Intestinal obstruction is one of the most frequent reasons for obtaining surgical consultation in newborns. Distal intestinal obstruction of the newborn may be anatomic (eg, imperforate anus, colonic atresia, colonic stenosis) or functional. [1, 2] Most cases of functional colonic obstruction are caused by Hirschsprung disease [3, 4] ; however, a subset of term or near-term babies experience colonic obstruction with a characteristic caliber reduction in the sigmoid and descending colon (see the image below) unrelated to meconium inspissation or aganglionosis.
This condition, which has a frequent association with maternal gestational diabetes mellitus and seldom requires surgical intervention, is termed the neonatalsmall left colon syndrome (NSLCS).
History of the Procedure
In 1974, Davis coined the term small left colon syndrome in his initial description of 20 infants with colonic obstruction not caused by a meconium plug or Hirschsprung disease.  In all patients, a contrast enema revealed a narrowed descending and sigmoid colon, with a caliber transition at the splenic flexure; of these, 17 patients experienced immediate and complete resolution of obstruction without operation. Although Davis observed that 8 of the 20 infants were born to mothers with diabetes mellitus, he hypothesized that the apparent dysmotility syndrome was neurogenically determined.
In 1975, Philippart et al reported 8 patients with a similar clinical and radiographic presentation, all born to mothers treated for gestational diabetes mellitus with either insulin or oral hypoglycemic agents.  In 4 of 8 cases, resolution of obstruction after contrast enema was uncomplicated. One patient presented with a cecal perforation requiring emergency operation, one patient underwent operation for suspected Hirschsprung disease (which was subsequently disproved by biopsy), and 2 patients required a delayed operation (one for persistent obstruction and the other for sudden distension and cecal perforation occurring after institution of oral feedings).
Philippart et al speculated on the effects that neonatal hypoglycemia have on intestinal motility via activation of the autonomic nervous system and through stimulated glucagon release.  They also identified a small group of patients who developed late complications and advocated close surveillance for the minority who did not respond promptly to decompressive enemas.
Neonatal small left colon syndrome is an uncommon cause of neonatal intestinal obstruction characterized by an abrupt intestinal caliber transition at or near the splenic flexure and associated, in approximately half of cases, with a maternal history of gestational diabetes mellitus.
The frequency with which neonatal small left colon syndrome occurs is difficult to estimate because the entire subject literature contains only case reports and a few case series.
In one institution's review of consecutive suction rectal biopsies performed in 456 pediatric patients (median age of 13 d) for symptoms of constipation, abdominal distension, and bloody stools, 61 cases of Hirschsprung disease (13%) were identified. The remaining cases included 7 neonates who had a clinical and radiologic picture consistent with neonatal small left colon syndrome. In this study cohort, the incidence of symptoms of distal intestinal obstruction and/or enterocolitis is 1.5%. 
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 neonatal small left colon syndrome with abnormalities of intestinal neurohistology.  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 4 of 20 patients with neonatal small left colon syndrome. They compared the histology from patients with small left colon syndrome with that of control subjects, including infants of diabetic mothers without colon changes, premature infants, and term infants. They concluded that the hypercellularity observed in the specimens from patients with neonatal small left colon syndrome most closely resembled the histology observed in the colons of premature infants. Despite this conclusion, they did not provide gestational age data on the patients; therefore, at least some of them assumably were premature.
In 1991, Schofield and Yunis reported an association in 7 patients with clinical and radiographic neonatal small left colon syndrome and suction rectal biopsy histology demonstrating intestinal neuronal dysplasia (IND).  In all 7 cases, the biopsies, which were 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 neonatal small left colon syndrome 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, which occur in response to neonatal hypoglycemia in developing a mechanistic explanation. 
Glucagon release and sympathoadrenal stimulation are typical in vivo responses to hypoglycemia, and both result in blood glucose stabilization through hepatic gluconeogenesis and glycogenolysis. Along with several effects on the 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 point 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. 
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 2 cases of neonatal small left colon syndrome 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 neonatal small left colon syndrome in the spectrum of obstructive conditions referred to as meconium plug syndrome, obstruction in neonatal small left colon syndrome is not typically associated with the presence of a mucus or meconium plug in the distal constricted segment. No analytical abnormality has been reported in the meconium of infants with neonatal small left colon syndrome, 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.
A more contemporary report illustrates 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 8 patients (38%) with Hirschsprung disease, 4 patients (19%) with small left colon syndrome, and 9 (43%) with meconium plug syndrome. 
A specific relationship has been identified between maternal diabetes and neonatal intestinal obstruction.  This was the subject of an analysis of an infant cohort born to diabetic mothers.  Of 105 offspring of diabetic mothers, 6 cases of intestinal obstruction (including a pair of twins) were reported with classic contrast enema findings of neonatal small left colon syndrome. Of these, 5 responded to conservative treatment, while the sixth was found to have sigmoid Hirschsprung disease.
The clinical features of infants described in all English language case series of neonatal small left colon syndrome are summarized in the table below. Most are born at or near term and are of normal birth weight. Approximately 50% have a history of maternal diabetes mellitus, and other maternal comorbidities (usually eclampsia), which contribute to neonatal stress, may also be present. All patients do not pass meconium within the first 24 hours of life, and they all develop abdominal distension with bilious vomiting or nasogastric aspirates. A small number of infants develop progressive distension leading to perforation, typically in the cecum, within the first 24-36 hours of life.
Table 1. Clinical Features of Infants Described in All English Language Case Series of NSLCS (Open Table in a new window)
|Investigator||Number of Cases||
Median Gestational Age
|Maternal History of Diabetes Mellitus||Other Perinatal History||Intestinal Perforation||Mortality||Surgery Performed|
|Davis et al ||20||Not stated||8||1 (Rh disease)||0||1 (Death was due to unrelated cause.)||2|
|Berdon et al ||11||37||3||4 (Eclampsia)||0||0||2|
|Philippart et al ||8||38||8||6 (Eclampsia)||2||0||4|
|Stewart et al ||4||37||3||2 (Eclampsia)||3||1||3|
|Woodhurst and Kilman ||2||36||0||0||1||1||2|
|Falterman and Richardson ||2||37||0||2 (Psychotropic drug use)||0||0||0|
|Total||52||38||23 (44%)||15 (29%)||6 (12%)||3 (6%)||14 (27%); 7 of 14 underwent colostomy for incorrect diagnosis of Hirschsprung disease|
As discussed in the sections below, the indications for operation in neonatal small left colon syndrome (NSLCS) include intestinal perforation and failure of resolution of obstruction following contrast enema administration.
The neonatal colon is the anatomy relevant to this discussion.
No absolute contraindications to surgery for neonatal small left colon syndrome (NSLCS) are recognized. Remember that the diagnosis is not definitive until Hirschsprung disease has been excluded by rectal biopsy findings; therefore, any surgical procedure must take into account this diagnostic similarity.
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