True about colonic volvulus

A volvulus is a twisting or axial rotation of a poion of bowel about its mesentery. When complete it forms a closed loop of obstruction with resultant ischaemia secondary to vascular occlusion. Volvuli may be primary or secondary.it is Common in psychiatric patients.The commonest spontaneous type in adults is sigmoid Ref: Bailey & Love&;s Sho Practice of Surgery,E25,Page-1191,1192