Figure 103-18. Female infant with low imperforate anus and vestibular fistula.

Diagnosis

Because surgical treatment of a high or intermediate anorectal malformation is different from that of

low lesion, a primary diagnostic goal is to determine whether an infant with imperforate anus has a

high or low malformation. A secondary diagnostic goal is to determine the specific anorectal

malformation as it relates to the rectourethral or rectovesicular fistula.

Clinical examination of an infant with low imperforate anus almost always reveals an external fistula

to the perineum or the vestibule. The classic radiographic study of newborns with imperforate anus is

the Wangensteen-Rice invertogram, with a lateral view of the pelvis obtained 12 to 24 hours after birth

with the infant in a head-down position. This technique has been largely replaced by ultrasound-directed

imaging.65 Real-time ultrasound is currently well-accepted as an accurate method of determining the

distal extent of the rectal pouch. Computed tomography (CT) imaging and MRI can be useful in

evaluating the pelvic striated muscle complex in difficult cases and, in particular, cloacal malformations.

MRI is also useful in evaluation of the distal spinal cord in these infants.

If there is a suspected perineal fistula or covered anus, diagnostic needle aspiration under anesthesia

may be useful. Aspiration of meconium not only localizes the rectum or fistula but can also provide an

estimation of the distance between the perineum and the rectum or the fistula. In general, low lesions

are within 1 cm of the perineum. An infant not clearly found to have a low lesion by physical

examination, radiographic studies, or examination under anesthesia should be considered to have a high

anorectal malformation and treated accordingly.

A voiding cystourethrogram is generally the procedure of choice for defining the rectourethral or

rectovesical fistula. In some instances, cystoscopy is a useful adjunct before repair of high imperforate

anus. For example, an infant with a large rectourethral fistula may require cystoscopic guidance of a

urinary catheter to avoid inadvertent placement of the catheter through the fistula and into the rectum.

Treatment

Imperforate anus by itself is not a life-threatening condition, and, in many instances, observation for 12

to 24 hours may help delineate the presence or absence of a fistula. The surgical management of

anorectal malformations has been well described elsewhere63 and a brief summary follows below.

Low Malformations. Definitive repair of most low anorectal malformations can be performed in the

newborn period with perineal procedures that do not require diverting colostomy. Simple dilatation of

the fistula or unroofing of a covered anus may relieve the anatomic obstruction. For more complex anal

stenoses or anterior perineal fistulas, a formal perineal anoplasty may be required. A common perineal

procedure performed is cutback anoplasty, in which the anterior fistula or anal orifice is opened

posteriorly by dividing the perineum to the external sphincter. More complex alternative approaches

may be preferred in female infants with low vaginal or anterior perineal fistulas. These lesions

generally require circumferential mobilization of the anterior fistula with transposition to the center of

the external sphincter. Anterior reconstruction of the perineal body is then performed. Transposition

anoplasty is designed to position the neoanus within the center of the external sphincter and separate

the neoanus from the vaginal introitus.

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Intermediate and High Malformations. Infants determined to have an intermediate, high, or

indeterminate anorectal malformation generally require diverting divided colostomy as initial surgical

management. Care must be taken to ensure that the proximal diverting colostomy provides adequate

length and mobility of the distal colon in anticipation of eventual anorectoplasty. A divided colostomy is

preferred over a loop colostomy by many surgeons to provide maximal fecal diversion from the

downstream rectourinary fistula. Following diverting colostomy, a distal contrast study into the rectal

pouch can also define the fistula and delineate the position of the rectum relative to the perineum.

Anorectoplasty is generally performed when the infant is approximately 8 to 12 months of age. Many

different approaches have been described, and considerable personal and institutional variation is

common. No single approach has superior results, and all have technical merits and difficulties. The

common surgical objectives in the treatment of anorectal malformations include (a) relief of the rectal

obstruction; (b) creation of a new anus; (c) position the rectum as normally as possible within the

striated muscle complex; and (d) divide the rectourinary fistula. In addition, preservation of the

surrounding structures (prostate, urethra, seminal vesicles, vaginal wall) is essential.

