Rare Breast Tumors Differring From Common Benign And Malignant Breast Tumors: Radiologic Findings And Correlation With Pathology

Objective:To characterize the MRI features of rare tumors of the breast differring from common benign and malignant breast tumors and correlate the MRI features with histopathology.Materials and Methods:MR images obtained from 15 women (aged 33～71 years old) with mucinous carcinoma of the breast,15 women (aged 37-60 years old) with intraductal papilloma and 5 women (aged 33～49 years old) with phyllodes tumor verified by histopathology were reviewed. The pathologic diagnosis was made according to the standard of the World Health Organization Classification of Tumors (2003). MR imaging of the breast was performed on 1.5 Tesla scanner (Signa Infinity, GE). MR examinations included Tl-Weighted and fat-suppressed T2-Weighted imaging, diffusion-weighted imaging (DWI) with the b value of 0,500 and 1000 s/mm2 by single-shot echo-planar imaging (EPI) sequence, and 3D dynamic contrast enhancement MRI (DCE-MRI) by using VIBRANT (Volume Imaging for Breast Assessment, VIBRANT) sequence. The MR findings were retrospectively studied according to the lexicon of Breast Imaging Reporting and Data System-Magnetic Resonance Imaging (BI-RADS-MRI) designed by American College of Radiology (ACR), including morphology, signal intensity on T1WI and T2WI before enhancement, internal structure after enhancement, kinetic curve pattern on dynamic study, and the mean value of apparent diffusion coefficients (ADC) on DWI.Results:(1) 12 patients were identified the pathologic subtype as pure type of mucinous carcinoma and 3 patients as a mixed type. The amounts of mucus counted 60%～90%. The maximum diameter of the tumors ranged from 1.2 cm to 5.5 cm. All 15 tumors presented as a mass on MRI with low signal on T1WI, and high or strongly high signal on FS T2WI. As regards an internal enhancement pattern,1 tumor revealed slightly inhomogeneous enhancement pattern,2 tumors showed inhomogeneous persistent enhancement, and the other tumors showed rim enhancement in early dynamic phases and gradually enhancement of central part of the lesion in delayed phase. All of the tumors showed high signal on DWI. The mean ADC value was 2.25±0.24 (×10-3mm2/s) with b value of 500 s/mm2 and 2.02±0.19 (×10-3mm2/s) with b value of 1000 s/mm2. (2) 13 lesions were identified as pure intraductal papilloma and the other two lesions were identified as intraductal papilloma associated with secondary changes, one with infarction and one with congestion.9 lesions were round or oval and 6 were irregular in shape. The margins of these lesions were well-defined in 11 cases, and poorly defined or ill-defined in 4 cases. The maximum diameter of the tumors ranged from 0.3cm to 2cm. The signal intensity of intraductal papilloma was lower than or the same as that of the normal gland on T1WI and slightly higher, but it was not as high as cysts on T2WI. On dynamic images, all 15 lesions showed rapid initial enhancement, heterogeneous of 8 cases and homogenous of 7 cases. In the delayed phase, the most tumors (13/15) showed peripheral enhancement seen as ring-like enhancement. The patterns of time-signal intensity curves (TIC) were typeⅢ(washout) in 13 cases and typeⅡ(plateau) in 2 cases. And the mean initial wash-in phase enhancement ratio was 158.28%±21.95%. The mean value of ADC was 1.12±0.30 (×10-3mm2/s) with b value of 1000 s/mm. (3) The pathologic diagnosis of the 5 phyllodes tumors was 1 benign,2 borderline and 2 malignant. Four tumors were lobular and one was oval in shape. The signal intensity of tumor was lower than that of normal breast tissue on T1WI, and higher on T2WI. Moreover, there were internal septations which appeared low signal intensity on FS T2WI in one tumor. Four patients underwent DCE-MRI, all of the tumors showed rapidly enhancement in early dynamic phases, TIC of 3 tumors were plateau and the other one was slightly washout. All the five tumors showed high signal on DWI, and the value of ADC was lower than that of the normal breast tissue and lower than the threshold value used to differentiate benign and malignant lesions of the breast. In this study,3 patients underwent 1H-MR spectroscopy, all of the tumors showed elevated levels of choline compounds.Conclusion:(1) The MRI features of mucinous carcinoma of the breast on T2WI, DCE-MRI, and DWI show differences from invasive ductal carcinomas, and this may reflect its distinct histological pattern. The combination of these MRI findings may lead to a pre-operative diagnosis of this tumor.(2) MRI is a useful adjunct for the detection of intraductal papillomas. Usually, small size, well-defined margins, rapid initial enhancement and typeⅢcurve, and relative lower ADC value are helpful in the diagnosis of intraductal papillomas on MR imaging. However, it is one or more suspicious morphologic findings and/or dynamic enhancement features that make it difficult to differentiate intraductal papilloma from small breast cancer, when excision for pathologic diagnosis is necessary.(3) MR imaging is helpful in the diagnosis of phyllodes tumors, but the final diagnosis still depends on the histopathologic examination.