52. Anterior abdominal wall, hernias in general and congenital abdominal wall defects

1. Definition

• Hernia → abnormal protrusion of a viscus, or part of it, through a defect in the wall of the cavity that contains it
• External abdominal hernia → through the abdominal wall (groin, umbilicus, incision)
• Internal hernia → into a pocket or opening inside the abdomen
• Congenital abdominal wall defect → failure of the abdominal wall to close in the fetus: exomphalos (omphalocele) and gastroschisis

2. Epidemiology

• Hernias → about 5% of people; lifetime risk of a groin hernia 27–43% in men, 3–6% in women
• Frequency → inguinal (about 75%), then incisional, umbilical, femoral
• Groin hernias → third commonest cause of bowel obstruction in the West (after adhesions and cancer); commonest in many low-income countries
• Exomphalos → about 1 in 5,000–7,000 births
• Gastroschisis → about 1 in 4,000–7,000 births, rising; young mothers, smoking, drugs

3. Aetiology and risk factors

Anatomy of the anterior abdominal wall (revision)

• Layers from outside in:
  1. Skin
  2. Subcutaneous fat → Camper's (fatty) and Scarpa's (membranous) fascia below the umbilicus
  3. External oblique → fibres "hands in pockets"; aponeurosis forms the inguinal ligament
  4. Internal oblique
  5. Transversus abdominis
  6. Transversalis fascia
  7. Extraperitoneal fat
  8. Parietal peritoneum
• Rectus abdominis in the rectus sheath; linea alba in the midline; linea semilunaris at the lateral edge of rectus
• Arcuate line (about one-third of the way from umbilicus to pubis) → below it all aponeuroses pass in front of rectus; posterior sheath absent
• Blood supply → superior and inferior epigastric arteries (inside the sheath, behind rectus)
• Nerves → T7–T12, iliohypogastric and ilioinguinal (L1); run between internal oblique and transversus
• On the inside → median umbilical fold (urachus), medial folds (obliterated umbilical arteries), lateral folds (inferior epigastric vessels)

Causes of hernia

• Congenital → patent processus vaginalis (indirect inguinal), umbilical ring not closed
• Acquired → weak wall plus raised pressure:
  • Raised pressure → chronic cough, constipation, straining to pass urine (prostate), heavy lifting, obesity, pregnancy, ascites, peritoneal dialysis
  • Weak wall → age, smoking, collagen disorders (Ehlers-Danlos, Marfan's), previous incision, wound infection, nerve injury

Congenital wall defects

• Exomphalos → gut fails to return from the umbilical cord at week 10–12
• Gastroschisis → defect of the wall beside the cord, probably from a vascular accident

4. Pathogenesis

Parts of a hernia

1. Defect (orifice) in the wall
2. Sac → peritoneum: neck, body, fundus
3. Contents → omentum (omentocele), small bowel (enterocele), others
4. Coverings → layers of the wall pushed in front of the sac

Strangulation sequence

1. Tight neck compresses the contents
2. Venous and lymphatic return blocked → oedema
3. Pressure rises → arterial inflow stops
4. Ischaemia → gangrene → perforation → peritonitis, sepsis
5. Bowel can die within 6 hours

5. Classification

By site

• Groin → inguinal (indirect, direct), femoral
• Ventral → umbilical, paraumbilical, epigastric, Spigelian, incisional
• Lumbar (Petit's inferior triangle, Grynfeltt's superior triangle), obturator, perineal, sciatic
• Internal → paraduodenal, foramen of Winslow, diaphragmatic

By state

• Reducible → contents go back
• Irreducible (incarcerated) → cannot be reduced, adhesions or narrow neck; blood supply intact
• Obstructed → bowel lumen blocked; blood supply intact
• Strangulated → blood supply cut off → urgent surgery

Special hernias

• Richter's → only part of the bowel wall is trapped; can strangulate without obstruction
• Littré's → contains a Meckel's diverticulum
• Amyand's → appendix in an inguinal hernia
• De Garengeot's → appendix in a femoral hernia
• Sliding (hernia en glissade) → a retroperitoneal organ (colon, bladder) forms part of the sac wall
• Maydl's (W-hernia) → two loops in the sac; the middle loop inside the abdomen strangulates
• Pantaloon → direct and indirect together, either side of the inferior epigastric vessels