For repair of high and intermediate anorectal malformations, the most widely used procedure in the

United States is the posterior sagittal anorectoplasty described in detail by Peña.63 The infant is placed

prone and a posterior sagittal incision following the gluteal crease is used. The external sphincter and

the striated muscle complex are divided posteriorly along the midline to expose the rectal pouch. A

muscle stimulator is used to define and map the striated muscle complex and to confirm symmetric

dissection along the midline. Typically, the rectal pouch can be adequately dissected by this approach to

allow enough length to reach the perineum. Infrequently, a combined abdominoperineal approach is

required. The mobilized rectal pouch is opened and the rectourinary fistula identified and closed

directly. The rectal pouch is placed centrally within the striated muscle complex, which is reconstructed

circumferentially around the rectum. The neoanus is centered within the external sphincter and the

mucosa is sutured to the perineum.

Other accepted and practiced surgical approaches to imperforate anus include a sacroperineal

approach as proposed by Stephens,66 and an approach that uses components of endorectal dissection as

attributed to Rehbein.67 Both these surgical procedures are characterized by blind pull-through of the

distal rectum to the perineum without direct visualization of the striated muscle complex. Experience

with laparoscopic dissection and division of the rectourinary fistula with perineal pull-through

reconstruction has been reported.68 It appears that personal preference, experience and familiarity

rather than differences in outcome dictate the selection of procedure. In general, diverting colostomy in

all of these procedures is maintained until the anorectoplasty has completely healed, after which the

colostomy is closed electively.

Results, Complications, and Outcome

Mortality following anorectoplasty is related to the presence of associated congenital anomalies other

than imperforate anus. A careful review of 284 infants undergoing repair of anorectal malformations

observed an 18.7% mortality,69 suggesting that this group is at moderate to high risk for complications

and death secondary to coexisting congenital anomalies.

Complications are similar to other gastrointestinal surgical procedures and include infection, leak,

recurrent fistula, or anastomotic stricture. Leak or stricture formation is observed in 5% to 10% of

infants undergoing tapering rectoplasty during posterior sagittal anorectoplasty. Anorectal strictures are

treated by gradual postoperative anal dilatation for weeks to months. Recurrent rectourethral fistula or

urethral stricture is uncommon.

Long-term functional outcome in infants with low malformations is generally good given the

relatively normal descent of the distal rectum within the striated muscle complex. Infants with higher

lesions have a less predictable prognosis and are much more likely to have difficulty with fecal

continence. Currently, the outcomes appear to be independent of the type of surgical reconstruction

performed and more related to anatomic patient factors, including degree of rectal descent, integrity of

the striated muscle complex, and sacral innervation. Few or perhaps none of these children have

completely normal bowel habits after operation. About half of the infants have acceptable to good

results with episodic fecal soilage that can be improved with bowel management programs enemas and

cathartics.70–72 A comprehensive bowel management program is essential in preventing fecal impaction

and subsequent motility dysfunction in the rectum. The remaining children require major adjustments in

lifestyle secondary to fecal incontinence, chronic constipation, or fecal smearing and odor. In some

instances, socially acceptable continence can be assisted by the use of daily antegrade enemas via a

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cecostomy or appendicostomy. In other situations, a permanent diverting colostomy may be desirable.

Necrotizing Enterocolitis

Pathophysiology

4 NEC is a neonatal disease characterized by an initial intestinal mucosal injury that may ultimately

progress to transmural bowel necrosis. NEC is the most frequently encountered neonatal surgical

emergency and a major cause of morbidity and mortality in the premature infant. Despite its frequency

and extensive study, the pathogenesis remains obscure, and surgical treatment is directed largely at

controlling the complications of intestinal necrosis. The development of NEC occurs in association with

a variety of associated conditions, including perinatal stress, sepsis, respiratory failure, hypoxemia,

hypotension, and congenital cardiac defects. In general, NEC is observed in the premature infant with

multiple risk factors and potential etiologic events and conditions. Current clinical and experimental

data support the concept that the pathophysiology of NEC remains enigmatic and multifactorial.

The intestinal mucosal injury observed in NEC is likely to be the end result of an ischemic insult in a

susceptible host. Normally, the neonatal pulmonary and systemic vascular smooth muscle undergoes

rapid structural and physiologic changes shortly after birth. The premature infant appears to be

particularly vulnerable to vasoconstriction. With regard to NEC, it is hypothesized that hypoperfusion

and ischemia of the premature neonatal intestinal tract may be the result of uncontrolled splanchnic

vasoconstriction. This situation may be worsened in critically ill premature infants with low cardiac

output states impairing oxygen delivery to the intestines.

A common characteristic of NEC is the host inflammatory response to the initiating mucosal injury.

Experimental data are consistent with an important role for inflammatory mediators in the propagation

of intestinal injury in NEC.73 More than 90% of cases of NEC occur after the initiation of enteral

feeding, and several studies document that the osmolarity or rate of initial feeding may be important.

