Hypertrophic pyloric stenosis (HPS)

• Progressive hypertrophy and hyperplasia of the circular muscle of the pylorus narrow the gastric outlet, so milk cannot pass into the duodenum and is vomited forcefully.
• Onset typically 2–8 weeks of age (most often 3–6 weeks); infants are normal at birth.
• Risk factors: male sex (about 4 times more common), firstborn, family history, and early macrolide exposure (oral erythromycin or azithromycin given to the infant in the first weeks of life).
• Because the obstruction is above the ampulla of Vater, vomitus contains no bile.
• Repeated loss of gastric acid (hydrogen and chloride ions) causes hypochloremic, hypokalemic metabolic alkalosis. The kidney conserves sodium in exchange for potassium and later hydrogen ions (paradoxical aciduria), deepening hypokalemia.

Hirschsprung disease (congenital aganglionic megacolon)

• Failure of neural crest cells to migrate to the distal bowel leaves a segment without ganglion cells (in the submucosal and myenteric plexuses). The aganglionic segment always begins at the internal anal sphincter and extends upward a variable distance — most often the rectosigmoid (short segment); occasionally the whole colon.
• The aganglionic bowel cannot relax or propel stool → functional obstruction; the normal bowel above it dilates (megacolon).
• More common in males; associated with Down syndrome and some other genetic syndromes and familial forms.
• The most dangerous complication is Hirschsprung-associated enterocolitis (HAEC) — stasis, bacterial overgrowth, and mucosal inflammation that can progress to sepsis, perforation, and death. It can occur before or after surgery.

Anorectal malformation (imperforate anus) — the main look-alike in a newborn who passes no meconium

• A spectrum of congenital defects of the distal anus and rectum that may also involve the urinary and genital tracts; about 1 in 5,000 live births.
• The rectum ends without a normal anal opening. It may end blindly or open through an abnormal tract (fistula) to the perineum, to the urethra or bladder neck in boys, or to the vestibule in girls. In a cloaca (girls), the rectum, vagina, and urinary tract join in one common channel.
• Often occurs with other anomalies: part of the VACTERL association (vertebral, anal, cardiac, tracheoesophageal fistula, renal, limb); genitourinary defects in about half of affected infants; tethered spinal cord in about a quarter.

Pyloric stenosis

• Projectile, nonbilious vomiting shortly after feeding, becoming more frequent and forceful over days
• Hungry immediately after vomiting ("hungry vomiter") — distinguishes it from illness-related vomiting
• Weight loss or poor gain, fewer wet diapers, dehydration (sunken fontanel, dry mucous membranes, lethargy, tachycardia)
• Palpable firm, mobile, olive-shaped mass in the epigastrium or right upper quadrant — easiest to feel when the stomach is empty and the infant relaxed
• Visible gastric peristaltic waves moving left to right across the upper abdomen after feeding
• Vomitus may be coffee-ground if gastritis develops (not normal — report it)

Hirschsprung disease

• Newborn: failure to pass meconium within the first 24–48 hours (the most important early clue), abdominal distension, bilious vomiting, feeding refusal
• Digital rectal examination: tight anal canal and empty rectum, followed by an explosive release of gas and stool ("squirt" sign)
• Older infant or child: chronic constipation dating from birth, ribbon-like, foul-smelling stools, abdominal distension, poor growth; unlike functional constipation, stool soiling (encopresis) is uncommon and the rectum is empty
• HAEC: fever, explosive foul-smelling (sometimes bloody) diarrhea, abdominal distension, lethargy, vomiting, signs of shock

Anorectal malformation — newborn perineal inspection

• No anal opening in the normal place, or a small misplaced opening, seen on the first newborn examination
• Meconium often does not appear at the perineum until at least 16–24 hours, because abdominal pressure must build before it is pushed through a fistula; a clean perineum at birth does not yet show the type of defect
• Signs of a low defect (perineal fistula): meconium on the perineum, a "bucket-handle" skin bridge at the anal dimple, an anal membrane with meconium visible behind it, or (in boys) a midline raphe filled with meconium that looks like a dark ribbon
• Flat bottom (no midline gluteal fold and no anal dimple): very poor perineal muscles, usually a high defect, managed with a colostomy first
• Meconium in the urine in a boy points to a recto-urinary fistula
• Girls: the most common defect is a rectovestibular fistula (normal urethra and vagina plus a third opening in the vestibule). A single perineal opening means a cloaca; a lower abdominal mass may be a distended vagina (hydrocolpos)

