Use of intraoperative strain elastography of small renal masses to differentiate between angiomyolipoma and renal cell carcinoma

Purpose: Elastography is a novel ultrasound modality that evaluates tissue stiffness. This modality has been applied for the preoperative diagnosis of breast, liver, prostate, kidney, and thyroid cancers. In this study we assessed the diagnostic value of intraoperative elastography in patients with renal tumors.

Materials and Methods: This prospective study included 46 patients (mean age 62.4 years; range 38–85 years) with a renal tumor or tumors who underwent partial or radical nephrectomy from May 2014 to February 2016. Strain elastography was performed intraoperatively and strain ratios (tumor versus normal parenchyma) were evaluated before renal artery dissection in 46 renal tumors (mean size 41.5 mm; range 9.0–127 mm). Histology of the resected tumors revealed clear cell renal cell carcinoma (RCC) in 32, chromophobe RCC in 3, papillary RCC in 1, multilocular cystic RCC in 1, invasive urothelial carcinoma (UC) in 1, oncocytoma in 1, angiomyolipoma (AML) in 6 and leiomyoma in 1.

Results: The median tumor diameters were 41 mm (range 12–80 mm) for clear cell RCC, 25 mm (range 18–52 mm) for chromophobe RCC, 39 mm for papillary RCC, 18 mm for multilocular cystic RCC, 66 mm for invasive UC, 17mm for oncocytoma, 13.5 mm (range 9.0–127 mm) for AML, and 79 mm for leiomyoma. The median strain ratios were 1.67 (range 0.37–4.75) for clear cell RCC, 1.30 (range 0.81–2.52) for chromophobe RCC, 4.11 for papillary RCC, 2.29 for multilocular cystic RCC, 6.00 for invasive UC, 1.85 for oncocytoma, 1.13 (range 0.30–2.29) for AML, and 1.68 for leiomyoma. For tumors smaller than 40 mm, the median strain ratio was significantly higher in RCCs (clear cell, chromophobe, papillary, and multilocular cystic; n=20) compared with AMLs (n=5) (2.09 [range 0.37–4.11] versus 1.11 [range 0.30–1.18]) (p=0.010). According to receiver operating characteristic curve analysis, the optimal cut-off value for distinguishing between RCCs and AML was 1.29, with a sensitivity and specificity of 85% and 100%, respectively. The area under the curve was 0.880.

Conclusion: Intraoperative strain elastography may be a useful modality for differentiating between AML and RCCs in patients with renal masses smaller than 40 mm.