Elsevier

Clinical Radiology

Volume 68, Issue 4, April 2013, Pages 365-370
Clinical Radiology

Angiomyolipoma with minimal fat: Differentiation from papillary renal cell carcinoma by helical CT

https://doi.org/10.1016/j.crad.2012.08.028Get rights and content

Aim

To evaluate whether helical computed tomography (CT) images can be used to differentiate angiomyolipomas (AMLs) with minimal fat from papillary renal cell carcinomas (PRCCs) based on their morphological characteristics and enhancement features.

Materials and methods

This retrospective study was approved by the institutional review board. Informed consent was waived. Forty-four patients (21 with AMLs with minimal fat and 23 with PRCCs) who underwent enhanced helical CT before total or partial nephrectomy were included. Two radiologists, who were blinded to the histopathology results, read the CT images and recorded the attenuation value, morphological characteristics, and enhancement features of the tumours, which were subsequently evaluated. An independent samples t-test, χ2 test, and rank sum test were performed between the tumours. The predictive value of a CT finding was determined by multivariate logistic regression analysis.

Results

AML with minimal fat had an apparent female prevalence (p < 0.01). Intra-tumoural vessels were noted in 11 cases of AML with minimal fat and three PRCC cases (p < 0.01). The unenhanced attenuation characteristic was significantly different between the two diseases (p < 0.001). The absolute attenuation values (AAVs) and the corrected attenuation values (CAVs) of the AML with minimal fat group of unenhanced and two phases of enhanced images were greater compared with that of the PRCC group (p < 0.05). After contrast medium injection, the tumour enhancement value (TEV) of the AML with minimal fat group in the corticomedullary phase was greater than that of the PRCC group (p < 0.01). Most cases of both tumour types demonstrated early enhancement characteristics; the enhancement value of the AML with minimal fat group was greater compared with that of the PRCC group (p < 0.01). The unenhanced attenuation characteristic, intra-tumoural vessels, and CAVs of unenhanced and early excretory phase scans were valuable parameters to differentiate between AML with minimal fat and PRCC tumours by multivariate logistic regression analysis (p < 0.05 for all).

Conclusion

The unenhanced attenuation characteristic, intra-tumoural vessels, and the attenuation values of unenhanced and early excretory phase scans are valuable parameters in differentiating AML with minimal fat from PRCC at CT.

Introduction

Angiomyolipoma (AML) is the most common solid benign renal tumour.1 Histopathological analysis reveals that AML is composed of abnormal blood vessels, adipose tissue, and smooth muscle in proportions that vary greatly among individual tumours.1, 2 In most cases, AML can be diagnosed accurately by identifying the intra-tumoural fat component on computed tomography (CT) images. Unfortunately, approximately 4–5% of AML tumours either do not contain any fat cells or contain an insufficient amount of fat cells to provide a CT image-based diagnosis; this tumour type is termed atypical AML or AML with minimal fat.3, 4

One of the challenges for a radiologist in diagnosing AML with minimal fat is differentiation from papillary renal cell carcinoma (PRCC). PRCC is the second most common carcinoma of the proximal renal tubules and accounts for 10–15% of renal neoplasms.5 It is difficult to differentiate the two tumour types because they both appear as solid tumours without obvious enhancement at CT; however, differentiating these two diseases is of significant clinical significance. Most asymptomatic or small AML can be left untreated or followed, whereas PRCC is typically resected.

A previous study has demonstrated several methods of differentiation between the two tumours with overlapping CT features,6 but the authors did not include a detailed analysis. Therefore, the purpose of the present study was to investigate the CT attenuation values and characteristics of morphology and enhancement to differentiate the two diseases.

Section snippets

Materials and methods

This retrospective study was approved by the institutional review board of the first affiliated hospital of China Medical University, and informed consent was waived. Between January 2006 and November 2010, 21 patients with AML with minimal fat (18 women and three men; mean age 45.1 years; range 23–70 years) and 23 patients with PRCC (10 women and 13 men; mean age 52.35 years; range 24–72 years) who were identified from a pathological database were enrolled in this study. All patients had a

Results

All of the lesions were nearly circular and had smooth margins. There was no significant difference in age or tumour size between the two patient groups (p > 0.05). The AML with minimal fat group had an apparent female prevalence compared with the PRCC group (85.7% versus 43.5%, p < 0.01). Intra-tumoural calcification was found in one case of AML with minimal fat and three cases of PRCC (p > 0.05). Intra-tumoural haemorrhage was found only in one case of AML with minimal fat but not in any PRCC

Discussion

CT has been widely used for the evaluation of renal tumours because CT can provide detailed tumour information. Furthermore, with the use of helical CT, it is possible to analyse the dynamic enhancement pattern of the tumour, which enables the differentiation of many renal neoplasms.8, 9, 10, 11, 12

According to the results of the multivariate logistic regression analysis, the unenhanced attenuation characteristic, intra-tumoural vessels, and the CAVs of unenhanced and early excretory phase

Acknowledgements

This study was supported by grants from the Foundation of Education Department of Liaoning Province, P.R. China (L2010665) to R. X. and the Foundation of Science and Technology Department of Liaoning Province, P.R. China (20092250085) to Y.L.

References (19)

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