Abdominal Hernias: A Complete Reference

1. Definition and Classification

• Inguinal (direct and indirect) - most common
• Femoral
• Umbilical (congenital and acquired)
• Epigastric (through the linea alba above the umbilicus)
• Incisional (at a prior surgical scar)
• Spigelian (through the linea semilunaris)
• Lumbar (through the lumbar triangles)
• Obturator, sciatic, perineal - rare pelvic floor hernias
• Internal hernias - bowel entrapment within the peritoneal cavity (paraduodenal fossa, foramen of Winslow, mesenteric defects)
• Diaphragmatic (hiatal, Bochdalek, Morgagni)

2. Etiology: Predisposing and Precipitating Factors

Anatomical (predisposing) causes

1. Natural absence of muscle: The lumbar triangles (Petit's and Grynfeltt's); the posterior wall of the inguinal canal
2. Passages for structures entering/leaving the abdomen: The inguinal canal (for the spermatic cord/round ligament), the femoral canal, the oesophageal hiatus, the umbilical cicatrix, the obturator foramen
3. Developmental abnormalities: The most common is failure of the processus vaginalis to close, predisposing to indirect inguinal hernia; calcitonin gene-related peptide and hepatocyte growth factor influence this closure, suggesting a hormonal mechanism
4. Disruptions of the wall: Prior surgery (incisional hernia), trauma, infection
5. Anatomical shape: Wider, shorter pelvis increases inguinal hernia risk

Predisposing systemic factors

• Age: Connective tissue degeneration
• Sex: Males far more commonly affected for inguinal hernias (due to the inguinal canal anatomy)
• Obesity: Increased intra-abdominal pressure + weakened musculature
• Connective tissue disorders (Ehlers-Danlos, Marfan): defective collagen
• Nutritional deficiencies / malnutrition
• Collagen synthesis defects: Smokers have altered metalloproteinase activity affecting connective tissue turnover

Precipitating factors (raise intra-abdominal pressure)

• Chronic cough (COPD, asthma)
• Straining at stool (constipation)
• Urinary straining (benign prostatic hyperplasia)
• Heavy lifting and strenuous physical work
• Pregnancy and multiparity
• Ascites
• Abdominal masses / organomegaly

3. Key Anatomical Elements of a Hernia

1. The defect (hernial ring / hernial orifice): The weakness or gap in the musculofascial wall through which herniation occurs. It is usually the narrowest part of the hernia. A small, rigid-walled defect is more dangerous than a large one because it more easily traps contents.
2. The hernial sac: A pouch of peritoneum pushed through the defect into the subcutaneous tissues. The sac has:
   • Neck - the narrowest part at the abdominal wall defect; acts as the constriction ring
   • Body - the main portion of the sac
   • Fundus - the blind end
3. The contents: What is inside the sac:
   • Preperitoneal fat alone (many epigastric hernias)
   • Omentum (commonest bowel-free content)
   • Small bowel (most dangerous)
   • Large bowel
   • Bladder (in direct inguinal hernia as a "sliding" component)
   • Meckel's diverticulum (Littre's hernia)
   • Other viscera (appendix in Amyand's hernia)
4. Coverings: The layers of the abdominal wall that are carried outward, thinned and attenuated, over the hernia sac.

4. Clinical Presentation of Uncomplicated Abdominal Hernias

• The patient notices a lump in the abdominal wall, groin, or umbilical area - self-diagnosis is common
• The hernia is usually painless, but an aching or heavy sensation is frequent
• Sharp, intermittent pain suggests pinching of tissue at the neck
• The lump may appear only on exertion, straining, or standing, and disappear when lying down (reducible hernia)
• The patient may be able to reduce the hernia manually

• The patient should be examined supine first, then standing; the Valsalva manoeuvre and coughing increase the hernia size
• Expansile cough impulse: Gentle pressure on the lump while the patient coughs confirms the hernia communicates with the peritoneal cavity; however, there may be no cough impulse when the neck is tight (as in femoral hernia - lack of impulse does not exclude a hernia)
• Skin: Normal colour over an uncomplicated hernia; overlying cellulitis = surgical emergency
• Reducibility: Can the hernia be pushed back? The patient may be more experienced in reducing it than the surgeon
• Assess both sides: occult contralateral hernia is present in up to 20% of patients
• For groin hernias: examine the scrotal contents; distinguish from lymph node, saphena varix, femoral artery aneurysm, psoas abscess

• Ultrasound - dynamic, useful in irreducible hernias, to distinguish hernia from lymph node, hydrocele, saphena varix; helpful postoperatively to differentiate seroma/haematoma from recurrence
• CT scan - for complex ventral/incisional hernias: maps defect number and size, identifies contents, shows adhesions, excludes intra-abdominal pathology; CT with oral iodinated contrast helps determine bowel content type; enhanced CT identifies strangulation
• MRI - sportsman's groin; distinguishes occult hernia from orthopaedic injury
• Laparoscopy - identifies occult contralateral defects; not useful for intraparietal hernias (Spigelian, epigastric)

