1. Normal embryologic development of the gut

The gut arises from the yolk sac consisting of three anatomic sections each supplied by a different artery:

• Foregut: celiac trunk
• Midgut: superior mesenteric artery (SMA) (Fig. 1D)
• Hindgut: inferior mesenteric artery (IMA)

Development starts at week 4 of gestation. At this time the midgut starts to grow disproportionately to the abdominal cavity. By 6 weeks, the midgut herniates through the umbilical cord (Fig. 1). This herniation remains in place until week 10. During this stage, both the cephalad (duodenum, jejunum and proximal ileum) and caudad (distal ileum, cecum, colon) portion of the midgut rotate 90° counterclockwise (from a frontal point of view) around the SMA (Fig. 2-3).  As a result, the cephalad portion of the midgut lies on the right side of the SMA and the caudad portion of the midgut lies on the left side of the SMA. Within this stage, after the initial rotation, the duodenojejunal portion starts to grow and rotates another 90° counterclockwise [2].

By week 10, the abdominal cavity has enlarged sufficiently at which point the midgut re-enters the abdominal cavity. During this intra-abdominal reduction the duodenojejunal portion undergoes a final 90° counterclockwise rotation while the colon undergoes a 180° counterclockwise rotation. As a final result, the duodenal part of the midgut lies on the left of the SMA and is located posteriorly while the colon lies on the right side of the SMA and is located anteriorly (Fig. 4). By this time, both parts of the midgut have rotated 270° in a counterclockwise manner.

Throughout the further gestation, fixation of the gut to the posterior abdominal wall occurs ensuring the normal anatomy. The small bowel is fixated by a broad mesenteric attachment from the duodenojejunal junction to the ileocecal valve. This broad attachment is a safety mechanism against small bowel volvulus.

2.   Malrotation types

 
As mentioned above, the term malrotation comprises a range of malrotation types, each reflecting the time at which a failure occurs during the embryologic rotation. Three main types are described, i.e. nonrotation, partial malrotation and reversed malrotation [2,5].

In nonrotation, only the initial 90° counterclockwise rotation occurs so that the duodenojejunal junction lies on the right side and the colon lies of the left side of the SMA (Fig. 5-A).

Partial (incomplete) malrotation implies a failure during the final 180° counterclockwise rotation. This term is used in all malrotation types between a nonrotation and a normal rotation (Fig. 5-B).

When rotation is clockwise, the result is termed reversed malrotation in which the duodenum lies anteriorly to the colon.

In the classification of intestinal malrotation, an anomalous fixation of the mesentery must be mentioned as it may be the cause of an intestinal internal herniation [6].

3.     Complications

Due to an abnormal rotation, the normal subsequent mesenterial attachment is disturbed. The result may be a narrow(ed) mesenterial attachment predisposing to volvulus, a well-known cause of intestinal obstruction. Although this complication can occur in any type of malrotation, it is more frequently seen in partial malrotation than in a complete nonrotation. This twist of the midgut can compromise the normal vascular supply making it a surgical emergency due to the potential life-threatening result of midgut ischemia and gangrene.

Another complication is caused by the so-called Ladd’s bands, which are peritoneal bands formed to attach an incompletely rotated cecum and is another well-known cause of intestinal obstruction (Fig. 6).

As mentioned before, anomalous fixation of the mesentery can  give rise to an internal herniation with potential life-threatening complications such as bowel strangulation and ischemia [3].

4.     Imaging features and different imaging modalities

• Plain X-ray:

Conventional radiography is neither sensitive nor specific for intestinal malrotation [3,7].  Several potentially abnormal air-patterns can be found: an abnormal air distribution (Fig. 7), a so-called double-bubble appearance, a gasless abdomen and a dilated duodenum and stomach with paucity of gas in the further abdominal tract (Fig. 8)[2].

• Upper GI series

The imaging modality of choice remains the upper GI study. Knowledge of the normal embryologic development and the normal anatomic result is important in performing and interpreting upper GI-series. The duodenojejunal junction is located to the left of the vertebral body (left-sided pedicle) and this at the level of the duodenal bulb on a standard AP-view [1]. On a lateral view the duodenojejunal junction is located posteriorly [1]. Besides the AP and the lateral view, we use the (prone) right anterior oblique (RAO) view as it depicts the typical inversed C-shape configuration of the normal course of the duodenum (Fig. 9).

