Pyloric stenosis seems to be multifactorial, with some genetic and some environmental components. It is four times more likely to occur in males, and is also more common in the first born. Rarely, infantile pyloric stenosis can occur as an autosomal dominant condition.

It is uncertain whether it is a congenital anatomic narrowing or a functional hypertrophy of the pyloric sphincter muscle.

Males are more commonly affected than females, with firstborn males affected about four times as often, and there is a genetic predisposition for the disease. It is commonly associated with people of Scandinavian ancestry, and has multifactorial inheritance patterns. Pyloric stenosis is more common in Caucasians than Hispanics, Blacks, or Asians. The incidence is 2.4 per 1000 live births in Caucasians, 1.8 in Hispanics, 0.7 in Blacks, and 0.6 in Asians. It is also less common amongst children of mixed race parents. Caucasian male babies with blood type B or O are more likely than other types to be affected.

Infants exposed to erythromycin are at increased risk for developing hypertrophic pyloric stenosis, especially when the drug is taken around two weeks of life and possibly in late pregnancy and through breastmilk in the first two weeks of life.

The exact causes are not known. It is not associated with a particular gene, but there is some evidence of recurrence in families.

Fetal and neonatal intestinal atresia are treated using laparotomy after birth. If the area affected is small, the surgeon may be able to remove the damaged portion and join the intestine back together. In instances where the narrowing is longer, or the area is damaged and cannot be used for period of time, a temporary stoma may be placed.

Approximately 20–40 percent of all infants with duodenal atresia have Down syndrome. . Approximately 8% of infants with Down syndrome have duodenal atresia.

The most common cause of non-duodenal intestinal atresia is a vascular accident in utero that leads to decreased intestinal perfusion and ischemia of the respective segment of bowel. This leads to narrowing, or in the most severe cases, complete obliteration of the intestinal lumen.

In the case that the superior mesenteric artery, or another major intestinal artery, is occluded, large segments of bowel can be entirely underdeveloped. Classically, the affected area of bowel assumes a spiral configuration and is described to have an "apple peel" like appearance; this is accompanied by lack of a dorsal mesentery.

Ileal atresia can also result as a complication of meconium ileus.

This can lead to a number of disease manifestations such as:

- Acute midgut volvulus

- Chronic midgut volvulus

- Acute duodenal obstruction

- Chronic duodenal obstruction

- Internal herniation

- Superior mesenteric artery syndrome

Delay in the diagnosis of SMA syndrome can result in fatal catabolysis (advanced malnutrition), dehydration, electrolyte abnormalities, hypokalemia, acute gastric rupture or intestinal perforation (from prolonged mesenteric ischemia), gastric distention, spontaneous upper gastrointestinal bleeding, hypovolemic shock, and aspiration pneumonia.

A 1-in-3 mortality rate for Superior Mesenteric Artery syndrome has been quoted by a small number of sources. However, after extensive research, original data establishing this mortality rate has not been found, indicating that the number is likely to be unreliable. While research establishing an official mortality rate may not exist, two recent studies of SMA syndrome patients, one published in 2006 looking at 22 cases and one in 2012 looking at 80 cases, show mortality rates of 0% and 6.3%, respectively. According to the doctors in one of these studies, the expected outcome for SMA syndrome treatment is generally considered to be excellent.

Early treatment includes removing fluids from the stomach via a nasogastric tube, and providing fluids intravenously. The definitive treatment for duodenal atresia is surgery (duodenoduodenostomy), which may be performed openly or laparoscopically. The surgery is not urgent. The initial repair has a 5 percent morbidity and mortality rate.

With early intervention, morbidity and mortality of cases of intestinal obstruction is low. The outcome is in part dependent upon congenital comorbidities and delays in diagnosis and management.

Subglottic stenosis is a congenital or acquired narrowing of the subglottic airway. Although it is relatively rare, it is the third most common congenital airway problem (after laryngomalacia and vocal cord paralysis). Subglottic stenosis can present as a life-threatening airway emergency. It is imperative that the otolaryngologist be an expert at dealing with the diagnosis and management of this disorder. Subglottic stenosis can affect both children and adults.

Subglottic stenosis can be of three forms, namely congenital subglottic stenosis, idiopathic subglottic stenosis (ISS) and acquired subglottic stenosis. As the name suggests, congenital subglottic stenosis is a birth defect. Idiopathic subglottic stenosis is a narrowing of the airway due to an unknown cause. Acquired subglottic stenosis generally follows as an after-effect of airway intubation, and in extremely rare cases as a result of gastroesophageal reflux disease (GERD).

Subglottic stenosis is graded according to the Cotton-Meyer classification system from one to four based on the severity of the blockage.

Grade 1 – <50% obstruction

Grade 2 – 51–70% obstruction

Grade 3 – 71–99% obstruction

Grade 4 – no detectable lumen

Treatments to alleviate the symptoms of subglottic stenosis includes a daily dose of steroids such as prednisone, which reduces the inflammation of the area for better breathing. Other medications such as Methotrexate is also being tested by patients but results are pending.

The resulting syndrome depends on the structure affected.