5. Treatment of Uncomplicated Abdominal Hernias

Conservative management (watchful waiting)

• Not all hernias require repair. Indications to watch rather than operate:
  • Asymptomatic inguinal hernia in elderly patients (annual crossover to surgery ~10%)
  • Small umbilical and epigastric hernias containing fat/omentum with very low complication risk
  • Large incisional hernias in obese, elderly patients where operative risk exceeds benefit (wide neck = low strangulation risk)
• A truss can mechanically control a hernia but is rarely recommended now
• Surgery is always indicated for: femoral hernia (high strangulation risk), symptomatic hernias, irreducible hernias, narrow-necked hernias, growing hernias, and younger patients

Surgical management (general principles)

1. Reduction of hernial contents into the peritoneal cavity; excise non-viable tissue if present
2. Sac management: Excision and closure of the peritoneal sac (small sacs may be reduced intact); in laparoscopic repair the sac is pulled back intraperitoneally
3. Closure of the defect with sutures, if feasible
4. Mesh reinforcement - primary closure alone has high recurrence; mesh (polypropylene or similar) dramatically reduces recurrence rates

Mesh types and placement

• Net/knitted meshes - allow tissue ingrowth; become integrated within months
• Sheet meshes - do not allow ingrowth; require strong non-absorbable fixation
• Positioning: onlay (over the defect), inlay (edge-to-edge - NOT recommended), sublay (retromuscular), IPOM (intraperitoneal), or extraperitoneal (in TEP/TAPP inguinal repair)
• Intraperitoneal mesh requires a composite design with an anti-adhesion surface to prevent bowel adhesion

Approaches

• Open (Lichtenstein, Shouldice, McVay, Bassini, etc.)
• Laparoscopic (TEP - totally extraperitoneal; TAPP - transabdominal preperitoneal) - particularly useful for bilateral or recurrent inguinal hernias

6. Incarcerated Hernia: Concept, Pathology, and Types

Definition

Pathological sequence

1. Irreducibility: Contents become trapped in the hernial sac and cannot return to the abdominal cavity (due to adhesions, narrow neck, or swelling of contents)
2. Venous obstruction: Tight neck impedes venous return → oedema of hernial contents → increased pressure within the sac
3. Pain and tenderness develop from tension and ischaemia
4. Bowel obstruction: If bowel is trapped, partial or complete obstruction follows
5. Arterial compromise → Strangulation: If pressure rises sufficiently, arterial inflow is cut off → ischaemia → infarction
6. Perforation/gangrene: The bowel wall perforates, releasing infected toxic content into the sac and eventually the peritoneal cavity → peritonitis, sepsis, death

Types of incarceration

7. Rare Types of Incarceration

W-shaped Incarceration (Maydl's Hernia / Retrograde Incarceration)

• First described by Karel Maydl in 1895.
• Two intestinal loops are present in the hernial sac, connected by an intra-abdominal intermediate (retrograde) loop, forming a "W" or omega (Ω) shape.
• The two loops in the sac may appear viable at surgery, but the intra-abdominal connecting loop is ischaemic/necrotic because it is being strangulated by the hernial ring from within the peritoneal cavity.
• Clinically resembles any strangulated hernia, but the true ischaemia is inside the abdomen, not visible through the hernial incision.
• Critical surgical implication: Simply opening the hernial sac is insufficient - the surgeon MUST explore the intra-abdominal loop through laparotomy or laparoscopy to rule out necrosis. Failure to do so results in missed gangrenous bowel being left in the abdomen.
• Type 1: all loops are small intestine; Type 2: small intestine + colon; Type 3: only colon.

Richter's Incarceration (Richter's Hernia)

• Only the anti-mesenteric portion of the bowel wall enters the hernial sac - not the full lumen.
• Because the lumen is not completely obstructed, bowel obstruction symptoms may be absent or mild, even as the herniated wall segment undergoes ischaemia and necrosis.
• The hernia may be small and difficult to detect clinically - particularly treacherous in femoral hernia, where it can be easily missed.
• Necrosis and perforation of the bowel wall can occur with life-threatening consequences without any preceding bowel obstruction.
• Incidence of necrosis at surgery is reported at ~69%.
• Mortality up to 17% in strangulated Richter's hernias.
• Most commonly involves the terminal ileum; the femoral ring is the classic site (narrow and rigid).