Although controversy exists, most neonatal centers now avoid rapid advancement of hyperosmolar

enteral feedings and attempt to prevent excessive fluid volume in premature infants.74,75 A multicenter,

randomized controlled clinical trial using Bifidobacterium and Lactobacillus as a probiotic given with

initial feeding demonstrated significant reduction in death from NEC in very low–birth-weight

premature infants.76

The most common site of involvement of NEC is the terminal ileum and right colon. NEC may be

localized, segmental, or it may involve the entire gastrointestinal tract. Histopathologic examination of

intestinal tissue from infants with NEC demonstrates submucosal edema, hemorrhage, and

microvascular thrombosis leading to transmural necrosis. The histopathology of NEC resembles that of

experimental intestinal ischemia, with areas of reversible mucosal injury adjacent to areas of transmural

necrosis. Dissection of intraluminal gas through the injured mucosa leads to gas within the bowel wall,

known as Pneumatosis intestinalis. The finding of pneumatosis intestinalis is a classic radiographic and

pathologic feature of NEC. Initially, the gas may be localized in the submucosa or lymphatic vessels, but

it may dissect into the muscularis, the portal venous tract, or into the subserosa. Intestinal perforation,

inflammatory phlegmon, and diffuse peritonitis are common with advanced NEC.

Clinical Presentation

Over the past three decades, advancements in technology, prenatal care, and neonatology have

improved overall outcome in premature infants who were previously unable to survive. In the United

States alone, low–birth-weight infants (less than 2,500 g) account for more than 250,000 births a year.

At least half of all infants with NEC are extremely low–birth-weight infants weighing less than 1,500 g.

In a study of 302 infants with NEC treated over two decades, the average birth weight fell from 1,645

to 1,505 g, and in similar fashion, the mean gestational age fell from 32.4 weeks to 30.4 weeks.77 NEC

is estimated to occur in 1 to 3 of 1,000 live births and 30 per 1,000 low-birth-weight births.78 NEC may

also occur in term infants, and in this group, it has a tendency to involve the colon and may present

without classic signs.79 The actual incidence of NEC remains difficult to determine because the diagnosis

is subjective; classic signs on physical examination and diagnostic imaging are not always uniformly

present. The classic clinical signs of NEC include abdominal distention, feeding intolerance, bilious

emesis, and either occult or gross blood in the stool. Gastrointestinal mucosal bleeding is present in the

vast majority of cases (80% to 90%) but is rarely significant from a hemodynamic standpoint. On

physical examination, abdominal tenderness with distention is common, and individual loops of

thickened or fixed bowel may be palpable. Edema, erythema, crepitus, or discoloration of the

abdominal wall suggests intestinal necrosis, perforation, or intra-abdominal abscess (Fig. 103-19).

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Hematochezia or guaiac-positive stool is typical. Systemic signs of inflammation and sepsis such as

temperature instability, apnea, bradycardia, hypoxemia, acidosis, and thrombocytopenia are also

common. The primary diagnostic goal during initial clinical evaluation is to determine whether

irreversible, transmural intestinal necrosis is present. There is no single physical finding or laboratory

test that makes this distinction.

Figure 103-19. Clinical presentation of diffuse staining of abdominal wall in an extremely low–birth-weight infant with perforated

necrotizing enterocolitis.

Diagnosis

The diagnosis of NEC relies on clinical evaluation and judgment based on symptoms and signs in the

appropriate setting. Table 103-4 summarizes diagnostic criteria and a staging system for NEC most

commonly used in the United States.80 Radiographic confirmation of NEC requires only plain abdominal

films. During the acute inflammatory phase, contrast studies may be hazardous and are contraindicated.

The classic radiographic finding of pneumatosis intestinalis (Fig. 103-20) confirms the diagnosis in the

appropriate clinical setting but is variably present. Other radiographic findings consistent with NEC

include thickened bowel loops, ascites, and portal venous gas. Serial abdominal films, including a left

lateral decubitus or upright film, should be obtained every 6 to 8 hours during the early course of the

disease. These sequential studies help document the progression or resolution of the inflammatory

process and, importantly, evaluate for the presence of intestinal perforation presenting as free

intraperitoneal gas or pneumoperitoneum. The presence of pneumoperitoneum mandates operative

intervention; however, up to half of infants with perforated NEC do not have discernible

pneumoperitoneum on plain films.

