Hernia: Clinical Classification, General Characteristics, and Rare Forms

Definition

1. The orifice (defect in the aponeurotic wall)
2. The hernia sac (composed of peritoneum with abdominal contents)

I. General Characteristics

Structural Components

• Hernia orifice/neck — the fascial defect through which contents protrude
• Hernia sac — peritoneal lining enclosing the herniated contents
• Hernia contents — commonly omentum, small bowel; less often colon, bladder, ovary, etc.

Congenital vs. Acquired

• Congenital — due to a pre-existing anatomical defect (e.g., patent processus vaginalis → indirect inguinal hernia in infants)
• Acquired — from weakening of the abdominal wall due to aging, repetitive strain, surgery, or increased intra-abdominal pressure (obesity, ascites, pregnancy, chronic cough, constipation)

II. Clinical Classification

A. By Reducibility (most clinically important)

A wide-necked hernia may contain non-reducible bowel with no compromise of blood supply and no symptoms other than a bulge. Conversely, smaller hernias carry a greater risk of strangulation — up to 40% of femoral hernias are strangulated at first presentation, vs. only 2% of incisional hernias.

— Sleisenger and Fordtran's Gastrointestinal and Liver Disease

B. By Location

1. External (protrude through the abdominal wall)

2. Internal Hernias (contained within the peritoneal cavity)

The "whirl sign" on CT (mesenteric vessels and bowel appearing to twist around a point) is a key diagnostic finding for internal hernia.

C. By Aetiology

III. Rare (Uncommon) Forms of Hernia

1. Spigelian Hernia

• Protrudes through a defect in the lateral edge of the rectus abdominis at the level of the semilunar (Spigelian) line and near the arcuate line
• The defect is in the transverse abdominal aponeurosis (spigelian fascia)
• Usually an intramural / interparietal hernia — the sac remains within the abdominal wall layers and may not be visible externally; therefore frequently missed on clinical examination
• Typically in patients aged 40–70 years
• Incarceration rate up to 20% (often contains omentum)
• Diagnosis confirmed with ultrasound or CT

2. Obturator Hernia ("Little Old Lady's Hernia")

• Occurs through the obturator foramen (greater and lesser foramina)
• Almost exclusively in older, cachectic, multiparous women (obturator foramen is larger in women; weight loss depletes the fatty plug)
• Accounts for ~1% of hernia repairs in Asia; 0.07% in the West
• Typically presents as small bowel obstruction
• Pathognomonic signs:
  • Howship-Romberg sign — paresthesia/pain in the inner thigh, worsened by hip extension/adduction/internal rotation, relieved by flexion (pressure on obturator nerve); seen in 25–50%
  • Hannington-Kiff sign — absent adductor reflex on percussion above the knee
• Richter-type strangulation is common; diagnosis frequently delayed and often made at laparotomy

3. Sciatic Hernia

• Protrudes through the greater or lesser sciatic foramen (formed by the sciatic notch and the sacrospinous/sacrotuberous ligaments)
• May contain ovary, ureter, bladder, or bowel
• Even rarer than obturator hernia: <100 cases reported in the literature
• More common in older women; occasionally seen in children

4. Perineal Hernia

• Occurs through the soft tissues of the perineum; very rare
• Primary: through the urogenital diaphragm (anterior) or between levator ani and coccygeus muscles (posterior); more common in middle-aged women
• Secondary (postoperative): after abdominoperineal resection, pelvic exenteration, or hysterectomy; occurs in <3% of pelvic exenterations and <1% of APRs

5. Lumbar Hernia

• Protrudes through the lumbar triangle (Petit's — inferior lumbar triangle, or Grynfeltt-Lesshaft — superior lumbar triangle)
• Rare; presents as a posterior flank mass
• May be primary (congenital/spontaneous) or secondary (post-traumatic, post-surgical)

6. Richter Hernia (special variant, not rare in femoral region)

• Only one wall of the bowel (most often the antimesenteric side) is caught in the hernia orifice
• Key danger: strangulation can occur without complete intestinal obstruction, making it a diagnostic trap
• Most common in association with femoral hernias; also inguinal
• A complete obstruction can develop if more than half of the bowel circumference becomes incarcerated

7. Paraduodenal (Mesocolic) Hernia

• Most common congenital internal hernia
• Herniation of small bowel into peritoneal folds/fossae adjacent to the duodenojejunal junction
• Left-sided more common than right-sided
• Presents with recurrent episodes of partial bowel obstruction

8. Foramen of Winslow Hernia

• Herniation through the epiploic foramen (posterior to the porta hepatis)
• Very rare; usually contains small bowel, rarely cecum or gallbladder
• High risk of strangulation due to narrow neck

9. Supravesical Hernia

• Protrudes through the supravesical fossa (space anterior to the bladder)
• May be internal or external (appears as inguinal hernia clinically)
• ~30% of cases have associated bladder compression symptoms

10. Broad Ligament Hernia (in females)

• Herniation through a defect in the broad ligament of the uterus
• Can cause chronic pelvic pain; bowel obstruction in ~50%
• May contain small bowel, sigmoid colon, appendix, omentum, or ureter

IV. Hernia-Related Epidemiology (Key Facts)

• Hernias of all types are the second leading cause of small bowel obstruction in Western countries (after adhesions)
• Lifetime risk of groin hernia requiring repair: 27% in men, 3% in women
• ~800,000 groin hernia repairs/year in the USA; 80–90% performed in men
• Indirect inguinal hernias account for 65–70% of groin hernias in both sexes
• Among patients operated for SBO due to hernia, ischemia occurs in up to 75%, necrosis in >25%