Imaging features of focal breast fibrosis: mammographic-pathologic correlation of noncalcified breast lesions.

OBJECTIVE: Our objective was to describe the spectrum of imaging and histologic findings of focal breast fibrosis with an emphasis on noncalcified lesions, thereby offering a means of confirming mammographic-pathologic concordance on core biopsy of this increasingly encountered diagnosis. MATERIALS AND METHODS: Retrospective review of 610 core needle biopsies revealed the histologic diagnosis of focal fibrosis in 89 (15%). Thirty-nine cases were excluded: 17 in which focal fibrosis was not the primary diagnosis and 22 in which calcifications were the main imaging findings. The 50 remaining patients with noncalcified lesions that proved on histology to be focal fibrosis constituted the basis of the study. RESULTS: Mammographically, focal fibrosis presented as a mass in 68% of patients (n = 34), architectural distortion in 12% (n = 6), and asymmetric density in 10% (n = 5); focal fibrosis was mammographically occult in 10% (n = 5). Sonographically, 72% (n = 36) of cases of focal fibrosis presented as masses with three echo texture patterns: hypoechoic, isoechoic, and centrally echogenic with a peripheral hypoechoic rim. The sonographic margins were well circumscribed (n = 21), lobulated (n = 10), or ill defined (n = 5). Histologic review revealed three morphologic patterns of collagen deposition: perilobular, septal, and haphazard fibrosis. Correlation with the imaging findings showed that septal and perilobular fibrosis most often presented as hypoechoic or centrally echogenic masses, whereas the haphazard form was more often seen with architectural distortion. CONCLUSION: Focal fibrosis often presents as a noncalcified mass on mammography or sonography. The diagnosis of focal fibrosis on core needle biopsy can be considered concordant for a mass exhibiting well-circumscribed or partially obscured margins. Imaging findings discordant with focal fibrosis, such as marginal spiculation, require excisional biopsy.