Treatment

Nonoperative. The vast majority of infants with NEC can be managed medically. Initial management

of NEC includes proximal decompression with a nasogastric or orogastric tube, bowel rest, and broadspectrum intravenous antibiotics. Prompt correction of hypotension, hypoxemia, and inadequate

ventilation must be undertaken. Intravenous fluid management, with particular attention to electrolytes

and acid–base status, is essential. Central venous access is secured and TPN is initiated. Oxygen delivery

and cardiac performance must be maintained, which in a premature neonate may require operative

closure of a patent ductus arteriosus; this approach is preferable over the use of indomethacin in the

setting of NEC.81 Serial physical examinations and blood work are useful in monitoring disease progress.

STAGING

Table 103-4 Necrotizing Enterocolitis

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Most infants with NEC improve with medical management. Typically, reversal of the systemic

inflammatory response occurs rapidly, and the abdominal distention and ileus resolve over a period of

days. Nasogastric tube decompression and intravenous antibiotics are usually continued for 7 to 14 days.

Enteral feeding usually is resumed once antibiotics have been discontinued and there has been return of

gastrointestinal function. The usual course of medically treated NEC is rapid clinical response and

stabilization in the first 24 to 36 hours. Infants with significant intestinal necrosis typically have signs of

either pneumoperitoneum or clinical deterioration during the initial 24 to 72 hours of treatment.

2973

Figure 103-20. Plain abdominal film demonstrating pneumatosis intestinalis (arrows) in an infant with necrotizing enterocolitis.

Indications to abandon medical management and escalate surgical therapy include evidence of

intestinal perforation or clinical deterioration with persistent or progressive systemic illness despite

maximal medical therapy. Evidence of persistent or progressive systemic sepsis includes temperature

instability, refractory hypotension, acidosis, hypoglycemia, neutropenia, and thrombocytopenia. Local

findings such as portal venous gas, abdominal wall cellulitis, or crepitus also may signal intestinal

necrosis and the need for operative intervention. A palpable, fixed abdominal mass consistent with

intestinal perforation with an inflammatory phlegmon or abscess also may be a relative indication for

operation. Because there is not complete agreement on what constitutes clinical deterioration, some

controversy exists regarding operative indications for NEC in the absence of pneumoperitoneum.

Because the interpretation of clinical deterioration criteria remains subjective, the decision to operate

remains a multifactorial clinical judgment. In equivocal situations, abdominal paracentesis of ascitic

fluid may be helpful in diagnosing intestinal necrosis with perforation in the absence of

pneumoperitoneum if the aspirate contains bacteria or stool.82

Operative

Operative indications in NEC include the presence of intestinal necrosis with or without frank intestinal

perforation. Conventional operative intervention is aimed at treating the complications of NEC (i.e.,

intestinal necrosis). In general, resection of intestine involved with NEC does not prevent further

extension of disease in other involved areas of the bowel. For isolated segmental disease, the traditional

surgical treatment of NEC is resection of necrotic bowel with proximal enterostomy and distal mucous

fistula placement. In infants with diffuse NEC, multiple resections with several enterostomies may be

required. The primary operative goal is an expedient operation with preservation of as much intestinal

length as possible, including the ileocecal valve. Because the risk of developing short-gut syndrome is

substantial in infants with diffuse disease, preservation of marginal areas of involved intestine with a

planned second-look operation to reevaluate intestinal viability may be useful. Accurate measurement of

the remaining bowel length is important from a diagnostic and prognostic standpoint, with the length of

bowel resected determined by the extent of transmural intestinal necrosis. Resection with primary

anastomosis in selected infants with NEC has been reported,83 with a recent study observing recurrent

NEC in 22% and strictures in 17% of 18 treated infants following primary anastomosis.84 Complete

intestinal necrosis of the small intestine and the colon is uncommon and is not compatible with longterm survival without the sequelae of short-gut syndrome and the potential need for intestinal

transplantation (Fig. 103-21).

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Figure 103-21. Fulminant necrotizing enterocolitis involving the entire gastrointestinal tract in a premature infant. Note the

presence of pneumatosis intestinalis.

