You Shall Not Pass

The newborn nursery team is called to reevaluate a female infant who had not yet passed stool at 36 hours of age. The infant was born to a 33-year-old gravida 4 para 2–2–0–4 mother with a medical history of anxiety disorder, depression, and opioid use disorder managed for 3 years with daily methadone. Maternal medications also included prenatal vitamins, docusate, and as-needed metoclopramide. The mother received routine prenatal care.The patient was born at 39 weeks’ and 2 days’ gestation via spontaneous vaginal delivery at a birthweight of 3005 g. Her delivery was uncomplicated, with rupture of membranes 7 hours and 10 minutes before delivery and Apgar (appearance, pulse, grimace, activity, and respiration) scores of 8 and 9 at 1 and 5 minutes of life. She was given vitamin K, hepatitis B vaccine, and erythromycin eye ointment, then was admitted to the mother’s room. Due to the concern of opioid withdrawal, she was started on the Eat, Sleep, Console protocol with 24-kcal formula for increased caloric intake, which she tolerated well with no emesis.1 The infant was exclusively formula fed because the mother declined to breastfeed. Preprandial glucose checks were discontinued after normal values were obtained for the first 12 hours after birth. She voided at 8 hours of age and continued to void every 4 to 8 hours.Vitals signs are within normal limits. Examination is notable for a well-appearing infant with a soft, nontender, nondistended abdomen, with bowel sounds present, a bifid gluteal cleft without sacral dimples or abnormal skin findings, and a patent anus with normal positioning and tone. Due to the patient’s reassuring examination findings, further evaluation is delayed until 44 hours of age, when the patient still has not stooled. An abdominal radiograph is obtained to rule out obstruction, and it shows mottled lucency compatible with stool throughout the colon to the rectum. Spinal ultrasonography is performed at the same time to rule out a tethered cord and is read as normal. Laboratory tests are performed, including a normal basic metabolic panel and complete blood cell count. A lower gastrointestinal series (Figure 1) shows a relatively narrowed rectum and sigmoid colon with transition at the descending-sigmoid junction.Delayed passage of meconium is defined as failure to stool in the first 48 hours after birth. Within the first 24 hours after birth, 99% of term infants pass meconium. The percentage is slightly lower in preterm infants at 76%.2 Although failure to pass meconium within 48 hours does not necessarily indicate underlying pathology,3 it warrants further investigation with review of history, physical examination, and consideration of diagnostic studies. The causes of delayed passage of meconium can be broken down into 3 main groups: functional ileus, distal obstruction, and proximal obstruction (Table 1).Most cases of normal anatomy and delayed passage of meconium are due to functional ileus secondary to 1 of the following risk factors: maternal magnesium or ganglionic block agents during labor, functional ileus secondary to critical illness, electrolyte abnormalities, prematurity, and hypothyroidism.3 There are a few case reports describing delayed passage of meconium associated with use of antiretroviral agents.4 This patient has none of these known risk factors. In a review of the literature about methadone exposure in utero, there is not a known association with delayed passage of meconium.5,6,7 Although constipation is a known adverse effect of opioid use, most newborns with neonatal abstinence syndrome and methadone withdrawal experience increased stool frequency or diarrhea.8The second important consideration for delayed passage of meconium is distal causes of obstruction, such as meconium plug syndrome (1 in 500 to 1 in 1000 births), Hirschsprung disease (1 in 4000 births), small left colon, and anorectal malformation (1 in 4000 to 1 in 8000 births). These conditions typically present with an initial symptom of delayed passage of meconium and may later develop abdominal distention and vomiting. Patients with suspected meconium plug syndrome should undergo a rectal suction biopsy because 15% of patients with meconium plug syndrome also have Hirschsprung disease.9In addition, more proximal intestinal obstruction, including intestinal atresia, webs, malrotation with midgut volvulus, as well as meconium ileus (1 in 2800 births), can cause delayed passage of meconium.2 These causes are distinguished by emesis with abdominal distention and tenderness early in the course of illness. Typical abdominal radiography findings include paucity of distal air with gaseous distention proximal to an obstruction. Most patients with meconium ileus have cystic fibrosis.Last, rare causes of delayed passage of meconium include hypoganglionosis and intestinal neuronal dysplasia types A and B. Very rare causes include megacystis-microcolon–intestinal hypoperistalsis syndrome and Currarino triad.2,10Megacystis-microcolon–intestinal hypoperistalsis syndrome is a rare congenital condition characterized by a dilated urinary bladder (megacystis), microcolon, and dysmotility or absent intestinal peristalsis.3 The Currarino triad is an extremely rare type of caudal regression characterized by a triad of presacral mass, sacrococcygeal bone defect, and anorectal malformation.10The patient was made nil per os, started on intravenous fluids, and transferred to the NICU for further monitoring as well as rectal suction biopsy by the pediatric surgery team. Biopsy results showed ganglion cells throughout the sample, ruling out Hirschsprung disease and making meconium plug the most likely diagnosis.9,11 On admission she was started on a regimen of twice-daily rectal saline irrigations and subsequently stooled on day 3 after birth. The rectal irrigation was discontinued on day 9 after birth, and the infant was spontaneously stooling on day 10 after birth. For neonatal abstinence syndrome, the patient required as-needed morphine and nasogastric feedings due to poor feeding by mouth and irritability on the Eat, Sleep, Console protocol. She was eventually discharged on day 13 after birth after regaining birthweight, tolerating an ad lib diet, and stooling spontaneously. Unfortunately, the patient was lost to follow-up, so her current stooling patterns are unknown. Results of the newborn metabolic screen, which includes cystic fibrosis, returned after discharge and were normal.Meconium plug syndrome, also known as functional immaturity of the colon, occurs when the meconium is abnormally thick and sticky, leading to temporary obstruction in the colon. It can be idiopathic or associated with conditions such as prematurity and dehydration.2Infants with meconium plug syndrome typically present with delayed passage of meconium, abdominal distention, and possibly vomiting. Although meconium plug syndrome can cause discomfort and feeding difficulties, it usually resolves spontaneously without long-term complications. Treatment may involve gentle rectal stimulation, such as the administration of glycerin suppositories or rectal irrigation, to help evacuate the meconium plug, particularly in premature infants.12,13If an infant has not stooled by 48 hours after birth, they should undergo evaluation for causes of delayed passage of meconium, which has a differential diagnosis that includes functional ileus, distal obstruction, and proximal obstruction, with a variety of causes in each category (Table 1).Causes of delayed passage of meconium in infants with normal intestinal anatomy may include maternal magnesium during labor or ganglionic blocking agents, and functional ileus secondary to critical illness, electrolyte abnormalities, or prematurity.2,3