Differential diagnosis and prognosis of small renal masses: association with collateral vessels detected using contrast-enhanced computed tomography

Abstract

Background: Active surveillance (AS) is one of the treatment methods for patients with small renal masses (SRMs; < 4 cm), including renal cell carcinomas (RCCs). However, some small RCCs may exhibit aggressive neoplastic behaviors and metastasize. Little is known about imaging biomarkers capable of identifying potentially aggressive small RCCs. Contrast-enhanced computed tomography (CECT) often detects collateral vessels arising from neoplastic angiogenesis in RCCs. Therefore, this study aimed to evaluate the association between SRM differential diagnoses and prognoses, and the detection of collateral vessels using CECT.

Methods: A total of 130 consecutive patients with pathologically confirmed non-metastatic SRMs (fat-poor angiomyolipomas [fpAMLs; n = 7] and RCCs [n = 123]) were retrospectively enrolled. Between 2011 and 2019, SRM diagnoses in these patients were confirmed after biopsy or surgical resection. All RCCs were surgically resected. Regardless of diameter, a collateral vessel (CV) was defined as any blood vessel connecting the tumor from around the kidney using CECT. First, we analyzed the role of CV-detection in differentiating between fpAML and RCC. Then, we evaluated the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of RCC diagnosis based on CV-detection using CECT. We also assessed the prognostic value of CV-detection using the Fisher exact test, and Kaplan-Meier method and the log-rank test.

Results: The sensitivity, specificity, PPV, NPV, and accuracy of CV-detection for the diagnosis of small RCCs was 48.5, 45.5, 100, 100, and 9.5% respectively. Five of 123 (4.1%) patients with RCC experienced recurrence. CV-detection using CECT was the only significant factor associated with recurrence (p = 0.0177). Recurrence-free survival (RFS) was significantly lower in patients with CV compared with in those without CV (5-year RFS 92.4% versus 100%, respectively; p = 0.005). In addition, critical review of the CT images revealed the CVs to be continuous with the venous vessels around the kidney.

Conclusions: The detection of CVs using CECT is useful for differentiating between small fpAMLs and RCCs. CV-detection may also be applied as a predictive parameter for small RCCs prone to recurrence after surgical resection. Moreover, AS could be suitable for small RCCs without CVs.

Keywords: Collateral vessel; Contrast-enhanced computed tomography; Diagnostic accuracy; Fat-poor angiomyolipoma; Renal cell carcinoma; Small renal masses.

Fig. 1

Flowchart of the patient selection procedure

Fig. 2

Representative images showing the appearance of CVs on CECT. We defined CVs as blood vessels of any diameter, with a definite connection between the tumor and the perirenal region. The yellow arrows indicate the CVs. CV, collateral vessel; CECT, contrast-enhanced computed tomography

Fig. 3

Representative images showing the appearance of AI and OBS on CECT. A The AI in the parenchymal phase was defined as an angle of 90° or less (black lines). (B) A contact length ≥ 3 mm of the bulging portion of the renal tumor onto the renal surface was indicative of a positive OBS (black arrows). AI, angular interface; OBS, overflowing beer sign; CECT, contrast-enhanced computed tomography

Fig. 4

CVs in five patients with RCC and recurrence. A–E The white arrows indicate CVs detected in the five patients with RCC and recurrence. CV, collateral vessel; RCC, renal cell carcinoma

Fig. 5

Kaplan–Meier curves depicting the 5-year RFS in patients with small RCC after surgical resection. A The 5-year RFS after surgical resection of all patients with small RCCs was 96.8%. B Patients with CV had a significantly worse 5-year RFS than those with CV (p = 0.005). The 5-year RFS of patients with and without CV was 92.5 and 100%, respectively. RFS, recurrence-free survival; RCC, renal cell carcinoma; CV, collateral vessel