MI is either simple or complicated. Each occurs with a frequency of approximately 50%. In the simple form, thickened meconium begins to form in utero and, as it obstructs the mid ileum, proximal dilatation, bowel wall thickening, and congestion occur. In complicated MI, thickened meconium and obstruction lead to complications such as: segmental volvulus, atresia, necrosis, perforation, meconium peritonitis (generalized), and giant meconium pseudocyst formation.
After birth, both simple and complicated MI should be managed as a newborn intestinal obstruction. Resuscitative measures including mechanical respiratory support, if necessary, and IV hydration are initiated along with gastric decompression, evaluation, and correction of any coagulation disorders and with empiric antibiotic coverage. When MI is suspected or diagnosed, immediate pediatric surgical consultation should be obtained.
Simple MI usually presents with abdominal distension at birth (Fig. 43-3). Failure to pass meconium, bilious vomiting, and progressive abdominal distention will eventually occur. Often, dilated loops of bowel become visible on exam and have a doughy character that indents on palpation. Typically, the rectum and anus are narrow, a finding which may be misinterpreted as anal stenosis.
Abdominal distension in an infant with MI. Note visible loops of bowel (Δ). (From Irish MS, Gollin Y, Borowitz DS, et al. Meconium ileus: antenatal diagnosis and perinatal care. Fetal Matern Med Rev 2010;8:79–93, with permission.)
Complicated MI presents more dramatically. At birth, severe abdominal distension with abdominal wall erythema and edema may be present. Abdominal distension may be so severe as to cause respiratory distress. Signs of peritonitis include tenderness, abdominal wall edema, distension, and clinical evidence of sepsis. A palpable mass may indicate pseudocyst formation. Often, the neonate needs urgent resuscitation and surgical exploration.
Uncomplicated MI is characterized by a pattern of unevenly dilated loops of bowel on abdominal radiograph with variable presence of air-fluid levels (Fig. 43-4). As air mixes with the tenacious meconium, bubbles of gas may be seen. This soap bubble (Fig. 43-5) appearance depends on the viscosity of the meconium and is not a constant feature. However, this radiographic feature is pathognomonic and distinguishes MI from other causes of newborn intestinal obstruction. In a review of 58 neonates with CF and MI, Lang reported that 26% of neonates were found to have abdominal calcifications, although only half of this number were visible on plain radiograph. While each of these features alone is not diagnostic for MI, collectively, and with a family history of CF, they strongly suggest the diagnosis.
Distended loop of ileum due to MI. (From Irish MS, Gollin Y, Borowitz DS, et al. Meconium ileus: antenatal diagnosis and perinatal care. Fetal Matern Med Rev 2010;8:79–93, with permission.)
“Soap bubble” appearance (Δ) of meconium mixed with water-soluble contrast material. (From Irish MS, Gollin Y, Borowitz DS, et al. Meconium ileus: antenatal diagnosis and perinatal care. Fetal Matern Med Rev 2010;8:79–93, with permission.)
If MI is clinically and radiographically suspected, a contrast enema of barium may be performed for diagnosis, followed by a therapeutic Gastrografin® (Bracco Diagnostics Inc., Princeton, NJ) enema, if MI is likely. Some advocate water-soluble contrast initially for both diagnosis and treatment. In MI, contrast instillation is followed fluoroscopically and will demonstrate a colon of small caliber, described as the microcolon of disuse (Fig. 43-6A and B), often containing small “rabbit pellets” (scybala) of meconium (Fig. 43-7). Escobar found that 48% of neonates with CF and MI demonstrated microcolon on barium enema. Progression of the contrast proximally may also outline pellets of inspissated meconium. If contrast is successfully refluxed proximal to the obstruction, dilated loops of small bowel will be seen.
“Microcolon of disuse” (Δ) (A) as seen on contrast enema radiography, and (B) at operation compared with dilated ileum (▴). (From Irish MS, Gollin Y, Borowitz DS, et al. Meconium ileus: antenatal diagnosis and perinatal care. Fetal Matern Med Rev 2010;8:79–93, with permission.)