Infants with NEC are typically fragile and premature, and complications in this population are not

well tolerated. Survival in this situation may be more dependent upon disease severity and coexisting

medical problems than the operative approach. For the high-risk, low–birth-weight infant, initial

management with primary bedside peritoneal drainage rather than laparotomy and bowel resection may

be useful as either a temporizing measure or, in some instances, a definitive procedure.85 A multicenter,

randomized controlled surgical trial comparing laparotomy with primary peritoneal drainage in

premature infants with perforated NEC found that overall survival, dependence upon TPN, and length of

stay were independent of the type of operation performed.86

Complications, Results, and Outcome

Most infants with NEC are treated successfully without operative intervention. Morbidity and mortality

for this group are related primarily to problems associated with prematurity. Given the delay of bowel

function and the need for TPN, cholestatic jaundice commonly occurs but is generally reversible. Infants

placed on broad-spectrum antibiotics for an extended period are at risk for developing fungal sepsis. For

infants with intestinal necrosis from NEC, infectious complications including wound sepsis, central

venous catheter infections, and pneumonia with respiratory failure may occur.

The overall surgical complication rate in infants with NEC is at least 20% to 40%. Virtually every

infant with NEC has a significant complication, an associated medical problem, or both. Immediate

technical complications in treating NEC include intestinal leak, fistula formation, stoma necrosis,

bleeding, and liver injury during exploration (Table 103-5). These complications are obviously

magnified in the extremely low–birth-weight infant with preexisting intestinal injury. Fluid and

electrolyte losses from proximal diverting enterostomies can be significant and even life-threatening in

extremely low–birth-weight infants whose circulating blood volume is less than 50 to 100 mL. A review

of 68 infants treated surgically for NEC observed a 26% mortality rate and a 68% complication rate

related to the stoma or its closure in the perioperative survivors.87 Complications included intestinal

stricture, incisional or parastomal hernia, stoma prolapse, intussusception, wound dehiscence or

infection, small bowel obstruction, and anastomotic failure. The complications associated with diverting

enterostomy in this unique population provide a compelling rationale for early enterostomy closure

once the inflammation from peritonitis has resolved. A prospective, randomized trial comparing

resection and enterostomy with resection and primary anastomosis in the treatment of NEC has not

been reported.

COMPLICATIONS

Table 103-5 Operations for Necrotizing Enterocolitis

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Intestinal stricture formation following NEC, whether managed operatively or nonoperatively, is not

uncommon. This consequence usually results from a normal host inflammatory response to transmural

intestinal injury. The degree of fibrosis and subsequent stricture formation are clearly related to the

severity and extent of disease. Less frequently, mesenteric vascular compromise secondary to an intraabdominal adhesion may lead to stricture formation. Although stricture can develop anywhere in the

gastrointestinal tract involved with NEC, a higher rate of demonstrable stricture is observed in the left

colon, occurring in as many as 36% of medically treated infants.88 Routine contrast enema 4 to 6 weeks

after clinical resolution of NEC treated operatively or nonoperatively has been advocated in some

institutions. Symptomatic strictures generally require segmental resection with anastomosis, although

fluoroscopically guided balloon catheter dilatation has been reported.

Overall survival rates for infants with NEC have improved significantly over the past three decades

and is currently about 60% to 80% for both operative and nonoperative groups.89 The observed

improvement in survival is thought to reflect improved neonatal intensive care, the use of TPN, and

early, aggressive treatment of suspected NEC. Most neonatal intensive care units initiate aggressive

medical treatment in any infant with suspected NEC. Whether surgical interventions such as resection

with primary anastomosis or limited primary peritoneal drainage can improve morbidity and mortality

in these critically ill infants remains to be fully determined. Long-term outcome for NEC survivors

generally reflects associated problems of prematurity. In particular, many of these infants have

persisting neurodevelopmental, ophthalmologic, and pulmonary diseases, but morbidity from the

gastrointestinal system generally is limited to infants with short-gut syndrome following extensive

bowel resection. These infants present complex ethical and management issues beyond the scope of this

review. Most NEC survivors (75%) enjoy a good to excellent quality of life, suggesting that the

treatment cost relative to the potential benefit for these infants is worthwhile.90

Meconium Ileus

Meconium ileus is a descriptive term for small bowel obstruction in a newborn infant with CF. About

10% to 20% of infants with CF initially present with meconium ileus. A review of CF is useful to

understand the pathophysiology and treatment of meconium ileus.