Congenital defects

• Exomphalos minor (< 5 cm, bowel only) and major (> 5 cm, liver too)

6. Clinical picture

Symptoms

• Lump that appears on standing or straining and goes away on lying down
• Dragging ache, worse at the end of the day
• Strangulation → sudden severe pain, tender, tense, irreducible lump, no cough impulse; colicky pain, vomiting, distension, no flatus

Signs

• Examine standing and lying, both sides
• Cough impulse, reducibility
• Strangulation → red, hot, tender lump; tachycardia, fever; signs of obstruction or peritonitis
• Look for causes → chest, abdomen (masses, ascites), prostate, scars

Newborn defects

• Exomphalos → central defect at the umbilicus; contents in a membrane sac (amnion and peritoneum); cord inserts into the sac
• Gastroschisis → defect right of the umbilicus; no sac; bowel thick, oedematous and matted from exposure to amniotic fluid; cord normal

7. Diagnosis

• Hernia → clinical in most
• Ultrasound → small or uncertain groin hernia, occult hernia
• CT → obese patients, incisional hernia, obturator hernia, strangulation
• MRI → athletes' groin pain
• Blood tests in strangulation → FBC, U&E, lactate, group and save
• Abdominal X-ray → bowel obstruction

Congenital defects

• Antenatal ultrasound and raised maternal serum AFP
• Exomphalos → karyotype, echocardiography (cardiac defects), renal ultrasound, blood glucose (Beckwith-Wiedemann)
• Gastroschisis → look for intestinal atresia (10–20%); other anomalies rare

8. Differential diagnosis

• Groin lump → see inguinal and femoral hernia: lymph node, saphena varix, femoral aneurysm, lipoma, hydrocele, undescended testis, psoas abscess
• Ventral lump → lipoma, divarication of the recti (no defect, no risk of strangulation), desmoid, rectus sheath haematoma
• Strangulated hernia versus torsion of the testis, inguinal lymphadenitis

9. Treatment

Conservative

• Watchful waiting → small, minimally symptomatic inguinal hernia in men, or patients unfit for surgery
• Correct risk factors → stop smoking, weight loss, treat cough and constipation, prostate
• Truss → little value; not for femoral hernias
• Never try forceful reduction (taxis) of a strangulated hernia → "reduction en masse" hides dead bowel

Surgical: principles of hernia repair

1. Herniotomy → dissect, open, inspect, reduce and remove the sac (children: herniotomy alone)
2. Herniorrhaphy → sutured repair of the defect (Shouldice, McVay, Mayo)
3. Hernioplasty → tension-free mesh reinforcement (Lichtenstein, TEP, TAPP) → standard in adults
4. Mesh → polypropylene (permanent); biological or absorbable mesh in contaminated fields
5. Mesh positions → onlay, inlay, sublay (retromuscular or preperitoneal), intraperitoneal (IPOM)
6. Open or laparoscopic; local, regional or general anaesthesia

Surgical: strangulated hernia

1. Resuscitate → IV fluids, NG tube, catheter, analgesia, antibiotics
2. Emergency operation
3. Open the sac first, hold the contents (to avoid them slipping back unseen)
4. Release the constriction
5. Check viability → colour, peristalsis, mesenteric pulsation; wrap in warm saline-soaked swabs for 5–10 min
6. Non-viable bowel → resection and anastomosis
7. Repair → mesh if clean; sutured or biological mesh if contaminated

Surgical: congenital defects

• Gastroschisis:
  • Cover the bowel in cling film, NG tube, IV fluids (large losses), warmth, antibiotics
  • Primary reduction and closure, or preformed silo with gradual reduction over 7–10 days, then closure
  • Parenteral nutrition until the gut works (weeks)
• Exomphalos:
  • Protect the sac; look for other anomalies
  • Minor → primary closure
  • Major → paint the sac (silver sulfadiazine) to let it epithelialise ("paint and wait"); repair the ventral hernia later (about 1 year)

10. Complications

• Hernia → incarceration, obstruction, strangulation, perforation, peritonitis
• Repair → haematoma, seroma, wound infection, recurrence, chronic pain, mesh infection, injury to bowel, bladder or vessels
• Gastroschisis → short bowel, long parenteral feeding, sepsis, necrotising enterocolitis; survival > 90%
• Exomphalos → prognosis depends on associated anomalies (chromosomal, cardiac)