Why is a left-sided hernia a risk factor for developing a contralateral (opposite side) hernia?

Left-Sided Hernia as a Risk Factor for Contralateral Hernia Development

Left-sided inguinal hernias significantly increase the risk of developing a contralateral (right-sided) hernia, with studies showing patients with primary left-sided hernias have 2.5-2.7 times higher odds of developing a metachronous contralateral inguinal hernia compared to those with initial right-sided hernias. 1, 2

Anatomical and Developmental Factors

• Congenital diaphragmatic hernias occur more commonly on the left side (80%) due to incomplete development of the diaphragm during gestation 3
• In pediatric inguinal hernias, involution of the left processus vaginalis precedes that of the right, which explains why 60% of indirect inguinal hernias occur on the right side 3
• When a left-sided hernia is present, it may indicate a more generalized weakness in the abdominal wall structures or incomplete developmental closure of the processus vaginalis bilaterally 3, 4

Epidemiological Evidence

• Adult patients with primary left-sided inguinal hernia repair have 2.66 times higher odds of developing a contralateral hernia compared to those with right-sided repairs 1
• In children, the incidence of metachronous contralateral inguinal hernia (MCIH) is significantly higher in those with initial left-sided (9%) versus right-sided (3%) hernias (OR 2.55,95% CI: 1.56-4.17) 2
• The overall incidence of MCIH after unilateral repair in children is approximately 6%, but this risk increases to 8-9% when the initial hernia is left-sided 5, 2

Pathophysiological Mechanisms

• A left-sided hernia may indicate a more generalized weakness in abdominal wall structures or connective tissue that predisposes to bilateral herniation 4
• The presence of a patent processus vaginalis (PPV) on the contralateral side significantly increases the risk of developing a contralateral hernia (OR 4.17,95% CI: 1.25-13.9) 5, 2
• Left-sided hernias may be associated with delayed diagnosis (as they are less common), potentially allowing more time for contralateral weakness to develop 3, 1

Clinical Implications

• In adults undergoing unilateral inguinal hernia repair, the incidence of contralateral hernia development increases over time, reaching 5.9% at 5 years, 16.7% at 15 years, and 29.0% at 25 years 1
• Risk factors for contralateral hernia development include primary left-sided inguinal hernia repair, lower BMI, and older age 1
• During laparoscopic totally extraperitoneal (TEP) repair, consideration should be given to contralateral exploration, especially in patients with left-sided hernias 6

Management Considerations

• When considering prophylactic repair of the contralateral side, the yearly risk of developing a contralateral hernia (approximately 1.2% after negative exploration) must be balanced against potential complications 6
• All inguinal hernias in infants should be repaired to avoid the risk of bowel incarceration and gonadal infarction/atrophy 4
• In pediatric patients with left-sided hernias, closer follow-up may be warranted due to the increased risk of contralateral hernia development 5, 2

Common Pitfalls and Caveats

• Failing to examine both sides for hernias can lead to missed diagnoses, especially in patients with left-sided hernias who have higher risk of contralateral development 4
• The physical features of a hernia (size of abdominal wall defect, amount of herniating intestine, ease of reduction) do not consistently predict the risk of incarceration or contralateral development 4
• Not all patients with a patent processus vaginalis will develop a clinical hernia; studies show that only 25-50% of PPVs result in clinical hernias 3