Types of Hernia
Hernias are classified into three main categories: external (abdominal wall) hernias, internal hernias, and diaphragmatic hernias 1.
External/Abdominal Wall Hernias
These involve protrusion of abdominal contents through a defect in the abdominal wall and represent the most commonly encountered hernias in clinical practice 1. The major subtypes include:
Primary Ventral Hernias
- Inguinal hernias (groin hernias) - the most common type overall 2
- Femoral hernias (crural hernias) - also groin-related but through the femoral canal 2
- Umbilical hernias - through the umbilical ring 2
- Epigastric hernias - through the linea alba above the umbilicus 2
- Spigelian hernias - through the spigelian fascia (lateral ventral abdominal wall) 2
Incisional Hernias
These develop through previous surgical incisions and represent a distinct category of abdominal wall hernias 2, 3. They are iatrogenic in nature and can present with complex abdominal wall defects 4.
Within inguinal hernias specifically, recent evidence identifies two pathogenetically distinct subtypes of medial (direct) hernias: traction hernias (supravesical type involving superficial preperitoneal fat layers) versus pulsion hernias (conventional medial type involving deep layers, driven by increased intra-abdominal pressure) 5.
Internal Hernias
These involve protrusion of viscera (usually small bowel) through openings in the peritoneum or mesentery into compartments within the abdominal cavity 1, 6. They account for 5.8% of small bowel obstructions 6.
Congenital Internal Hernias
- Paraduodenal hernias (left and right) - through peritoneal fossae near the duodenum 6
- Epiploic foramen hernias (foramen of Winslow) 6
- Transomental hernias - through defects in the omentum 6
- Transmesenteric hernias - through mesenteric defects 6
- Pericecal hernias - around the cecum 6
- Broad ligament hernias - in females 6
Acquired Internal Hernias
These result from surgical procedures creating peritoneal or mesenteric defects 6:
- Post-Roux-en-Y surgery hernias
- Post-colorectal resection hernias
Diaphragmatic Hernias
These involve protrusion of abdominal contents into the thoracic cavity 1.
Hiatal Hernias
Four distinct types exist 7:
- Type I (sliding) - gastroesophageal junction and stomach slide into thorax (most common)
- Type II (paraesophageal) - stomach herniates beside the esophagus while GE junction remains in place
- Type III (combined) - elements of both types I and II
- Type IV (giant paraesophageal) - large herniation with other organs potentially involved
Other Diaphragmatic Hernias
- Bochdalek hernias - posterolateral congenital defects 8
- Morgagni hernias - anterior/retrosternal defects 8
- Traumatic diaphragmatic hernias - from blunt or penetrating trauma 8
- Eventration - abnormal elevation of intact diaphragm 8
Critical Clinical Considerations
Emergency presentations require immediate recognition: When intestinal strangulation is suspected in any hernia type, emergency repair should be performed immediately 2. SIRS, contrast-enhanced CT findings, elevated lactate, CPK, and D-dimer levels predict bowel strangulation 2. Delayed diagnosis beyond 24 hours significantly increases mortality 2.
Internal hernias are particularly dangerous as they account for surgical emergencies with high strangulation risk but can be clinically occult, requiring CT imaging for diagnosis 6, 9. Traumatic diaphragmatic hernias are frequently overlooked in polytrauma patients but carry constant strangulation risk 8.