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203 Colonic manometry and contrast enemas 9 ( n =9, 56%) or without HAPCs ( n =1, 50%, P = .747). Four children had a rectal diameter >6 cm but ≤6.5 cm. Lowering the cutoff value for megacolon/megarectum to 6 cm did not result in a significant difference between the groups (58% vs 69% vs 50%, P = .785). TABLE 4. Comparison of mean SCS ratios in FC patients vs normative data Measurement Reference values a T-value Mean SD 95% CI P -value Rectosigmoid length/L2 b 10.50 (±3.15) 5.71 13.91 3.46 12.57-15.26 <.0001 Descending colon length/L2 b 5.28 (±1.42) 4.84 7.45 2.40 6.41-8.49 <.0001 Rectum diameter/L2 b 1.52 (±0.27) 1.52 1.69 0.54 1.48-1.90 .140 Sigmoid diameter/L2 b 1.10 (±0.21) 3.81 1.42 0.49 1.22-1.61 .0007 Descending diameter/L2 b 1.48 (±0.26) -0.41 1.11 0.27 1.00-1.22 .683 a Recently published normative data were used for comparison: Koppen IJN, Yacob D, Di Lorenzo C, et al . Assessing colonic anatomy normal values based on air contrast enemas in children younger than 6 years. Pediatr Radiol 2017;47:306-312. Data are expressed as mean (±standard deviation). b one missing value because distance between pedicles L2 could not be determined in one patient with prematurely terminating HAPCs. Bold values indicate significant results ( P < .05). DISCUSSION In our sample, dysmotility was present in the majority of patients with intractable FC, ranging from absence of HAPCs to prematurely terminating HAPCs. Overall, the colonic diameter, adjusted for body size, was significantly smaller in colonic segments with HAPCs than in segments without HAPCs. The same was true for colonic segments with and without HAPCs within the group of children with prematurely terminating HAPCs. Moreover, the colonic diameter in children with prematurely terminating HAPCs was significantly larger than in children with fully propagating HAPCs and children without HAPCs. Furthermore, SCS ratios for the length of the rectosigmoid and the descending colon and the diameter of the sigmoid colon were significantly larger in children with FC compared to the normative population. Thus, in our sample, colonic dilation was associated with dysmotility, especially with premature termination of HAPCs. Although the link between segmental colonic dilation and colonic dysmotility is incompletely understood, it is intuitive that a chronically distended, large diameter colon will present impaired contractile function. Colonic contractility depends on a multitude of elements including smooth muscle cells, connective tissue and the enteric and extrinsic nervous system. In a study utilizing intracolonic barostat in adults with chronic constipation and megacolon, excessively high colonic fasting volumes and increased colonic