Richter-Littre Hernia (Littre's Hernia)

• The hernial sac contains Meckel's diverticulum (with or without the adjacent ileal loop).
• Littre's hernia should be distinguished from Richter's: in Littre's hernia, it is the Meckel's diverticulum that is incarcerated (no general bowel obstruction unless the ileal loop accompanies it); in Richter's, only a partial bowel wall is strangulated.
• Most commonly found in inguinal, umbilical, or femoral hernias.
• Since Meckel's diverticulum is a blind-ending structure, it is prone to rapid ischaemia once incarcerated.
• Diagnosis is almost always intraoperative.
• Treatment: resection of the Meckel's diverticulum; if the adjacent ileal loop is involved, resection and anastomosis of the ileal segment is required.
• Incidence: ~1% of patients with a Meckel's diverticulum will develop a Littre's hernia.

8. Clinical Presentation and Diagnosis of Incarcerated Hernia

Symptoms

• Acute onset of severe pain at the hernia site, often following an episode of straining
• Pain does not resolve with rest; persists between paroxysms (unlike a simple reducible hernia)
• Nausea and vomiting (reflex initially; later from bowel obstruction)
• Abdominal distension (may be asymmetrical)
• Inability to reduce the hernia (previously reducible hernias that suddenly become irreducible = emergency)
• Symptoms of bowel obstruction (colicky pain, obstipation, vomiting) if bowel is in the sac
• Note: Richter's hernia may lack obstructive symptoms entirely

Signs of progressing strangulation

• Tense, painful, firm, irreducible mass at the hernia site
• No cough impulse (trapped contents)
• Tenderness and rebound at the hernia site
• Overlying skin changes: erythema, oedema, blistering = sign of impending gangrene and phlegmon
• Systemic: fever, tachycardia, leukocytosis, metabolic acidosis, raised lactate = signs of strangulation/sepsis
• Gradually worsening shock if left untreated
• Bloody fluid in vomit, intestinal excreta, or on abdominal puncture = sign of bowel infarction
• Asymmetrical distension with palpable, tender intestinal loops

Diagnosis

• Clinical diagnosis is primary in most cases; any irreducible, tender hernia with systemic upset should be operated on without delay.
• CT abdomen (with or without oral contrast):
  • Confirms incarceration and identifies contents
  • Shows bowel dilation, mesenteric thickening, wall oedema
  • Enhanced CT detects bowel ischaemia/strangulation (absent enhancement, free fluid in sac, pneumatosis)
  • Particularly valuable for obturator and femoral hernias, which are not easily palpated
• Ultrasound: useful but operator-dependent; can be used if CT is not immediately available
• Laboratory: CBC (leukocytosis), metabolic panel, lactate, blood gas (acidosis), blood cultures if septic

9. Indications and Contraindications for Surgery in Incarcerated Hernia

Indications for emergency surgery

• All incarcerated hernias with signs of strangulation (skin changes, fever, tachycardia, peritonism) - absolute emergency
• Failed manual reduction (taxis): If the hernia cannot be reduced within a reasonable attempt under analgesia/sedation
• Bowel obstruction not resolving
• Richter's hernia: even without obstruction, because bowel wall necrosis can be silent
• Maydl's hernia: always requires laparotomy to inspect the intra-abdominal loop

When to attempt taxis (manual reduction) before surgery

• Taxis (gentle forceful reduction with analgesia and/or sedation) may be attempted in:
  • Short duration of incarceration (<2 hours)
  • No signs of strangulation (no skin changes, no fever, no peritonism, no systemic upset)
  • Patient is stable
• If taxis succeeds: Admit, observe, and schedule elective repair within 3-5 days (high risk of recurrence otherwise)
• Taxis is CONTRAINDICATED if:
  • There are signs of strangulation (skin erythema, oedema, blistering, fever, peritonism)
  • Suspected perforation or peritonitis
  • Prolonged incarceration
  • Richter's hernia (reducing an already gangrenous partial bowel wall into the abdomen is disastrous)

Contraindications to immediate surgery

• Phlegmon of the hernial sac (see topic 11): requires a modified surgical approach (laparotomy first, not direct incision over the hernial sac)
• Severe cardiovascular or respiratory decompensation requiring initial stabilisation (but resuscitation and surgery should proceed in parallel in true strangulation, not sequentially)
• Relative contraindication only: very high anaesthetic risk - must be weighed against the certain mortality of untreated strangulated hernia

10. Specifics of Surgery for Incarcerated Hernia and Signs of Bowel Viability

Surgical principles

1. Approach: For most hernias, a standard hernia incision is made first to assess contents. If bowel resection is needed (or if Maydl's hernia/W-incarceration is suspected), a midline laparotomy provides better access.
2. Open the hernial sac and inspect contents carefully.
3. Release the constricting ring: An incision on the anteromedial aspect of the defect (to avoid epigastric/iliac vessels) releases the neck. This may allow spontaneous reduction or facilitate manual reduction.
4. Assess bowel viability before deciding on resection vs. retention.
5. Bowel resection and anastomosis if non-viable.
6. Repair the defect: Always close/repair the hernia at the same operation - leaving it open risks re-incarceration. In contaminated fields, primary suture repair (without mesh) is generally preferred; a biological mesh or synthetic anti-infective mesh may be used if the surgeon is confident about contamination control.
7. Laparoscopic approach (TAPP, TEP, diagnostic laparoscopy via hernia sac): advantages include visualisation of entire peritoneal cavity, easier bowel reduction, identification of occult hernias, and lower wound infection rates. Convert to open if needed.

