Chapter 397

Malrotation is a term used to describe a spectrum of anatomic abnormalities resulting from incomplete rotation and fixation of the intestine during early fetal development. Variants include incomplete, nonrotation, or reversed rotation. Midgut volvulus is a devastating consequence of the lack of bowel fixation that results in ischemic infarction of much of the small and large intestine, with short gut syndrome ensuing if volvulus is not recognized and treated emergently.

### Epidemiology

Malrotation is reported to occur with a frequency of 1 in 3500 to 6000 live births, although the actual incidence of malrotation is unknown because many rotational anomalies remain asymptomatic throughout life and are therefore undiagnosed.1 Either sex can be affected, with the anomaly slightly more common in boys.

### Pathophysiology

As described in Chapter 381, the midgut normally herniates out of the peritoneal cavity into the umbilical stalk at about week 5 of development in the human fetus. As the intestine returns to the abdominal cavity between the 10th and 12th week of gestation, a process of rotation turns it around the axis of the superior mesenteric artery and fixation of the intestine occurs, culminating with localization of the duodenojejunal junction (ligament of Treitz) in the left upper abdomen and the cecum in the right lower quadrant in the full-term infant (see eFig. 381.5). This results in the oblique broad-based fixation of the mesentery to the posterior abdominal wall that prevents volvulus from occurring. The various forms of malrotation result from aberrant rotation and fixation of the bowel, as well as associated abnormal mesenteric bands that may obstruct the bowel (Ladd bands).

In nonrotation or incomplete rotation, the most common form of malrotation, the cecum typically resides in the upper abdomen just to the left of midline, and the duodenaljejunal segment lies anteriorly and just to the right of midline; fixation of the mesentery is absent. This anatomic derangement allows axial rotation of the midgut around the superior mesenteric artery, resulting in midgut volvulus with the potential for intestinal obstruction, ischemia, and necrosis.

Mixed rotational anomalies are a less common and highly variable group of anomalies in which the rotational process is arrested or disrupted, causing a spectrum of anatomic variations. Mesocolic (paraduodenal) hernias are a rare group of malformations that result from failure of the normal fixation of either the right or left mesocolon to the posterior body wall. The resulting spaces create the potential for intestinal obstruction due to sequestration and entrapment of the small intestine between the mesocolon and the posterior body wall.

Rare cases of familial malrotation suggest a genetic link in some cases.2

### Clinical Features and Differential Diagnosis

The clinical consequences of malrotation vary depending upon the length of the superior mesenteric artery pedicle and the fixation of the bowel.3 Volvulus is the most ominous and ...

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