Neonatal Small Left Colon Syndrome

Although the precise cause of this form of neonatal intestinal obstruction, which has a typical radiologic picture but is distinctly unusual, is unknown, numerous theories have been proposed, including neural, humoral, and drug-induced etiologic mechanisms.

In 1974, Davis et al reported the association of NSLCS with abnormalities of intestinal neurohistology. ^[6] Their initial report described increased numbers of immature small ganglion cells in the myenteric plexus (in both the narrowed and dilated portions of the colon) in four of 20 patients with NSLCS. They compared the histology from NSLCS patients with that from control subjects, including infants of diabetic mothers without colon changes, premature infants, and term infants.

Davis et al concluded that the hypercellularity observed in the specimens from patients with NSLCS most closely resembled the histology observed in the colons of premature infants. ^[6] Despite this conclusion, they did not provide gestational age data on the patients; therefore, at least some of them presumably were premature.

In 1991, Schofield et al reported an association in seven patients with clinical and radiographic NSLCS and suction rectal biopsy histology demonstrating intestinal neuronal dysplasia (IND). ^[7] In all seven cases, the biopsies, stained with hematoxylin and eosin (H&E) and acetylcholinesterase (AChE), demonstrated an increase in the number of AChE-stained fibers in the mucosa and increased submucosal ganglia or large ganglia. These changes are also observed with prematurity, and because most of the infants with NSLCS in this report were indeed premature, gestational age seems to have had a confounding effect on the biopsy results.

In a 1975 report, Philippart et al focused on humoral and autonomic nervous system changes that occur in response to neonatal hypoglycemia to develop a mechanistic explanation. ^[8]  Glucagon release and sympathoadrenal stimulation are typical responses to hypoglycemia in vivo, and both result in blood glucose stabilization through hepatic gluconeogenesis and glycogenolysis. Along with several effects on the gastrointestinal (GI) tract, glucagon release is known to decrease motility in the jejunum and left colon.

Hypoglycemia also stimulates sympathetic and parasympathetic arms of the autonomic nervous system. Maximal vagal (parasympathetic) stimulation results in increased motility in its area of distribution, which ends at the splenic flexure, whereas sympathetic stimulation results in diminished motility. Therefore, a composite effect of glucagon release with sympathetic and parasympathetic nervous system stimulation would hypothetically be an overall diminution in intestinal motility, with a functional block in the colon beyond the splenic flexure.

Philippart et al pointed out that precipitants other than hypoglycemia (eg, stress) may mediate the same changes through similar mechanisms, thereby explaining the phenomenon when it occurs in the absence of maternal diabetes mellitus. ^[8]

Other possible contributors to intestinal hypomotility include maternal drugs used during the third trimester that cross the placenta and affect the fetus. This concept is supported by the report of two cases of NSLCS in infants born to mothers using psychotropic drugs with known anticholinergic effects and the recognized association between hypermagnesemia (in infants born to eclamptic mothers treated with magnesium sulfate) and hypomotility conditions.

Although earlier reports of neonatal colonic obstruction undoubtedly included cases of NSLCS in the spectrum of obstructive conditions referred to as meconium plug syndrome, obstruction in NSLCS is not typically associated with the presence of a mucus or meconium plug in the distal constricted segment. No analytic abnormality has been reported in the meconium of infants with NSLCS, with the exception of a single case report of an infant with cystic fibrosis who presented with a meconium ileus–like obstruction at the splenic flexure with distal microcolon.

In contrast, the meconium in meconium plug syndrome is reported to have an elevated protein content with altered enzymatic activity, suggesting that the obstruction is caused by an immobile luminal obturator rather than mural constriction and diminished peristalsis. ^{[9, 10]}

A subsequent report illustrated the continued challenges of an accurate and etiologic diagnosis of the cause of neonatal meconium plug obstruction. This review of 21 neonates with meconium obstruction revealed eight patients (38%) with Hirschsprung disease, four (19%) with NSLCS, and nine (43%) with meconium plug syndrome. ^[11]

A specific relation has been identified between maternal diabetes and neonatal intestinal obstruction. ^[12] This was the subject of an analysis of an infant cohort born to diabetic mothers. ^[13] Of 105 offspring of diabetic mothers, six cases of intestinal obstruction (including a pair of twins) were reported with classic contrast enema findings of NSLCS. Of these, five responded to conservative treatment, and the sixth was found to have sigmoid Hirschsprung disease.

The frequency with which NSLCS occurs is difficult to estimate because the entire subject literature contains only case reports ^{[5, 14, 15]} and a few case series.

In one institution's review of consecutive suction rectal biopsies performed in 456 pediatric patients (median age, 13 d) for symptoms of constipation, abdominal distention, and bloody stools, 61 cases of Hirschsprung disease (13%) were identified. The remaining cases included seven neonates who had a clinical and radiologic picture consistent with NSLCS. In this study cohort, the incidence of symptoms of distal intestinal obstruction, enterocolitis, or both was 1.5%. ^[7]

Most infants completely respond to contrast enema decompression and are able to progress quite rapidly to full enteral feedings. Numerous patients who have undergone follow-up examinations of their colon have demonstrated normalization of caliber within a few weeks. In a 1975 report, Philippart et al warned of the small number of patients who experience a delayed complication, either recurrent or persistent obstruction or delayed perforation, mandating close surveillance during the first 1-2 weeks of life. ^[8]