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INTRODUCTION

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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. A basic understanding of the embryological development of the gastrointestinal (GI) system is necessary for the management of malrotation. The spectrum of disease ranges from complete nonrotation to various degrees of incomplete rotation and rarely can even result in reverse rotation.

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EMBRYOLOGY

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An initial and simple understanding of GI tract development and rotation can be ascertained by imagining the GI tract as a long tube. The most cranial portion of the tube becomes the oral cavity, and the most caudal portion transforms into the anus. The tube has oral, thoracic, and intra-abdominal portions. During development, the intra-abdominal portion, the midgut, elongates rapidly until it passes through the base of the umbilicus into the extraembryonic coelom. This extension into the coelom is termed physiologic herniation and occurs as a result of lack of space for the rapidly growing midgut.

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During elongation, from the sagittal view, the midgut forms a U shape with the superior mesenteric artery (SMA) bisecting the U into to equal parts. The proximal cranial limb (prearterial) becomes the distal duodenum, jejunum, and ileum while the distal caudal portion (postarterial) forms the cecum, appendix, and proximal two-thirds of the transverse colon. The positions of these limbs change during the first 90-degree counterclockwise rotation relative to the SMA, which places the proximal limb to the right of the SMA, and the distal caudal limb to the left of the SMA.

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Around 10 weeks of gestation, the proximal cranial loop returns first to the intra-abdominal cavity in a counterclockwise rotation, placing the distal duodenum to the left of the SMA, along with the jejunum in the left upper abdomen. The distal caudal limb then follows intra-abdominally rotating 180 degrees from its starting position to the left of the SMA, placing the cecum in the right upper abdomen. As the ascending colon elongates, the cecum then falls to the right lower quadrant. After the final positioning of the midgut, the mesenteries fix posteriorly to the abdominal wall from the ligament of Treitz, located in the left upper abdomen, to the cecum. The ascending colon mesentery fuses with the parietal peritoneum, and is obliterated. making the ascending colon a retroperitoneal structure. Of note, the fixation process cannot occur unless rotation is completed. It is important to understand that the rotation of the 2 limbs of the midgut happen simultaneously.

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PATHOGENESIS AND EPIDEMIOLOGY

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Nonrotation

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The term nonrotation is used to describe the arrest in the initial steps of midgut loop herniation and rotation, also known as stage 1. This arrest leads to the failure in formation of a broad-based mesentery, due to the close ...

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