Quantitative CT Imaging of Ventral Hernias: Preliminary Validation of an Anatomical Labeling Protocol

<div><p>Objective</p><p>We described and validated a quantitative anatomical labeling protocol for extracting clinically relevant quantitative parameters for ventral hernias (VH) from routine computed tomography (CT) scans. This information was then used to predict the need for mesh bridge closure during ventral hernia repair (VHR).</p><p>Methods</p><p>A detailed anatomical labeling protocol was proposed to enable quantitative description of VH including shape, location, and surrounding environment (61 scans). Intra- and inter-rater reproducibilities were calculated for labeling on 18 and 10 clinically acquired CT scans, respectively. Preliminary clinical validation was performed by correlating 20 quantitative parameters derived from anatomical labeling with the requirement for mesh bridge closure at surgery (26 scans). Prediction of this clinical endpoint was compared with similar models fit on metrics from the semi-quantitative European Hernia Society Classification for Ventral Hernia (EHSCVH).</p><p>Results</p><p>High labeling reproducibilities were achieved for abdominal walls (±2 mm in mean surface distance), key anatomical landmarks (±5 mm in point distance), and hernia volumes (0.8 in Cohen’s kappa). 9 out of 20 individual quantitative parameters of hernia properties were significantly different between patients who required mesh bridge closure versus those in whom fascial closure was achieved at the time of VHR (p<0.05). Regression models constructed by two to five metrics presented a prediction with 84.6% accuracy for bridge requirement with cross-validation; similar models constructed by EHSCVH variables yielded 76.9% accuracy.</p><p>Significance</p><p>Reproducibility was acceptable for this first formal presentation of a quantitative image labeling protocol for VH on abdominal CT. Labeling-derived metrics presented better prediction of the need for mesh bridge closure than the EHSCVH metrics. This effort is intended as the foundation for future outcomes studies attempting to optimize choice of surgical technique across different anatomical types of VH.</p></div

Results of preliminary statistical analyses.

<p>(a) and (b) shows the number of false predictions and number of included variables over different alpha values using cross-validated elastic net regularized logistic regression, respectively. Generally, a larger alpha value yields stronger regularization, and thus involves less variables for the regression model. Note that the blue dashed curves represent the regression results using EHSCHV variables, while the green solid curves use the variables derived from labeling. (c) presents a hyper-plane using support vector machine to separate the two groups of patients with distinct technical outcomes by the two remaining labeling-derived variables of an exploratory regression model built upon all observations.</p

Fascial boundaries and bony structures reliability measured by Euclidean distance (ED) of centroids in mm.

<p>Fascial boundaries and bony structures reliability measured by Euclidean distance (ED) of centroids in mm.</p

Illustration of VH characteristics in terms of processed label results.

<p>The first row, from (a) to (c), demonstrates a matchup between the original image data and the processed labels, where the abdominal walls were interpolated. The second row, from (d) to (f), demonstrates the coherence of interpolated abdominal walls with the original image in three different views. The third row, from (g) to (i), illustrates a combined model of abdominal wall and hernia volume for shape-related VH characteristics, the relative location of VH with respect to the linea alba and linea semilunaris, and the relative location of VH with respect to skeletal landmarks and the umbilicus. The fourth row, from (j) to (l), demonstrates feasibility of measuring the VH defect size, width and length of VH, and ratio of volume size between the hernia sac and the abdominal cavity.</p

Two VH cases in volume rendering and tri-planar views.

<p>Although the two examples have almost the same hernia volume size (a = 125 cm³, b = 109 cm³), (a) is a long, shallow rupture at the umbilicus, while (b) is a short, deep protrusion of the abdominal wall. In addition, the patients’ body sizes are quite different, and the hernia in (b) is further away from the umbilicus.</p

Hernia volume reliability.

<p>Hernia volume reliability.</p

Illustration of VH characteristics on CT for four patients.

<p>In each section, the first row illustrates the location of the VH; the second row illustrates the VH defect size at the anterior abdominal wall; the third row demonstrates the volume size of the hernia sac (red) and the abdominal cavity (blue).</p

Clinically relevant quantitative parameters for describing VH.

<p>^a Not currently accessible via CT imaging</p><p>Clinically relevant quantitative parameters for describing VH.</p

Overview of the anatomical labeling protocol.

<p>(a) Axial and sagittal slices to label are determined in terms of the size and resolution of the volume. (b) On the selected axial slices, the anterior (outer and inner borders) and posterior abdominal wall is traced. At the same time, linea alba and linea semilunaris are labeled on the appropriate axial slices. (c) The VH is labeled entirely on every axial slice where the hernia exists. (d) On the selected sagittal slices, the outer and inner borders of the anterior abdominal wall are traced. Note the previous VH and abdominal wall labels can be helpful references. (e) The umbilicus and skeletal landmarks are labeled. (f) The complete set of labels is reviewed.</p

Statistical comparison of 20 metrics between two groups of patients with distinct outcomes.

<p>^a Each index refers to a metric in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141671#pone.0141671.t002" target="_blank">Table 2</a></p><p>* indicates significant difference between the two groups</p><p>Statistical comparison of 20 metrics between two groups of patients with distinct outcomes.</p