“Rabbit pellets” or scybala (Δ). (From Irish MS, Gollin Y, Borowitz DS, et al. Meconium ileus: antenatal diagnosis and perinatal care. Fetal Matern Med Rev 2010;8:79–93, with permission.)
Radiologic findings in complicated MI vary with the complication. Speckled calcification seen on abdominal plain films is highly suggestive of intrauterine intestinal perforation and meconium peritonitis. A pseudocyst is suggested by radiographic findings of obstruction and a large dense mass with a rim of calcification. Historically, as many as one third of cases of complicated MI have no radiologic findings suggesting any complication. Furthermore, it is important to remember that in utero perforation (CF or non-CF related) can lead to meconium peritonitis or meconium pseudocyst formation. Therefore, in these situations, only intraoperative inspection may differentiate CF versus non-CF–related meconium peritonitis or meconium pseudocyst formation.
In 1969, Noblett introduced the use of enemas of Gastrografin® in treating 4 infants with MI. Gastrografin® is meglumine diatrizoate, a hyperosmolar, water-soluble, radiopaque solution containing 0.1% polysorbate 80 (Tween 80), and 37% organically bound iodine. The osmolarity of the solution is 1900 mOsm/L. Upon instillation, fluid is drawn into the intestinal lumen, hydrating and softening the meconium mass. Both transient osmotic diarrhea and diuresis follow. Thus, adequate preenema resuscitation and hydration anticipating these fluid losses are paramount.
Under fluoroscopic control, a 25% to 50% solution of Gastrografin® is infused slowly at low hydrostatic pressure through a catheter inserted into the rectum. To minimize the risk of rectal perforation, balloon inflation is avoided. Upon completion, the catheter is withdrawn and an abdominal radiograph is obtained to rule out perforation. The infant is then returned to the neonatal care unit for intensive monitoring and fluid resuscitation. Warm saline enemas containing 4% N-acetylcysteine may be given to help complete the evacuation. Usually there is rapid passage of semi-liquid meconium, which continues in the ensuing 24 to 48 hours. Radiographs should be taken in 8 to 12 hours, or as clinically indicated, to confirm evacuation of the obstruction and to exclude late perforation. In the nonoperative management of MI, if evacuation is incomplete, or if the first attempt at Gastrografin® evacuation does not reflux contrast into dilated bowel, a second enema may be necessary. In a small study of very low birth weight infants, Shinohara concluded that reflux of the enema into the terminal ileum was essential for the bowel obstruction to be relieved. Serial Gastrografin® enemas can be performed at 12- to 24-hour intervals if necessary. However, if progressive distension, signs of peritonitis, or clinical deterioration occur, surgical exploration is indicated.
Following successful evacuation and resuscitation, we have used 5 mL of a 4% N-acetylcysteine solution be administered every 6 hours through a nasogastric (NG) tube to liquefy upper gastrointestinal (GI) secretions. Feedings, along with supplemental pancreatic enzyme replacement therapy (PERT) for those infants confirmed with CF, may be initiated when signs of obstruction have subsided, usually within 48 hours. The success rate of patients with uncomplicated MI, treated with Gastrografin® enemas, historically range as high as 83%. Multiple contemporary studies report much lower success rates closer to 36% to 39%. Copeland and colleagues analyzed the reasons for reduced rates of success in a recent study. They hypothesized that surgeons are attempting few enemas per patient before transitioning to surgical treatment, some institutions are using enema solutions with lower osmolarity than Gastrografin® (thereby resulting in less effective meconium hydration due to decreased osmotic activity), and the enema attempts are less aggressive. Conversely, all of these help explain why the complication rates for Gastrografin® enema are decreasing.
