Teaching Case

Section

Uroradiology & genital male imaging

Case Type

Clinical Cases

Authors

Maria Alexandratou,Vasileios Rafailidis, Panos Prassopoulos

Department of Radiology, AHEPA University Hospital, Aristotle University of Thessaloniki, Greece

Patient

55 years, female

Categories

Area of Interest Abdomen ; Imaging Technique Ultrasound, Ultrasound-Colour Doppler ;

Procedure Contrast agent-intravenous, Contrast agent-other ; Special Focus Cysts, Dysplasias ;

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Clinical History

A 55-year-old female patient presented with lower extremity deep vein thrombosis. During her imaging work-up an incidental lesion was detected in the right kidney. Past medical history was unremarkable.

Differential Diagnosis List

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Angiomyolipoma

Clear cell renal cell carcinoma

Papillary renal cell carcinoma

Cyst containing haemorrhagic or proteinaceous material (hyperechoic)

Oncocytoma

Imaging Findings

A well-circumscribed homogeneously hyperechoic lesion was detected on B-mode US, showing only mild vascularity on colour and power Doppler US (Fig. 1A, B). A contrast-enhanced ultrasound (CEUS) study was performed to evaluate the enhancement pattern of the lesion. The lesion showed homogeneous enhancement which was slower and lower than the adjacent renal parenchyma and no wash-out (Fig. 2). The diagnosis was further confirmed with CT, where the lesion was partially of macroscopic fat density, also containing parts of soft tissue density, but without calcifications (Fig. 3). Of note, CEUS outperformed CT in visualizing enhancement of the macroscopic fat component, the earlier enhancement of soft tissue parts in real-time, while arterial phase CT revealed aneurysmal dilatation of intratumoural vascularity.

Discussion

Renal angiomyolipoma (AML) is a benign renal neoplasm consisting of varying amounts of vessels, fat and smooth muscle tissue [1]. AML may be sporadic or associated with tuberous sclerosis, is usually unilateral, shows a female predilection and a slow growth rate. Syndromic tumours tend to grow faster and be multifocal. Although typically asymptomatic, AMLs larger than 4 cm may present with spontaneous rupture and haemorrhage, associated to tumour vascularity [2]. The elastin-poor intratumoural vessel walls render them prone to aneurysm formation and thus rupture [2]. The risk for rupture, malignant sarcomatous transformation and the reported potential of synchronous occurrence of oncocytoma or renal cell carcinoma (RCC) justify closer surveillance instead of surgical removal [2-4].

Imaging features of AML stem from the combination of various proportions of fat, smooth muscle tissue and vascular structures. AMLs containing macroscopic fat appear hyperechoic and circumscribed on greyscale ultrasound [5]. Nevertheless, lipid-poor AMLs appear isoechoic, due to the paucity of macroscopic fat and thus need to be differentiated from RCC for treatment decision making [6]. Small RCC can be particularly problematic as they appear homogeneous and can mimic AML.[5]. Lipid-poor AML represents a diagnostic conundrum not only for US but also for other modalities. The use of contrast-enhanced imaging provides a much more accurate characterization of such indeterminate renal lesions [6,7]. Contrast-enhanced ultrasound (CEUS) provides information regarding the enhancement intensity and homogeneity, the wash in and wash out pattern and perilesional rim-like enhancement of a renal mass [8]. It involves no ionizing radiation, has rare and mild adverse reactions and is a real-time study of the tumour vascularity thanks to the blood-pool contrast agent employed [8]. On CEUS AML presents as homogeneously hypo-enhancing or iso-enhancing with a delayed enhancement pattern compared to the adjacent renal parenchyma [8]. Thanks to the technique’s optimal contrast resolution, the vascularity is accurately visualized even on the macroscopic fat component of the tumour, which shows only minimal enhancement on CT. Time-intensity-curve analysis can be used to quantify the enhancement pattern of these tumours and suggest the diagnosis of a hyper- or hypo-vascular type of lesion [9,10]. CEUS is currently recommended for the characterization of the indeterminate renal lesion according to EFSUMB and ACR appropriateness criteria [11,12]. Limitations of CEUS compared to CT and MR is the limited depth in obese patients, bowel gas interposition, the narrow field of view and the operator-dependent nature [8].

References

[1] Koo KC, Kim WT, Ham WS, Lee JS, Ju HJ, Choi YD. Trends of presentation and clinical outcome of treated renal angiomyolipoma. Yonsei Med J. 2010 Sep;51(5):728-34. doi: 10.3349/ymj.2010.51.5.728. PMID: 20635448; PMCID: PMC2908871.

