Midgut volvulus is a possible complication of malrotation of the midgut loop without fixed mesentery. The small intestines twist around the vasculature that is providing support for them. This can result in ischemic necrosis of the intestine. Diaphragmatic atresia is not a cause of volvulus. Subhepatic cecum is due to failure of the descent of the cecal bud and results in the absence of an ascending colon. Duplication of the intestine would not cause volvulus because there would still be a fixed mesentery and no free movement of the intestines. Congenital megacolon is due to faulty migration of neural crest cells into the wall of the colon, which causes a lack of parasympathetic postganglionic neurons.