Anorectal malformation vs. Hirschsprung disease

Because ultrasound now detects HPS early, many infants have normal electrolytes at diagnosis; classic alkalosis indicates longer-standing vomiting.

Anorectal malformation: every affected newborn needs an abdominal and pelvic ultrasound to look for urinary tract defects, plus urinalysis for meconium. If no clinical sign shows the level of the defect by 24 hours, a cross-table lateral radiograph (prone, pelvis elevated, marker on the perineum) shows how far the rectal air column lies from the skin. Spinal imaging looks for tethered cord and sacral defects.

Pyloric stenosis — not a surgical emergency; a medical emergency first

• Correct dehydration and electrolytes before surgery. Isotonic fluid boluses (commonly normal saline 20 mL/kg) if dehydrated, then maintenance dextrose-saline solution with potassium chloride added only after urine output is confirmed.
• Surgery waits until chloride and bicarbonate normalize: uncorrected alkalosis depresses respiratory drive and increases the risk of postoperative apnea.
• NPO; nasogastric decompression if vomiting persists or per surgeon.
• Pyloromyotomy (Ramstedt, usually laparoscopic): the hypertrophied muscle is split lengthwise down to the mucosa; the mucosa is not opened. Cure is expected.
• Postoperative feeding usually begins within hours; many centers use ad libitum feeding with breast milk or formula rather than slow glucose-water advancement, which is not required. Some vomiting in the first 24–48 hours is common.

Potassium chloride safety: never give IV push or bolus; use an infusion pump; add to fluids only after the infant voids; follow maximum concentration and rate limits for peripheral lines; monitor serum potassium and ECG changes; watch for IV site irritation and infiltration.

Hirschsprung disease

• Decompression before surgery: gentle rectal irrigations with warm normal saline (never plain tap water — risk of water intoxication and hyponatremia; avoid hypertonic phosphate enemas in infants — hyperphosphatemia and hypocalcemia).
• Definitive surgery — pull-through procedure (e.g., transanal endorectal, Soave, Duhamel, Swenson): the aganglionic bowel is removed and normal ganglionated bowel is brought down to the anus. Often done as a single stage in infancy.
• Staged approach with a temporary colostomy or ileostomy (placed in normally innervated bowel) for infants who are very ill, have enterocolitis, severe dilation, or long-segment disease; the stoma is closed after the pull-through.
• HAEC treatment: NPO, IV fluids, nasogastric decompression, rectal saline irrigations, and IV broad-spectrum antibiotics including anaerobic coverage (e.g., metronidazole — nausea, metallic taste, rarely neurotoxicity with prolonged use; avoid alcohol-containing products). Severe cases need a diverting stoma.
• Postoperative bowel problems (constipation, soiling, recurrent enterocolitis) are managed with bowel programs, dilations, or further surgery.

Anorectal malformation — initial care

• After birth: IV line for fluids and antibiotics and a nasogastric tube to keep the stomach decompressed and prevent vomiting and aspiration
• The surgeon watches the perineum and urine for 16–24 hours before deciding: a newborn anoplasty for a perineal fistula, or a colostomy for higher defects and recto-urinary fistulas, with definitive posterior sagittal repair later
• The usual colostomy is a descending colostomy with two separate stomas: the proximal stoma passes stool; the distal stoma (mucous fistula) drains only small amounts of mucus

Analgesia (all conditions): acetaminophen (weight-based dose; count all sources; hepatotoxicity) and opioids when needed (respiratory depression — infants after pyloromyotomy are at increased risk of apnea; monitor SpO₂ and respiratory rate continuously).

Listed in priority order.