[2] Yamakado K, Tanaka N, Nakagawa T, et al. (2002) Renal angiomyolipoma: relationships between tumor size, aneurysm formation, and rupture. Radiology 225: 78-82. (PMID: 12354988)

[3] De Luca S, Terrone C, Rossetti R. Management of renal angiomyolipoma: a report of 53 cases. BJU International 1999;83:215-218. (PMID: 10233482)

[4] Ignee A, Straub B, Schuessler G, Dietrich CF. Contrast enhanced ultrasound of renal masses. World J Radiol. 2010 Jan 28;2(1):15-31. doi: 10.4329/wjr.v2.i1.15. PMID: 21160736; PMCID: PMC2998906.

[5] Hartman DS, Goldman SM, Friedman AC, Davis CJ Jr, Madewell JE, Sherman JL. Angiomyolipoma: ultrasonic-pathologic correlation. Radiology. 1981 May;139(2):451-8. doi: 10.1148/radiology.139.2.7220890. PMID: 7220890.

[6] Barr RG, Peterson C, Hindi A. Evaluation of indeterminate renal masses with contrast-enhanced US: a diagnostic performance study. Radiology. 2014 Apr;271(1):133-42. doi: 10.1148/radiol.13130161. Epub 2013 Nov 18. PMID: 24475802.

[7] Zarzour JG, Lockhart ME, West J, Turner E, Jackson BE, Thomas JV, Robbin ML. Contrast-Enhanced Ultrasound Classification of Previously Indeterminate Renal Lesions. J Ultrasound Med. 2017 Sep;36(9):1819-1827. doi: 10.1002/jum.14208. Epub 2017 Apr 21. PMID: 28429490.

[8] Zhang F, Li R, Li G, Jin L, Shi Q, Du L. Value of Contrast-Enhanced Ultrasound in the Diagnosis of Renal Cancer and in Comparison With Contrast-Enhanced Computed Tomography: A Meta-analysis. J Ultrasound Med. 2019 Apr;38(4):903-914. doi: 10.1002/jum.14769. Epub 2018 Sep 11. PMID: 30203542.

[9] King KG, Gulati M, Malhi H, Hwang D, Gill IS, Cheng PM, Grant EG, Duddalwar VA. Quantitative assessment of solid renal masses by contrast-enhanced ultrasound with time-intensity curves: how we do it. Abdom Imaging. 2015 Oct;40(7):2461-71. doi: 10.1007/s00261-015-0468-y. PMID: 26036794.

[10] Lu Q, Li CX, Huang BJ, Xue LY, Wang WP. Triphasic and epithelioid minimal fat renal angiomyolipoma and clear cell renal cell carcinoma: qualitative and quantitative CEUS characteristics and distinguishing features. Abdom Imaging. 2015 Feb;40(2):333-42. doi: 10.1007/s00261-014-0221-y. PMID: 25139641.

[11] Sidhu PS, Cantisani V, Dietrich CF, Gilja OH, Saftoiu A, Bartels E, Bertolotto M, Calliada 11.F, Clevert DA, Cosgrove D, Deganello A, D'Onofrio M, Drudi FM, Freeman S, Harvey C, Jenssen C, Jung EM, Klauser AS, Lassau N, Meloni MF, Leen E, Nicolau C, Nolsoe C, Piscaglia F, Prada F, Prosch H, Radzina M, Savelli L, Weskott HP, Wijkstra H. The EFSUMB Guidelines and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound (CEUS) in Non-Hepatic Applications: Update 2017 (Long Version). Ultraschall Med. 2018 Apr;39(2):e2-e44. English. doi: 10.1055/a-0586-1107. Epub 2018 Mar 6. PMID: 29510439.

[12] Expert Panel on Urologic Imaging, Wang ZJ, Nikolaidis P, Khatri G, Dogra VS, Ganeshan D, Goldfarb S, Gore JL, Gupta RT, Hartman RP, Heilbrun ME, Lyshchik A, Purysko AS, Savage SJ, Smith AD, Wolfman DJ, Wong-You-Cheong JJ, Lockhart ME. ACR Appropriateness Criteria® Indeterminate Renal Mass. J Am Coll Radiol. 2020 Nov;17(11S):S415-S428. doi: 10.1016/j.jacr.2020.09.010. PMID: 33153554.

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