Mesh-Related SIN Syndrome. A Surreptitious Irreversible Neuralgia and Its Morphologic Background in the Etiology of Post-Herniorrhaphy Pain

Purpose: The ubiquitous use of synthetic materials in hernia surgery has brought about a new clinical syndrome: Surreptitious Irreversible Neuralgia (SIN). It is surreptitious because it is of slow onset, unsuspected and enigmatic to clinicians; irreversible because the pain is progressive, unrelenting and unresponsive to treatment. Removal of the mesh does not guarantee pain relief. Neuralgia following mesh insertion, when it occurs, remains a poorly understood phenomenon. Methods: Ten specimens in each group: virgin tissue, scar tissue and explanted mesh from the posterior inguinal wall were examined histologically to assess nerve density, nerve size and nerve and vessel ingrowth into the deformed mesh and within its pores. Results: There was no significant difference in nerve density between virgin, scar and mesh samples. All of the explanted meshes had nerves within the scar tissue encasing the mesh (interstitial infiltration). Nerve ingrowth through the pores of the mesh (micro-entrapment) was detected in 90% of the explanted mesh specimens. Additionally, nerves were detected entrapped within the folds and deformations of mesh explants. Ingrown vessels showed congestion and focal fibrin thrombi. Conclusion: The presence of mesh does not significantly affect nerve density, while the nerves and their terminal ends are in a vulnerable position about the mesh and within its pores. These pores need to be viewed as “mini-compartments” of biological tissue where the vasculature, nerves and their receptors are exposed to potential mechanical and chemical factors: scarring, entrapment, compression, tugging, deformation, contraction, hypoxia/acidosis, inflammation and edema.