Quantification of Pancreas Surface Lobularity on CT: A Feasibility Study in the Normal Pancreas

Abstract

Objective: To assess the feasibility and reproducibility of pancreatic surface lobularity (PSL) quantification derived from abdominal computed tomography (CT) in a population of patients free from pancreatic disease.

Materials and methods: This retrospective study included 265 patients free from pancreatic disease who underwent contrast-enhanced abdominal CT between 2017 and 2019. A maximum of 11 individual PSL measurements were performed by two abdominal radiologists (head [5 measurements], body, and tail [3 measurements each]) using dedicated software. The influence of age, body mass index (BMI), and sex on PSL was assessed using the Pearson correlation and repeated measurements. Inter-reader agreement was assessed using the intraclass correlation coefficient (ICC) and Bland Altman (BA) plots.

Results: CT images of 15 (6%) patients could not be analyzed. A total of 2750 measurements were performed in the remaining 250 patients (143 male [57%], mean age 45 years [range, 18-91]), and 2237 (81%) values were obtained in the head 951/1250 (76%), body 609/750 (81%), and tail 677/750 (90%). The mean ± standard deviation PSL was 6.53 ± 1.37. The mean PSL was significantly higher in male than in female (6.89 ± 1.30 vs. 6.06 ± 1.31, respectively, p < 0.001). PSL gradually increased with age (r = 0.32, p < 0.001) and BMI (r = 0.32, p < 0.001). Inter-reader agreement was excellent (ICC 0.82 [95% confidence interval 0.72-0.85], with a BA bias of 0.30 and 95% limits of agreement of -1.29 and 1.89).

Conclusion: CT-based PSL quantification is feasible with a high success rate and inter-reader agreement in subjects free from pancreatic disease. Significant variations were observed according to sex, age, and BMI. This study provides a reference for future studies.

Keywords: Anatomy; Pancreatic lobule; Quantitative.

Fig. 1. Flowchart of the study.

CT = computed tomography, PSL = pancreas surface lobularity

Fig. 2. Example of PSL measurement in a 41-year-old male patient.

A-C. Figures show magnified contrast enhanced computed tomography (single acquisition, split-bolus injection protocol) with measurement performed on the anterior margin of the head (A), body (B), and tail (C), respectively. The software automatically generates smooth polynomial lines to mimic a smooth pancreatic surface (red lines) and detects the actual surface of the pancreas (green lines). The distance between the detected pancreatic margin and the polynomial line was measured on a pixel-by-pixel basis and expressed as tenths of a millimeter. The mean PSL score was 6.11. PSL = pancreas surface lobularity

Fig. 3. Distribution of PSL according to age.

A. Overall distribution of the entire cohort, the red line corresponds to the sliding PSL average over ten years, and shows a progressive increase of PSL with age. B. Difference between male (black dots), and female (white dots). In both groups, PSL was significantly correlated with age (r = 0.39, p < 0.001 in male and r = 0.35, p < 0.001 in female). PSL = pancreas surface lobularity

Fig. 4. Box plots representing the distribution of PSL according to age categories (i.e. 18–30, 31–50, 51–70, and 71 or more years old), in the head, body and tail of the pancreas, and for the entire pancreas.

PSL was found to significantly increase with age in all parts of the pancreas, except in the body. Boxes represent the 10th–90th percentile, whiskers 1st–99th percentile, and dots are outliers. The central bar represents the median. Post-hoc comparisons: ^*Head: all paired comparisons were significant except for 18–30 vs. 31–50 and 51–70 vs. ≥ 71, ^†Tail: only 18–30 vs. 51–70 found significant. Other paired comparisons were not significant, ^‡All: 18–30 vs. 51–70, 18–30 vs. ≥ 71 and 31–50 vs. 5–70 were found significant. Other paired comparisons were not significant. PSL = pancreas surface lobularity

Fig. 5. Distribution of PSL according to BMI.

A. shows the difference between male (black dots) and female (white dots). In both groups, PSL was significantly correlated with BMI, but the correlation was stronger in male (r = 0.40, p < 0.001) than in female (r = 0.21, p < 0.031). B. Box plots representing the distribution of PSL according to BMI categories (i.e., < 18.5, 18.5–24.9, 25–29.9, and ≥ 30 kg/m²), head, body, and tail of the pancreas, and in the entire pancreas. PSL was found to significantly increase with BMI categories in all parts of the pancreas. Boxes represent the 10th–90th percentile, whiskers 1st–99th percentile, and dots are outliers. The central bar represents the median. Post-hoc comparisons: ^*Head: only 18.5–24.9 vs. ≥ 30 was significant, ^†Body: only 18.5–24.9 vs. ≥ 30 was significant, ^‡All: 18.5–24.9 vs. ≥ 30 and 25–29.9 vs. ≥ 30 were significant. BMI = body mass index, PSL = pancreas surface lobularity

Fig. 6. Heat map representing PSL values according to age (by increment of 5 years) and BMI categories (i.e. < 18.5, 18.5–24.9, 25–29.9, and ≥ 30 kg/m²).

The map shows the progressive increase of PSL with both age and BMI. BMI = body mass index, PSL = pancreas surface lobularity