Nyhus Classification for Adult Inguinal Hernias
The Nyhus classification is an anatomically-based system that categorizes adult inguinal hernias into four types based on the size and location of the hernia defect, guiding surgical approach selection.
Classification System Structure
The Nyhus classification divides adult inguinal hernias into the following categories 1, 2:
Type I: Indirect Inguinal Hernia
- Internal inguinal ring is normal (tight)
- Hernia sac passes through the internal ring
- Typically seen in pediatric patients and young adults 1
Type II: Indirect Inguinal Hernia
- Internal inguinal ring is enlarged but posterior wall remains intact
- Hernia defect measures less than 3 cm in transverse diameter 3
- Does not encroach on the floor of the inguinal canal 1
Type III: Posterior Wall Defects
This category encompasses multiple subtypes 1, 2:
Type IIIA: Direct inguinal hernia
- Defect in the posterior wall medially
- Transversalis fascia weakness
Type IIIB: Large indirect inguinal hernia
- Dilated internal ring (>3 cm transverse diameter) 3
- Destroys the posterior inguinal wall
- May extend into the scrotum (scrotal hernia)
Type IIIC: Femoral hernia
- Defect below the inguinal ligament through the femoral canal
- Higher risk of strangulation 4
Type IV: Recurrent Hernias
- Any hernia that has recurred after previous repair 1, 2
- Subdivided based on the anatomic location (direct, indirect, femoral, or combined)
- Represents increased complexity requiring specialized approach 5
Clinical Application and Measurement
Intraoperative assessment is the gold standard for accurate classification 3, 2:
- Measurement standards: The transverse diameter of the hernial orifice determines size categorization 3
- Small (Type I): <1.5 cm
- Medium (Type II): 1.5-3.0 cm
- Large (Type IIIB): >3.0 cm
- Localization codes: 'M' for medial (direct), 'L' for lateral (indirect), 'F' for femoral 3
- Combined hernias: When both medial and lateral defects exist, diameters are added and classified according to the medial component with index 'c' 3
Diagnostic Accuracy
Diagnostic laparoscopy achieves the highest accuracy for preoperative hernia classification with sensitivity of 0.93 and specificity of 1.00, superior to both clinical examination and Doppler ultrasonography 2. This allows for individualized, type-related surgical planning before definitive repair 2.
Surgical Implications
The classification directly guides operative technique selection 1, 5, 2:
- Type I-II hernias: Anterior approach (Lichtenstein repair) is typically sufficient 5
- Type III hernias: May require preperitoneal approaches (open Nyhus/Stoppa or laparoscopic TAPP/TEP) 5
- Type IV (recurrent) hernias: Preperitoneal mesh repair via open or laparoscopic approach is preferred to avoid previously dissected tissue planes 5
- Giant bilateral hernias: Stoppa approach with progressive preoperative pneumoperitoneum may be necessary 5
Critical Considerations
Emergency presentations require immediate assessment for complications regardless of Nyhus type 6, 4:
- Systemic inflammatory response syndrome (SIRS), elevated lactate, CPK, and D-dimer levels predict bowel strangulation 6, 4
- Patients with suspected intestinal strangulation require emergency repair immediately, as delayed treatment beyond 24 hours significantly increases mortality 6, 7
- Type IIIC (femoral) hernias have higher strangulation risk and warrant urgent surgical referral 4, 8