In malrotation, the distal duodenum has an abnormal course. On a strict AP-view, this can be seen as an anomalous position of the duodenojejunal junction to the right of the vertebral body and, in some cases, with a lower level of the duodenal bulb (Fig 10A). This duodenojejunal junction can have an anterior location, which can be depicted on a lateral view. In the RAO-view, we often see a C-shape configuration (Fig. 10B) of the duodenal course as opposed to the inversed C-shape configuration of the normal duodenum (Fig. 9B).

In case of an intestinal volvulus, the distal duodenum and the proximal jejunum can have a “corkscrew” configuration (Fig. 11). Once seen, urgent surgery is required in order to avoid catastrophic events such as bowel ischemia and gangrene.

In case of an obstruction due to Ladd’s bands, a Z-shaped configuration of the duodenum can be depicted.

Since the upper GI study is of paramount importance in diagnosing malrotation, additional attention should be given to the implementation of this examination:

As a first key rule, documentation of the first bolus through the duodenum is mandatory in making an adequate diagnosis! Once the contrast medium passes beyond the duodenum, identification of duodenal bulb and duodenojejunal junction becomes difficult.

As a second key rule, both duodenal bulb and duodenojejunal junction should be documented in AP, lateral and RAO projections. This can be obtained by rotating the patient in a RAO (and over to the lateral) position once the duodenojejunal flexure is reached in a frontal projection.

• Contrast Enema

Contrast enema can be used to illustrate the anatomic position of the colon and the cecum (Fig. 7, Fig. 12). However, this examination is nonspecific [3] because cecal location can be variable in patients without malrotation. On the other hand, the cecum can have a normal position in patients where intestinal malrotation is present. This explains why contrast enema is no longer the primary imaging modality of choice.

Nevertheless, in cases of an unequivocal upper GI study, a contrast enema can be of value in diagnosing doubtful cases of malrotation. Acquirement of delayed abdominal radiographs, performed after an initial and unequivocal upper GI study, serves as a good alternative in documentating the cecal position [1].

• Ultrasound (US)

US is frequently requested by the clinician in order to exclude pyloric stenosis, another cause of neonatal vomiting. Although clinical presentation is very different in these two entities (bilious versus non-bilious vomiting), US is a readily available investigation in the assessment of both the pyloric canal as well as the normal relationship of the SMV and SMA.

An inversion of the normal relationship of SMV and SMA (the SMV swirls to the left of the SMA) is indicative for malrotation (Fig. 11A; Fig. 13). Because these sonographic findings are not very sensitive [2,8], further investigation is warranted in order to exclude intestinal malrotation.

Although ultrasound is an excellent imaging modality, it’s results are strongly operator-dependent. Additionally, due to the superimposed intestinal air, both the SMV and the SMA are not always clearly detectable.

• Cross-sectional imaging modalities (CT and MRI)

These imaging modalities are not considered to be the first imaging modalities of choice. However, the diagnosis of intestinal malrotation with cross-sectional imaging is frequently an incidental finding (Fig. 14, Fig. 15), mainly in adolescents and adults [2,3].

Both Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can be used to display the relationship between SMV and SMA as well as signs of volvulus such as the “whirlpool” sign. CT and MRI can also depict the orientation of both small and large bowel. An additional advantage of these imaging techniques is that other abnormalities, in association with syndromes or anomalies, can be illustrated.

5.     Treatment options

The most frequently used surgical approach in patients with malrotation is the Ladd’s procedure in which there is a reduction of the midgut volvulus, followed by a dissection of the obstructing peritoneal bands and a reorganization of both small and large bowel in their normal anatomical position. Finally, an appendectomy is performed [2,6].

Nowadays, this procedure is performed using a laparoscopic technique in patients with uncomplicated intestinal malrotation. In complicated cases there may be need for an open approach.

Follow-up is warranted due to postoperative complications such as infections and adhesions. Although rare, recurrent volvulus can occur after a Ladd’s procedure [2].