Midgut Malrotation And Volvulus
Toshinori Aihara MD*, Albert Lam MD FRACR DDU
Departments of Medical Imaging, Saitama Children's Medical Centre*, Japan and Royal Alexandra Hospital for Children, University of Sydney, NSW

Introduction
Midgut malrotation is the most important cause of upper intestinal obstruction in the neonate and young infant. Volvulus is one of the complications of this congenital malformation. It is the most severe catastrophe that can occur in the intestinal tract and if not promptly diagnosed and treated leads to death or a lifelong dependence on total parenteral nutrition resulting from a short-gut syndrome.

The gastrointestinal tract begins in foetal life as a straight, short tube, which later elongates and assumes an orderly, stable but complex arrangement in the peritoneal cavity in the process of normal rotation. Malrotation is the term used to denote any variation of intestinal rotation and its classification is of little clinical significance.

The malfixation of the midgut associated with malrotation is the real cause of acute abdomen. When the duodenojejunal junction and the caecum, the normal points of fixation of the mesentery, are not in their usual positions, the mesentery will have a narrow pedicle. There is a tendency for the intestine to twist (undergo volvulus) around the pedicle in a clockwise direction. This leads to extrinsic compression of the bowel, causing bowel obstruction and, if persisting, to occlusion of the mesenteric vessels and gut ischaemia. In addition to the short mesenteric attachment, there are aberrant peritoneal bands present. The Ladd's bands extend from the malpositioned caecum across the duodenum and attach to the liver, posterior peritoneum, or abdominal wall, and thus lead to extrinsic duodenal compression. There is also an absence of the ligament of Treitz, which is a suspensory ligament of connective tissue and smooth muscle that extends from the root of the superior mesenteric artery to the third and fourth parts of the duodenum.

Conclusion
The upper gastrointestinal barium study is the study of choice to demonstrate malrotation. The location of the duodenojejunal junction is to the left of the spine and is at the level of the duodenal bulb. When obstruction occurs, there may be partial or complete duodenal obstruction; occasionally, the pathognomonic corkscrew pattern of the twisted duodenum and jejunum is seen. When sonography is used to investigate vomiting in an infant, one should look for the sonographic feature of malrotation or volvulus. The relationship of the SMV and SMA in the axial plane should be clarified, and if a "whirlpool sign" is present, additional colour Doppler study should be performed to exclude the possibility of volvulus. In our institutions, if the clinical condition of the child allows, an upper gastrointestinal series is performed to confirm the diagnosis and exclude other causes of upper gastrointestinal obstruction.