为了确定未分类肾细胞癌（RCC）的临床行为以及CT和MRI上的特征性影像学表现。本回顾性研究的对象是在世界卫生组织（WHO）2022年标准下被诊断为未分类RCC的10名患者，这些患者在手术前进行了CT和/或MRI检查。在临床行为方面，评估了TNM分类、分期、术后复发、复发时间和术后生存。在影像学结果方面，评估了肿瘤大小、生长模式、CT密度、动态对比增强（DCE）模式、内部表现、假包膜存在情况以及MRI上的信号强度。我们对临床行为和影像学结果进行了比较，并研究了它们之间的关联。由于其他原因导致的死亡，有一名患者不能进行随访。4名患者出现术后复发，其中所有患者均为3期RCC。在其余的5名没有复发的患者中，所有患者均为2期或以下。在影像学上，未分类RCC倾向于较大（58.7毫米），呈实性（100%），内部呈不均匀（80%），囊性变性（80%）和扩散加权成像（DWI）上呈高信号强度（71.4%）是常见的。比较具有和无复发的患者，以下发现在复发组和无复发组之间呈差异倾向：肿瘤大小（73.4 ± 33.9毫米 vs. 50.2 ± 33.9毫米，P = 0.286），生长模式（浸润型：100% vs. 0%，扩张型：0% vs. 100%，P = 0.008），DCE模式（进行性增强模式：66.7% vs. 0%，消退模式：0% vs. 66.7%，P = 0.135 each）和假包膜的存在（25% vs. 80%，P = 0.167）。未分类RCC的临床行为变化范围广泛。虽然影像学表现也不确定，但大的、不均匀的肿瘤伴有囊性变性和DWI高信号强度的发现是常见的。几种影像学发现，如较大的肿瘤大小、浸润性生长、进行性增强模式和无假包膜，可能有助于预测未分类RCC的预后。©2023. 作者。

To ascertain the clinical behaviors of unclassified renal cell carcinoma (RCC) and its characteristic imaging findings on CT and MRI.Subjects in this retrospective study were 10 patients who had received a histological diagnosis of unclassified RCC based on World Health Organization (WHO) 2022 and who had undergone CT and/or MRI prior to surgery. In terms of clinical behaviors, TNM classification, stage, postoperative recurrence, time to recurrence, and postoperative survival were evaluated. In terms of imaging findings, tumor size, growth pattern, CT density, dynamic contrast-enhancement (DCE) pattern, internal appearance, presence of a pseudocapsule, and signal intensity on MRI were evaluated. We compared clinical behaviors and imaging findings, and investigated associations between them.One patient could not be followed-up due to death from other causes. Postoperative recurrence was observed in 4 patients, all of whom had Stage 3 RCC. In the remaining 5 patients without recurrence, all 5 patients showed Stage 2 or below. On imaging, unclassified RCC tended to be large (58.7 mm) and solid (100%), and heterogeneous interiors (80%), cystic degeneration (80%) and high intensity on diffusion-weighted imaging (DWI) (71.4%) were common. Comparing patients with and without recurrence, the following findings tended to differ between recurrence and recurrence-free groups: tumor size (73.4 ± 33.9 mm vs. 50.2 ± 33.9 mm, P = 0.286), growth pattern (invasive: 100% vs. 0%, expansive: 0% vs. 100%, P = 0.008 each), DCE pattern (progressive enhancement pattern, 66.7% vs. 0%, washout pattern, 0% vs. 66.7%, P = 0.135 each) and presence of a pseudocapsule (25% vs. 80%, P = 0.167).The clinical behavior of unclassified RCC varies widely. Although imaging findings are also variable, findings of large, heterogeneous tumors with cystic degeneration and high intensity on DWI were common. Several imaging findings such as large size, invasive growth, progressive enhancement pattern and no pseudocapsule may enable prediction of prognosis in unclassified RCC.© 2023. The Author(s).