Several potential complications exist with the use of hyperosmolar enemas in treating MI. The risk of rectal or colonic perforation can be avoided with careful placement of the catheter under fluoroscopic guidance and avoidance of inflating balloon-tipped catheters. A small study of 22 patients found a 23% perforation rate in patients when inflated balloon catheters were used. Copeland recently reported only a 2.7% perforation rate. Early perforation occurring during the administration of the enema is usually readily apparent under fluoroscopy. The risk of perforation increases with repeated enemas. Late perforation occurring between 12 and 48 hours following the enema can occur. Potential causes for late perforation include severe bowel distension by fluid osmotically drawn into the intestine or direct injury to the bowel mucosa by the contrast medium. The former appears to be the etiology in experimental models. Reports of delayed perforation associated with extensive bowel necrosis have been made. The pathogenesis of intestinal perforation associated with necrotizing enterocolitis is believed to be the ischemia produced by intestinal distension. Hypovolemic shock is a profound risk when delivering hypertonic enemas. Ischemia caused by overdistension is worsened by hypoperfusion caused by hypovolemia due to poor fluid resuscitation. Adequate fluid resuscitation (150 mL/kg/day, minimum) with anticipation of fluid losses due to osmotic diarrhea and diuresis is mandatory. Hepatotoxicity is a reported complication as well. The addition of 1% N-acetylcysteine added to the enema solution has been hypothesized to aid in dissolution of the inspissated meconium. Slow infusion carefully monitored under fluoroscopy is necessary.
The prognosis for infants with MI was uniformly poor despite surgical treatment prior to 1948, when Hiatt and Wilson of Babies Hospital in New York reported the first successful surgical management of 5 infants with MI through intraoperative disimpaction of meconium with saline instilled into the bowel via a tube enterostomy (Fig. 43-8). In 1989, Fitzgerald proposed a similar technique in which an appendectomy is performed and a cecostomy catheter is placed through the appendiceal stump for insertion of irrigant and evacuation of impacted meconium (Fig. 43-9). Over the years, a number of surgical approaches in the treatment of uncomplicated MI have been proposed. Success rates with each of these methods have been variable. The approach to each infant should be individualized. The goal of operative management in simple, uncomplicated MI is evacuation of meconium from the intestine with preservation of maximal intestinal length.
Technique of intraoperative irrigation of inspissated meconium via a tube enterostomy as described by Hiatt and Wilson.
Technique of intraoperative bowel irrigation and evacuation of meconium via the appendiceal stump as described by Fitzgerald.
Several variations upon the theme of Hiatt and Wilson's technique have involved placing indwelling ostomy tubes for purposes of postoperative bowel irrigation decompression, and/or feeding. In 1970, O'Neill described success with tube enterostomy with and without resection (Fig. 43-10). Harberg described a similar procedure in which a T-tube enterostomy is used (Fig. 43-11). The Harberg group later reported that 87% of MI resolved with T-tube placement and postoperative irrigation. In either situation, irrigations are begun on the first postoperative day and, after successful clearance of the obstruction (7-14 days), the tube may be removed and the enterocutaneous fistula allowed to spontaneously close.
Technique of indwelling tube ileostomy for postoperative irrigation as described by O'Neill.
Technique of indwelling T-tube ileostomy for postoperative irrigation as described by Harberg.
Further surgical techniques have revolved around resection, anastomosis, and enterostomy through which postoperative irrigations can be delivered. The Mikulicz double-barreled enterostomy (Fig. 43-12), first reported by Gross, has 3 distinct advantages. First, because complete evacuation of inspissated meconium is not necessary, operating and anesthetic times are reduced. Second, an intraabdominal anastomosis is avoided preventing the risk of anastomotic leakage. Third, the bowel can be opened following complete closure of the abdominal wound, thereby reducing the risk of intraperitoneal contamination. Following surgery, solubilizing agents can be given through both the proximal and distal limbs of the stoma as well as per rectum or via a NG tube. As classically described, a crushing clamp may be applied to the 2 limbs to create continuity for distal flow of intestinal fluids. Disadvantages of this and other procedures employing resection and stoma(s) are potential postoperative fluid losses through high-volume stomas, bowel shortening by resection, and the need for a second procedure to reestablish intestinal continuity.
The Mikulicz double-barreled enterostomy as described by Gross.
