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Differential Diagnosis of Invasive Thymoma and Thymic Carcinoma by CT Findings
侵襲性胸腺瘤與胸腺上皮癌在電腦斷層上的鑑別診斷
摘要
由於侵襲性胸腺瘤與胸腺上皮癌的臨床表現及預後迥異，而電腦斷層檢查為目前最普遍及先進的影像學檢查方式。因此，重要的是電腦斷層檢查的判讀結果對兩者的鑑別診斷是否有其實用性。我們回顧分析自1984至1999年於本院接受電腦斷層(CT)檢查之該類病患的影像資料，計十七名侵襲性胸腺瘤及二十五名胸腺上皮癌患者，希能從中發現兩者在CT影像上的差異所在。所有病患的前縱膈腫瘤皆由外科切除或綑針穿刺取得樣本，交由病理切片得以證實。電腦斷層影像的評估重點在病灶的均勻度，X光衰減，對鄰近心血管組織，縱膈淋巴腺病變及肋膜的侵犯，胸腺外轉移，以及鈣化。並探用費雪氏正確率檢查及logistic迴歸模式，對兩種惡性胸腺瘤在電腦斷層影像的各項表徵，進行單變數及多變數分析。週遭心血管組織的侵犯見於三例侵襲性胸腺瘤(17%)及二十例胸腺上皮癌(80%)病患。有意義的縱膈淋巴腺腫大見於二例侵襲性胸腺瘤(12%)及九例胸腺上皮癌(36%)病患。肋膜散播見於八例侵襲性胸腺瘤(47%)及十二例胸腺上皮癌(48%)病患。遠端轉移至肺、腎上腺、肝、骨、脾、或後腹腔淋巴腺可見於十二例胸腺上皮癌(48%)病患，但未見於本系列侵襲性胸腺瘤病患中。基於費雪氏正確率檢查結果，可能有四種電腦斷層徵像有關於對二者的鑑別診斷：(1)不均勻腫塊內含成分，(2)心包膜被侵犯及增厚，(3)大血管被包覆，(4)胸腺外轉移。經採用logistic迴歸模式分析，二者的鑑別診斷與心包膜被侵犯及增厚和大血管被包覆兩種徵像有較強的關連。其中又以心包膜被侵犯及增厚因素較大血管被包覆因素有更高的預測率。如果藉由細針穿刺或生化染色技術來確定腫塊細胞起源自胸腺組織，並且在電腦斷層影像上出現心包膜被侵犯及增厚和大血管被腫塊包覆兩種徵像，胸腺上皮癌的可能性將遠高於侵襲性胸腺瘤。
並列摘要
The clinical behavior and prognosis of invasive thymoma and thymic carcinoma are different, and computed tomography is the most widely applied and advanced imaging modality for diagnosis of these diseases. It is important to evaluate the usefulness of CT characteristics in their differentiation. Retrospectively, we evaluated the CT findings of invasive thymoma and thymic carcinoma to determine the differential points between them. Seventeen patients with invasive thynioma and 25 patients with thynfic carcinoma, that were confirmed by surgical resection or by fine needle biopsy, were included in this study. All tumors were located in the anterior mediastinal prevascular space. Special attention was given to the following CT findings: homogeneity, attenuation, invasion of adjacent cardiovascular structure, mediastinal lymph nodes, pleural implants, extrathymic metastases, and calcification. Univariate and multivariate analyses were performed with Fisher's exact test and binary logistic regression. Invasion of adjacent cardiovascular structure was seen in three patients (17%) with invasive thymoma, and 20 patients (80%) with thymic carcinoma. Significant mediastinal lymphadenopathy was seen in two patients (12%) with invasive thymoma, and nine patients (36%) with thymic carcinoma. Pleural implants were observed in eight patients (47%) with invasive thymoma, and 12 patients (48%) with thymic carcinoma. Metastases to the lung, adrenal gland, liver, bone, spleen, or retroperitoneal lymph nodes were observed in 12 patients (48%) with thymic carcinoma, but were absent from patients with invasive thymoma. According to Fisher's exact test, there are four significant signs by CT findings associated with differentiation between thymic carcinoma and invasive thymonia: (1) inhomogeneous mass content, (2) infiltration of adjacent pericardium, (3) encasement of great vessels, and (4) extrathymic metastases. Binary logistic regression analysis shows that thymic carcinoma is more likely rather than invasive thymoma with the presence of infiltration of adjacent pericardiumn and encasement of great vessels. Infiltration of adjacent pericardium is more predominant in predicting thymic carcinoma than is encasement of great vessels. If a tumor can be attributed to thymic origin by fine needle cytological study or by biochemical stain, then thymic carcinoma would be more likely with the presence of infiltration of adjacent pericardium and encasement of great vessels on CT scan.