A BI-RADS-associated MR mammography algorithm can accurately diagnose breast tumors, German researchers found. However, due to false-negative and false-positive MR mammography results, histology is still necessary, they said.
MR mammography (MRM) has been used to characterize suspicious clinical or mammographic examinations, but MRM techniques vary. In 1999 the Lesion Diagnosis Working Group crafted recommendations for standard MRM terms based on architectural features described by the American College of Radiology (ACR) BI-RADS. The lexicon was further refined and includes recommendations for reporting clinical history, technical parameters for MRM, descriptions for general breast composition, morphological and kinetic characteristics of mass lesions or regions of abnormal enhancement, overall impression, and management recommendations.
Dr. Christian Sohns, from the department of cardiology and pneumology at Georg-August-University of Göttingen in Germany, and colleagues assessed whether a BI-RADS-associated MRM algorithm can distinguish between benign and malignant tumors and found it can (Eur Radiol, 31 July 2011).
Between April 2004 and January 2008, 207 female patients with histologically proven breast lesions were evaluated. All the patients underwent preoperative MR mammography (Symphony and Sonata, Siemens Healthcare) and digital mammography (Senographe 2000D, GE Healthcare). The patients were also imaged with a bilateral axial T2-weighted turbo spin-echo sequence and an axial T1-weighted gradient-echo sequence. Two examiners classified the MR images according to BI-RADS.
They found a significant correlation between specific histology and MRM-tumor-morphology could not be reported. More than 70% (70.5%) of the malignant tumors were categorized as mass, 23.2% as nonmass, and seven malignant tumors were inconspicuous at MRM but had positive mammography or ultrasound investigation. Of the mass lesions, significance was raised with irregular shape (88%), speculated margin (97%), rim enhancement (98%), fast initial increase (90%), post initial plateau (65%), and intermediate T2 result (82%).
As far as benign lesions, Sohns and colleagues found oval mass (79%), slow initial increase (94%), a hyperintense T2 result (77%), and an inconspicuous MRM result (77%) were often seen in benign histology. Symmetry (90%) and further post initial increase (90%) were significant, whereas a regional distribution (74%) was lowly significant for benignity, the authors wrote.
Shape of the mass enhancement in histologically proven malignant and benign tumors
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Margin of the mass enhancement in histologically proven malignant and benign tumors
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Distribution of the nonmass-like enhancement into histologically proven malignant and benign tumors
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"Specific BI-RADS criteria are strong and significant predictors for malignancy in unsuspected MRM mass lesions," the authors wrote. "Such confirmation led in about 65% of cases to a malignant diagnosis."
The BI-RADS descriptions were also predictive for malignancy of otherwise unsuspected MRM nonmass-like lesions, demonstrated in the tables.
Furthermore, as seen in the tables, the results indicate 88% of the tumors with irregular shape were highly significant malignant. Those tumors with an oval or lobulated shape were in 78.6% (oval) and 56% (lobulated) benign. "However, in these cases only a mean significance was reached," the authors wrote. "This leads to the conclusion that a lesion with an irregular shape is with the utmost probability malignant. In contrast, tumors with oval or lobulated shape suspect to be benign, without verifiable significance."
However, the researchers are quick to point out evidence-based algorithms are needed to guide the radiologist through image assessment and to describe morphologic features. Thus, concerning the form of internal enhancement, the range was essentially exceeded. Twenty-eight of the malignant tumors showed heterogeneous enhancement, which led to significance in malignancy in only 62%. Marks for benignity were reticular (75%) and stippled/punctuated enhancement (70.6%).
In addition, symmetry was very important to deliver a prognosis. Ninety percent of the cases with symmetric-appeared enhancement (9.5% of the benign tumors) were significantly benign, the researchers found. Asymmetric-appeared enhancement was highly significant for malignancy.
"Based on the BI-RADS classification, that an objective comparability and highly significant statement of diagnosis can be made," the researchers concluded. "The combination of several marker and characteristics is still essential to determine malignancy. Due to numerous false-negative and false-positive MRM results, histology is still essential."
