OBJECTIVEThe ability of the rectum to evacuate is valuable information in patients with constipation, or those who find defecation difficult. However, few published studies are available to evaluate this ability in most common examinations of anorectal function. A new, low-radiation, real-time scintigraphic technique has been used by several investigators to outline the 'neo-rectum' following ileoanal pouch anastomosis and the efficiency of rectal evacuation in adult patients with constipation. There was no similar report about the abilities of rectal evacuation in children with constipation. The aim of this study was to investigate the value and reliability of isotope defecography as an objective method for evaluation of anorectal function in patients with chronic idiopathic constipation.

METHODSTwenty five patients (10 were male and 15 were female, range of age was 5 - 15 years, mean age 8.99 years) suffering from chronic idiopathic constipation and 11 normal children were assessed by isotope defecography. The radiopharmaceuticals used were rehydrated potato labelled with 200 MBq (99m)TcO(4)(-). The volume of the potato paste used in each subject was determined by prior balloon proctometrogram studies, which measured the maximum rectal capacity. The patient was seated upright on a commode, and the computer was then set for the dynamic acquisition of 3-second images over 5 min per session. Using a region of interest program on computer, the dynamic radioactivity in anorectum during defecation showed as emptying curves by computer. The half defecation time, the rectal emptying rate and the residual rate could be calculated from the rectal emptying curves. The anorectal angles were measured from the images of anorectum during resting, squeezing and evacuation. All patients underwent X-ray defecography and colonic transit time measurement simultaneously.

RESULTSThe rectal emptying curves showed a prompt evacuation in normal children, but it disappeared in most of patients with idiopathic constipation. The abilities of evacuation were damaged severely in patients. In normal group the half defecation time, the rectal emptying rate and the residual rate were 1.97 +/- 0.86 minutes, 78.30% +/- 12.03% and 20.50% +/- 7.67%, respectively, whereas they were 15.16 +/- 3.67 minutes, 44.84% +/- 14.00% and 53.52% +/- 15.02%, respectively, in patients group. There were significant differences between two groups (P < 0.05). According to the results of colonic transit time there were 6 patients with slow transit constipation, 17 patients with outlet dysfunction and 2 patients with normal colonic transit time. The abilities of evacuation were more seriously impaired in patients with outlet dysfunction compared with those patients with slow transit constipation. For the isotope defecography the mean anorectal angles at resting in patient group and normal group were 109 +/- 12 degrees and 101 +/- 17 degrees. There were no significant differences in anorectal angles between patient group and normal group or by both methods of isotope defecography and X-ray defecography. The correlation coefficients for anorectal angles at resting, squeezing and evacuation were 0.87, 0.82 and 0.73, respectively.

CONCLUSIONThe isotope defecography can be used to evaluate the anorectal function and the ability of defecation dynamically, also it was simple and safe because of the low dose radiation involved.