Metastatic urothelial carcinoma is a rare cause of pleural effusions. We report a case of urothelial carcinoma of the upper urinary tract in an oldest-old male patient, a smoker, with situs inversus totalis, that presented uniquely with malignant pleural effusion at presentation without evidence of a primary tumor on imaging. Cytological smears of the massive left pleural effusion revealed epithelioid neoplastic cells arranged in short cords, small-to-large clusters, and raspberry-like morules, mimicking mesothelioma; cell block preparations highlighted the presence of tubules and nest-like structures. The tumor cells showed a high nuclear-to-cytoplasmic ratio, nuclear grooves, and mitotic figures. Cytomorphologic features coupled with the immunophenotype of neoplastic cells (p63, GATA3, and uroplakin II positive) allowed the diagnosis of metastatic urothelial carcinoma and a possible nested subtype. These findings were supported by a total body computed tomography (CT) showing no evidence of a mass in the bladder or elsewhere in the urinary tract but a concentric parietal thickening of the proximal left ureter, suggesting malignancy. To our knowledge, a malignant effusion as a primary manifestation of urothelial carcinoma with nest-like features originating in the upper urinary tract has never been described previously. Our case focuses on the value of cell block in the working-up of neoplastic effusions by revealing the architectural pattern of an uncommon malignancy and the correlation between cytopathology and imaging gross findings to reach an accurate diagnosis.

中文翻译：

---

具有巢状特征、表现为恶性胸腔积液的转移性上尿路尿路上皮癌

转移性尿路上皮癌是胸腔积液的罕见原因。我们报告一例上尿路尿路上皮癌，患者为一名年龄最大的男性患者，吸烟者，全反位，其独特的表现是恶性胸腔积液，影像学上没有原发性肿瘤的证据。左侧大量胸腔积液的细胞学涂片显示上皮样肿瘤细胞排列成短索状、从小到大的簇状和覆盆子状桑葚状，类似于间皮瘤；细胞块制剂突出显示了小管和巢状结构的存在。肿瘤细胞表现出高核质比、核沟和有丝分裂像。细胞形态学特征与肿瘤细胞的免疫表型（p63、GATA3 和 uroplakin II 阳性）相结合，可以诊断转移性尿路上皮癌和可能的嵌套亚型。这些发现得到了全身计算机断层扫描（CT）的支持，显示没有证据表明膀胱或尿路其他部位有肿块，但左输尿管近端同心壁增厚，提示恶性肿瘤。据我们所知，恶性积液作为起源于上尿路的具有巢状特征的尿路上皮癌的主要表现，以前从未被描述过。我们的案例重点关注细胞块在肿瘤渗出物处理中的价值，通过揭示罕见恶性肿瘤的结构模式以及细胞病理学和影像学大体结果之间的相关性来达到准确的诊断。