Abstract：
IgG4-related disease is a rare fibroinflammatory disorder characterized by the infiltration of IgG4-rich plasma cells. Herein, we report a case of IgG4-related disease of the subcutaneous tissue with atypical MRI findings and difficulties in the histopathological examination using needle biopsy. Based on the clinical presentation and MRI findings, the patient was diagnosed with a benign myxoid or cystic tumor. Additionally, histopathological findings from a needle biopsy suggested a myxoma. Therefore, the correct diagnosis of IgG4-related disease was not made preoperatively. The resected specimens confirmed IgG4-related disease with an IgG4/IgG ratio > 80%. Previous reports have shown that the MRI findings of IgG4-related disease mimic both malignancy and inflammation; surprisingly, the features of subcutaneous IgG-related disease, including tail sign, unclear border, and heterogeneous enhancement, were similar to those found in sarcoma. Therefore, histopathological findings are needed for a correct diagnosis. Furthermore, careful examination is essential because the neoplasm and inflammation may overlap with IgG4-related disease, and needle biopsy is not fully reflective of the tumor. As is highlighted in the present case, IgG4-related disease is often misdiagnosed; therefore, clinicians should adequately recognize that even if the histopathological findings in biopsy were consistent with those observed in the MRI, misdiagnosis may occur.
摘要：
IgG4相关疾病是一种罕见的纤维炎症性疾病，其特征是富含IgG4的浆细胞浸润。在这里，我们报告了一例与IgG4相关的皮下组织疾病，其MRI表现不典型，并且在穿刺活检的组织病理学检查中存在困难。根据临床表现和MRI表现，患者被诊断为良性粘液样肿瘤或囊性肿瘤。此外,穿刺活检的组织病理学发现提示粘液瘤。因此,术前未能正确诊断IgG4相关疾病.切除的标本证实IgG4相关疾病，IgG4/IgG比率>80％。以前的报道表明，IgG4相关疾病的MRI表现与恶性肿瘤和炎症相似；令人惊讶的是，皮下IgG相关疾病的特征，包括尾部标志,边界不清,和异构增强，与在肉瘤中发现的相似。因此,正确诊断需要组织病理学检查结果.此外，仔细检查是必要的，因为肿瘤和炎症可能与IgG4相关疾病重叠，穿刺活检不能完全反映肿瘤。正如本案所强调的那样，IgG4相关疾病经常被误诊；因此，临床医生应充分认识到，即使活检的组织病理学发现与MRI观察到的一致，可能出现误诊。
