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Contributors PSL, LJ and NPT wrote the manuscript. SJN provided the histology images, description of the key features and expert advice. All authors critically appraised and approved the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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