid and lactate peaks. These findings support the diagnosis of radionecrosis.


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