Role of Interface Sign and Diffusion-Weighted Magnetic Resonance Imaging in Differential Diagnosis of Exophytic Renal Masses

Abstract

Purpose We aimed to investigate the role of interfaces of exophytic solid and cystic renal masses on magnetic resonance imaging (MRI) and the added value of diffusion-weighted imaging in differentiating benign from malignant lesions. Methods The Institutional Review Board approved this retrospective study, and informed consent was waived. A total of 265 patients (109 [41%] women and 156 [59%] men) with a mean age of 57 ± 12 (standard deviation) years were enrolled in this study. Preoperative MRI (n = 238) examinations of patients with solid or cystic renal masses and MRI (n = 27) examinations of patients with Bosniak IIF cysts without progression were reviewed. Solid/cystic pattern, interface types and apparent diffusion coefficient (ADC) values were recorded by 2 radiologists. The diagnostic performance of combining normalized ADC values with interface sign were evaluated. Results Among 265 renal lesions (109 cystic and 156 solid), all malignant lesions (n = 192) had a round interface. No malignant lesions showed an angular interface. For prediction of benignity in cystic lesions, sensitivity (82.86% vs 56.16%), negative predictive value (92.50% vs 85.71%), and accuracy (94.50% vs 87.92%) ratios of angular interface were higher compared to all (solid plus cystic) lesions. The best normalized ADC cutoff values for predicting malignancy in lesions with round interface were as follows: for all (solid plus cystic), ≤ 0.75 (AUROC = 0.804); solid, ≤ 0.6 (AUROC = 0.819); and cystic, ≤ 0.8 (AUROC = 0.936). Conclusions Angular interface can be a predictor of benignity for especially cystic renal masses. The evaluation of interface type with normalized ADC value can be an important clue in differential diagnosis especially in patients avoiding contrast.

Are There Ultrasound Features to Distinguish Small (<3 cm) Peripheral Renal Angiomyolipomas From Renal Cell Carcinomas?

“…Verma 9 showed an angular interface was a strong predictor of an exophytic AML or a cyst on MRI. Likewise, Kulali 8 showed an angular interface was never present with RCC on MRI and was only seen with benign lesions. In fact, of their 192 malignant lesions, all 192 (or 100%) were round and none had an angular interface.…”

“…Other imaging features of these exophytic renal masses have been studied with CT or MRI to help distinguish between benign entities, such as AMLs or renal cysts, from RCCs. Some of the features that have been analyzed include an angular interface, often occurring more commonly with AMLs or renal cysts rather than RCCs, with MRI 8,9 . Others have found that for exophytic renal masses, the “overflowing beer” sign has been helpful in distinguishing fat‐poor AMLs from RCCs on CT 7 .…”

“…Some of the features that have been analyzed include an angular interface, often occurring more commonly with AMLs or renal cysts rather than RCCs, with MRI. 8,9 Others have found that for exophytic renal masses, the "overflowing beer" sign has been helpful in distinguishing fat-poor AMLs from RCCs on CT. 7 This name is derived from the appearance of the AML overflowing from the renal capsule, although the AML may be stretching rather than overflowing or penetrating the renal capsule. While many of these features have been studied with CT and/or MRI, they have not been widely studied with sonography.…”

“…Others have tried to use power Doppler or Tumor‐to‐Renal‐Cortex echogenicity to help differentiate AMLs from RCCs 5,6 . There have been several morphological features seen on CT or MR of exophytic or peripheral AMLs that have been shown to be helpful in distinguishing AMLs from RCCs, such as the shape of the AML having an angular interface or “overflowing beer” sign in peripheral renal masses 7–9 . However, these shapes have not been widely studied on ultrasound.…”

“…5,6 There have been several morphological features seen on CT or MR of exophytic or peripheral AMLs that have been shown to be helpful in distinguishing AMLs from RCCs, such as the shape of the AML having an angular interface or "overflowing beer" sign in peripheral renal masses. [7][8][9] However, these shapes have not been widely studied on ultrasound. Thus, we compare the demographics of patients with small peripheral renal masses and evaluate several ultrasound features of those masses to see if they are useful in distinguishing AMLs from RCCs.…”