A distal chimney enterostomy, described by Bishop and Koop (Fig. 43-13), involves resection with anastomosis between the end of the proximal segment and the side of the distal segment of bowel approximately 4 cm from the opening of the distal segment. The open end is brought out as the ileostomy. This technique allows normal GI transit while providing a means for managing distal obstruction through the ileostomy should it occur. The reverse of the Bishop-Koop enterostomy is the proximal enterostomy described by Santulli in 1961 (Fig. 43-14). Here, following resection, the end of the distal limb is anastomosed to the side of the proximal limb. The end of the proximal limb is brought out as the enterostomy. With this arrangement, proximal irrigation and decompression is enhanced and it is not necessary to evacuate the proximal small bowel at the time of surgery. Like the distal chimney enterostomy, catheter access to the distal limb is placed, exiting through the stoma, thus providing means of irrigating the distal bowel. The apparent disadvantage with this technique is the presence of a high-output stoma and the inherent risk of dehydration. Care must be taken to replenish fluids, electrolytes, and nutrients in accordance with the stomal output. Reinstillation of stomal output from the proximal to the distal limb is often performed via the indwelling catheter.
The Bishop-Koop distal chimney enterostomy as described by Bishop.
Proximal enterostomy or “reverse Bishop-Koop” as described by Santulli.
Resection with primary anastomosis (Fig. 43-15), first suggested by Swenson in 1962, met with initial difficulty and complication with leakage from the anastomosis. Improved results were reported by later investigators that emphasize the necessity of adequate resection of compromised bowel, complete proximal and distal evacuation of meconium, and preservation of adequate blood supply to the anastomosis. In a recent study, Karimi reviewed 41 patients with MI and compared resection with primary anastomosis to resection with enterostomy. They found that 21% of the primary anastomosis group developed peritonitis whereas none of the resection with enterostomy group did. Jawaheer found a 31% complication rate in a report of MI treated with primary anastomosis. Del Pin, however, found no difference in morbidity with primary anastomosis versus resection with enterostomy. Thus far, studies have not been large enough to indisputably identify best practices for the surgical treatment of MI.
Resection with primary anastomosis for meconium ileus as described by Swenson.
We prefer a modification of the technique originally described by Gross in 1953 in managing infants with uncomplicated MI (Fig. 43-16). Celiotomy is performed. Upon exploration, the decision to create an enterotomy for irrigation and evacuation of the meconium, or, to resect the segment of impacted intestine, is made based on the viability and length of bowel involved. We then create side-by-side, separate enterostomies without creating a common wall (Fig. 43-16A). Stomas are placed within the abdominal incision to the right (Fig. 43-16B) and may be covered with a single ostomy collecting device. Postoperatively, each stoma may be irrigated to remove any residual meconium. Instillation of dilute enteral feedings high in glutamine, via the distal stoma, may also be performed to stimulate growth of the unused distal bowel. Intestinal continuity is generally restored within 6 to 12 weeks if bowel function has resumed, and the infant is tolerating oral feedings.
The author's preferred method of side-by-side enterostomy when resection is necessary in the management of MI. Irrigating catheters may be inserted through either the proximal or distal stoma for irrigation, or through the distal stoma for feeding.
Surgery is always indicated in cases of complicated MI. Complications necessitating surgical management include persistent or worsening abdominal distension, persistent bowel obstruction, enlarging abdominal mass, intestinal atresia, volvulus, perforation, meconium cyst formation with peritonitis, and bowel necrosis. Resection is more often necessary in cases of complicated MI than with simple MI, and always requires temporary stomas.
Initial postoperative management involves ongoing resuscitation. The fluid losses from preoperative diuresis and diarrhea, if Gastrografin® enema has been attempted, and from surgical losses must be carefully replaced. Ongoing maintenance fluids and replacement of insensible fluids, as well as GI losses (NG suction and ileostomy) must be adjusted accordingly. Instillation of 4% N-acetylcysteine via a NG tube or via ileostomy may help solubilize residual meconium. Stomas placed in the course of surgical management should be closed as soon as possible (6-12 weeks) to help avoid prolonged problems with fluid, electrolyte, and nutritional losses.