Hernia — Comprehensive Overview

Definition

Anatomy of a Hernia

1. The sac — a pouch of peritoneum lined with serous membrane; has a neck, body, and fundus
2. The sac contents — typically omentum, small bowel, or large bowel; occasionally bladder, ovary, or Meckel's diverticulum
3. The coverings — layers of the abdominal wall that cover the sac as it protrudes

Classification

By Reducibility

Strangulation occurs when any degree of ischemia results from compression of bowel within the neck of a hernia. The risk is inversely related to neck size — femoral hernias have the smallest neck and strangulate in up to 45% of cases, whereas incisional hernias strangulate in only ~2%. — Sleisenger & Fordtran's GI and Liver Disease

By Origin

• Congenital — e.g., indirect inguinal hernia from patent processus vaginalis, congenital diaphragmatic hernia
• Acquired — due to weakness of the abdominal wall from aging, obesity, pregnancy, chronic cough, ascites, prior surgery

Sites of Abdominal Wall Hernias

1. Inguinal Hernia

Anatomy of the Inguinal Canal

• Anterior wall: external oblique aponeurosis
• Posterior wall: transversalis fascia (medially reinforced by the conjoint tendon)
• Roof: arching fibres of internal oblique and transversus abdominis (forming the conjoint tendon medially)
• Floor: inguinal ligament (Poupart's) and lacunar ligament (Gimbernat's) medially

Indirect Inguinal Hernia (Lateral / Oblique)

• Sac enters the deep inguinal ring lateral to the inferior epigastric vessels, passes through the entire inguinal canal, and may descend into the scrotum
• In children: always indirect, caused by failure of closure of the processus vaginalis (a peritoneal finger-like projection accompanying the descending testis)
• High incidence in premature infants; spontaneous resolution does not occur in children — surgical repair is always indicated
• In adults: may be congenital (persistent PPV) or acquired

All congenital hernias in children are by definition indirect inguinal hernias. — Schwartz's Principles of Surgery, 11th ed.

Direct Inguinal Hernia (Medial)

• Sac protrudes directly forward through the posterior wall of the inguinal canal (Hesselbach's triangle) medial to the inferior epigastric vessels
• Always acquired — results from weakening of the transversalis fascia / conjoint tendon
• Rarely enters the scrotum; typically a wide-necked reducible bulge
• Lower strangulation risk than indirect

• Medially: lateral edge of rectus abdominis
• Laterally: inferior epigastric vessels
• Inferiorly: inguinal ligament

Pantaloon Hernia

2. Femoral Hernia

• Protrusion through a defect in the transversalis fascia below the inguinal ligament, medial to the femoral vein and lateral to the lacunar ligament (Gimbernat's), into the femoral canal
• Presents as a mass in the medial thigh / femoral triangle, below and lateral to the pubic tubercle
• More common in women (though inguinal is still the commonest hernia overall in women)
• Very high strangulation risk (up to 45%) due to the narrow, rigid femoral ring — unyielding lacunar ligament medially
• Management: elective repair is urgently recommended due to strangulation risk

3. Umbilical & Para-umbilical Hernia

• Traverses the fibromuscular umbilical ring
• In children: mostly congenital; often resolves spontaneously by age 5 if <2 cm. Surgical repair if persistent past age 5, >2 cm, or incarcerated
• In adults: acquired; associated with obesity, ascites, multiparity, large intra-abdominal masses
• More prone to incarceration and strangulation in adults than children
• Para-umbilical hernias (through linea alba adjacent to umbilicus) are more common in overweight multiparous women

4. Epigastric Hernia

• Occurs through the linea alba, between xiphoid and umbilicus
• Usually small, containing preperitoneal fat; may cause disproportionate pain relative to size
• Found in ~4% of children evaluated for hernias; in adults, typically discovered incidentally or due to pain

5. Incisional Hernia

• Occurs at a prior surgical incision site in up to 20% of patients following abdominal surgery
• Risk factors: wound infection, poor closure technique, obesity, malnutrition, immunosuppression, chronic cough
• Recurrence rate after primary repair: 20–50% (significantly reduced with mesh)
• Larger defects paradoxically have lower incarceration risk (wider neck)
• Contents may include omentum, small bowel, or colon

6. Spigelian Hernia

• Occurs through a defect at the lateral edge of the rectus muscle at the level of the arcuate line (semilunar line)
• Located in the lower abdomen; often interparietal (between muscle layers) so may not be visible externally
• Relatively rare; can be difficult to diagnose — ultrasound or CT often required

7. Hiatal Hernia

• Type I (Sliding) — GEJ slides upward into the thorax; most common (95%). LES separated from crural diaphragm → promotes GERD
• Type II (Rolling / Para-oesophageal) — gastric fundus rolls up alongside the oesophagus while GEJ remains below diaphragm; rare
• Types III & IV — mixed or with additional organs (colon, spleen, small bowel)

