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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.
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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.
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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).
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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.
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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.
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Rare cases of familial malrotation suggest a genetic link in
some cases.2
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Clinical Features
and Differential Diagnosis
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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 ...