Cancer causes inflammation as it progresses through healthy tissue. The differentiation of tumoral growth from the surrounding inflammatory change is paramount in planning surgeries seeking to preserve function. This retrospective study aims at illustrating how a careful use of imaging (computed tomography (CT)/magnetic resonance imaging (MRI)) can help to draw the line between infiltration and inflammation. Out of 72 cases of parosteal osteosarcoma in our institution we selected 22 which had pretreatment imaging, and out of those, 14 that had both MRI and CT. Using Fisher's exact test, we evaluated the performance of each technique on accurately diagnosing medullary tumor infiltration, using histological analysis as a gold standard. All cases (14/14) demonstrated medullary abnormality on MRI, but only 6/14 (42.9%) demonstrated abnormality on CT. The 8/14 cases with MRI abnormality but no CT abnormality (57.1%) showed inflammation with no tumoral cells present on histological analysis. In the cases where the two examinations showed medullary abnormality (6/14) histology demonstrated tumoral infiltration. MRI demonstrated high sensitivity and negative predictive value, but low specificity and low positive predictive value and accuracy (P=1). CT demonstrated high sensitivity, specificity, high positive and negative predictive values and accuracy (P = 0.000333). MRI is highly sensitive for the detection of medullary abnormality but lacks specificity for tumor invasion. Correlation with CT is recommended in all cases of positive MR to add specificity for tumors. The adequate use of the two imaging methods allows to differentiate between inflammatory change and tumoral infiltration in POS, relevant for surgical planning.

中文翻译：

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炎症和浸润：放射线医生能划清界线吗？MRI与CT对比可准确评估髓样累及骨旁骨肉瘤。

癌症通过健康组织发展时会引起炎症。肿瘤生长与周围炎症变化的区别在计划寻求保留功能的手术中至关重要。这项回顾性研究旨在说明仔细使用成像（计算机断层扫描（CT）/磁共振成像（MRI））如何有助于在浸润和炎症之间划清界限。在我们机构的72例骨旁骨肉瘤病例中，我们选择了22例进行了预处理成像的患者，其中14例同时进行了MRI和CT检查。使用Fisher的精确检验，我们使用组织学分析作为金标准，评估了每种技术在准确诊断髓样肿瘤浸润方面的性能。所有病例（14/14）在MRI上均显示出髓样异常，但只有6/14（42。9％）表现为CT异常。MRI异常但未见CT异常的8/14例（57.1％）在组织学分析中显示炎症，没有肿瘤细胞。在两次检查均显示髓样异常（6/14）的情况下，组织学表现为肿瘤浸润。MRI表现出高灵敏度和阴性预测值，但特异性低，阳性预测值和准确性低（P = 1）。CT显示出高灵敏度，特异性，高阳性和阴性预测值和准确性（P = 0.000333）。MRI对髓样异常的检测高度敏感，但对肿瘤浸润缺乏特异性。在所有MR阳性的病例中均建议与CT相关，以增加对肿瘤的特异性。