1. Reduced basal LES pressure (loss of intra-abdominal LES segment)
2. Increased frequency of transient LES relaxations during gastric distention
3. "Acid pocket" retained in the hernial sac — acts as a reservoir for acidic refluxate
4. Large (≥3 cm) non-reducible hernias are especially prone to reflux

Hiatal hernia occurs in 54%–94% of patients with reflux oesophagitis — a rate strikingly higher than in the healthy population. — Sleisenger & Fordtran's

8. Internal Hernias

• Herniation through an opening in the peritoneum, mesentery, or omentum rather than through the abdominal wall
• Congenital: most commonly paraduodenal (through the foramen of Winslow)
• Iatrogenic (most common type): following Roux-en-Y gastric bypass, colectomy, pancreaticoduodenectomy — bowel herniates through the mesenteric defect
• Obturator hernia: through the obturator canal; rare but classically presents with medial thigh pain (Howship–Romberg sign); more common in thin elderly women
• Sciatic hernia: through the greater or lesser sciatic foramen; extremely rare

Complications

Among all patients undergoing surgery for SBO, incarcerated hernia is associated with intestinal ischemia in up to 75% and intestinal necrosis in more than 25%. — Sleisenger & Fordtran's

Clinical Features & Diagnosis

• Dragging, aching groin / abdominal pain; worse on standing, coughing, straining
• Visible or palpable reducible bulge; disappears on lying down
• In strangulation: severe pain, tenderness, skin erythema, systemic toxicity

• Cough impulse — the hallmark of a hernia; expansile impulse on coughing
• In inguinal hernia: relation of the bulge to the pubic tubercle
  • Indirect: sac lies superomedial to pubic tubercle, may descend into scrotum
  • Direct: bulge directly anterior, medial
  • Femoral: mass lies inferolateral to pubic tubercle
• Transillumination helps distinguish hydrocele (lights up) from hernia (does not)
• "Getting above" the swelling: if you cannot get above a scrotal swelling, it has originated from the inguinal canal

• Clinical diagnosis is usually sufficient
• Ultrasound: useful for dynamic assessment, especially occult hernias
• CT abdomen/pelvis: required for obese patients, suspected internal hernias, or complex incisional hernias
• MRI groin: for chronic/occult groin pain with equivocal imaging

Management

Conservative / Non-operative

• Watchful waiting appropriate for asymptomatic inguinal hernias in men with minimal symptoms (risk of strangulation ~0.2%/year)
• Trusses/supports: generally not recommended; do not prevent strangulation
• Contraindicated as sole management in femoral hernias (high strangulation risk)

Reduction of Incarcerated Hernia

• Gentle manual pressure directed toward the internal ring; more successful for groin and umbilical hernias
• Light sedation / Trendelenburg positioning may facilitate reduction
• Contraindications: skin erythema, tenderness, suspected strangulation
• After successful reduction: expeditious surgical repair

Surgical Repair — Open Approaches

Pediatric Herniorrhaphy

• High ligation of the sac at the internal ring — repair of the inguinal floor is not required in children
• Recurrence <1%; typically from missed sac, direct component, or femoral hernia

Adult Hernioplasty (Inguinal)

Femoral Hernia

• Lockwood (low) approach: below inguinal ligament through femoral canal — simplest
• Lotheissen (high) approach: through inguinal canal
• McEvedy (extraperitoneal): superior incision; best access for emergency/strangulated cases

Surgical Repair — Laparoscopic / Minimally Invasive

Special Scenarios

Paediatric Inguinal Hernia

• 10:1 male:female ratio; more common on right
• Incarceration risk is high in infants due to narrow internal ring
• Urgent manual reduction under sedation; herniorrhaphy within 24 hours
• Laparoscopic approach increasingly favoured in children <2 years

Hernia and Small Bowel Obstruction

• Hernia is the second most common cause of SBO after adhesions
• However, operative intervention rate is higher for hernia-related SBO
• CT confirms diagnosis in obese patients or unclear cases

Hernia in Pregnancy

• Umbilical and inguinal hernias may enlarge due to raised intra-abdominal pressure
• Surgical repair generally deferred until post-partum unless emergency

Rare Hernias

Summary

Hernia — Causes & Risk Factors

I. Fundamental Mechanism: The Two Requirements

1. A weakness or defect in the containing wall (congenital opening, fascial degradation, or a surgical scar)
2. A force driving contents through that weakness (intra-abdominal pressure)

II. Congenital Causes

1. Patent Processus Vaginalis (PPV)

• During fetal development, the testis descends from the abdomen to the scrotum, dragging with it a peritoneal finger-like extension called the processus vaginalis
• Normally, the processus vaginalis obliterates a few months before birth
• If it remains patent, a communication persists between the peritoneal cavity and the groin → indirect inguinal hernia
• Partial obliteration → trapped fluid → hydrocele (communicating hydrocele behaves effectively as a hernia)
• Premature infants are at especially high risk because obliteration hasn't yet occurred; incidence of inguinal hernia in premature infants is 9–11% vs. 1–5% in full-term newborns

Closure of the processus vaginalis normally occurs a few months prior to birth. This explains the high incidence of inguinal hernias in premature infants. — Schwartz's Principles of Surgery, 11th ed.

