Magnetic resonance imaging of induration in the irradiated breast

The causes of induration (hardness) in the breast many years after tumour excision and whole breast radiotherapy for early stage breast cancer are not well established. The purpose of this study is to describe morphological magnetic resonance imaging (MRI) appearances and MRI-derived microvascular functional characteristics of the indurated breast several years post-treatment.

Fifteen women with moderate or marked induration at the electron boost site after breast preserving surgery and radiotherapy for early breast cancer (median 6 years; range, 2-15 years) underwent MRI, including 6/15 with very marked breast shrinkage and 8/15 with marked induration. Morphological T1- and T2-weighted and STIR images were obtained followed by a dynamic contrast medium enhanced sequence. The breast skin and underlying parenchyma of the irradiated breast were evaluated for thickening, oedema and the presence of enhancement compared to the contralateral breast. Particular note of boost site findings was made.

No evidence of tumour recurrence was seen. Fat necrosis was seen in 2/15 cases. Skin thickening and skin oedema not evident clinically were seen in 11/15 patients. Increased parenchymal oedema at the electron boost site was seen in 12/15 patients. The parenchymal oedema was not confined to the electron boost site, but was strongest in this location in 9/12 patients. Post-contrast images in 12/14 patients showed persistent parenchymal enhancement in nine (marked in three, who also had severe breast shrinkage and marked induration), a finding consistent with, but not diagnostic of tissue fibrosis.

Fat necrosis is not likely to contribute to breast induration several years after radiotherapy in more than a minority of patients. Increased fluid content in the breast parenchyma and skin oedema are likely to be more important contributors to palpable induration. Increased fluid content may be related to persistent capillary leakage even many years post-treatment, an expression of radiation-induced vascular injury. Fibrosis cannot be scored directly on MRI, but persistent parenchymal enhancement in a high proportion of post-contrast images is compatible with this pathology.