Magnetic resonance imaging features of idiopathic granulomatous mastitis: is there any contribution of diffusion-weighted imaging in the differential diagnosis?

PURPOSE: To identify the magnetic resonance imaging (MRI) appearance of idiopathic granulomatous mastitis, and the usefulness of diffusion-weighted magnetic resonance imaging (DW-MRI) in distinguishing idiopathic granulomatous mastitis (IGM) from malignant breast lesions.
MATERIAL AND METHODS: A total of 37 women (mean age 36 + 8; range 20-67 years) with histopathologic diagnoses of idiopathic granulomatous mastitis were enrolled in the study. Five patients had bilateral IGM, which were evaluated as ten cases. Dynamic MRI findings were categorized as enhancing mass lesion, non-mass enhancement, or both together. The frequency of quadrant involvement, retroareolar involvement, accompanying abscess, ductal ectasia, skin thickening, breast edema, extension to pectoral muscle, and presence of fistula were investigated. The mean apparent diffusion coefficient (ADC) values for lesions, contralateral normal breast parenchyma, pectoralis major muscle, and sternum were measured in patients with invasive cancers (n = 42) and those with mastitis (n = 42). The ADC ratio of the lesions to the contralateral normal breast parenchyma, pectoralis major muscle, and sternum were determined.
RESULTS: The findings of idiopathic granulomatous mastitis on MRI were total (in all quadrants) or wide (2 or 3 quadrants) in 30 (71.5 %), retroareolar space involvement in 28 (66.7 %), skin thickening in 21 (50 %), breast edema in 21 (50 %), extension to pectoral muscle in 18 (42.9 %), accompanying abscess formation in 33 (78 %), ductal ectasia in 17 (40.5 %), and fistulas in 13 (31 %). On dynamic contrast-enhanced MRI, 69 % of the patients had mass appearance of IGM. The most frequent enhancement patterns were rim enhancement in 20 (78 %) in masses and clustered ring in 11 (48 %) in non-mass lesions. Early enhancement pattern of IGM was obtained as 'slow' in 29 cases (69 %), 'medium' in 11 cases (26.1) and 'rapid' in 2 (5 %) cases. Time-signal intensity curves were detected as Type-1 in 27 cases (64 %) and Type-2 in 15 cases (36 %). IGM showed significantly lower mean ADC values when compared with the normal parenchyma. When IGM was compared with malignancy, mastitis ADC was 0.98 ± 0.188 × 10-3, and invasive cancer ADC was 0.95 ± 0.229 × 10-3. The difference in ADC values of mastitis and invasive cancers proved not to be significant (P = 0.185). Our results had no discriminatory power for IGM versus malignant lesions for either ADC values and ADC ratios of normal breast parenchyma, pectoralis major muscle, and sternum.
CONCLUSION: Although not characteristic for idiopathic granulomatous mastitis, masses with rim enhancement or clustered-ring non-mass lesions with segmental distribution on MRI are the most common features of the disease. Ductal ectasia and periductal enhancement were commonly accompanying; this and kinetic analysis are valuable findings for distinguishing IGM from invasive cancer. IGM shows similar ADC values to invasive cancers despite being benign, DW-MRI is not helpful in the differentiation with malignant lesions.