CF is the most common fatal hereditary disease in Europe and North America. It is an autosomal

recessive disorder found with a heterozygous carrier incidence rate of 1 in 20 to 25 in white

populations. The estimated incidence rate of homozygous gene expression and phenotypic manifestation

of CF is about 1 in 2,000 to 2,500 in this population.91 The CF gene has been cloned and the single most

common mutation characterized.92,93 The most common point mutation is a three-base-pair deletion

found in 70% to 75% of the carrier population. This mutation leads to deletion of a phenylalanine

residue in amino acid position 508 of the CF transmembrane conductance regulator (CFTR) gene. In

addition, there are about 200 more infrequent mutations of the CFTR gene that lead to clinical CF. The

molecular heterogeneity of CFTR gene mutations produces practical implications in the development

and use of carrier screening tests in the general population. Currently, widespread use of molecular

genetic screening tests in the general population to identify asymptomatic carriers and at-risk couples

without a family history of CF is not recommended; there are significant technical, ethical, and social

issues that must be prospectively addressed.94 Screening of at-risk couples with a family history of CF is

recommended, however, and in this setting, carrier discovery approaches 100% so that appropriate

genetic counseling can be provided. Molecular genetic screening should also be offered to parents and

infants with clinically suspected CF as well as asymptomatic infants born to at-risk couples. This

2976

approach allows rapid identification and confirmation of virtually all infants homozygous for CF.

Pathophysiology

The clinical manifestations of CF are caused by an epithelial electrolyte transport defect that results in

impermeability to the chloride (Cl−) ion.95 The epithelial defect occurs in apocrine sweat glands and the

tracheobronchial tree as well as the pancreas, gastrointestinal tract, and liver. In sweat glands, failure of

normal Cl− ion reabsorption following beta-adrenergic stimulation leads to an obligate sodium chloride

loss despite a normal adenosine triphosphate (ATP)-dependent sodium–potassium pump. This

mechanism is the basis for the traditional diagnostic sweat chloride test.

Reduction of Cl− permeability in the tracheobronchial tree leads to diminished secretion volume as

well as increased absorption of sodium chloride. As a result, airway secretions in CF patients are low in

volume and particularly viscous. Because of the tenacious nature of the airway secretions, airway

clearance is impaired, which leads to chronic, recurrent infection with bronchitis, and pneumonia. As

the disease advances, bronchiectasis and progressive pulmonary parenchymal destruction ensues.

Recurrent pulmonary bacterial infection is common, and airway colonization by Pseudomonas aeruginosa

is predictable. Chronic pulmonary disease accounts for more than 90% of the deaths in advanced CF,

with a mean life expectancy approaching 30 years.

Pancreatic exocrine function is also affected by impaired Cl− permeability. Pancreatic duct

obstruction resulting from inspissated viscous secretion is followed by glandular autolysis, acinar

atrophy, and pancreatic fibrosis. Pancreatic exocrine insufficiency is a classic early clinical feature of CF

and is thought to account for some of the gastrointestinal manifestations of the disease. In particular,

the deficiency of pancreatic proteinases, impaired chloride permeability, and abnormal epithelial

mucous secretion leads to meconium ileus in the newborn, characterized by abnormally thick and viscid,

protein-laden meconium that causes mechanical gastrointestinal obstruction. The obstruction is usually

observed in the terminal ileum just proximal to the ileocecal valve (Fig. 103-22). Infants with

meconium ileus have small pellets, or concretions, of pale, nonbilious meconium in the terminal ileum

with a distal microcolon. Proximal to the obstruction, the meconium is variably mixed with gas and

often is thick and tarry in consistency. The bowel containing the thick meconium is often grossly,

distended, and thickened. Microscopically, the muscularis is hypertrophied; distended mucous glands

with prominent goblet cells may be present. The most proximal jejunum is typically normal.

Figure 103-22. Meconium ileus causing obstruction of the terminal ileum from abnormally thick, inspissated meconium.

In utero events such as proximal volvulus of the dilated segment of ileum, perforation from

distention, or atresia occur in approximately one-third to one-half of fetuses with meconium ileus. These

clinical entities are characterized together as complicated meconium ileus. A classic clinical presentation

of complicated meconium ileus is in utero intestinal perforation with sterile meconium peritonitis and

formation of a calcified pseudocyst (Fig. 103-23). Gastrointestinal conditions presenting later in life

occur in 10% of children with CF and include acute appendicitis, recurrent rectal prolapse, and

intussusception. These conditions reflect abnormal transit of thick, inspissated stool causing proximal

distention or obstruction of the bowel lumen. Small-bowel obstruction in CF outside the neonatal period

was historically called meconium ileus equivalent, and is now termed distal intestinal obstruction syndrome

(DIOS). Treatment of DIOS is similar to initial nonoperative management of uncomplicated meconium

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