Types of Hernia
Hernias are broadly classified into two major categories: abdominal wall hernias (external hernias) and diaphragmatic hernias, with abdominal wall hernias further subdivided into primary hernias (inguinal, femoral, umbilical, epigastric, spigelian) and incisional hernias. 1, 2
Primary Classification Framework
Hernias can be systematically organized into three main anatomical categories 1, 2:
1. Abdominal Wall (External) Hernias
These involve protrusion of abdominal contents through a defect in the abdominal wall 2:
Groin Hernias:
- Inguinal hernias - classified as indirect (lateral to inferior epigastric vessels) or direct (medial to inferior epigastric vessels), representing the most common type of abdominal wall hernia 3, 4
- Femoral hernias - occur through the femoral canal, more common in women and have higher strangulation risk 1, 4
Ventral Hernias:
- Umbilical hernias - occur at the umbilical ring 5
- Epigastric hernias - occur in the midline between the xiphoid process and umbilicus 5
- Spigelian hernias - occur through the spigelian fascia (lateral edge of rectus abdominis) 4
- Incisional hernias - develop at sites of previous surgical incisions 6
2. Diaphragmatic Hernias
These involve protrusion of abdominal contents into the thoracic cavity and are classified into congenital and acquired types 1:
Congenital Diaphragmatic Hernias (CDH):
- Bochdalek hernia - the most common CDH (95%), occurring posterolaterally, predominantly on the left side (85% vs 15% right), with adult incidence of 0.17% 1
- Typically present on the left side (80% overall) due to incomplete diaphragmatic development during the eighth week of gestation 1
Acquired Diaphragmatic Hernias (ADH):
Hiatal hernias - classified into four types 1, 7:
- Type I (sliding): Most common (90%), with gastroesophageal junction displaced above the diaphragm 1
- Type II (paraesophageal): Gastric fundus herniates while gastroesophageal junction remains in normal position (10% of hiatal hernias) 1
- Type III: Combined Type I and II with displaced gastroesophageal junction 1
- Type IV: Large defect accommodating stomach, colon, and spleen 1
Traumatic diaphragmatic hernias (TDH) - caused by blunt (3-8% of cases) or penetrating trauma (65% of TDH cases), with diaphragmatic rupture occurring in 2.1% of blunt trauma and 3.5% of penetrating trauma 1
Iatrogenic hernias - occurring as surgical complications 1
3. Internal Hernias
These involve protrusion of viscera through the peritoneum or mesentery into compartments within the abdominal cavity 2
Clinical Significance by Complexity
Understanding hernia type impacts management decisions regarding:
- Strangulation risk - femoral hernias carry higher risk than inguinal hernias 1, 4
- Surgical approach - traumatic diaphragmatic hernias from blunt trauma (50-80% left-sided) require evaluation for associated intra-abdominal injuries 1
- Mesh utilization - appropriate in clean and clean-contaminated fields but requires careful consideration in contaminated or dirty wounds (CDC Class III-IV) 1
Common Pitfall: Diaphragmatic hernias, particularly Bochdalek hernias in adults and traumatic diaphragmatic hernias, are frequently missed due to their rarity, nonspecific presentation, and low clinical suspicion 1. Left-sided traumatic injuries predominate in hospitalized patients due to the protective effect of the liver on the right hemidiaphragm, though autopsy studies show right-sided predominance in fatal cases 1.