Pyloric stenosis, also known as infantile hypertrophic pyloric stenosis, is a common condition affecting infants and characterized for causing severe nonbilious vomiting after feeding. It is caused by an abnormal thickening of the pyloric portion of the stomach, causing obstruction of the gastric outlet. Pyloric stenosis presents itself only within a brief phase of development, which may be delayed in premature infants. The onset of symptoms typically occurs at 2 - 8 weeks of age with a peak occurrence at 3 - 5 weeks.
The incidence of pyloric stenosis is about 2 to 4 per 1000 live births in Western populations, but this decreases in the case of African or Asian countries. Males are more susceptible than females, but the cause of this difference is unknown. The condition also exhibits familial clustering, but not in a Mendelian pattern.
Pyloric stenosis can also occur in adults occasionally, but it is much less common than its paediatric variant, with less than 200 cases reported in the English literature. In its adult form, pyloric stenosis affects predominantly middle aged males.
The immediate cause of pyloric stenosis is a narrowing of the opening from the stomach to the intestines due to an enlargement (hypertrophy) of the muscle surrounding the pylorus. Although pyloric stenosis is the most common surgical condition producing forceful or projectile vomiting (emesis) in infancy, its etiology remains unknown. The occurrence of the condition has been associated with several variables such as genetic, environmental and mechanical factors.
Pyloric stenosis has been associated with genetic syndromes such as Smith-Lemli-Opitz and Cornelia de Lange, as well as with several chromosomal abnormalities, including partial trisomy of chromosomes 9 and 13, partial monosomy of chromosome 18 and a translocation of chromosomes 8 and 17. Although a specific gene responsible for the condition has not yet been discovered, several susceptible loci have been identified.
Among the environmental and mechanical factors that have been advanced as a potential explanation, it can be mentioned that the sleeping position, maternal smoking (both supported by an association with Sudden Infant Death Syndrome), exposure to antibiotics (specifically erythromycin) and Helicobacter pylori infection can all be possible causes of pyloric stenosis.
The function and motility of the pyloric sphincter is under a complex control system which involves the enteric nervous system, gastrointestinal hormones and interstitial cells of Cajal. Some abnormalities in hormonal control have been identified in patients, leading some investigators to postulate this as a potential etiological cause, but there is still some controversy on whether these abnormalities are the consequence or the cause for the condition.
The symptoms for pyloric stenosis in infants typically take place 3 - 5 weeks after birth and include:
- Repeated projectile vomiting (usually after a feeding episode with the infant)
- Abdominal pain
- Constant hunger
- Dehydration (aggravated after continuous vomiting)
- Weight loss/failure to gain weight
- Wave-like motion of the abdomen after a feeding episode
A definitive diagnosis for pyloric stenosis is achieved through a combination of physical examination and radiographic studies. Palpation of a hypertrophied pyloric muscle, or "olive", can be the sole basis of the diagnosis, with a 99% positive predictive value. However, there is presently a trend in the medical community toward increased reliance on imaging as a substitute or complement to physical examination. This may be related to earlier presentation of patients in recent times, since less emaciated, healthier, and more vigorous infants are more difficult to examine.
Ultrasonography is the preferred imaging method for diagnosis of pyloric stenosis, as it is noninvasive, can be performed quickly, bypasses the need of radiation exposure and exhibits an accuracy close to 100%. The hypertrophied pyloric canal may range from 14 mm to more than 20 mm in length, and it is important to observe the lack of relaxation in real time.
Alternatively, a fluoroscopic upper gastrointestinal contrast study (upper GI series) can be used for diagnosis, with the patient drinking the contrast agent from a bottle. The thickened muscle causes an external impression on the gastric antrum (the "shoulder sign") that can be visualized by fluoroscopy. The drawbacks of this method are that it is time consuming and involves the use of radiation.
The vomiting of gastric contents that is one of the telltale symptoms of pyloric stenosis leads to depletion of sodium, potassium and hydrochloric acid, resulting in hypokalemic, hypochloremic metabolic alkalosis. This can be detected by running blood tests, and the results may be useful to confirm the diagnosis.
The treatment of pyloric stenosis involves a surgical procedure in a vast majority of cases. Surgery consists of pyloromyotomy (known as Ramstedt's procedure), which involves extramucosal longitudinal splitting of the pyloric muscle without suturing. The laparoscopic technique, first described in this context in 1991, has since gained popularity among pediatric surgeons and gradually replaced the classic opening technique. The complication rate appears to be similar, and the risk of wound infection actually decreases.
Since pyloric stenosis is a relatively common condition in infants and pyloromyotomy is a simple procedure, the operation is often performed by general surgeons without subspecialty training in pediatric surgery. There is a controversy regarding this practice, since some evidence appears to show that outcomes such as length of stay and complication rates are better when the operation is performed by pediatric surgeons. However, it should be kept in mind that it is not practical to recommend that all infants with a diagnosis of pyloric stenosis be operated on by a pediatric surgeon, particularly in rural areas where one may not be readily available.
Nonoperative management for pyloric stenosis has been virtually abandoned these days given the satisfactory results provided by Ramstedt's procedure. When medical treatment is chosen for some reason (for example, an allergic reaction to anesthesia), it usually involves intravenous or oral atropine, an acetylcholine inhibitor. The objective of this approach is to suppress muscular contractions and decrease gastrointestinal peristalsis, and therefore it is based on the assumption that muscular spasms cause the hypertrophy and exacerbates the fixed obstruction underlying the symptoms. Endoscopic or image-guided balloon dilation of the pylorus has also been described, but the technique has not been widely adopted due to unacceptably high rates of perforation and failure to relieve the obstruction.
Most infants with pyloric stenosis require hospitalization and intravenous fluid replacement therapy before they can be referred to surgery. The degree of dehydration can be estimated by clinical examination, urine output, and serum chloride and bicarbonate levels. Infants with severe dehydration initially receive boluses with isotonic saline solution, and potassium chloride is later added to the fluids once urine output has been demonstrated.
Pyloromyotomy has a low incidence of morbidity and mortality in infants. The complication rate is believed to be around 10%. The most common complications include duodenal perforation, wound infection and persistent emesis. Repeat operations after pyloromyotomy are rarely performed, and are usually due to an incomplete first operation or less commonly to an unrecognized perforation. Gastroesophageal reflux and gastritis are the most common causes for persistent vomiting postoperatively. Pyloric stenosis generally has no long term side-effects or impact on the infant's future.
At present, the causes leading to the development of symptoms for this condition are poorly understood. Therefore there are no specific guidelines aimed at preventing pyloric stenosis in infants.
Pyloric stenosis is an acute condition whose symptoms become evident shortly after birth. Surgical intervention provides immediate relief, and the disease never becomes chronic.
Considerable progress has been made in the recent years towards the identification of the causative factors for pyloric stenosis, especially in the areas of genetics and pyloric innervation. The role of nitric oxide is becoming more evident with the identification of the nitric oxide synthase 1 (NOS1) gene as a susceptibility locus for the condition. An animal model has also been generated exhibiting symptoms that resemble those observed in humans. This model promises to shed additional light on the etiology of the disease. There is also increasing evidence suggesting that quantitative or qualitative abnormalities in the innervation of smooth muscle cells may underlie the presence of symptoms.
Surgical treatment of pyloric stenosis is likely to be greatly enhanced in the future by advances in minimally invasive pediatric surgery for infants. Some of the techniques currently in development include single-incision laparoscopic surgery, natural orifice transluminal endoscopic surgery and robotic surgery.