1. “SIN Syndrome” – A new mechanism for mesh inguinodynia
R. Bendavid & V. Iakovlev
Shouldice Hospotal, Richmond Hill, Canada
Department of Pathology, St. Michael’s Hospital and Keenan research Centre of the Li Ka Shing Knowledge Institute, University of Toronto, Toronto, Canada

2. I have given opinion for medicolegal cases
Disclaimer:
I have given opinion for medicolegal cases

3. Background
Surgical polypropylene meshes were introduced in late 1950’s
Applications spread to non-hernia sites, presently annual worldwide use is several million devices
Depending on site 2-8% are excised for complications (infection, pain, hernia recurrence, mucosal erosion, transmigration) – abundant material to study
Many (likely >50%) of explanted meshes are not examined microscopically. * Even if they are pathologists are not aware of mesh related issues.
Paradoxically, with the availability of abundant material from humans most conclusions are based on animal studies
* Smith T.M., Smith S.C., Delancey J.O., Fenner D.E., Schimpf M.O., Roh M.H., Morgan D.M., “Pathologic evaluation of explanted vaginal mesh: interdisciplinary experience from a referral center,” Female Pelvic Med Reconstr Surg., vol. 19,no. 4, pp , Jul

4. Appearance of mesh in histological sections
Mesh is encased in scar tissue, on the outside and within the pores and folds.
Bendavid, R. , Lou, W. , Koch, A., Iakovlev, V.
Mesh-Related SIN Syndrome. A Surreptitious Irreversible Neuralgia and Its Morphologic Background in the Etiology of Post-Herniorrhaphy Pain. International Journal of Clinical Medicine, 2014, 5:

5. reinnervation and neoinnervation
Is scar within mesh innervated?
Nerve structures of any caliber (nerves, nerve twigs, individual nerve fibers)
can grow into the mesh
in the process of
reinnervation and neoinnervation
S100 stain, nerve branches are stained brown
Cross-sectioned mesh filaments are filled yellow in the pictures

6. Does mesh affect nerve growth into the scar?
3 groups of samples:
10 virgin tissue at primary repair
10 scar sample at revision after non-mesh repair
10 biopsied mesh samples at surgery for recurrence
Bendavid, R. , Lou, W. , Koch, A., Iakovlev, V.
Mesh-Related SIN Syndrome. A Surreptitious Irreversible Neuralgia and Its Morphologic Background in the Etiology of Post-Herniorrhaphy Pain. International Journal of Clinical Medicine, 2014, 5:

7. Significance of mesh and nerves interaction
Innervated tissue is exposed to all regular pain mechanisms:
Direct mechanical irritation
Inflammation
Compression due to edema
Ischemia
Migrating mesh stretched a nerve
Bendavid, R. , Lou, W. , Koch, A., Iakovlev, V.
Mesh-Related SIN Syndrome. A Surreptitious Irreversible Neuralgia and Its Morphologic Background in the Etiology of Post-Herniorrhaphy Pain. International Journal of Clinical Medicine, 2014, 5:

8. Nerve ingrowth with entrapment
Possible pain mechanisms
Nerve ingrowth with entrapment

9. Nerve ingrowth with entrapment
Possible pain mechanisms
Nerve ingrowth with entrapment

10. Possible/contributing pain mechanisms
Inflammation

11. Mesh hardening, shrinking, attachment to tissues
Possible/contributing pain mechanisms
Mesh hardening, shrinking, attachment to tissues

12. Possible/contributing pain mechanisms
Edema within mesh compartments
Mini-compartment syndrome?

13. Ischemic pain or ischemia driven scar expansion?
Possible/contributing pain mechanisms
Ischemic pain or ischemia driven scar expansion?

14. Interposition with striated muscle
Possible/contributing pain mechanisms
Interposition with striated muscle

15. Mesh migration into organs and tissue deformation
Possible/contributing pain mechanisms
Mesh migration into organs and tissue deformation

16. Mesh migration into organs and tissue deformation
Possible/contributing pain mechanisms
Mesh migration into organs and tissue deformation

17. Conclusions
Innervated tissue is exposed to all regular pain mechanisms
Density of ingrown nerves is higher in hernia meshes removed for reasons of pain than in meshes removed for recurrence
Nerve entrapment appears to be one of the main mechanisms of pain for these patients
Other possible or contributing factors are:
Inflammation
Mesh hardening, shrinking and attachment to tissues
Edema within mesh compartments
Muscle interposition
Ischemia
Important to answer these questions to guide future technical development and treatment strategies

18. Questions