Signs of bowel viability

• Normal pink/red colour (not dusky, blue, black, or grey)
• Peristalsis present on observation
• Mesenteric pulse palpable
• Glistening serosal surface
• Normal bowel wall tone and thickness

• Black, green, or grey colour
• No peristalsis after warm saline application and waiting
• No mesenteric pulse
• Dull, opaque serosa
• Thin, friable, or perforated wall
• Haemoserous fluid in the sac

• Intravenous fluorescein + Wood's lamp examination - fluoresces viable bowel wall
• Indocyanine green (ICG) + infrared imaging angiography - modern, highly sensitive method for assessing bowel perfusion

11. Phlegmon of the Hernial Sac: Presentation, Diagnosis, and Surgery

Definition

• Femoral hernia (highest rate of strangulation)
• Women (femoral hernias are more common in women)
• Delayed presentation (>24-48 hours of strangulation)

Clinical presentation

• Local signs:
  • Tense, painful, hard, irreducible, non-impulsive mass at the hernia site
  • Overlying skin: erythema, oedema, warmth
  • Blistering or skin necrosis - pathognomonic of advanced phlegmon
  • Fluctuation (if abscess has formed)
  • May have cutaneous fistula in extreme neglect
• Systemic signs:
  • High fever, rigors
  • Tachycardia
  • Leukocytosis with left shift
  • Signs of sepsis/SIRS; metabolic acidosis
  • Symptoms of bowel obstruction or peritonitis

Diagnosis

• Clinical - the combination of a strangulated hernia with local skin inflammatory changes (redness, oedema, blistering) is sufficient to diagnose phlegmon.
• CT scan: confirms gangrenous bowel, soft tissue inflammatory changes, free gas in sac/soft tissues, associated peritonitis.
• Blood: leukocytosis, elevated CRP/procalcitonin, lactate.

Surgical treatment - critical specifics

1. Release infected/gangrenous contents before the intra-abdominal portion is controlled
2. Contaminate the peritoneal cavity from below

1. Step 1 - Laparotomy (midline incision) FIRST:
   • Enter the peritoneal cavity through a clean, uncontaminated incision
   • Identify and resect the gangrenous bowel loop from the abdominal side, above the hernial ring
   • Restore bowel continuity (anastomosis) or bring out a stoma (depending on contamination and patient stability)
   • The hernial sac is left in place - the necrotic content is not pulled back into the abdomen
2. Step 2 - Incision over the hernial sac:
   • After bowel resection and peritoneal toilet, the sac is then approached from outside
   • The sac contents (now disconnected from the bowel) are removed, necrotic tissue is debrided
   • The hernial sac is drained and packed open
   • The wound is left open or loosely approximated to allow drainage (do NOT close primarily over infected tissue)
3. Hernia defect repair:
   • Mesh is contraindicated in infected/contaminated fields
   • Primary suture repair of the defect is performed if possible, or the defect is managed temporarily
   • Definitive hernia repair (with mesh) is deferred to a later elective procedure (typically 3-6 months later, when infection has fully resolved)
4. Supportive care:
   • Broad-spectrum antibiotics (active against bowel flora, including anaerobes)
   • Resuscitation, vasopressors if septic shock
   • Postoperative wound care and drainage management

Sources

• Bailey and Love's Short Practice of Surgery, 28th ed., Chapter 64, pp. 1080-1087
• Fischer's Mastery of Surgery, 8th ed.
• Mulholland and Greenfield's Surgery, 7th ed. (hernia classification tables)
• StatPearls: Richter Hernia (NCBI Bookshelf, NBK537227)
• Yang XF & Liu JL: "Acute incarcerated external abdominal hernia," Annals of Translational Medicine 2014
• Ndiaye M et al.: "Maydl's Hernia: An Unusual Cause of Strangled Inguinal Hernia," J Clin Med Images 2021
• Heraldopenaccess.us: "Pyostercoral Phlegmon: A Rare and Historical Complication of Strangulated Hernia"
• EAST: "Repair of Incarcerated Hernias" (surgical protocol)