Malrotation of the Midgut

This disorder occurs in fetal development,when the midgut supplied bythe superior mesenteric artery growstoo rapidly to be accommodated inthe abdominal cavity. Prolapse intothe umbilical cord occurs around thesixth week of gestation. Between thetenth and eleventh weeks, the midgutretracts from its location at the exocelomicumbilical stalk back into theabdominal cavity. During this return,the midgut undergoes a 270-degreecounterclockwise rotation about theaxis of the superior mesenteric artery,followed by fixation to the posteriorabdominal wall. Malrotationresults from failure of the midgut toproperly rotate and affix itself to thiswall. This disorder occurs approximatelyonce in 500 live births.The malrotated bowel itself doesnot cause any significant problem.However, the intestine remains freeon a narrow-based mesentery thatmay twist around itself, producing amidgut volvulus. In addition, denseperitoneal bands (Ladd bands) (A)may extend from the malpositionedcecum across the second part of theduodenum to the liver, posterior peritoneum,or abdominal wall, therebycausing abdominal obstruction. Lackof fixation of the mesentery of thecolon and duodenum results in theformation of potential hernial pouches.Internal hernias--the most commonof which are right and left mesocolichernias--can cause entrapmentof the bowel.Symptoms resulting from malrotationmay occur at any age. Half tothree quarters of patients who becomesymptomatic do so in the firstmonth of life; approximately 90% ofpatients are symptomatic within thefirst year. Vomiting--often bilious--isthe usual presenting sign. Blood inthe stool suggests ischemia and possiblegangrene of the bowel. Abdominaldistension is usually not remarkablein the initial stage. Once infarctionoccurs, painful abdominaldistension and shock develop. Olderchildren with malrotation may presentwith recurrent abdominal pain,intermittent vomiting, chronic diarrhea,malabsorption, and failure tothrive.Associated anomalies are foundin 30% to 60% of patients with malrotation.These include diaphragmatichernia, omphalocele, gastroschisis,intestinal atresia, imperforate anus,Meckel diverticulum, mesentericcyst, Hirschsprung disease, congenitalheart disease, and heterotaxia.Plain abdominal radiographsmay show a distended stomach andproximal duodenum with a paucity ofair in the distal small bowel. Multipledilated loops of bowel or multiple airfluidlevels are usually not seen unlessthe child has a volvulus complicatedby bowel infarction or an internal herniacomplicated by intestinal obstruction(B). An upper GI tract series isthe study of choice and may help revealthe abnormal position of the duodenojejunaljunction and duodenalobstruction. This abnormality has acharacteristic "corkscrew," "coiled," or"bird's beak" appearance (C).Early surgical intervention is imperativein a symptomatic patient tominimize the risk of midgut gangrene.Preoperative measures includeintravenous hydration to restore fluidand electrolyte balance, nasogastricsuction, and intravenous antibiotics(because a bowel resection may benecessary). The procedure ofchoice--the Ladd procedure--includesevisceration of the midgut andinspection of the mesenteric root,counterclockwise derotation of thevolvulus, division of Ladd bands fromthe cecum across the duodenum, appendectomy,and placement of thececum in the left lower quadrant. Theappendectomy is performed becausethe cecum is located in an atypical position,which makes a future diagnosisof appendicitis difficult. Nonviableintestinal segments are resected andprimary anastomosis is performed. Ifviability of the bowel remains in question,the abdomen is closed and thepatient is given supportive therapy. Asecond-look procedure is performedat 24 to 36 hours.For the asymptomatic childyounger than 2 years, timely repair isindicated because most of the potentialcomplications occur at earlierages. The management of the olderasymptomatic patient is controversial.Some experts believe that correctivesurgery should be performedunless compelling contraindicationsare present.