Plain film features are typical of a sigmoid volvulus with a distended loop of large bowel arising from the pelvis. Absence of rectal gas and distension of the descending colon suggest it is causing complete obstruction.
Contrast per rectum confirms complete obstruction. The beaked appearance is classical of sigmoid volvulus.
The contrast study does not need to be performed. A CT would be more helpful although in most cases (especially where there is a prior history) further imaging is not required and decompression with a flatus tube or rigid sigmoidoscope can be performed.