Introduction

Non-mass enhancing (NME) lesions are a diagnostic challenge and one of the most frequent causes of false-positives findings with DCE-MRI [1] with a wide spectrum of both benign and malignant diseases associated [2]. Diffusion-weighted imaging (DWI) is a non-contrast MRI parameter, which provides a strong surrogate marker for tissue microstructure, membrane integrity, and cell density, and can be quantified by calculation of the apparent diffusion coefficient (ADC) [3]. Decreased ADC values indicate a diffusion hindrance, indicative of malignancy [4–6]. Sensitivities of DWI with ADC mapping of up to 96% for breast cancer detection and specificities of up to 100% for breast tumor characterization have been reported [7–11]. Limited data for NME characterization with DWI, suggesting is less sensitive and specific in these diagnostically challenging lesions. It has been shown that 2D ROI ADC measurement approach in the part of the enhancing tumor with the visually assessed lowest ADC is the most practical [12–14], it remains unclear the best measurement approach in NME. The aim of the study was to investigate the influence of region-of-interest (ROI) placement and different ADC metrics on diagnostic accuracy of DWI and to assess intra and inter-reader agreement of ADC measurements with DWI in NME breast tumors

Methods

In this IRB-approved single-institution study and retrospective data analysis 95 patients, with multiparametric MRI (DCE/DWI) and diagnosed with NME breast lesion (BI-RADS 4/5) were included. 29 had to be excluded due to; suboptimal quality n=5, non-visibility n=24 of the lesion on DWI. Two readers independently assessed DWI and DCE in two separate randomized readings. For DWI readers recorded ADC mean values using a) Whole tumor ROI, b) Darkest part tumor 10 mm ROI and c) point tumor 3 mm ROI, (Fig 1). NME were classified as a benign (>1.3 x10-3 mm2/s) or malignant (1.3 x 10-3 mm2/s). Histopathology as standard of reference. ROC curves were plotted and the area under the curve (AUC) was determined. Concordance correlation coefficient (CCC) was performed for agreement on continuous measures (MRI features) obtained by the two independent readers

Results

66 patients (mean ages 51.8 ±10.8 yo, range 26-76 yo) were included for analysis with a mean size lesion of 40±25 mm, range 5 mm-98 mm): 39 malignant (59%) and 27 benign (41%). The best diagnostic performance for DWI for both readers and readings were achieved with Dptu mean with AUC range 0.512 and 0.709 (Figure 2). CCC varied among the different ADC metrics was fair-to-moderate. The best results for CCC were achieved for Dptu max ADC (0.420) in the second reading (Figure 3). Similar results were obtained for the intra-reader agreement with the best CCC for Wtu mean with 0.435 for R1 and 0.412 for R2 (figure 4)

Discussion

The recent concerns about the safety of gadolinium contrast agents, recommendations state “gadolinium based contrast agents should only be administered if the information so provided is necessary, and specifically expected to increase the confidence in correct disease diagnosis or assessment thereof, or disease exclusion” [15]. Several unenhanced MR imaging parameters have been explored in this context. Advances in imaging techniques and hardware, as better gradient systems and multi-channel coils have overcome some limitations such as susceptibility and respiratory motion artifacts, establishing DWI as an essential part of oncologic imaging protocols. DWI with ADC mapping can be easily implemented in a routine breast MRI protocol without significantly increasing scan time [19, 20], has emerged as the most robust and reliable adjunct to DCE-MR with sensitivities of up to 96% and specificities of up to 100% [4-6]. The majority of data available is for mass enhancing tumors and there are concerns that DWI is limited in small masses and NME lesions [9]. Our results confirm that diagnostic accuracy of DWI with ADC mapping is limited in lesions presenting as NME on DCE-MRI with only moderate inter-reader agreement. Whereas Wtu ADC mean measurement is the most repeatable, 2DROI ADC measurements is the most accurate for breast cancer diagnosis. It has to be noted, in this study 24 (27%) patients with NME on DCE-MRI the lesion (12 benign/ 12 malignant) was not discernible on DWI. A limitation of our study is the small number of cases, yet to our knowledge is the largest series of that investigated MpMRI of the breast for NME lesions. Our findings need to be verified in further larger-scale studies

Conclusions

Diagnostic accuracy of DWI with ADC mapping is limited in breast tumors presenting as NME. Best results are achieved using 2D ROI measurements approach and ADC mean. A substantial number of lesions not visible on DWI alone and therefore DCE-MRI is still indispensable for detection and characterization of breast cancers presenting NME lesions.

Acknowledgements

No acknowledgement found.

References

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