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195 Colonic manometry and contrast enemas 9 INTRODUCTION Segmental colonic dilation is often encountered in children with severe constipation, both of functional and organic origin. 1–7 In early life, this phenomenon is usually associated with congenital organic diseases such as Hirschsprung's disease, anorectal malformations or other birth defects such as intestinal atresia. 8–11 However, segmental colonic dilation can also be observed in older children with long-standing symptoms of functional constipation (FC), in whom underlying organic pathology has been ruled out. 6,7,12 The phenomenon of segmental dilation has also been described in adults and this has led to the definitions of megacolon andmegarectum, defined by Preston et al . as a colonic/rectal width of >6.5 cm. 13 Absolute cut-off values for megacolon and megarectum have not been established for children and the adult criteria have been used for children in previous studies. 14,15 In addition to segmental colonic dilation, an elongated or tortuous aspect of the colon, frequently referred to as colonic redundancy or dolichocolon, may also be observed and reported by pediatric radiologists. In a study by Yik et al ., nuclear transit scintigraphy studies were compared between children with slow transit in the proximal colon, normal proximal colonic transit with anorectal retention, and rapid proximal transit with or without anorectal retention. 16 The authors reported that elongation of the transverse colon was more common in children with slow transit constipation compared to the other two groups and that elongation of the sigmoid colon was similar for all groups. However, this study did not include a healthy control group and it is therefore unknown how these findings relate to the normative population. The clinical relevance of these radiologic findings of colonic dilation and elongation is incompletely understood. It has been suggested that colonic dilation results in colonic dysmotility due to an impaired contractile function of the dilated segment or vice versa that abnormal colonic motility may lead to stasis of fecal content and stretching of the colonic lumen. 3–5,17 The same may be true for colonic elongation. 16 These observations have been utilized to advocate for surgical interventions (e.g., partial resection of the dilated segment of the colon). 7,12 However, to date there is a lack of published data on the relationship between colonic dilation and colonic motility in children with FC. Currently, the most appropriate way to assess colonic motility is via colonic manometry, which enables evaluation of intraluminal colonic pressures and their coordination, thereby allowing the assessment of colonic motor patterns. The most well-described colonic motor patterns are high-amplitude propagating contractions (HAPCs). HAPCs are forceful