胸腺瘤240例临床病理特征及诊断

目的探讨胸腺瘤的组织病理学特征、诊断与鉴别诊断。方法收集240例胸腺瘤,病例行HE及免疫组化染色观察分析,并复习相关文献。结果240例胸腺瘤中,男女比例约1∶1.2,发病高峰年龄45~60岁,B1型、B2型较其他类型胸腺瘤发病年龄约早10年。组织学上,AB型、B2型、B3型较容易形成纤维间隔,B1型、B2型均有极其丰富的淋巴组织背景,这也是B1型、B2型胸腺瘤常常观察到髓质分化形成的基础;腺样结构只见于A型和AB型胸腺瘤,出现率分别为21%和29%;宽大的血管周围间隙,在B2型和B3型中更为常见,出现率分别为64%和79%,而A型、AB型及B1型的血管周围间隙则明显较小或缺少;移行区域仅见于所有AB型胸腺瘤,而在A型胸腺瘤中,也只见于B样区域,范围不足以诊断AB型胸腺瘤。被膜及被膜外侵犯可发生于所有类型的胸腺瘤,但B2型和B3型胸腺瘤更具侵袭性,分别为75%和89%。细胞学上,具有髓质上皮分化特点的A型、AB型胸腺瘤,与皮质上皮分化的B1型、B2型、B3型胸腺瘤明显不同。髓质上皮分化的特点是肿瘤细胞圆形/卵圆形及梭形,常混合存在,胞质稀少,核小非空泡状,核仁不明显。而皮质上皮分化特点是肿瘤细胞圆形/卵圆形,胞质丰富,核空泡状,嗜酸性核仁明显。免疫组化:A型和AB型CD20阳性,大部分表现为斑驳、斑片状或散在小灶状且强弱不等;而皮质上皮分化的B1型、B2型、B3型胸腺瘤为阴性。结论①丰富的淋巴组织背景、髓质分化、血管周围间隙、纤维间隔、腺样结构、胸腺小体、移行区域等结构,在胸腺瘤的诊断和鉴别诊断中具有重要意义;②细胞学上,皮质上皮分化与髓质上皮分化的胸腺瘤有明显不同,不可忽视;③免疫标记CD20特异性强,在区分A型、AB型与B1型、B2型、B3型胸腺瘤上,诊断价值较高;其他标记(如CD3、CD5、CD117、AE1/AE3、p63、p40、CK19、TdT)则可以帮助确定肿瘤细胞存在与否及分布模式。采用这种诊断思路和分析方法,可获得较高的可重复性和一致性。不同类型的胸腺瘤间均可按不同比例混合存在,可分别报告。

Clinicopathological features and diagnosis of thymoma:analyses of 240 cases

Objective To investigate the histopathological features,diagnosis and differential diagnosis of thymoma.Methods A total of 240 cases of thymoma were collected and histological analysis and immunohistochemical staining were used in this study with review of literature.Results Among 240 cases of thymoma,the ratio of male to female was about 1∶1.2.The peak age of onset was between 45 and 60 years.The onset age of patients with B1 and B2 thymoma was about 10 years earlier than other types of thymoma.Histologically,AB,B2 and B3 types were more likely to form fibrous septum;B1 and B2 types had abundant lymphoid tissue background,which was the basis for the formation of medullary differentiation in B1 and B2 thymomas;adenoid structures were only found in types A and AB thymomas,with the occurrence rates of 21%and 29%respectively;wide perivascular space was more commonly found in types B2 and B3,with higher occurrence rate.The perivascular spaces of types A,AB and B1 were significantly smaller or absent,and the transitional areas were found only in all AB thymomas;while in type A thymomas,the B-like areas were not enough to diagnose AB thymomas.Capsule and extracapsular invasion might occur in all types of thymoma,but types B2 and B3 thymoma were more invasive,being 75%and 89%respectively.Cytologically,types A and AB thymomas with differentiation of medullary epithelium were significantly different from those of types B1,B2 and B3 thymomas with differentiation of cortical epithelium.Medullary epithelial differentiated tumor cells were round/oval and spindle-shaped,often mixed,with sparse cytoplasm,small non-vacuolar nuclei and no obvious nucleoli.The differentiated cortical epithelial neoplasm cells were round/oval,with abundant cytoplasm,vacuolar nuclei and obvious eosinophilic nucleoli.Immunohistochemistry showed that types A and AB were positive for CD20,mostly mottled,patchy or scattered in small foci with varying degrees of intensity,while types B1,B2 and B3 thymomas were negative for CD20.Conclusion The abundant lymphoid background,medullary differentiation,perivascular space,fibrous septum,adenoid structure,thymic corpuscles,transitional area and other structures are of great significance in the diagnosis and differential diagnosis of thymoma.Cytologically,the differentiation of cortical and medullary epithelial thymomas is typically different and should not be neglected.CD20 shows strong specificity and high diagnostic value in differentiating types A and AB from types B1,B2 and B3 thymoma.Other immune markers,such as CD3,CD5,CD117,AE1/AE3,P63,P40,CK19 and TdT,can help to determine the existence and distribution pattern of cancer cells.In the practice of thymoma diagnosis,this diagnostic thinking and analysis method can achieve high repeatability and consistency.Different types of thymoma can be mixed in different proportions and should be reported separately.