Hernia - Overview: Types, Anatomy & Pathophysiology

Classification

• Maingot's Abdominal Operations classifies hernia as: external abdominal wall (congenital or acquired), internal, and incisional.

Groin Hernias

1. Indirect Inguinal Hernia (most common overall)

• The hernia sac passes through the internal (deep) inguinal ring and travels along the inguinal canal, potentially reaching the scrotum.
• Located lateral to the inferior epigastric vessels.
• The developmental basis is a patent processus vaginalis - failure of this structure to close after testicular descent.
• More common in males; affects ~5% of full-term infants and up to 30% of preterm infants.
• 30% of hernias in children younger than 3 months become incarcerated - referral for elective repair is important even if asymptomatic.

2. Direct Inguinal Hernia

• Protrudes directly through the muscular and fascial wall of the abdomen (Hesselbach's/inguinal triangle), medial to the inferior epigastric vessels.
• Does not travel along the inguinal canal.
• An acquired condition caused by progressive weakening of the myofascial wall due to aging and repetitive stress from raised intraabdominal pressure.
• Carries a lower risk of incarceration because the hernia orifice is typically wide.
• Second most common groin hernia.

1. Indirect starts lateral to the inferior epigastric vessels; direct is medial.
2. Indirect hernia contents strike the tip of an examining finger (travels down the canal); direct hernia bulges against the pad of the finger.
3. Pressure over the internal ring after reduction prevents recurrence of an indirect hernia during Valsalva, but not a direct hernia.
4. A hernia filling the scrotum is almost always indirect.

3. Pantaloon Hernia

4. Femoral Hernia

• Occurs inferior to the inguinal ligament through a defect in the transversalis fascia.
• Contents enter the femoral canal (medial to femoral vein, lateral to the lacunar ligament), presenting as a medial thigh mass below the inguinal ligament.
• More common in women.
• The small fascial defect creates a very high incarceration risk - up to 45% are incarcerated at presentation.
• Up to 40% are strangulated at first presentation (far higher than inguinal or incisional hernias).

Ventral (Abdominal Wall) Hernias

5. Umbilical Hernia

• Traverses the fibromuscular ring of the umbilicus.
• Most common in infants and children (congenital); often resolves spontaneously by age 5. Repair is indicated if it persists beyond 5 years, is larger than 2 cm, or becomes incarcerated.
• In adults, acquired umbilical hernias arise from increased intraabdominal pressure (obesity, ascites, pregnancy).
• Umbilical hernias account for ~15% of emergency hernia surgery, with up to 60% showing strangulation at the time of surgery.

6. Incisional Hernia

• Occurs in up to 1 in 5 patients following abdominal surgery.
• Risk is increased by poor wound healing (e.g., wound infection).
• Recurrence rates of 20-50% after repair.
• Incarceration risk is inversely related to defect size - larger defects have lower incarceration risk.

7. Epigastric Hernia

• Occurs in the midline through the linea alba, typically between the xiphoid and umbilicus.
• Usually small; in adults, contains preperitoneal fat rather than bowel.
• Found in ~4% of pediatric patients evaluated for hernias.

8. Spigelian Hernia

• Rare. Protrudes through a defect at the lateral edge of the rectus muscle at the semilunar line near the arcuate line (through the spigelian fascia).
• Typically affects patients aged 40-70.
• Incarceration rate (often with omentum) reported as high as 20%.
• Ultrasound may be a useful adjunct for diagnosis.

Internal Hernias

• Herniation of bowel at an opening in the peritoneum, mesentery, or omentum.
• Congenital types: mostly paraduodenal or through the foramen of Winslow (posterior to the porta hepatis).
• The most common type today is iatrogenic - resulting from operations dividing the mesentery (Roux-en-Y gastric bypass, colectomy, pancreaticoduodenectomy).
• Also include: obturator canal hernias and sciatic notch hernias.
• Internal hernias are sometimes diagnosed on CT but often found at laparotomy for presumed adhesive small bowel obstruction (SBO). - Sleisenger & Fordtran's Gastrointestinal and Liver Disease

Pathophysiology: Key States

Epidemiology & Predisposing Factors

• Hernias of all types are the second most common cause of bowel obstruction in Western countries, after adhesions.
• Factors raising intraabdominal pressure that predispose to acquired hernias include: chronic cough, chronic constipation, straining to urinate (e.g., BPH), obesity, ascites, and pregnancy.
• Congenital hernias are related to developmental failures (patent processus vaginalis for inguinal; umbilical ring closure failure for umbilical hernias).