异位性错构瘤性胸腺瘤的临床病理观察

Clinicopathological features of ectopic hamartomatous thymoma

目的结合文献探讨异位性错构瘤性胸腺瘤(EHT)的临床病理特征。方法对患者的左锁骨上区肿物组织标本进行HE染色,并采用免疫组化LSAB法检测瘤细胞的CK、EMA、vimentin、SMA、myoglobin、desmin、S_100、CD99和CD34的表达情况。结果肿瘤有完整包膜,由梭形细胞、脂肪细胞灶和上皮细胞巢构成。上皮细胞呈网格状,实体性或腺管样排列;梭形细胞是肿瘤的主要成分,呈编织状、车辐状分布,细胞具有较长的梭形细胞核及较空亮的胞质,少数梭形细胞呈肌细胞样具有嗜酸性胞质,类似纤维细胞或平滑肌细胞;脂肪细胞分化良好,呈灶状分布于梭形细胞和上皮细胞岛之间。梭形细胞和上皮细胞均无明显异型性,未见核分裂象。免疫组化示梭形细胞和上皮细胞CK弥漫强(+),大部分梭形细胞SMA(+)、myoglobin弱(+),少数梭形细胞vimentin(+),上皮细胞vimentin、desmin、S_100、CD34和CD99(-)。结论异位性错构瘤性胸腺瘤是非常罕见的良性肿瘤,应与双向性滑膜肉瘤、恶性神经鞘瘤、皮肤附件或涎腺起源的混合瘤、胸腺脂肪瘤以及梭形细胞胸腺瘤相鉴别。

Objective Ectopic hamartomatous thymoma （EHT） is a rare benign neoplasm. Since it was firstly reported by J.Rosai in 1984, only 30 cases had been described in English literatures until 2004. As far as we knew, there was no report about this tumor in Chinese. We herein report one case of EHT occurred in lower neck region, investigate its immunohistochemical feature and review the literatures related to EHT. Methods The tumor was taken from the left supmclavicular region in a 40-year-old man. Sections were prepared and stained with hematoxylin and eosinLSAB immunohistochemieal staining was used for detecting the expression of cytokeratin （CK）, epithelial membrane antigen （EMA）, vimentin, smooth muscle actin （SMA）,mynglobin, desmin, S-100, CD99 and CD34 in the tumor cells. Results The tumor was well circumscribed and contained spindle cells, adipose cell and epithelial cell nests. The epithelial cell component consisted of lattice-like, solid or glandular epithelial islands. Spindle cell was the main component of the tumor, and arranged in fascicles or a storiform-like pattern. The spindle cells had oval-shaped nucleus with brightly cytoplasm. Portion of spindle cells was myoid cells with eosinophilic cytoplasm,looking like fibroblast or smooth muscle cells. Adipose cells were well differentiated, and distributed in the form of islands bounded by the epithelial cells and spindle cells without obvious atypia. There was no mitosis found in the neoplastic cells.Immunohistochemical staining revealed that both spindle cells and epithelial cell had strongly positive reaction for cytokeratin. Most of spindle cells showed positive for SMA and weakly positive for myoglobin. However, neoplastic cells had negative reaction for desmin, S-100, CD34 and CD99. Conclusion The morphological features and immunohistochemical phenotype of this tumor are accorded with EHT. Biphasic synovial sarcoma, malignant peripheral nerve sheath tumor, mixed tumors of skin adnexal or salivary gland origin, thymolipoma, and spindle cell thymoma should be differentiated from EHT.