Examples of vascular stenotic lesions include:

- Intermittent claudication (peripheral artery stenosis)

- Angina (coronary artery stenosis)

- Carotid artery stenosis which predispose to (strokes and transient ischaemic episodes)

- Renal artery stenosis

The types of stenoses in heart valves are:

- Pulmonary valve stenosis, which is the thickening of the pulmonary valve, therefore causing narrowing

- Mitral valve stenosis, which is the thickening of the mitral valve (of the left heart), therefore causing narrowing

- Tricuspid valve stenosis, which is the thickening of the tricuspid valve (of the right heart), therefore causing narrowing

- Aortic valve stenosis, which is the thickening of the aortic valve, therefore causing narrowing

Stenoses/strictures of other bodily structures/organs include:

- Pyloric stenosis (gastric outflow obstruction)

- Lumbar, cervical or thoracic spinal stenosis

- Subglottic stenosis (SGS)

- Tracheal stenosis

- Obstructive jaundice (biliary tract stenosis)

- Bowel obstruction

- Phimosis

- Non-communicating hydrocephalus

- Stenosing tenosynovitis

- Atherosclerosis

- Esophageal stricture

- Achalasia

- Prinzmetal angina

- Vaginal stenosis

A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure. It is also sometimes called a stricture (as in urethral stricture).

Stricture as a term is usually used when narrowing is caused by contraction of smooth muscle (e.g., achalasia, prinzmetal angina); stenosis is usually used when narrowing is caused by lesion that reduces the space of lumen (e.g., atherosclerosis). The term coarctation is another synonym, but is commonly used only in the context of aortic coarctation.

Restenosis is the recurrence of stenosis after a procedure. The term is from Ancient Greek στενός, "narrow".

SMA syndrome is extremely rare, evident in only 0.3% of upper-gastrointestinal-tract barium studies. However, unfamiliarity with this condition in the medical community coupled with its intermittent and nonspecific symptomatology probably results in its underdiagnosis.

As the syndrome involves a lack of essential fat, more than half of those diagnosed are underweight, sometimes to the point of sickliness and emaciation. Females are impacted more often than males, and while the syndrome can occur at any age, it is most frequently diagnosed in early adulthood. The most common co-morbid conditions include mental and behavioral disorders including eating disorders and depression, infectious diseases including tuberculosis and acute gastroenteritis, and nervous system diseases including muscular dystrophy, Parkinson's disease, and cerebral palsy.

Pancreaticobiliary maljunction is a congenital malformation, in which the pancreatic and bile ducts join anatomically outside the duodenal wall, forming a markedly long common channel. This anomaly prevents normal control by the sphincter of Oddi located in the duodenal wall, allowing regurgitation of pancreatic juices into the biliary tract and possibly leading to a higher probability of pancreaticobiliary cancers.

Medication (to prevent spasms) or Sphincterotomy (surgical procedure to cut the muscle) are the standard treatments for sphincter of Oddi dysfunction. One or the other may be better based on the classification of the condition.

The diagnosis is suspected based on polyhydramnios in uteru, bilious vomiting, failure to pass meconium in the first day of life, and abdominal distension. The presentations of NBO may vary. It may be subtle and easily overlooked on physical examination or can involve massive abdominal distension, respiratory distress and cardiovascular collapse. Unlike older children, neonates with unrecognized intestinal obstruction deteriorate rapidly.

Sphincter of Oddi dysfunction may be suggested by pain which seems to come from a biliary origin, which may or may not be associated with transient increases of liver or pancreatic enzymes. Common bile duct dilation and episodes of pancreatitis are also signs.

Laryngotracheal stenosis refers to abnormal narrowing of the central air passageways. This can occur at the level of the larynx, trachea, carina or main bronchi.

In a small number of patients narrowing may be present in more than one anatomical location.

Frisch & Simonsen (2016) carried out a very large scale study in Denmark, which compared the incidence of meatal stenosis in Muslim males (mostly circumcised) with the incidence of meatal stenosis in ethnic Danish males (mostly non-circumcised). The risk of meatal stenosis in circumcised males was found to be as much 3.7 times higher than in the intact, non-circumcised males.

If untreated, severe symptomatic aortic stenosis carries a poor prognosis with a 2-year mortality rate of 50-60% and a 3-year survival rate of less than 30%. Prognosis after aortic valve replacement for people who are younger than 65 is about five years less than that of the general population; for people older than 65 it is about the same.

The epidemiology of pulmonary valve stenosis can be summed up by the congenital aspect which is the majority of cases, in broad terms PVS is rare in the general population.

Laryngotracheal stenosis is an umbrella term for a wide and heterogeneous group of very rare conditions. The population incidence of adult post-intubation laryngotracheal stenosis which is the commonest benign sub-type of this condition is approximately 1 in 200,000 adults per year. The main causes of adult laryngotracheal stenosis are:

A left ventricular outflow tract obstruction (LVOTO) may be due to a defect in the aortic valve, or a defect located at the subvalvar or supravalvar level.

- Aortic valve stenosis

- Supravalvar aortic stenosis

- Coarctation of the aorta

- Hypoplastic left heart syndrome

A right ventricular outflow tract obstruction (RVOTO) may be due to a defect in the pulmonic valve, the supravalvar region, the infundibulum, or the pulmonary artery.

- Pulmonary atresia

- Pulmonary valve stenosis

- Hypoplastic right heart syndrome

- Tetralogy of Fallot