Pyloric Stenosis

Gastroenterology (12%) Core Clinical Conditions

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Definition Aetiology Pathophysiology Sign and Symptoms Investigations Management

Pyloric stenosis, also known as infantile hypertrophic pyloric stenosis (IHPS), is a medical condition that affects babies, specifically newborns up to six months old. It is characterised by the narrowing of the pylorus, which is the opening between the stomach and the small intestine. This narrowing restricts the passageway of food, leading to various symptoms and complications if left untreated.

Genetic Factors: There is evidence to suggest that genetic factors play a significant role in the development of pyloric stenosis. The condition tends to run in families, indicating a genetic predisposition. Studies have identified multiple genetic variations associated with pyloric stenosis, particularly in genes related to muscle development. These variants may affect the functionality and coordination of the muscles around the pylorus, leading to thickening and narrowing of the passage.
Sex and Age: Pyloric stenosis is more commonly observed in males than females, with males being four times more likely to develop the condition. Typically, pyloric stenosis manifests itself during the first few weeks of a baby's life, usually between the second and eighth weeks. Although the exact reasons for male predilection and age distribution remain unclear, it suggests that hormonal and developmental factors might contribute to its onset.
Maternal Factors: Various maternal factors have been identified as potential risk factors for pyloric stenosis. For example, there is an increased risk if the mother had pyloric stenosis herself during infancy. Certain medications, such as macrolide antibiotics (e.g., erythromycin), taken during pregnancy have also been linked to an elevated risk of the infant developing pyloric stenosis. However, the overall contribution of maternal factors to the development of pyloric stenosis is still not fully understood.
Environmental Factors: Some studies have proposed environmental factors as potential contributors to pyloric stenosis. For instance, there is some evidence suggesting an association with bottle-feeding and the consumption of specific infant formulas. However, these findings remain controversial, and further research is needed to establish a definitive link between environmental factors and the development of pyloric stenosis.

The pathophysiology of pyloric stenosis primarily revolves around hypertrophy and hyperplasia of the pyloric muscles. Although the exact cause is still unknown, several factors contribute to the development of this condition. One of the prevailing theories suggests that genetic predisposition plays a significant role, as pyloric stenosis is known to run in families.
At birth, the pylorus contains smooth muscle cells that serve to regulate the passage of food from the stomach into the intestines. In pyloric stenosis, however, these smooth muscle cells undergo abnormal growth and proliferation. The precise mechanism behind this hypertrophic and hyperplastic response remains unclear, but it is thought to involve disruptions in genetic signalling pathways.
This excessive growth of smooth muscle cells ultimately leads to the thickening of the pyloric wall. As the muscle wall thickens, it narrows the lumen of the pylorus, making it progressively more difficult for food and fluid to pass through. Over time, this narrowing becomes severe enough to impede the normal function of the gastric outlet.
As a result, individuals with pyloric stenosis experience a range of symptoms. The hallmark symptom is projectile vomiting, which occurs shortly after feeding and is often forceful and persistent. This vomiting is a direct consequence of the gastric contents being unable to pass through the narrowed pylorus efficiently. As the condition progresses, affected individuals may experience weight loss, dehydration, and electrolyte imbalances.
If left untreated, pyloric stenosis can lead to more severe complications. The constant vomiting can cause dehydration and electrolyte disturbances, such as hypokalemia and hypochloremic metabolic alkalosis. Infants may exhibit signs of malnutrition and failure to thrive. Additionally, prolonged obstruction can result in gastric distension and gastric outlet obstruction, which may require emergency medical intervention.

1. Projectile Vomiting:
One of the most prominent signs of pyloric stenosis is projectile vomiting. Infants suffering from this condition typically vomit forcefully after feeding. The vomit may shoot out in a fountain-like manner and may travel a significant distance. Projectile vomiting occurs due to the obstruction caused by the narrowed pylorus, preventing the normal passage of food from the stomach. The vomiting episodes are often repeated after every feeding, becoming more frequent and forceful over time.
2. Persistent Hunger and Poor Weight Gain:
Since food cannot pass easily through the stomach in pyloric stenosis, affected infants can experience persistent hunger despite regular feeding. They may display signs of increased appetite, seemingly wanting to eat more frequently than usual. However, due to the blockage at the pylorus, nutrients aren't effectively reaching the intestines for absorption. As a result, infants with pyloric stenosis often have poor weight gain or may even lose weight gradually.
3. Abdominal Distention:
Pyloric stenosis can cause the stomach to enlarge due to the accumulation of undigested food. As a result, affected infants may have a visibly distended abdomen. This swelling typically occurs after feeding and can be accompanied by discomfort or colicky pain. Caregivers should be observant of any abnormal abdominal bloating and seek medical attention if noticed.
4. Decreased Urine Output:
In severe cases of pyloric stenosis, infants may experience decreased urine output. The reduced flow of food through the digestive system can lead to dehydration. Insufficient fluid intake combined with excessive vomiting can disturb the balance of fluids in the body, resulting in reduced urine production. Caregivers should monitor the frequency and amount of urine passed by the infant and consult a healthcare professional if abnormalities are noticed.
5. Visible Wave-Like Motion in the Abdomen:
By observing the abdomen of an infant with pyloric stenosis, it may be possible to detect a visible peristaltic wave. This wave-like motion occurs as the stomach muscles contract forcefully in an attempt to push food through the narrowed pylorus. The peristaltic wave can be observed moving from left to right across the upper abdomen, sometimes referred to as the "olive sign."

History and Physical Examination: The PA will take a detailed history, focusing on the infant's feeding patterns, vomiting episodes, and weight loss. Physical examination may reveal signs of dehydration, such as decreased skin turgor and dry mucous membranes. The presence of a palpable olive-shaped mass in the right upper abdomen, representing the hypertrophic pyloric muscle, is a classic finding in pyloric stenosis.
Ultrasound: Ultrasound is a key diagnostic tool for pyloric stenosis. It allows visualisation of the pylorus to measure its dimensions accurately. The ultrasound will show the thickened muscular wall of the pylorus and the narrowing of the channel. This examination aids in confirming the diagnosis and ruling out other gastrointestinal conditions.

Intravenous Fluids: Infants with pyloric stenosis usually require rehydration due to vomiting and fluid loss. Intravenous fluids help restore electrolyte balance and maintain hydration until surgical intervention or improvement in the condition.
Surgical Intervention: The mainstay of treatment for pyloric stenosis is a surgical procedure called a pyloromyotomy. This surgery involves making a small incision in the hypertrophied muscle to widen the passage and allow food to pass freely into the small intestine. It is a safe and effective procedure with a high success rate.

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