Morphologic Features of Magnetic Resonance Imaging as a Surrogate of Capsular Contracture in Breast Cancer Patients With Implant-based Reconstructions

Abstract

Purpose: Capsular contracture (CC) is a serious complication in patients receiving implant-based reconstruction for breast cancer. Currently, no objective methods are available for assessing CC. The goal of the present study was to identify image-based surrogates of CC using magnetic resonance imaging (MRI).

Methods and materials: We analyzed a retrospective data set of 50 patients who had undergone both a diagnostic MRI scan and a plastic surgeon's evaluation of the CC score (Baker's score) within a 6-month period after mastectomy and reconstructive surgery. The MRI scans were assessed for morphologic shape features of the implant and histogram features of the pectoralis muscle. The shape features, such as roundness, eccentricity, solidity, extent, and ratio length for the implant, were compared with the Baker score. For the pectoralis muscle, the muscle width and median, skewness, and kurtosis of the intensity were compared with the Baker score. Univariate analysis (UVA) using a Wilcoxon rank-sum test and multivariate analysis with the least absolute shrinkage and selection operator logistic regression was performed to determine significant differences in these features between the patient groups categorized according to their Baker's scores.

Results: UVA showed statistically significant differences between grade 1 and grade ≥2 for morphologic shape features and histogram features, except for volume and skewness. Only eccentricity, ratio length, and volume were borderline significant in differentiating grade ≤2 and grade ≥3. Features with P<.1 on UVA were used in the multivariate least absolute shrinkage and selection operator logistic regression analysis. Multivariate analysis showed a good level of predictive power for grade 1 versus grade ≥2 CC (area under the receiver operating characteristic curve 0.78, sensitivity 0.78, and specificity 0.82) and for grade ≤2 versus grade ≥3 CC (area under the receiver operating characteristic curve 0.75, sensitivity 0.75, and specificity 0.79).

Conclusions: The morphologic shape features described on MR images were associated with the severity of CC. MRI has the potential to further improve the diagnostic ability of the Baker score in breast cancer patients who undergo implant reconstruction.

Fig. 1

Clinical case demonstrating the shape of the implant is more rounded and rising more superiorly on the chest wall when the patient develops severe capsular contracture (grade 3) compared with grade 1 capsular contracture.

Fig. 2

Chronology of surgery, radiation therapy (RT), magnetic resonance imaging (MRI), and Baker’s grade. The time reported for capsular contracture, MRI and Baker’s classification was calculated in months from the time of surgery.

Fig. 3

Capsular contracture (CC) thickness measured on the T2-weighted sagittal magnetic resonance image. Capsule thickness was calculated at 4 points (red arrows) around the implant on the central-most image slice (left). The box plot (right) shows the capsule thickness calculated as a function of CC grade. (A color version of this figure is available at www.redjournal.org.)

Fig. 4

Morphologic shape features of roundness, eccentricity, solidity, extent, ratio length, and volume with respect to capsular contracture (CC) grade for the implant. Each shape feature is represented by a boxplot, in which the box represents the 25th and 75th percentiles and the horizontal line in the box the median value.

Fig. 5

Muscle thickness and magnetic resonance imaging intensity histogram features of median, kurtosis, and skewness of volume with respect to the capsular contracture grade for the pectoralis major muscle. Thickness was measured in the pectoralis muscle that lay immediately caudal to the superior aspect of the implant. An attempt was made to contour a consistent 2 cm of pectoralis muscle on 2 central slices. Each feature is represented by a boxplot, with the box representing the 25th and 75th percentiles and the horizontal line in the box the median value.