Department of Radiology, Neuroradiology Section, University of Alabama at Birmingham, Birmingham, Alabama, USA.
Radiographics. 2012 Sep-Oct;32(5):1343-59. doi: 10.1148/rg.325125002.
Radiation necrosis in the brain commonly occurs in three distinct clinical scenarios, namely, radiation therapy for head and neck malignancy or intracranial extraaxial tumor, stereotactic radiation therapy (including radiosurgery) for brain metastasis, and radiation therapy for primary brain tumors. Knowledge of the radiation treatment plan, amount of brain tissue included in the radiation port, type of radiation, location of the primary malignancy, and amount of time elapsed since radiation therapy is extremely important in determining whether the imaging abnormality represents radiation necrosis or recurrent tumor. Conventional magnetic resonance (MR) imaging findings of these two entities overlap considerably, and even at histopathologic analysis, tumor mixed with radiation necrosis is a common finding. Advanced imaging modalities such as diffusion tensor imaging and perfusion MR imaging (with calculation of certain specific parameters such as apparent diffusion coefficient ratios, relative peak height, and percentage of signal recovery), MR spectroscopy, and positron emission tomography can be useful in differentiating between recurrent tumor and radiation necrosis. In everyday practice, the visual assessment of diffusion-weighted and perfusion images may also be helpful by favoring one diagnosis over the other, with restricted diffusion and an elevated relative cerebral blood volume being seen much more frequently in recurrent tumor than in radiation necrosis.
脑放射性坏死通常发生在三种不同的临床情况下，即头颈部恶性肿瘤或颅内轴外肿瘤的放射治疗、脑转移的立体定向放射治疗（包括放射外科手术），以及原发性脑肿瘤的放射治疗。了解放射治疗计划、放射野中包含的脑组织量、放射类型、原发性恶性肿瘤的位置以及放射治疗后时间的长短，对于确定影像学异常是放射性坏死还是复发性肿瘤极为重要。这两种病变的常规磁共振（MR）成像表现有很大的重叠，即使在组织病理学分析中，肿瘤与放射性坏死混合也是常见的发现。扩散张量成像和灌注 MR 成像（计算某些特定参数，如表观扩散系数比、相对峰值高度和信号恢复百分比）、磁共振波谱和正电子发射断层扫描等高级成像方式有助于区分复发性肿瘤和放射性坏死。在日常实践中，通过评估弥散加权和灌注图像，也可以通过限制扩散和相对脑血容量升高来支持其中一种诊断，这种情况在复发性肿瘤中比放射性坏死更为常见。
