I second the diagnosis by Chriss ! Absence of gas shadow in lower pelvis region i.e, empty rectum! or distal cut-off sign ! The abrupt cut - off and a proximal dilated descending and transverse colon are further proof to the diagnosis. So my diagnosis is -Hirschsprung disease aka congenital megacolon ! More usually one would see some air - fluid levels proximal to the obstruction ( not evident in this case ). So in another case u may just see a lot of distended bowel ( with air - fluid levels ) which could well overlap and obscure the area of the recto-sigmoid and the cut-off may be not that clear, like in the example below In such cases, the absence of gas in the lower abdomen ( and of course the Hx ) holds the clue ! (-:
