Evaluation of Preoperative Imaging Accuracy in Small <scp>cT3a</scp> Renal Cell Carcinoma

Surgical strategies for non-metastatic small RCC depend on clinical stage. Partial nephrectomy is recommended for cT1a tumors [1, 2], whereas suspected pT3a disease requires radical nephrectomy even when small. Thus, accurate preoperative imaging is crucial, yet invasion is often difficult to assess in small renal masses. Although risk factors for pathological upstaging to pT3a in clinical T1a tumors have been reported [3, 4], few studies have focused on small cT3a tumors confirmed as pT3a. This study aimed to describe the current performance of preoperative imaging-based diagnosis of small cT3a RCC and identify clinical factors that may improve accuracy. We retrospectively analyzed 101 patients with cT3a RCC ≤ 7 cm who underwent radical nephrectomy at our institution between January 2016 and April 2025. All patients had multiphase contrast-enhanced CT (non-contrast, corticomedullary, nephrographic, and excretory phases; 3-mm slices) before surgery, and staging was based on these images. cT3a was defined by any of the following: renal vein invasion (filling defect or enhancing thrombus within the renal vein), perinephric fat invasion (capsular breach with nodular irregular margin into perinephric fat), sinus fat invasion (nodular extension into sinus fat with irregular margin), or urinary collecting system invasion (nodular protrusion into the pelvis or calyces with irregular margin). The clinical T3a assessment was based on preoperative imaging reports interpreted by board-certified radiologists specialized in genitourinary imaging at our institution. The diagnostic accuracy was evaluated by comparing the preoperative imaging findings with the final pathological results. The clinical characteristics of the patients stratified according to the pT1 and pT3a stages are presented in Figure 1A. The overall diagnostic accuracy of cT3a was 63.4%. Among the 25 patients with tumors of ≤ 4 cm in diameter, the diagnostic accuracy was 44.0%, whereas it was 69.7% in 76 patients with tumors measuring > 4 cm to ≤ 7 cm. Among the imaging-based cT3a features, RVI was suspected in 73 cases (72.3%), PFI in 15 (14.9%), SFI in 9 (8.9%), and UCSI in 36 (35.6%). The diagnostic accuracies for each feature were as follows: RVI, 49/73 (67.1%); PFI, 8/15 (53.3%); SFI, 3/9 (33.3%); and UCSI, 9/36 (25.0%). When comparing the pT1 and pT3a groups, significant differences were identified in tumor size and the number of imaging-based cT3a features. We selected representative cases diagnosed as cT3a RCC based on preoperative imaging, but a pathological examination revealed pT1 disease. In Case 1, RVI was suspected based on early-phase contrast-enhanced CT, which showed a hyperenhancing lesion within the renal vein, suggestive of a tumor thrombus (Figure 1B-1,2). In Case 2, the tumor protruded into the renal pelvis with irregular margins, raising the suspicion of UCSI (Figure 1B-3,4). In Case 3, the tumor appeared to extend into the surrounding adipose tissue, raising the suspicion of PFI (Figure 1B-5,6). In Case 4, the tumor appeared to extend into the sinus fat tissue, raising the suspicion of SFI (Figure 1B-7,8). As shown by these cases, patients who were diagnosed with cT3a according to preoperative imaging findings were not always pathologically diagnosed with T3a. Therefore, we investigated factors that could aid in making an accurate preoperative diagnosis using a logistic regression analysis associated with pT3a (Figure 1C). In the multivariable analysis, variates were selected based on clinical relevance. Sex and tumor size were chosen based on prior reports, and the number of cT3a factors was included because the coexistence of multiple imaging features was hypothesized to reflect a higher likelihood of pathological T3a disease [5, 6]. In the univariate analysis, tumor size (odds ratio [OR] 1.04, 95% confidence interval [CI] 1.01–4.30, p = 0.020) and the number of cT3a factors (OR 3.69, 95% CI 1.33–10.30, p = 0.007) were significantly associated with a diagnosis of pT3a. In multivariate analysis, tumor diameter (OR 1.04, 95% CI 1.00–1.08, p = 0.040) and the number of cT3a features remained significant (OR 3.51, 95% CI 1.24–9.90, p = 0.018). Variance inflation factors from the final model were near 1 (1.03–1.04). Receiver operating characteristic analysis showed an area under the curve of 0.72. Tumor diameter and the presence of multiple cT3a features may be associated with improved accuracy in preoperative imaging-based diagnoses. The preoperative diagnosis of T3a disease in small RCC can be challenging in some cases. The presence of multiple cT3a imaging features may serve as a useful indicator for identifying pT3a cases. The combined assessment of imaging and clinical information may improve diagnostic accuracy, which could assist in appropriate surgical decision-making. This study did not include an analysis of cases that were upstaged from cT1 to pT3a. Further prospective studies with larger cohorts of small renal cell carcinoma, including both cT1 and cT3a cases, are warranted to validate these results and to improve preoperative risk stratification in patients with small RCC. Taisuke Tobe: data curation, writing – original draft, formal analysis. Jun Teishima: writing – review and editing. Kotaro Suzuki: writing – review and editing. Takuto Hara: writing – review and editing. Koji Chiba: writing – review and editing. Hideaki Miyake: conceptualization, writing – review and editing, supervision. The authors have nothing to report. The study protocol was approved by the Institutional Review Board of Kobe University Hospital (approval no. B240116). Written informed consent was obtained from all patients. Hideaki Miyake and Jun Teishima are the Editorial Board members of the International Journal of Urology and the co-authors of this article. To minimize bias, they were excluded from all editorial decision-making related to the acceptance of this article for publication.