Radiological progression of end colostomy trephine diameter and area

Abstract

Background: Development of a parastomal hernia is common following abdominoperineal excision (APE). The true incidence is difficult to assess fully owing to differing lengths of follow-up and techniques used to assess herniation; radiological or clinical. The primary aim of this study was to evaluate colostomy diameter by studying the rate of change of axial and sagittal trephine diameters, trephine area, and the ratio of the trephine over time. A secondary aim was to investigate variation in trephine area and variables affecting parasternal hernia over time.

Methods: Serial CT scans performed after APE from January 2006 to December 2014 were reviewed. Variables analysed included age, sex, trephine position relative to rectus abdominis muscle (RAM), type of incision for stoma creation, and axial and sagittal trephine diameters measured on follow-up CT. A Bayesian hierarchical modelling framework was used to examine the relationship of trephine diameters, area and ratio over time.

Results: Of 112 patients undergoing APE, 103 were eligible for analysis; this included 91 colostomies (88·3 per cent) through the RAM and 12 (11·7 per cent) lateral to the RAM. Median age of the patients was 68 years. Sixty patients (58·3 per cent) had a circular and 43 (41·7 per cent) a cruciate incision for stoma creation. The sagittal trephine diameter increased by 0·22 (95 per cent credible interval 0·12 to 0·32) mm/month for both sexes. Women reported a significant increase in axial trephine diameters; the male : female ratio difference was -0·17 (-0·30 to -0·03) mm/month and for trephine areas -6·21 (0·96 to 13·7) mm²/month. Patient age, colostomy trephine location and shape of incision were not statistically significant variables for parasternal hernia.

Conclusion: Female sex was the only variable affecting the rate of increase in axial trephine diameter and trephine area over time.

Figure 1

Postoperative CT scan from a single patient: a axial trephine diameter measurement (3·17 cm) and hernial sac (9·72 cm); b sagittal trephine diameter measurement (3·18 cm). Trephine area was approximated as: Area = π(A/2)(B/2), where A represents sagittal diameter and B represents axial diameter

Figure 2

Patient flow diagram for a retrospective study on the radiological progression of permanent end colostomy trephine diameter and area over time

Figure 3

Kaplan–Meier analysis of the estimated incidence of parastomal hernia in 103 patients according to the European Hernia Society classification of parastomal hernia. Approximate 95 per cent confidence intervals have been added to represent sampling uncertainty (as described by Kalbfleisch and Prentice14)

Figure 4

Change in mean axial trephine diameter in men and women over time after surgery. The curves reflect people aged 65 years (the mean in the sample) who had a colostomy positioned lateral to the rectus abdominis muscle (age, stoma position and shape of trephine incision during colostomy formation were not significant in the model). Means are shown with 95 per cent credible intervals. The difference in trephine diameter in men compared with women was −0·17 (95 per cent credible interval − 0·30 to −0·03) mm/month (P = 0·008)

Figure 5

Change in mean axial trephine area in men and women over time after surgery. The lines reflect people aged 65 years (the mean in the sample) who had a colostomy positioned lateral to the rectus abdominis muscle (age, stoma position and shape of trephine incision during colostomy formation were not significant in the model). Means are shown with 95 per cent credible intervals. The difference in trephine area in men compared with women was −6·21 (95 per cent credible interval 0·96 to 13·70) mm²/month (P = 0·009)