Babies with this condition usually present any time in the first weeks to months of life with progressively worsening vomiting. The vomiting is often described as non-bile stained ("non bilious") and "projectile vomiting", because it is more forceful than the usual spittiness (gastroesophageal reflux) seen at this age. Some infants present with poor feeding and weight loss but others demonstrate normal weight gain. Dehydration may occur which causes a baby to cry without having tears and to produce less wet or dirty diapers due to not urinating for hours or for a few days. Symptoms usually begin between 3 to 12 weeks of age. Findings include epigastric fullness with visible peristalsis in the upper abdomen from the person's left to right. Constant hunger, belching, and colic are other possible signs that the baby is unable to eat properly.

Pyloric stenosis is a narrowing of the opening from the stomach to the first part of the small intestine (the pylorus). Symptoms include projectile vomiting without the presence of bile. This most often occurs after the baby is fed. The typical age that symptoms become obvious is two to twelve weeks old.

The cause of pyloric stenosis is unclear. Risk factors in babies include birth by cesarean section, preterm birth, bottle feeding, and being first born. The diagnosis may be made by feeling an olive-shaped mass in the baby's abdomen. This is often confirmed with ultrasound.

Treatment initially begins by correcting dehydration and electrolyte problems. This is then typically followed by surgery. Results are generally good both in the short term and in the long term. Some treat the condition without surgery by using atropine.

About one to two per thousand babies are affected. Males are affected about four times more often than females. The condition is very rare in adults. The first description of pyloric stenosis was in 1888 with surgery management first carried out in 1912 by Conrad Ramstedt. Before surgical treatment most babies died.

The diagnosis of duodenal atresia is usually confirmed by radiography. An X-ray of the abdomen shows two large air filled spaces, the so-called "double bubble" sign. The air is trapped in the stomach and proximal duodenum, which are separated by the pyloric sphincter, creating the appearance of two bubbles visible on x-ray. Since the closure of the duodenum is complete in duodenal atresia, no air is seen in the distal duodenum.

Atresias occurring distal to the duodenum are usually caused by vascular accidents or ischemic insult, such as jejunoileal atresia.

Prognosis is usually very good, although complications are more likely to occur when there are serious congenital anomalies. Late complications may occur in about 12 percent of patients with duodenal atresia, and the mortality rate for these complications is 6 percent.

The main symptom is vomiting, which typically occurs after meals of undigested food, devoid of any bile. A history of previous peptic ulcers and loss of weight is not uncommon. In advanced cases, signs to look for on physical examination are wasting and dehydration. Visible peristalsis from left to right may be present. Succussion splash is a splash-like sound heard over the stomach in the left upper quadrant of the abdomen on shaking the patient, with or without the stethoscope. Bowel sound may be increased due to excessive peristaltic action of stomach. Fullness in left hypochondrium may also be present.

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.

Gastric outlet obstruction (GOO) is a medical condition where there is an obstruction at the level of the pylorus, which is the outlet of the stomach. Individuals with gastric outlet obstruction will often have recurrent vomiting of food that has accumulated in the stomach, but which cannot pass into the small intestine due to the obstruction. The stomach often dilates to accommodate food intake and secretions. Causes of gastric outlet obstruction include both benign causes (such as peptic ulcer disease affecting the area around the pylorus), as well as malignant causes, such as gastric cancer.

Causation related to ulcers may involve severe pain which the patient may interpret as a heart condition/attack.

Treatment of the condition depends upon the underlying cause; it can involve antibiotic treatment when Helicobacter pylori is related to an ulcer, endoscopic therapies (such as dilation of the obstruction with balloons or the placement of self expandable metallic stents), other medical therapies, or surgery to resolve the obstruction.

Gastric atresia is the complete occlusion of the pyloric outlet of the stomach and is an extremely rare event.

Stenoses of the vascular type are often associated with unusual blood sounds resulting from turbulent flow over the narrowed blood vessel. This sound can be made audible by a stethoscope, but diagnosis is generally made or confirmed with some form of medical imaging.

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

Functional disorders of the gallbladder, bile duct and pancreas have been defined and classified by the Rome criteria for functional gastrointestinal disorders. The criteria outline three variants of functional disorders of the gallbladder, bile duct and pancreas, termed "functional gallbladder disorder", "functional biliary sphincter of Oddi disorder" and "functional pancreatic sphincter of Oddi disorder". All of the following criteria need to be met for as part of the definition of a functional disorder of the gallbladder:

- the pain must be located in the upper part of the abdomen and/or the right upper quadrant of the abdomen

- episodes of pain must last at least 30 minutes

- the symptoms must be recurrent, and occur at differing intervals

- the pain must incrementally increase to a "steady level"

- the pain must be severe enough the patient's daily activities are affected, or that the patient must attend the emergency department

- the pain must not be relieved by any of bowel movements, change in posture, or antacids; and,

- other structural disorders that could explain the symptoms must be excluded.

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.

Individuals are classified as having a functional gallbladder disorder if the above criteria are met, if the gallbladder is present, and if the testing of liver enzymes, conjugated bilirubin, and pancreatic enzymes (amylase and lipase) are normal.

The most common symptom of laryngotracheal stenosis is gradually-worsening breathlessness (dyspnea) particularly when undertaking physical activities (exertional dyspnea). The patient may also experience added respiratory sounds which in the more severe cases can be identified as stridor but in many cases can be readily mistaken for wheeze. This creates a diagnostic pitfall in which many patients with laryngotracheal stenosis are incorrectly diagnosed as having asthma and are treated for presumed lower airway disease. This increases the likelihood of the patient eventually requiring major open surgery in benign disease and can lead to tracheal cancer presenting too late for curative surgery to be performed.