2. Congenital Diaphragmatic Hernia (CDH)

• Caused by failure of closure of the pleuroperitoneal folds during fetal development
• Bochdalek hernia (posterolateral defect) — ~95% of CDH; left-sided predominance
• Morgagni hernia (anterior retrosternal) — ~5% of CDH
• Prevalence ~1–4 per 10,000 live births
• Results in pulmonary hypoplasia and pulmonary hypertension from visceral compression of the developing lungs

3. Umbilical Hernia in Infants

• Due to failure of complete closure of the umbilical ring after cord separation
• Physiologic herniation of the midgut occurs during development (weeks 6–10); failure of return or ring closure → persistent defect

III. Molecular & Biochemical Causes — Connective Tissue Pathology

Collagen Imbalance: Type I / Type III Ratio

• Type I collagen → thick fibres, high tensile strength
• Type III collagen → thinner fibres, temporary scaffolding during tissue remodelling

Matrix Metalloproteinase (MMP) Overexpression

Smoking — "Metastatic Emphysema"

• Decreased Type I : Type III collagen ratio
• Significantly elevated circulating serum elastolytic activity (systemic connective tissue degradation beyond the lungs)

Connective Tissue / Collagen Vascular Diseases

Various connective tissue disorders, such as osteogenesis imperfecta, Marfan syndrome, and Ehlers-Danlos syndrome, are associated with hernias. — Mulholland & Greenfield's Surgery

IV. Factors That Raise Intra-Abdominal Pressure (Mechanical Causes)

1. Obesity

• Central obesity raises resting and dynamic intra-abdominal pressure chronically
• Strongly linked to umbilical, para-umbilical, incisional, and hiatal hernias
• Raised intra-abdominal pressure is the likely mechanism for hiatal hernia and the marked increase in prevalence of reflux oesophagitis / Barrett's oesophagus in obese patients
• Also impairs wound healing → greater incisional hernia risk post-surgery

2. Chronic Cough / COPD / Smoking

• Repeated Valsalva-like surges in intra-abdominal pressure
• COPD is listed as a major independent risk factor for abdominal wall hernia development
• Smoking acts via two pathways: (a) MMP-mediated collagen destruction; (b) chronic cough-induced pressure surges

3. Straining at Stool / Constipation

• Chronic straining generates repeated episodes of raised intra-abdominal pressure
• Important contributing factor to inguinal and femoral hernia, especially in older patients

4. Prostatism / Bladder Outflow Obstruction

• Straining to void → chronic intra-abdominal pressure elevation
• Recognised risk factor for inguinal hernia

5. Ascites

• Sustained, markedly elevated intra-abdominal pressure
• Predisposes to umbilical hernia (often large and tense in cirrhotic patients with ascites)
• High complication risk (skin ulceration, spontaneous rupture)

6. Pregnancy

• Raised intra-abdominal pressure + hormonal-mediated connective tissue laxity
• Predisposes to umbilical, inguinal, and hiatal hernias
• May cause worsening GERD via hiatal hernia mechanism

7. Heavy Lifting / Occupational Factors

• A systematic review found no definitive causal relationship between single strenuous mechanical events and hernia formation
• However, a large Danish register-based cohort study showed that cumulative daily lifting and prolonged standing/walking at work was associated with increased risk of indirect inguinal hernia repair
• Hypothesis: patent processus vaginalis is more susceptible to cumulative pressure changes; direct hernias may involve connective tissue degradation through separate mechanisms

There is minimal evidence that vigorous abdominal wall activity is an independent risk factor for hernia development despite the overwhelming opinion to the contrary in the lay literature. — Mulholland & Greenfield's Surgery, 7th ed.

8. Peritoneal Dialysis

• The dialysate fills the peritoneal cavity, producing sustained raised intra-abdominal pressure
• Significantly associated with inguinal and umbilical hernia development

9. Thoracic or Abdominal Aortic Aneurysm

• Strongly associated with inguinal hernia — both conditions share the same underlying defect in ECM/collagen metabolism
• Patients undergoing AAA repair have high rates of concurrent or subsequent hernia

V. Surgical / Iatrogenic Causes — Incisional Hernia

Poor wound healing, e.g., because of infection, increases the likelihood of developing an incisional hernia. — Roberts & Hedges' Clinical Procedures in Emergency Medicine

VI. Evolutionary/Anatomical Predisposition

• In four-legged animals, the inguinal region bears minimal gravitational load
• In bipeds, the unprotected groin directly faces changes in intra-abdominal pressure with every movement
• The inguinal canal (necessary for testicular descent) represents an inherent structural compromise in the abdominal wall of all males — it is, in essence, a controlled weakness

In the evolution from a quadruped to a biped, the unprotected groin is more vulnerable to changes in intra-abdominal pressure, predisposing to inguinal herniation. — Mulholland & Greenfield's Surgery, 7th ed.

VII. Cause-Specific Summary by Hernia Type