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198 Chapter 9 Contrast enemas For the contrast enema, children were placed in the supine position. The patient's anus was catheterized with an enema tip. Water-soluble contrast was introduced into the colon in a controlled fashion under gravity enabling the pediatric radiologist to obtain radiographic images and assess the colonic anatomy. With the Centricity Enterprise™ (GE Healthcare Pty Ltd Piscataway, NJ, USA) picture archiving and communication system (PACS), the colonic diameter was measured starting 5 cm proximal from the anal verge up to the splenic flexure, using 5 cm intervals (Figure 1). Measurements were performed by one author (I.J.N.K) and cross-referenced by an experienced pediatric radiologist (B.P.T.). If possible, calibration of the PACS measurement tool was based on an external radiopaque ruler (Glow ‘N Tell Tape, LeMaitre Vascular, Inc., Burlington, MA, USA) used during the contrast enema. If such a ruler was not used during the contrast enema, calibration was achieved by measuring a bony structure (e.g., femoral head) from a separate radiological exam performed within a short period of time. Since the contrast enema and colonic manometry were performed within 12 months from each other, a recent abdominal X-ray was always available for calibration. Furthermore, the distance between the lateral margins of the pedicles of vertebra L2 was measured to provide a ratio (colonic diameter divided by the distance between the lateral margins of the pedicles of L2). We use the term“standardized colon size” (SCS) for this ratio throughout the manuscript. We chose to use this ratio, since this enables standardization of the colonic size for age and body size. Moreover, this technique does not require calibration with an external tool. This method has been described in another recent publication by our group, where we determined normative colon size characteristics in 119 children <6 years of age who underwent pneumatic reduction of intussusceptions. 21 The data from this publication were used to compare the data fromour current study with a normative population. Furthermore, the prevalence of megarectum/megacolon was determined, using the predefined cutoff value of a rectal/colonic width of >6.5 cm. 13 Statistical analysis Analyses were performed using SPSS (SPSS Statistics for Windows, Version 22.0. (IBM Corp, Armonk,NY,USA)andSAS(SASInstituteInc.,Cary,NC,USA). P < .05wereconsideredstatistically significant. Results are expressed as means (with standard deviation; SD) or medians (and interquartile range; IQR), depending on whether the data were normally distributed or not. We compared parametric data using  t  tests. Comparisons of non-parametric data for paired measurements were made usingWilcoxon signed rank test. Group comparisons were made using Kruskal – Wallis tests (>2 groups) and Wilcoxon rank sum tests (2 groups). Correction for multiple testing was achieved through Bonferroni correction.