Most damage to the pyloric valve occurs as a complication of gastric surgery. Other causes of biliary reflux may be:

- Peptic ulcer

- Gallbladder surgery (cholecystectomy)

A significant fraction of cases are idiopathic, with no identified specific etiology.

Many of the signs and symptoms of aqueductal stenosis are similar to those of hydrocephalus. These typical symptoms include: headache, nausea and vomiting, cognitive difficulty, sleepiness, seizures, balance and gait disturbances, visual abnormalities, and incontinence.

- Headache may be a result of the raised intracranial pressure from the disrupted flow of CSF, and sometimes this symptom may come on suddenly as a “thunderclap headache”.

- In children, cognitive difficulty and developmental delay have been seen in a range of severities. Mild developmental delay is characterized by motor and neurological development that is no greater than 2 standard deviations below average for the age of the child, and moderate delay is characterized by greater than 2 standard deviations below. A child with severe delay may be unable to use spoken language or control movement or interact with others, and can behave abusively towards themselves.

- A patient's level of consciousness may also deteriorate with time, and this can lead to coma or death.

- The visual abnormalities previously mentioned include “upward gaze palsy”, where a person has difficulty looking up.

- Tremors have also been reported as a symptom, but are not as common as these previously mentioned.

Signs of aqueductal stenosis other than those mentioned in “Causes of stenosis” include detection of an enlarged lateral and third ventricle in conjunction with a smaller fourth ventricle. This variation in ventricle size is indicative of a blockage in the aqueduct because it lies between the third and fourth ventricles. Another sign of stenosis is deformation of the midbrain, which can be severe. This is caused by the pressure gradient formed from a blockage in the aqueduct.

Biliary reflux, bile reflux or duodenogastric reflux is a condition that occurs when bile flows upward (refluxes) from the duodenum into the stomach and esophagus.

Biliary reflux can be confused with acid reflux, also known as gastroesophageal reflux disease (GERD). While bile reflux involves fluid from the small intestine flowing into the stomach and esophagus, acid reflux is backflow of stomach acid into the esophagus. These conditions are often related, and differentiating between the two can be difficult.

Bile is a digestive fluid made by the liver, stored in the gallbladder, and discharged into duodenum after food is ingested to aid in the digestion of fat. Normally, the pyloric sphincter prevents bile from entering the stomach. When the pyloric sphincter is damaged or fails to work correctly, bile can enter the stomach and then be transported into the esophagus as in gastric reflux. The presence of small amounts of bile in the stomach is relatively common and usually asymptomatic, but excessive refluxed bile causes irritation and inflammation.

Aqueductal stenosis is a narrowing of the aqueduct of Sylvius which blocks the flow of cerebrospinal fluid (CSF) in the ventricular system. Blockage of the aqueduct can lead to hydrocephalus, specifically as a common cause of congenital and/or obstructive hydrocephalus.

The aqueduct of Sylvius is the channel which connects the third ventricle to the fourth ventricle and is the narrowest part of the CSF pathway with a mean cross-sectional area of 0.5 mm in children and 0.8 mm in adults. Because of its small size, the aqueduct is the most likely place for a blockage of CSF in the ventricular system. This blockage causes ventricle volume to increase because the CSF cannot flow out of the ventricles and cannot be effectively absorbed by the surrounding tissue of the ventricles. Increased volume of the ventricles will result in higher pressure within the ventricles, and cause higher pressure in the cortex from it being pushed into the skull. A person may have aqueductal stenosis for years without any symptoms, and a head trauma, hemorrhage, or infection could suddenly invoke those symptoms and worsen the blockage.

Anal stricture or anal stenosis is a narrowing of the anal canal. It can be caused by a number of surgical procedures including: hemorrhoid removal and following anorectal wart treatment.

Urethral meatal stenosis or urethral stricture is a narrowing (stenosis) of the opening of the urethra at the external meatus , thus constricting the opening through which urine leaves the body from the urinary bladder.

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

Cardiac anomalies are the most common congenital malformation in individuals with tetrasomy 18p. However, there is no pathognomatic heart defect associated with the condition. Patent ductus arteriosus is the most common defect. Septal defects (ventricular septal defects and atrial septal defects) are also common, as are patent foramina ovalia. Other cardiac anomalies include mitral valve regurgitation, mitral valve prolapse, bicuspid pulmonary valve, hypoplastic transverse aortic arch, tricuspid valve regurgitation, right ventricular hypertrophy, and pulmonic stenosis.

In males, cryptorchidism is common. Abnormal genitalia in females is not a common feature. Renal abnormalities have been reported in a minority of patients. Horseshoe kidney and bladder diverticuli have been reported. Other abdominal malformations, including pyloric stenosis and hernias, have also been reported, though they are present in only a minority of patients.

Orthopedic anomalies also occur relatively frequently, with hip dysplasia being the most common orthopedic issue. Clubfoot and rocker bottom feet have also been reported.

Myelomeningocele is another known feature associated with tetrasomy 18p.

Neonatal complications (apart from congenital anomalies) are common. In a paper published in 2010, 41 of 42 individuals had some type medical problem in the first days of life, the most common being feeding difficulties. Respiratory difficulty and jaundice are also relatively frequent.

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

Supravalvular aortic stenosis is a congenital obstructive narrowing of the aorta just above the aortic valve. It is often associated with other cardiovascular anomalies and is one of the characteristic findings of Williams syndrome. The diagnosis can be made by echocardiography or MRI.