Embryology
During gestational weeks 4 through 6, the elongating midgut of the fetus grows too large for the developing abdominal cavity and herniates through the site of the future umbilicus. Subsequently, the midgut returns to the abdominal cavity during weeks 10 to 12, rotating 270 degrees counterclockwise with respect to the superior mesenteric artery (SMA). Upon reentry, the duodenal-jejunal junction is anchored to the SMA at the ligament of Treitz, and the cecum is attached to the right, lower, lateral abdominal wall. These two points of anchoring create a broad base for the small bowel mesentery.
Pathophysiology
Intestinal malrotation is a congenital anomaly in which the herniated bowel undergoes abnormal rotation and fixation, resulting in a displaced duodenal-jejunal junction and/or cecum. In the most common variant, there is abnormal rotation of both midgut loops, resulting in a rightward and inferiorly placed duodenal-jejunal junction and a cecum located in the epigastric region near the origin of the SMA. Adhesive peritoneal bands (Ladd’s bands) may extend from the displaced cecum over the second portion of the duodenum to the lateral abdominal wall and can produce duodenal obstruction. With malrotation, the base of the small bowel mesentery is typically narrow, making it prone twisting, which results in mechanical obstruction and ischemia. This complication, termed midgut volvulus, may lead to frank intestinal necrosis and is a surgical emergency.
Epidemiology
In the United States, intestinal malrotation occurs in about 1 in 500 live births, often appearing concurrently with other congenital anomalies such as diaphragmatic hernia, duodenal atresia, and abdominal wall defects such as omphalocele and gastrochisis. Symptomatic malrotation commonly occurs in infancy, with nearly two thirds of patients presenting within the first month of life.
Diagnosis and Evaluation
The characteristic presentation of malrotation is bilious emesis in a newborn. Although bilious emesis can result from a variety of causes, its manifestation in a newborn should be evaluated emergently until malrotation, with or without the midgut volvulus, has been excluded or appropriately treated. Other symptoms may include abdominal pain, feeding intolerance, upper abdominal distention, and other symptoms of acute intestinal obstruction. In older children, the presentation may involve intermittent abdominal pain and bilious vomiting, failure to thrive, malabsorption, and sometimes bloody stools or emesis.
An upper gastrointestinal contrast study (UGI) is currently the modality of choice for diagnosis, with imaging demonstrating a duodenal-jejunal segment displaced to the right and inferiorly. Narrowing of the bowel at any point of obstruction and a “corkscrew” appearance of the duodenum may be present.
Signs of abnormal rotation and volvulus may also be seen on abdominal plain films and ultrasound, but due to the higher rate of false negatives, these modalities are considered inferior to the UGI series in the diagnosis of malrotation. Plain films may reveal a “double bubble” sign and suggest a diagnosis of duodenal atresia. Ultrasound may show an abnormal location of the distal duodenum and reversal of the normal superior mesenteric vein (SMV) and superior mesentery artery (SMA) relationship, with the SMV located anterior and to the left instead of ventral and to the right of the SMA. If malrotation is complicated by volvulus, a “whirlpool sign” due to rotation of the SMV and its mesentery around the SMA may also be visualized. Contrast enema can also show findings of an abnormally positioned cecum. Computed tomography (CT) of the abdomen with intravenous contrast can demonstrate all of these anatomic abnormalities. However, the cost and radiation exposure associated with CT limit its use as the initial imaging test for diagnosis of malrotation.
Operative Management and Surgical Technique
Malrotation is treated surgically, ideally after appropriate resuscitation. Suspected or confirmed midgut volvulus is an emergency warranting surgical exploration without delay. If volvulus is present at the time of operation, the involved segment of bowel is first untwisted in a counterclockwise direction. If there is significant bowel ischemia at the time of laparotomy, the surgeon may decide to return the bowel to the abdomen or place the intestinal contents in a silo or bag and then re-examine the bowel in a second operation after 24 to 48 hours. At this time, any remaining necrotic bowel can be resected.
In the absence of volvulus or when the bowel appears viable after detorsion, the malrotation is treated with an operation called the Ladd procedure. In the Ladd procedure, adhesive peritoneal bands linking the colon to the lateral abdominal wall are carefully divided, relieving obstruction and straightening the course of the duodenum. Adhesive bands over the mesentery are also divided to widen the base of the mesentery and reduce the risk of future volvulus. A prophylactic appendectomy is recommended, as the cecum is not fixed in the right lower quadrant, and thus, the presentation of appendicitis will not be typical. An inversion-ligation appendectomy is the technique of choice to avoid contamination of the otherwise clean Ladd procedure. Finally, the cecum is placed in the left lower quadrant to allow the small bowel mesentery to be broadened maximally.
There has been recent interest in a laparoscopic approach to management of malrotation presenting without volvulus. An open approach has been historically advocated as it is thought to facilitate the formation of adhesions, which may keep the bowel its postoperative configuration with a widened mesentery, decreasing the risk of future volvulus. Because it is thought that fewer abdominal adhesions are likely to develop using a minimally invasive technique, it has been hypothesized that patients treated laparoscopic will remain more susceptible to volvulus in the future. Several retrospective studies comparing the two approaches have advocated laparoscopy as the initial procedure of choice, especially in radiographically ambiguous cases. These studies cite reduced post-operative hospital stay and earlier return of oral intake as advantages of the laparoscopic approach. However, data about long-term outcomes are not yet available.
In an asymptomatic patient in which malrotation is incidentally discovered, the management is controversial. Non-surgical, “watchful waiting” in older patients has been advocated, in an effort to avoid the risks associated with surgery and in accordance with evidence that volvulus risk decreases with age. Schey and colleagues have recommend treatment based on specific anatomic variants involving the positions of the ligament of Treitz and cecum on contrast studies. However, recent investigations suggest that these criteria may not be reliable and support empiric surgical intervention, at the very least, to verify or rule out suspected asymptomatic malrotation. Prasil and colleagues advocate a laparoscopic approach to diagnose, confirm, and treat suspected asymptomatic malrotation if UGI and barium enema studies are abnormal. Nehra and colleagues recommend operative management in all asymptomatic patients with malrotation unless significant operative risk due to other comorbidities exists, citing the difficulty assessing volvulus risk using age and currently available imaging modalities. Prospective trials studying outcomes in asymptomatic patients are needed to determine the optimal treatment for this group.
Postoperative Outcomes and Prognosis
In infants presenting with features of intestinal obstruction, symptoms are improved in the majority of patients undergoing the Ladd procedure. Recurrence of volvulus is possible, but uncommon, with the open approach. If volvulus is present at the time of laparotomy, however, up to 30% of affected infants die from associated midgut ischemia and gangrene.
References
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