BackgroundDevelopment 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.MethodsSerial 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.ResultsOf 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.ConclusionFemale sex was the only variable affecting the rate of increase in axial trephine diameter and trephine area over time.

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