Pyloric Stenosis


Summary 1) First Aid: USMLE Step 1 by Tao Le

Pyloric stenosis is of idiopathic etiology and develops as a result of congenital elongation and thickening of the pylorus, which in turn results in obstruction of the gastric outlet.

Pathophysiology 2) Wikipedia

String sign

The gastric outlet obstruction due to the hypertrophic pylorus impairs emptying of gastric contents into the duodenum. As a consequence, all ingested food and gastric secretions can only exit via vomiting, which can be of a projectile nature. While the exact cause of the hypertrophy remains unknown, Rogers has assembled compelling evidence that neonatal hyperacidity is involved.

This physiological explanation for the development of clinical pyloric stenosis at around 4 weeks and its spontaneous long term cure without surgery if treated conservatively, has recently been further reviewed. The vomited material does not contain bile because the pyloric obstruction prevents entry of duodenal contents (containing bile) into the stomach.

Persistent vomiting results in loss of stomach acid (hydrochloric acid). The chloride loss results in a low blood chloride level which impairs the kidney’s ability to excrete bicarbonate. This is the significant factor that prevents correction of the alkalosis.

A secondary hyperaldosteronism develops due to the decreased blood volume. The high aldosterone levels causes the kidneys to avidly retain Na+ (to correct the intravascular volume depletion), and excrete increased amounts of K+ into the urine (resulting in a low blood level of potassium). The body’s compensatory response to the metabolic alkalosis is hypoventilation resulting in an elevated arterial pCO2.

Causes 3) USMLE Step 1 Secrets by Thomas Brown

  • Genetics

Symptoms 4)First Aid: USMLE Step 1 by Tao Le5)Fundamentals of Pathology by Hussain Sattar

  • Difficulty feeding followed by projectile, nonbilious vomiting
  • Visible peristalsis 
  • Olive-like mass in the abdomen

Pyloric Stenosis: Ultrasound of the abdomen

Diagnosis 6) First Aid: USMLE Step 1 by Tao Le

  • Phvsical exam – classically shows a palpable mass (described as an “olive”) in the epigastric region. 
  • Lab tests – hvpochloremic, metabolic alkalosis secondary to loss of IIC1 in emesis and hypokalemia late in presentation.
  • Ultrasound – shows an elongalcd and liypertrophic pylorus 
  • Barium studies – String sign: Seen on barium swallow when barium moves through the Pylorus, Shoulder sign: Ihe pvlorus bulges into the antrum oflhe stomach, Double tract sign: Parallel streaks of barium seen in the narrow pvlorus.

Treatment 7) First Aid: USMLE Step 1 by Tao Le

  • Correction of lab abnormalities and hydration status prior to surgery 
  • Pyloromyotomy – longitudinal incision through the muscle of the pylorus with dissection lo the submucosa is definitive therapy

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