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Diagnostic performance of the “drooping” sign in CT diagnosis of exophytic renal angiomyolipoma

  • Kidneys, Ureters, Bladder, Retroperitoneum
  • Published:
Abdominal Radiology Aims and scope Submit manuscript

Abstract

Objective

To evaluate the prevalence of angular interface and the “drooping” sign in exophytic renal angiomyolipomas (AMLs) and the diagnostic performance in differentiating exophytic lipid-poor AMLs from other solid renal masses.

Methods

This IRB-approved, two-center study included 185 patients with 188 exophytic solid renal masses < 4 cm with histopathology and pre-operative CT within 30 days of surgical resection or biopsy. Images were reviewed for the presence of angular interface and the “drooping” sign qualitatively by three readers blinded to the final diagnosis, with majority rules applied. Both features were assessed quantitatively by cohort creators (who are not readers) independently. Free-marginal kappa was used to assess inter-reader agreement and agreement between two methods assessing each feature. Fisher’s exact test, Mann–Whitney test, and multivariable logistic regression with two-tailed p < 0.05 were used to determine statistical significance. Diagnostic performance was assessed.

Results

Ninety-four patients had 96 AMLs, and 91 patients had 92 non-AMLs. Seventy-four (77%) of AMLs were lipid-poor based on quantitative assessment on CT. The presence of angular interface and the “drooping” sign by both qualitative and quantitative assessment were statistically significantly associated with AMLs (39% (qualitative) and 45% (quantitative) vs 15% (qualitative) and 13% (quantitative), and 48% (qualitative) and 43% (quantitative) vs 4% (qualitative) and 1% (quantitative), respectively, all p < 0.001) in univariable analysis. In multivariable analysis, only the “drooping” sign in either qualitative or quantitative assessment was a statistically significant predictor of AMLs (both p < 0.001). Inter-reader agreement for the “drooping” sign was moderate (k = 0.55) and for angular interface was fair (k = 0.33). Agreement between the two methods of assessing the “drooping” sign was substantial (k = 0.84) and of assessing the angular interface was moderate (k = 0.59). The “drooping” sign both qualitatively and quantitatively, alone or in combination of angular interface, had very high specificity (96–100%) and positive predictive value (PPV) (89–100%), moderate negative predictive value (62–68%), but limited sensitivity (23–49%) for lipid-poor AMLs.

Conclusion

The “drooping” sign by both qualitative and quantitative assessment is highly specific for lipid-rich and lipid-poor AMLs. This feature alone or in combination with angular interface can aid in CT diagnosis of lipid-poor AMLs with very high specificity and PPV.

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Authors and Affiliations

  1. Department of Radiology, Stanford University School of Medicine, 300 Pasteur Drive, H1307, Stanford, CA, 94305, USA

    Luyao Shen, Justin R. Tse, Lindsey M. Negrete, Tie Liang & Aya Kamaya

  2. Department of Radiology, School of Medicine and Public Health, University of Wisconsin, 600 Highland Ave, Madison, WI, 53792, USA

    Rasheed Nawaz, Meghan G. Lubner & Giuseppe V. Toia

  3. Department of Radiology, School of Medicine and Public Health, University of Wisconsin, 1111 Highland Ave, Room 2425, Madison, WI, 53705, USA

    Andrew L. Wentland

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Correspondence to Luyao Shen.

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Conflict of interest

Aya Kamaya: Book royalties from Elsevier and research grant from Canon, Inc on items unrelated to this research. Meghan G. Lubner: Spouse is consultant at Elephas Bio on items unrelated to this research. Giuseppe V. Toia: consultant to GE Healthcare and Canon Medical on items unrelated to this research. Justin R. Tse: Pending grant from Bayer Healthcare on items unrelated to this research. All other authors disclose that they have no conflicts of interest.

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Shen, L., Nawaz, R., Tse, J.R. et al. Diagnostic performance of the “drooping” sign in CT diagnosis of exophytic renal angiomyolipoma. Abdom Radiol 48, 2091–2101 (2023). https://doi.org/10.1007/s00261-023-03880-7

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