1. Airway and aspiration — position the vomiting infant on the side or with head elevated; keep suction ready; monitor for postoperative apnea (pulse oximetry and apnea monitoring)
2. Fluid and electrolyte balance
   • Strict intake and output, weigh diapers, daily weight, urine specific gravity if ordered
   • Monitor electrolytes, glucose, and acid–base results; confirm voiding before potassium
   • Assess vital signs for tachycardia, tachypnea, hypotension, prolonged capillary refill (dehydration or shock)
3. Recognize HAEC early — fever, explosive diarrhea, distension, lethargy: notify the provider immediately
4. Pyloric stenosis care
   • Document the timing, character, and volume of vomiting (projectile? bile-free?)
   • After surgery, advance feeds as ordered; feed slowly, burp often, keep upright after feeds
   • Assess incisions for redness, drainage; report fever or persistent vomiting beyond the first days
5. Hirschsprung care
   • Measure abdominal girth at the same marked location at regular intervals
   • Perform saline irrigations as ordered; record returns
   • No rectal temperatures, suppositories, or rectal tubes after a pull-through unless the surgeon orders them
   • Stoma care: stoma should be red, moist, and slightly raised; report dusky, pale, or black color, retraction, prolapse, or bleeding; protect peristomal skin with barrier products; empty the pouch when one-third to one-half full
   • After pull-through: frequent stools cause perianal skin breakdown — gentle cleansing, barrier cream, open-air time
6. Anorectal malformation care
   • Inspect the perineum at the first newborn assessment; report a missing or misplaced anal opening at once
   • Record where and when meconium appears (perineum, urine, vestibule) — this guides the surgical decision
   • Keep the nasogastric tube patent and IV fluids running as ordered; report abdominal distension or vomiting
   • After a colostomy, care for both stomas as described above
7. Nutrition — adequate calories for growth; age-appropriate diet with fluids after recovery
8. Family support — reassure parents that pyloric stenosis is not caused by their feeding technique; teach ostomy and irrigation skills with return demonstration

Pyloric stenosis

• Some spitting up in the first days after surgery is common; call for forceful or persistent vomiting, vomit with bile (green) or blood, fever, redness or drainage at the incisions, fewer wet diapers
• Feed small amounts frequently at first, burp often, hold upright after feeds
• Keep incisions clean and dry; routine immunizations continue

Hirschsprung disease

• Enterocolitis can occur even after successful surgery — seek care immediately for fever, foul-smelling explosive diarrhea, swollen abdomen, vomiting, or lethargy
• Ostomy care, pouch changes, and skin protection; signs of stoma problems
• If saline irrigations are prescribed at home, use only warm normal saline in the prescribed volume and technique; never tap water
• Expect some constipation or soiling after pull-through; follow the bowel program; encourage fluids and a balanced diet with fiber as tolerated
• Toilet training may take longer; provide a positive, patient approach
• Genetic counseling for future pregnancies

• Pyloric stenosis: 2–8 weeks, male, firstborn; projectile nonbilious vomiting, hungry after vomiting
• Exam: olive-shaped mass in the epigastrium/RUQ, visible peristaltic waves
• Labs: hypochloremic, hypokalemic metabolic alkalosis
• Diagnosis: ultrasound; treatment: pyloromyotomy after fluid and electrolyte correction
• Add potassium only after urine output; never IV push
• Hirschsprung: absent ganglion cells → functional obstruction; associated with Down syndrome
• Newborn clue: no meconium in 24–48 hours, distension, bilious vomiting; DRE → explosive stool
• Older child: ribbon-like foul stools, chronic constipation, no soiling
• Definitive diagnosis: rectal biopsy; treatment: pull-through (± temporary ostomy)
• Enterocolitis (fever, explosive diarrhea, distension) is an emergency before and after surgery
• Irrigations: normal saline, never tap water; no rectal temperatures after pull-through
• Measure abdominal girth consistently
• Imperforate anus: no normal anal opening on inspection (Hirschsprung has a normal anus); meconium may take 16–24 hours to appear through a fistula; IV fluids, antibiotics, NG decompression; screen for VACTERL and urinary defects